EDIT: As others have pointed out, powerwalls have inverters built in so it's not totally apples to apples. You can get a beefy inverter for $5k and it's still cheaper and you wouldn't need an additional inverter every time you add a battery.
IIRC, the original idea was that they would pull older batteries from circulation when their capacities dipped, and then repurpose them as powerwalls, an application where weight is irrelevant.
This was back when they expected the batteries to plateau at ~80% capacity after a few years, and they had battery swapping on the roadmap, so they needed to plan for a future where they had a steady supply of batteries that car customers did not want.
The idea took hold, but the batteries lasted longer and swapping didn't pan out, so now they are competing with themselves for battery supply.
Electric car battery degradation has been super interesting, in that they are going way further than people thought they might. Jonny Smith on youtube bought a 300k+ mile Tesla and the battery is at like 75% health.
As far as I can tell if your battery isn't air cooled, it can go a very long way
There was some research[1] that strongly suggested that varied use makes them last much longer than the steady use that most battery tests do. That is, bursts of high-current draw followed by moderate draw etc vs the constant current load typically used when evaluating battery performance. From the paper:
Specifically, for the same average current and voltage window, varying the dynamic discharge profile led to an increase of up to 38% in equivalent full cycles at end of life.
This was unexpected, hence explains why they fared better than predicted.
Probably because the economics just don't make sense here. You'd have to have so many compatible cars on the road, driving all day with no opportunity to charge. I'm having a hard time imagining a place I've been to in North America where that'd seem logical.
That's not really apples-to-apples comparison. The Tesla batteries are AC coupled so they work with an (AC coupled) microinverter array. For a DC coupled battery you have to have a hybrid inverter and DC couple the batteries.
Your point that they are overpriced still stands though.
Ya as someone else pointed out, powerwalls essentially have an inverter built in. But this is really dumb to have inverters tied directly to each powerwall battery. This is like anti-scale.
I am writing this off grid, using about 15kwh of batteries and a $1200 (6kw) inverter. My entire system puls panels and racking those panels, plus wiring some un-powered shacks was about $10k, though I did the work myself (which would probably hae been another 3-5k if I could have found someone to do it.
> which would probably hae been another 3-5k if I could have found someone to do it.
Yo. If you can find an electrician to stop by my house and turn a light switch off for less than 1000$, please inform me. I got a quote for 25k$ to install a system that size, and that price. City code has me by the balls: I can't modify my main panel without inspection, the inspector won't show up without a licensed electrician, and electrician wants the labor. I pointed out that we're talking 8 hours of labor — call it 2500$, lawyer money — and he was like "what's your choice". I'm in Texas.
This is still not an accurate comparison. I'm not a Tesla fanboy but of all of the major players in the non-diy game (Enphase, Franklin, Tesla, Sol-Ark) they provide the best value for money, and are impressive pieces of equipment.
The EG4 18k has 11.5 kw backfeed capability, with a rather pathetic 65ish amp in-rush. Obviously 18kw usable solar capacity(they technically let you land up to 21kw, but only 18 is usable).
The Powerwall system you outlined can take 60kw of usable solar input, has 34kw standing backfeed capability, and a whopping 555 amp in-rush (not a typo, it's 185 amps per unit).
9-11 year payback isn't bad based on the projections. You could probably goose it a bit with inflation of electrical prices (depends on how the electrical policies change and what they pass through).
I'll also add theres some O&M coming down the line. Inverters @ year 10, small maintenance and Im assuming you re-did your roof before you installed. Anyone putting solar up make sure you do it at the same time as a roof because taking it down to redo a roof kills your economic value.
> I'm assuming you re-did your roof before you installed
In the UK I would expect the roof to be tile, which lasts basically forever unless a storm hits hard enough.
I did have to have my panels taken down and refitted, at a cost of well over £1000, because I hadn't bird-proofed underneath them (wasn't suggested by original installer). So watch out for that one.
It is essentially a bond return, with the caveat being that solar PV panels will last 25+ years with some degradation and reduction in output. To your point, the best arrangement (imho) is a standing seam metal roof (40-70 year lifetime) with the panels mounted via friction racking with no roof deck penetrations. This avoids the economic cost of pulling everything off the roof to re-roof, and should outlive any homeowner 40 years of age or older. I also expect labor willing to get on a roof becoming more scarce and expensive over time in the developed world, which I think should be taken into account. Your battery storage can be replaced 10-15 years from now at the end of its service life by anyone with a hand truck.
Significantly lower than a bond return, as the value of the installation will go down to zero eventually, while the initial principal of your bond investment will remain intact.
This is factually inaccurate. Solar PV panels will continue to produce power at 80-90% of rated output after 25 years, and battery storage will still have 80-90% capacity. I'm sure you can understand that as long as the system is storing and producing power at these levels, its value is not zero.
Why would you need to replace the batteries? Do they fail outright at around 10 years, become unsafe, or do they just lose capacity?
Curious!
Even if they're at 50% capacity, they would still work, right? But if there are other considerations, especially safety ones, then that would definitely be a consideration. I'm not sure where to learn about this type of thing.
Almost all simulations I've done across 3 countries with 3 different payback models for selling back to grid (one of the three doesn’t allow selling back almost anything above your consumption), I could never make investing in Solar not being a gamble.
You really need to gamble on odds of replacing equipment being very low for it to make sense. And in practice most people I anecdotally know that run it, after 5-7 years have already done additional purchases. The payback time keeps getting pushed back to the point that when payback will happen your panel will be worthless in efficiency compared to new ones. At industrial / commercial scale it makes sense, but humans like to move houses, and do stuff in the houses and that messes with the payback plans at the individual level.
So either I was in the wrong countries or most people just gamble on the equipment lifetime, but for that I'd rather buy SPY calls, less drama.
It could be as simple as a different model. In one of those it was easy to make it feasible if you had no cap on how much to sell back, but it was limited to consumption plus like 10% or something like that. Since the property used very little energy but had a big roof we thought itd be a good thing to produce green energy while making a little money or even just breaking even, but to break even we'd have to use way more energy which was completely against the original objective. So its not like the technology isn't able to do it but the rules can make it very hard and a few years less of operation for some components make the math very difficult if you're conservative and want to ensure break even within some reasonable timeline
Outside transfer switch and a 10-20kw portable generator is like $4-5k. It requires manual switching but it works for us in our hurricane-prone region. Helped with last years 1 in a 100 year winter storm in our southern region.
Battery/solar doesn’t make sense in my opinion. Too many years to break even like this parent comment said and by the time you break even at 10 years, your system either is too inefficient or needs replacing. At least with the portable generator, you can move it with you to a new home and use it for other things like camping or RVing.
99% of systems are grid tie, so unless you’re spending another $7k for an ATS and associated infrastructure or you’re 100% off grid, your power still goes off.
Whats funny about that -- is you assume thats the case - but a lot of solar isn't installed to be backup power. With Storage yes, but straight up solar -> no.
Don't forget that batteries and solar panels go down to zero value. Money would have performed better in a high yielding savings account.
I personally like simplicity, I'd rather have money in an index fund and just pay a monthly bill over having a complicated solar+battery+car charger install at my house that I have to manage through various apps and dashboards.
If it is about impact on the world, invest in a clean energy index fund. Large solar farms and neighbourhood batteries operate at a much higher efficiency than domestic installations.
Rather like the car, think of panels as buying 20+ years of electricity upfront rather than being exposed to market rates. You can buy a car upfront, on credit, lease it, or rent it; in all of those the longer you commit the cheaper it is.
Not for everyone, but definitely for homeowners with suitable roofs and local utilities.
> For example, CATL is one of four LFP battery suppliers at the Zhangbei National Wind-Solar-Storage Demonstration Project in China. CATL’s batteries are the only ones that have never been replaced, retaining over 90% of residual capacity after 14 years.
Batteries are not only not worthless after almost 15 years in service, they still have sufficient capacity to continue to operate. If you need that capacity back lost to degradation, add a battery ~15 years from now, they will only continue to get cheaper.
I get your point that in modern society, you can invest in an ETF in a few clicks, but in a way, owning your own infrastructure is simpler. Transform the sun into energy reserves with parts you can buy, understand, and install yourself from wholesalers.
A power company is opaque, carries overhead, and requires complexity to serve at an institutional level. ETFs have a similar complexity/abstraction to their customers.
battery life span is defined as when the reach 80% of their original capacity. it's possible that the decline will accelerate after that point but they aren't suddenly useless
Battery prices are getting really low, if you're willing to do some DIY. Just received a 15kWh battery from China. A 'Humsienk'. Combined it with a GroWatt SPA3000TL-BL inverter.
Total price, 1600 euros. So close to the magical 100 euros per kWh. Driving it with some interesting combinations of Raspberry PI's and serial interfaces and custom written Go code, but it works... :)
Did the same, got a solar installer to fit panels on garage and a solis hybrid inverter. They fitted a CT clamp on my meter and a lora device on both sides for it to communicate with the inverter.
Then bought a 16kwh battery for ~£1500, installation was plugging in a positive, negative and ethernet cable and configuring the inverter to use the battery. (if my home insnurer is reading this, I had an electrician friend double check while helping with some other work)
Definitely recommended for anyone who likes tinkering, thousands cheaper than installer pricing.
UK considerations: must be at least signed off by an approved electrician ("Part P" regulations), and for any situations involving subsidy needs to be MCS approved as well. https://mcscertified.com/
Surely it only needs to be signed off if you intend to sell the property with them or sell excess back to the grid. If youre just using the batteries how is anyone going to know?
If the DIY work wasn't the cause for the fire it shouldn't matter, but I half-expect someone to inform me that US insurance companies can (legally) deny coverage for reasons unrelated to the accident.
It "may" not be permitted, but if you live in a collection of shacks in rural Colorado that were themselves -already- completely un-permitted then you might decide that it's best to just do the work yourself.
I do wish I could have a good, in-depth tutorial on how to set this up myself. Along with (pipe dream) an explanation of how it would interact with my local utility. I worry that due to some silly technicality, I won't be able to export to my local utility, or else I won't be able to run off-grid when there's an outage.
I will do a write-up in a couple of days. It's all relatively simple, you just have to expect terrible documentation and do a bit of reverse engineering and serial sniffing. I expected the battery to be complicated, but it turned out that the inverter was.
You'll encounter stuff like: manual says use RS485 port on Battery for GroWatt inverter → need to use CAN port on Battery. Meter Port (RS485 [serial] over RJ45) wiring on GroWatt is unknown (A: white orange / B: white blue, cross them over). Dinky RS485 serial → USB converter needs a 120ohm resistor between pins for line termination. Growatt meter port expects a SDM630 meter, not a DTSU666 (hardcoded), so vibe code another emulator. DIP switches for RS232 connection need to be both on the ON position (undocumented). CH340 USB→serial converter for RS232 does not work, but one with a Prolific chip does. Etc. etc. etc :)
Oh, and the biggest one... I was expecting to be able to just send a command, 'charge at 500watts', now... 'discharge at 2000watts'. But no. You have to emulate a power meter and the inverter will try to bring the net power to 0. Fun! :)
Feel you have more unknowns on the safety front? vs. the expensive off-the-shelf. [in the USA, it’d also be “fewer names to sue” in that unlikely tragedy of combustion in home, but no euro/kWh targets there]
LFP batteries are as likely to burn down your house as a stack of wood is. I'd be worried about the inverter or botched DIY wiring (especially not to spec torque on terminal connections and botched crimps leading to hot spots), but not about the batteries themselves. For a person who wants to save some money, but doesn't know how to work with electricity, the best move is probably to get cheap LFP cells from China, but have a professional install a BMS and the remainder of the solar system.
On a tangent, I’m amazed at how bad most random crimps I see on the internet are. Also, the number of people who debate the use of solder on crimps without discussing potential issues with said solder is too high.
> especially not to spec torque on terminal connections and botched crimps leading to hot spots
This was indeed my greatest concern. However the battery came with pre-crimped very solid DC wires, and nice push connectors for the battery itself. The battery also has an integrated DC breaker (great!).
The system runs 3KW max, so I just added an additional breaker (with RCD integrated) in the conduit box. In NL this is something a DIY-home owner easily can do themselves :) (just use the right solid/flex stranded cabling for the connectors, etc...)
And further, my position has been that learning the correct methods, paying a lot of attention to details, and not being cheap with tools is -still- cheaper and probably more reliable than paying contractors. I have only used my hydraulic crimper for a pair of cables, but it was the correct tool and did good work.
I'm not interfacing with a grid, and there are already code issues with my places- I'd probably feel different if I could get insurance on my place.
Cheap chinese tooling and youtube (plus pretty good general literacy) go a long way in this world.
And FWIW, I live in the US west and am way more worried about fire coming from outside than from the batteries.
Where I am in California, there's a $30+/mo charge to connect to the grid, and the largest savings from a battery was being able to disconnect from the grid. There's lots of time I have excess power generation when I could give to the power grid, if I were connected, but I would have to pay extra to do so, so the potential goes unused.
Is delivering back to the grid economical in California? Where I'm from people disconnect solar panels on sunny days because it costs them money to return to the grid.
But is that rate always positive? Where I'm from during peak sun hours, the rate is negative and you end up paying money to deliver money to the grid. They do this to incentivise you to decouple your solar installation during peak sun hours so the net doesn't get flooded with too much energy.
Good analysis. And kudos to the author for saving money. But still 21.6MWh per year excluding solar production seems too high for a household. I use electric heating and drive an electric vehicle, and my household annual energy consumption is about one fifth of that.
It's more a stress test showing that even with unusually high consumption, solar + batteries + tariff optimisation can still materially change the cost curve
Their total household usage was actually ~17.3 MWh depending on what data source you're using for their usage.
Given 6 MWh of exports with only 3.2 MWh of total solar production, they are cycling their powerwall to get paid for the fact that their off-peak rate is half the price of their peak export tariff rate which is inflating the number you're looking at.
Not all homes are made equal: different appliances & electronics from different vintages, etc.
I have 2 EVs (Tesla and BMW), an electric oven, and a homelab rack (but no HVAC), and my usage was 34.4 MWh last year — with 100% from Solar and Powerwall.
I’m waiting on a quote for an hvac that uses its waste heat for the home hot water. Im irritated that I’m cooling the house, pushing out hot air, and heating water at the same time.
Get a basic heat recovery unit, it basically has no moving parts (just a few fans) and good ones recover 90%+ of the heat going out of your house. It's almost useless if you don't have an airtight envelope though.
All in one systems with water heating are way too complex and _will_ fail relatively quickly, mini heat pumps won't last 10 years, and by the time it dies you won't be able to find a replacement for your specific model
On that avenue, I do push hot air from my homelab into my upper garage for heat. If it below 50deg outside I also bring in some cold air from outside. Both are somewhat free offsets for heating/cooling.
We brought down our energy consumption substantially over the years starting not so far from that high figure, including swapping out racks of Sun servers for an RPi or two, and we are now slight net exporters of utility energy and with it roughly zero carbon...
That’s about double the average household so I would imagine spending that money and effort into energy efficiency would pay off way better that solar and batteries.
Yea, averages don't work well when talking about single units without any further details.
How many sq/ft is the house?
Is it filled with windows facing south?
Are they firing a continuous laser beam at the moon?
2-3x usage is actually pretty typical when looking at a single house when comparing to average. It's when you start getting close to an order of mag difference that you're an outlier.
I used about 64MWh last year, not counting what I used for EV charging (Which is on a separate meter). I also produced about 20MWh from Solar. With the EVs I would guess the total is around 70MWh.
Some of this extra is certainly my 6kw homelab + HVAC for that. ;)
It's high but it really depends on your lifestyle and appliances.
If you have a heat pump water heater and heat pump based floor heating you'll use 1/4th of the energy as the same house with resistive water/floor heating.
A house which barely passed regulation from 2010 will consume 5-10x the energy of a certified passive house.
etc.
That being said I think you have to draw the line somewhere. I'd much rather have inefficient appliances (resistive boiler/heaters) and be fully solar powered than spend 50k in heatpumps and other gimmicks that are rated for 10 years and cost a kidney in maintenance and the eventual replacement.
Overly complex and fragile in the long run, the savings are meaningless if you're already self sufficient. I'd much rather spend the money in insulation and self sufficiency than these voodoo appliances.
That's my reasoning my new build house with plenty of land. In other scenarios it might be more beneficial to go for them.
It depends where you live, where you get your electricity from, for how much, &c. It's an amazing tech don't get me wrong, and of course youtube tech nerds love these kind of things, no surprise here, I just don't think it's the silver bullet everybody imagine it is.
I'm talking about geothermal water/water installs for central heating.
No one is heating their place with air/air heat pumps besides americans who haven't figured out that heating spaces via air is shit tier in term of comfort and efficiency
> No one is heating their place with air/air heat pumps besides americans who haven't figured out that heating spaces via air is shit tier in term of comfort and efficiency
At least here in Finland a lot of people do. Very popular choice when replacing old oil furnaces (and as a "replacement" for direct electric heating offcourse)
Geothermal heatpump is something people mostly think about when building new.
Air heatpumps with the inside unit start from around 1000€ and 300€ to 500€ for the install. The price is mainly based on the size of the house (and in big houses you will need multiple or one with multiple inside units)
A fireplace for the couple really cold weeks to cut down the electricity bills are popular but people had those even before the air heatpumps so nothing new really.
Separation of concerns is the king of avoiding pricy maintenance and headaches.
You can already do most of that with a passive heat recovery ventilation system coupled to a ground/water exchanger. All systems are independent and the most high tech equipments you need are fans and a water pump
This number can mean wildly different things depending on the size of your house (and location).
I live in the Bay Area, CA in a 1,500 square foot house and consumed 7.8MWh in 2025 and 7.6 MWh in 2024.
Digging a bit more into our solar system data:
We produced a bit over 9MWh in solar each year and it looks like our Enphase batteries discharged 2MWh each year.
An average EV battery is what, around 70kWh? Add in a bit of charging losses and we'll say maybe 75kWh being generous here, and that's assuming a nearly dead battery to a full charge. Doing that every month is then 900kWh, or 0.9MWh/yr. That's ~4% of the energy usage of 21MWh/yr.
An average EV gets what, ~3.5mi/kWH? An average US car does ~12,000mi/yr. That theoretical average EV would then use ~3.5MWh. Two would be ~7. But this author is in the UK, where the average car only does ~7,500mi/yr or so or a little over 2MWh/yr. So for their two UK cars, assuming they drove an average mileage in an average EV efficiency, they would likely have used something like 4.3MWh/yr for their cars. About 20% of their total electricity usage. This drops a good bit if they're really getting closer to 4mi/kWh in efficiency, which is likely if they're not driving on many highways like one does in the US.
EV charging inefficiency typically loses 10-25% of the input energy, depending on temperature and battery level (low temps are bad, very low or high battery level also bad for efficient transfer).
In 2025 I produced 6.5MWh (solar) and consumed 12.7MWh (excluding solar production); this is a family of 4 in a 4 season climate with electric heating and a single electric car.
That was my highest year over the past 5 years.
An additional EV can really add up, especially if both people have long commutes.
This setup only really works because of a very specific combination of smart tariffs, EVs, and aggressive automation. Without those, the math would look very different
> The batteries can fill up on the off-peak rate overnight at £0.07/kWh, and then export it during the peak rate for £0.15/kWh, meaning any excess solar production or battery capacity can be exported for a reasonable amount.
Honestly I didn't know this was allowed.
I recently got a heat pump and am on a time-of-use tariff (https://octopus.energy/smart/cosy-octopus/) and have been thinking about pulling the plug on battery storage for a similar purpose (charge during the cheap hours; run the house off battery during the day). I am currently using between 40-50kWh per day - anyone have similar usage to this and can recommend batteries for this?
It benefits the grid to have people consume extra power when there's an oversupply, store it and give it back when there's undersupply. Why shouldn't it be allowed (even encouraged)?
The rooftop solar game in Texas is strongly into scam territory. Most homes I see with panels on the roof are two story homes where you have a negligible amount of area to work with relative to interior space. There was a point where you'd have to deal with a door-to-door salesman approximately every 48h for an entire summer.
The most realistic residential installation I've seen was firmly on the ground at a ~2 acre property. The panels were much larger and heavier (i.e., capable) than what you'd typically find on a roof. It's much easier to build and maintain a solar array when you don't need a ladder/crane to move things around.
I think that it's great that we want to participate in making things better, but not every situation makes sense. When you factor in all of the downstream consequences of sub-optimal, fly-by-night installs, it starts to look like a net negative on the environment. I'm not trying to claim that all rooftop solar projects are bad, but most of the residential ones I've seen make absolutely zero economic sense.
Large scale wind and solar projects are the best way forward. You get so much more bang for buck. I'd consider investing in these projects or their upstream suppliers and owners if you want to get involved financially in making the environment a better place.
This is indeed nice for a well-to-do home. But there is a tragedy of the commons issue here.
The grid needs to be up 24/7. And while peak usage is just that, the grid capacity still needs to support peak usage.
This can theoretically be done using batteries but not for an extended amount of time. To say we can have batteries for 2 weeks of normal consumption is highly improbable.
The metals do build those batteries do not exist. Or put in a worse way, the mines do not exist.
Residential solar with batteries greatly aids the grid and reduces costs for the entire system.
> The metals do build those batteries do not exist. Or put in a worse way, the mines do not exist.
Lithium and sodium, the two most promising battery metals, are not usually mined, though in Australia I hear there is mining. It's more of a brine process. All across the US, frackers are finding that all that water they are pulling out is a fairly rich lithium brine.
The amount of metal needed for 2 weeks of batteries is pretty trivial compared to the system we've built for extracting fossil fuels, and iron, etc. The bigger demands for electrification are acutally copper! Gotta wire everything....
Grid batteries on the GWh scale make a ton of sense financially and environmentally, and are revolutionizing the grid. Never before has the grid had a way to store electricity on a grand scale, which changes the entire nature of the beast. It's was one of the only massive systems we had where there wasn't buffering!
With storage, we can alleviate congested transmission without super costly transmission upgrades. On exist lines, we can the usage massively, reducing costs, because now we can buffer across time to shave off the peak demand.
Batteries are easy to build, environmentally friendly, and like a swiss army knife in their number of applications. We will be producing TWh of batteries a year in modern economies, and they last ~20 years, meaning that for the foreseeable economic growth in the coming decades, we'll easily have a peta-watthour of battery storage in use at a time.
Nobody needs that, but from my point of view batteries will be so cheap and abundant that we will likely get to having 2 weeks of storage just sitting around the grid or rolling on wheels.
People always underestimate where exponential cost decreases will take us. Current battery production grows by 10x in a mere 5 years. In a decade, the time it takes to build a nuclear power plant, we will grow our battery production by 100x. Not enough people take this seriously, or even know that the trend exists.
Yes, it does. I haven't tried it as a do not have the cable for it, but the user interface for discharge is there and the manual also talks about this feature.
It's probably not ideal for running a full house (as it would require some other electronics and installations), but a couple of appliances should work.
Those batteries must be connected to the internet to work, and the company could disable them anytime. Same for most of the inverters. I’m just hoping they don’t pull some nonsense like we have seen with other “cloud” devices. In that sense, I trust Tesla as much as BYD, and that is not at all.
this can be disallowed in the UK, depending on their agreement either their provider. the OP is exporting way more energy than they have ever produced through solar; in effect they’re selling back off-peak energy to the grid, which is making a profit
The equipment doesn’t have moving parts so I wouldn’t expect it to break down so quickly.
The real surprise for me was how much having solar panels on your roof adds to the cost of roofing work. Which is a problem because the roof is likely to need repairs more often than the solar panels.
Yeah it's a tradeoff on the roof. The panels also increase the lifetime of the roof.
Solar panels are incredibly durable, there's a thriving secondary market for used panels, and we're likely to see 30-50 years of usage out of any panel created today.
Cracking the problem of making the roof out of solar panels seems like a fantastic engineering challenge. But not one with small tiles, make the roof out of the bigger cheap large panels. I would love to see startups working on that. Asphalt roofs look like crap anyway, changing to shiny panels would be a huge improvement IMHO
I am just wondering would stacking up batteries, charging them off-peak and using/selling back during peak usage be as good as this, or even better? Seems like this shouldn't be a viable scenario, but given the prices and idle capacity, it seems just investing in batteries and charging them at night, to be used/sold to the grid during the day would be as good as a solar installation.
The author pays £0.07/kWh off peak, but can export at £0.15/kWh. The author paid ~£7500 per powerwall which has ~13.5kWh capacity. Assuming full charge/discharge every night, you can make ~£1.08 per day, which works out to about 19 years to pay back.
Utilities normally consider disincentivizing this type of behavior from residential customers as one of the factors when setting their export pricing.
You can usually save more by generating solar locally and using it to power the home and charge the battery, then discharging the battery during peak hours (usually around and just after sunset) to earn the most. Obviously higher upfront capex.
Pure grid cycling is also frowned on by some utilities.
Octopus in the UK has tariffs where it basically takes over your system (ie the batteries in particular) and subsumes them into its wider activities, eg:
>it seems just investing in batteries and charging
I mean a lot of companies already do this with megawatt/gigawatt installations.
The key is peaking and grid stabilization. If you're a huge provider you can pay for all your batteries in a year or two if there is some large grid emergency and rates skyrocket.
If you're a non-commercial user, it's going to be hard because the provider rates you pay/get paid are much more likely to be fixed at a pretty low rate.
Don't be surprised when the answer is "not much". Apply supply and demand to electric power generation. If your grid rate is getting hiked then so is the market price of used solar.
So what I take away is that he is using approx 3x electricity, that I do and that is including my electric car. I use an additional 5-7MWh of heat but on a heat pump that would still only be a max of 2MWh which doesn’t even bring me to half of his usage, for a family of 4.
Solar panel investment has slowed down substantially in Sweden. Basically, when the sun is shining, electricity is close to free. Similar situation with wind power.
Neither technology can move forward until there's a 100x leap in electricity storage costs. Like a bunch of us said 10 years ago, because we remembered high school physics.
It's wild how overpriced Tesla Powerwalls are.
16 kWh battery with all of the UL supported listings etc = $3300 [0]
13.5 kWh Tesla Powerwall is $12k~$15k
You would get your return way back quicker.
[0] - https://www.ruixubattery.com/product-page/lithi2-16-battery-...
EDIT: As others have pointed out, powerwalls have inverters built in so it's not totally apples to apples. You can get a beefy inverter for $5k and it's still cheaper and you wouldn't need an additional inverter every time you add a battery.
IIRC, the original idea was that they would pull older batteries from circulation when their capacities dipped, and then repurpose them as powerwalls, an application where weight is irrelevant.
This was back when they expected the batteries to plateau at ~80% capacity after a few years, and they had battery swapping on the roadmap, so they needed to plan for a future where they had a steady supply of batteries that car customers did not want.
The idea took hold, but the batteries lasted longer and swapping didn't pan out, so now they are competing with themselves for battery supply.
Electric car battery degradation has been super interesting, in that they are going way further than people thought they might. Jonny Smith on youtube bought a 300k+ mile Tesla and the battery is at like 75% health.
As far as I can tell if your battery isn't air cooled, it can go a very long way
There was some research[1] that strongly suggested that varied use makes them last much longer than the steady use that most battery tests do. That is, bursts of high-current draw followed by moderate draw etc vs the constant current load typically used when evaluating battery performance. From the paper:
Specifically, for the same average current and voltage window, varying the dynamic discharge profile led to an increase of up to 38% in equivalent full cycles at end of life.
This was unexpected, hence explains why they fared better than predicted.
[1]: https://www.nature.com/articles/s41560-024-01675-8 Dynamic cycling enhances battery lifetime (open access)
Any idea why swapping didn't pan out for Tesla? My understanding is they are doing that in China.
Probably because the economics just don't make sense here. You'd have to have so many compatible cars on the road, driving all day with no opportunity to charge. I'm having a hard time imagining a place I've been to in North America where that'd seem logical.
> they are doing that in China
Are they actually doing that at scale?
They have a 30% gross margin, they're just soaking up the federal US tax credit (which is also 30% for battery storage and extends through 2032).
Alternatives: https://electrek.co/2025/12/28/opinion-its-time-to-start-rec...
A few of the alternatives have been reviewed by Will Prowse as well. His YT is a treasure of information. https://www.youtube.com/@WillProwse
I think "overpriced" depends a lot on what problem you're trying to solve
That's not really apples-to-apples comparison. The Tesla batteries are AC coupled so they work with an (AC coupled) microinverter array. For a DC coupled battery you have to have a hybrid inverter and DC couple the batteries.
Your point that they are overpriced still stands though.
Ya as someone else pointed out, powerwalls essentially have an inverter built in. But this is really dumb to have inverters tied directly to each powerwall battery. This is like anti-scale.
You're comparing the cost of a battery with a full system. That 16 kWh battery requires a ~$3000 inverter to go along with it.
Well, the math still maths, right?
I am writing this off grid, using about 15kwh of batteries and a $1200 (6kw) inverter. My entire system puls panels and racking those panels, plus wiring some un-powered shacks was about $10k, though I did the work myself (which would probably hae been another 3-5k if I could have found someone to do it.
> which would probably hae been another 3-5k if I could have found someone to do it.
Yo. If you can find an electrician to stop by my house and turn a light switch off for less than 1000$, please inform me. I got a quote for 25k$ to install a system that size, and that price. City code has me by the balls: I can't modify my main panel without inspection, the inspector won't show up without a licensed electrician, and electrician wants the labor. I pointed out that we're talking 8 hours of labor — call it 2500$, lawyer money — and he was like "what's your choice". I'm in Texas.
That's fair.
Better comparison:
Author's config:
3x Powerwalls + inverters = 40 kWh
4.2 kW array
£39,360 = $53k USD
Alternative:
EG4 18kPV Hybrid Inverter = $5000
3x RIUXU = $9600
10x Trina Solar 435w panels = $1580
Cabling, installations, etc. = $5000
Total = $21k
It's not even close...
This is still not an accurate comparison. I'm not a Tesla fanboy but of all of the major players in the non-diy game (Enphase, Franklin, Tesla, Sol-Ark) they provide the best value for money, and are impressive pieces of equipment.
The EG4 18k has 11.5 kw backfeed capability, with a rather pathetic 65ish amp in-rush. Obviously 18kw usable solar capacity(they technically let you land up to 21kw, but only 18 is usable).
The Powerwall system you outlined can take 60kw of usable solar input, has 34kw standing backfeed capability, and a whopping 555 amp in-rush (not a typo, it's 185 amps per unit).
Not to get in to warranties, etc.
9-11 year payback isn't bad based on the projections. You could probably goose it a bit with inflation of electrical prices (depends on how the electrical policies change and what they pass through).
I'll also add theres some O&M coming down the line. Inverters @ year 10, small maintenance and Im assuming you re-did your roof before you installed. Anyone putting solar up make sure you do it at the same time as a roof because taking it down to redo a roof kills your economic value.
> I'm assuming you re-did your roof before you installed
In the UK I would expect the roof to be tile, which lasts basically forever unless a storm hits hard enough.
I did have to have my panels taken down and refitted, at a cost of well over £1000, because I hadn't bird-proofed underneath them (wasn't suggested by original installer). So watch out for that one.
The payback math almost certainly improves if electricity prices keep rising faster than inflation
It is essentially a bond return, with the caveat being that solar PV panels will last 25+ years with some degradation and reduction in output. To your point, the best arrangement (imho) is a standing seam metal roof (40-70 year lifetime) with the panels mounted via friction racking with no roof deck penetrations. This avoids the economic cost of pulling everything off the roof to re-roof, and should outlive any homeowner 40 years of age or older. I also expect labor willing to get on a roof becoming more scarce and expensive over time in the developed world, which I think should be taken into account. Your battery storage can be replaced 10-15 years from now at the end of its service life by anyone with a hand truck.
Significantly lower than a bond return, as the value of the installation will go down to zero eventually, while the initial principal of your bond investment will remain intact.
This is factually inaccurate. Solar PV panels will continue to produce power at 80-90% of rated output after 25 years, and battery storage will still have 80-90% capacity. I'm sure you can understand that as long as the system is storing and producing power at these levels, its value is not zero.
Can you point out what part of what I said is factually inaccurate?
https://magnifina.com/articles/rooftop-solar-yield/ explains it better than me attempting to write a wall of text.
Wont you need to replace the batteries around Year 10 and then this becomes a wash?
Why would you need to replace the batteries? Do they fail outright at around 10 years, become unsafe, or do they just lose capacity?
Curious!
Even if they're at 50% capacity, they would still work, right? But if there are other considerations, especially safety ones, then that would definitely be a consideration. I'm not sure where to learn about this type of thing.
> Do they fail outright at around 10 years, become unsafe, or do they just lose capacity?
LiFePO4 generally degrades to 80% capacity after 10 years, that's it. Safety isn't an issue.
Almost all simulations I've done across 3 countries with 3 different payback models for selling back to grid (one of the three doesn’t allow selling back almost anything above your consumption), I could never make investing in Solar not being a gamble.
You really need to gamble on odds of replacing equipment being very low for it to make sense. And in practice most people I anecdotally know that run it, after 5-7 years have already done additional purchases. The payback time keeps getting pushed back to the point that when payback will happen your panel will be worthless in efficiency compared to new ones. At industrial / commercial scale it makes sense, but humans like to move houses, and do stuff in the houses and that messes with the payback plans at the individual level.
So either I was in the wrong countries or most people just gamble on the equipment lifetime, but for that I'd rather buy SPY calls, less drama.
Having done 2 solar installs, one over 10 years and one 6 years, both going strong. Nothing else needed, it just sits there and produces.
So, from my experience, that's not the case. Maybe the people you know keep tweaking because they're enthusiasts like you have with cars.
It could be as simple as a different model. In one of those it was easy to make it feasible if you had no cap on how much to sell back, but it was limited to consumption plus like 10% or something like that. Since the property used very little energy but had a big roof we thought itd be a good thing to produce green energy while making a little money or even just breaking even, but to break even we'd have to use way more energy which was completely against the original objective. So its not like the technology isn't able to do it but the rules can make it very hard and a few years less of operation for some components make the math very difficult if you're conservative and want to ensure break even within some reasonable timeline
Having power when your entire neighborhood is off, priceless.
[edit: yes, I assume you also get batteries, I know that solar alone doesn't magically power your house.]
Outside transfer switch and a 10-20kw portable generator is like $4-5k. It requires manual switching but it works for us in our hurricane-prone region. Helped with last years 1 in a 100 year winter storm in our southern region.
Battery/solar doesn’t make sense in my opinion. Too many years to break even like this parent comment said and by the time you break even at 10 years, your system either is too inefficient or needs replacing. At least with the portable generator, you can move it with you to a new home and use it for other things like camping or RVing.
99% of systems are grid tie, so unless you’re spending another $7k for an ATS and associated infrastructure or you’re 100% off grid, your power still goes off.
Whats funny about that -- is you assume thats the case - but a lot of solar isn't installed to be backup power. With Storage yes, but straight up solar -> no.
It's not the default but you can get it installed that way or get it adapted later (less than ideal if you end up having to replace the inverter).
Yea, that costs extra. My dad went for the natural gas generator.
Well there are other, far cheaper ways to get that.
Don't forget that batteries and solar panels go down to zero value. Money would have performed better in a high yielding savings account.
I personally like simplicity, I'd rather have money in an index fund and just pay a monthly bill over having a complicated solar+battery+car charger install at my house that I have to manage through various apps and dashboards.
If it is about impact on the world, invest in a clean energy index fund. Large solar farms and neighbourhood batteries operate at a much higher efficiency than domestic installations.
I'm with you. I have no interest in owning, running, and maintaining my own personal electrical utility.
I'm happy to pay monthly to let my electrical provider handle all that, and I'll invest my money in something with a better return.
Rather like the car, think of panels as buying 20+ years of electricity upfront rather than being exposed to market rates. You can buy a car upfront, on credit, lease it, or rent it; in all of those the longer you commit the cheaper it is.
Not for everyone, but definitely for homeowners with suitable roofs and local utilities.
https://electrek.co/2026/01/06/catl-ev-batteries-significant...
> For example, CATL is one of four LFP battery suppliers at the Zhangbei National Wind-Solar-Storage Demonstration Project in China. CATL’s batteries are the only ones that have never been replaced, retaining over 90% of residual capacity after 14 years.
Batteries are not only not worthless after almost 15 years in service, they still have sufficient capacity to continue to operate. If you need that capacity back lost to degradation, add a battery ~15 years from now, they will only continue to get cheaper.
Is an ETF simple?
I get your point that in modern society, you can invest in an ETF in a few clicks, but in a way, owning your own infrastructure is simpler. Transform the sun into energy reserves with parts you can buy, understand, and install yourself from wholesalers.
A power company is opaque, carries overhead, and requires complexity to serve at an institutional level. ETFs have a similar complexity/abstraction to their customers.
> Large solar farms and neighbourhood batteries operate at a much higher efficiency than domestic installations.
Maybe, but that power is typically generated far from where it's consumed and so you have significant transmission losses.
battery life span is defined as when the reach 80% of their original capacity. it's possible that the decline will accelerate after that point but they aren't suddenly useless
Battery prices are getting really low, if you're willing to do some DIY. Just received a 15kWh battery from China. A 'Humsienk'. Combined it with a GroWatt SPA3000TL-BL inverter.
Total price, 1600 euros. So close to the magical 100 euros per kWh. Driving it with some interesting combinations of Raspberry PI's and serial interfaces and custom written Go code, but it works... :)
Did the same, got a solar installer to fit panels on garage and a solis hybrid inverter. They fitted a CT clamp on my meter and a lora device on both sides for it to communicate with the inverter.
Then bought a 16kwh battery for ~£1500, installation was plugging in a positive, negative and ethernet cable and configuring the inverter to use the battery. (if my home insnurer is reading this, I had an electrician friend double check while helping with some other work)
Definitely recommended for anyone who likes tinkering, thousands cheaper than installer pricing.
> Battery prices are getting really low, if you're willing to do some DIY.
Willing and allowed. In some countries it can only be done by certified electricians.
UK considerations: must be at least signed off by an approved electrician ("Part P" regulations), and for any situations involving subsidy needs to be MCS approved as well. https://mcscertified.com/
Surely it only needs to be signed off if you intend to sell the property with them or sell excess back to the grid. If youre just using the batteries how is anyone going to know?
I'd assume your fire insurance covers nothing if illegally installed batteries are found inside after a house fire.
If your house burns down for any reason, not necessarily the DYI batteries, the insurance company will know anyway.
If the DIY work wasn't the cause for the fire it shouldn't matter, but I half-expect someone to inform me that US insurance companies can (legally) deny coverage for reasons unrelated to the accident.
shrug if you can rely on nobody noticing, or non-enforcement, sure, but it is actually a criminal offence not just an administrative requirement.
I mean, it "can" be done without a certificate.
It "may" not be permitted, but if you live in a collection of shacks in rural Colorado that were themselves -already- completely un-permitted then you might decide that it's best to just do the work yourself.
I do wish I could have a good, in-depth tutorial on how to set this up myself. Along with (pipe dream) an explanation of how it would interact with my local utility. I worry that due to some silly technicality, I won't be able to export to my local utility, or else I won't be able to run off-grid when there's an outage.
I will do a write-up in a couple of days. It's all relatively simple, you just have to expect terrible documentation and do a bit of reverse engineering and serial sniffing. I expected the battery to be complicated, but it turned out that the inverter was.
You'll encounter stuff like: manual says use RS485 port on Battery for GroWatt inverter → need to use CAN port on Battery. Meter Port (RS485 [serial] over RJ45) wiring on GroWatt is unknown (A: white orange / B: white blue, cross them over). Dinky RS485 serial → USB converter needs a 120ohm resistor between pins for line termination. Growatt meter port expects a SDM630 meter, not a DTSU666 (hardcoded), so vibe code another emulator. DIP switches for RS232 connection need to be both on the ON position (undocumented). CH340 USB→serial converter for RS232 does not work, but one with a Prolific chip does. Etc. etc. etc :)
Oh, and the biggest one... I was expecting to be able to just send a command, 'charge at 500watts', now... 'discharge at 2000watts'. But no. You have to emulate a power meter and the inverter will try to bring the net power to 0. Fun! :)
Awesome.
Feel you have more unknowns on the safety front? vs. the expensive off-the-shelf. [in the USA, it’d also be “fewer names to sue” in that unlikely tragedy of combustion in home, but no euro/kWh targets there]
LFP batteries are as likely to burn down your house as a stack of wood is. I'd be worried about the inverter or botched DIY wiring (especially not to spec torque on terminal connections and botched crimps leading to hot spots), but not about the batteries themselves. For a person who wants to save some money, but doesn't know how to work with electricity, the best move is probably to get cheap LFP cells from China, but have a professional install a BMS and the remainder of the solar system.
> botched crimps
On a tangent, I’m amazed at how bad most random crimps I see on the internet are. Also, the number of people who debate the use of solder on crimps without discussing potential issues with said solder is too high.
> especially not to spec torque on terminal connections and botched crimps leading to hot spots
This was indeed my greatest concern. However the battery came with pre-crimped very solid DC wires, and nice push connectors for the battery itself. The battery also has an integrated DC breaker (great!).
The system runs 3KW max, so I just added an additional breaker (with RCD integrated) in the conduit box. In NL this is something a DIY-home owner easily can do themselves :) (just use the right solid/flex stranded cabling for the connectors, etc...)
And further, my position has been that learning the correct methods, paying a lot of attention to details, and not being cheap with tools is -still- cheaper and probably more reliable than paying contractors. I have only used my hydraulic crimper for a pair of cables, but it was the correct tool and did good work.
I'm not interfacing with a grid, and there are already code issues with my places- I'd probably feel different if I could get insurance on my place.
Cheap chinese tooling and youtube (plus pretty good general literacy) go a long way in this world.
And FWIW, I live in the US west and am way more worried about fire coming from outside than from the batteries.
We are finally starting to see Chinese prices externally.
It’s been crazy seeing the western home storage market with €/kWh being more expensive than buying a BEV.
https://www.docanpower.com/eu-stock/zz-48kwh-50kwh-51-2v-942...
Where I am in California, there's a $30+/mo charge to connect to the grid, and the largest savings from a battery was being able to disconnect from the grid. There's lots of time I have excess power generation when I could give to the power grid, if I were connected, but I would have to pay extra to do so, so the potential goes unused.
Is delivering back to the grid economical in California? Where I'm from people disconnect solar panels on sunny days because it costs them money to return to the grid.
PG&E does net metering, but even at a sub 1:1 rate past your net usage it does not make sense that it costs more to send energy back to the grid
The worst that happens is you get paid back at the wholesale rate (from your bill, not live market price) instead of discounting kwh-per-kwh.
But is that rate always positive? Where I'm from during peak sun hours, the rate is negative and you end up paying money to deliver money to the grid. They do this to incentivise you to decouple your solar installation during peak sun hours so the net doesn't get flooded with too much energy.
It probably means that you would contribute less than cost of maintaining your grid connection ($30/mo)
Good analysis. And kudos to the author for saving money. But still 21.6MWh per year excluding solar production seems too high for a household. I use electric heating and drive an electric vehicle, and my household annual energy consumption is about one fifth of that.
It's more a stress test showing that even with unusually high consumption, solar + batteries + tariff optimisation can still materially change the cost curve
Their total household usage was actually ~17.3 MWh depending on what data source you're using for their usage.
Given 6 MWh of exports with only 3.2 MWh of total solar production, they are cycling their powerwall to get paid for the fact that their off-peak rate is half the price of their peak export tariff rate which is inflating the number you're looking at.
That is still an enormous amount of electricity for a single family to consume.
It's less than 50kwh a day, high but seems reasonable with 2 electric cars.
Not all homes are made equal: different appliances & electronics from different vintages, etc.
I have 2 EVs (Tesla and BMW), an electric oven, and a homelab rack (but no HVAC), and my usage was 34.4 MWh last year — with 100% from Solar and Powerwall.
That’s an awful lot of power.
I’m waiting on a quote for an hvac that uses its waste heat for the home hot water. Im irritated that I’m cooling the house, pushing out hot air, and heating water at the same time.
Get a basic heat recovery unit, it basically has no moving parts (just a few fans) and good ones recover 90%+ of the heat going out of your house. It's almost useless if you don't have an airtight envelope though.
All in one systems with water heating are way too complex and _will_ fail relatively quickly, mini heat pumps won't last 10 years, and by the time it dies you won't be able to find a replacement for your specific model
On that avenue, I do push hot air from my homelab into my upper garage for heat. If it below 50deg outside I also bring in some cold air from outside. Both are somewhat free offsets for heating/cooling.
You just need an air source heat pump water heater and install the water heater next right to the outdoor unit for the HVAC.
We brought down our energy consumption substantially over the years starting not so far from that high figure, including swapping out racks of Sun servers for an RPi or two, and we are now slight net exporters of utility energy and with it roughly zero carbon...
https://www.earth.org.uk/saving-electricity.html
I can’t see any mention of hot water or cooking in the article, which may be relevant.
I was stoked at the power saving from turning off an espresso machine a bit sooner, a swapping out a nuc to a Mac mini.
Maybe there is a bit coin mining operation in his basement?
That’s about double the average household so I would imagine spending that money and effort into energy efficiency would pay off way better that solar and batteries.
The average household doesn't have two electric cars though
Yea, averages don't work well when talking about single units without any further details.
How many sq/ft is the house?
Is it filled with windows facing south?
Are they firing a continuous laser beam at the moon?
2-3x usage is actually pretty typical when looking at a single house when comparing to average. It's when you start getting close to an order of mag difference that you're an outlier.
I used about 64MWh last year, not counting what I used for EV charging (Which is on a separate meter). I also produced about 20MWh from Solar. With the EVs I would guess the total is around 70MWh.
Some of this extra is certainly my 6kw homelab + HVAC for that. ;)
maybe saving money they used more - in other words Jevon's paradox https://en.wikipedia.org/wiki/Jevons_paradox
thus perhaps leading to more global warming
It's high but it really depends on your lifestyle and appliances.
If you have a heat pump water heater and heat pump based floor heating you'll use 1/4th of the energy as the same house with resistive water/floor heating.
A house which barely passed regulation from 2010 will consume 5-10x the energy of a certified passive house.
etc.
That being said I think you have to draw the line somewhere. I'd much rather have inefficient appliances (resistive boiler/heaters) and be fully solar powered than spend 50k in heatpumps and other gimmicks that are rated for 10 years and cost a kidney in maintenance and the eventual replacement.
Heatpumps are not a gimmick - they're an excellent technology with lots of efficient and effective uses :)
Heatpumps, Shmeetpumps
Overly complex and fragile in the long run, the savings are meaningless if you're already self sufficient. I'd much rather spend the money in insulation and self sufficiency than these voodoo appliances.
That's my reasoning my new build house with plenty of land. In other scenarios it might be more beneficial to go for them.
Heat pumps are no more fragile than air conditioners.
Which are famously reliable and cheap to service...
Yes, and that's why I have none.
No fridge? That's a heat pump.
>heatpumps and other gimmicks
Anecdotally, two of the smartest people I know love heat pumps—doesn’t Technology Connections too?
Was probably this:
https://youtube.com/watch?v=7J52mDjZztoIt depends where you live, where you get your electricity from, for how much, &c. It's an amazing tech don't get me wrong, and of course youtube tech nerds love these kind of things, no surprise here, I just don't think it's the silver bullet everybody imagine it is.
Heat pumps aren't particularly expensive though and they can provide cooling.
Heatpumps can now be had for less than £10k .. if you don't have to replace your radiators.
I do think more people should consider mini-split reversible AC in the UK, but the subsidy system specifically excludes it.
UK government subsidy support for air-to-air was announced a couple of months ago:
https://www.gov.uk/government/news/discounts-for-families-to...
Who spends $50K on heat pumps? They're not anywhere near that expensive.
I'm talking about geothermal water/water installs for central heating.
No one is heating their place with air/air heat pumps besides americans who haven't figured out that heating spaces via air is shit tier in term of comfort and efficiency
> No one is heating their place with air/air heat pumps besides americans who haven't figured out that heating spaces via air is shit tier in term of comfort and efficiency
At least here in Finland a lot of people do. Very popular choice when replacing old oil furnaces (and as a "replacement" for direct electric heating offcourse)
Geothermal heatpump is something people mostly think about when building new.
Air heatpumps with the inside unit start from around 1000€ and 300€ to 500€ for the install. The price is mainly based on the size of the house (and in big houses you will need multiple or one with multiple inside units)
A fireplace for the couple really cold weeks to cut down the electricity bills are popular but people had those even before the air heatpumps so nothing new really.
Having one place to handle humidity, temperature, and exchange of fresh air makes ductwork the king of comfort and efficiency.
Separation of concerns is the king of avoiding pricy maintenance and headaches.
You can already do most of that with a passive heat recovery ventilation system coupled to a ground/water exchanger. All systems are independent and the most high tech equipments you need are fans and a water pump
When your annual temperature range is -40 to 40 C (or a bit over 100 F) central air HVAC is a life saver.
says the guy calling heat pumps "voodoo appliances"
I forgot HN doesn't understand humor, I'll try to turn it down next time my bad.
20MWh is around what my house used in both 2024 and 2025.
This number can mean wildly different things depending on the size of your house (and location).
I live in the Bay Area, CA in a 1,500 square foot house and consumed 7.8MWh in 2025 and 7.6 MWh in 2024.
Digging a bit more into our solar system data: We produced a bit over 9MWh in solar each year and it looks like our Enphase batteries discharged 2MWh each year.
From the article: "My wife and I both drive electric cars"
That probably explains it.
Yeah but they both work from home. The biggest reason for putting mileage on the car, commuting, is now out.
A single extra charge in a month can really mess the stats up.
An average EV battery is what, around 70kWh? Add in a bit of charging losses and we'll say maybe 75kWh being generous here, and that's assuming a nearly dead battery to a full charge. Doing that every month is then 900kWh, or 0.9MWh/yr. That's ~4% of the energy usage of 21MWh/yr.
An average EV gets what, ~3.5mi/kWH? An average US car does ~12,000mi/yr. That theoretical average EV would then use ~3.5MWh. Two would be ~7. But this author is in the UK, where the average car only does ~7,500mi/yr or so or a little over 2MWh/yr. So for their two UK cars, assuming they drove an average mileage in an average EV efficiency, they would likely have used something like 4.3MWh/yr for their cars. About 20% of their total electricity usage. This drops a good bit if they're really getting closer to 4mi/kWh in efficiency, which is likely if they're not driving on many highways like one does in the US.
EV charging inefficiency typically loses 10-25% of the input energy, depending on temperature and battery level (low temps are bad, very low or high battery level also bad for efficient transfer).
I think Scott's usage is high – I think he mentions between £300-400 / month – but then he's got a hot tub, server rack as well as the cars.
We still have an ICE car and gas central heating but our combined electricity and gas bill is around £140 / month
Plan to go to EV and heat pump in our next house though
I'm an example more towards the middle.
In 2025 I produced 6.5MWh (solar) and consumed 12.7MWh (excluding solar production); this is a family of 4 in a 4 season climate with electric heating and a single electric car.
That was my highest year over the past 5 years.
An additional EV can really add up, especially if both people have long commutes.
They have no commutes. They both work from home. I don’t even understand why they need two cars for that.
This setup only really works because of a very specific combination of smart tariffs, EVs, and aggressive automation. Without those, the math would look very different
> The batteries can fill up on the off-peak rate overnight at £0.07/kWh, and then export it during the peak rate for £0.15/kWh, meaning any excess solar production or battery capacity can be exported for a reasonable amount.
Honestly I didn't know this was allowed.
I recently got a heat pump and am on a time-of-use tariff (https://octopus.energy/smart/cosy-octopus/) and have been thinking about pulling the plug on battery storage for a similar purpose (charge during the cheap hours; run the house off battery during the day). I am currently using between 40-50kWh per day - anyone have similar usage to this and can recommend batteries for this?
Why wouldn't it be allowed? They're essentially renting their batteries and grids generally lack storage
It benefits the grid to have people consume extra power when there's an oversupply, store it and give it back when there's undersupply. Why shouldn't it be allowed (even encouraged)?
The rooftop solar game in Texas is strongly into scam territory. Most homes I see with panels on the roof are two story homes where you have a negligible amount of area to work with relative to interior space. There was a point where you'd have to deal with a door-to-door salesman approximately every 48h for an entire summer.
The most realistic residential installation I've seen was firmly on the ground at a ~2 acre property. The panels were much larger and heavier (i.e., capable) than what you'd typically find on a roof. It's much easier to build and maintain a solar array when you don't need a ladder/crane to move things around.
I think that it's great that we want to participate in making things better, but not every situation makes sense. When you factor in all of the downstream consequences of sub-optimal, fly-by-night installs, it starts to look like a net negative on the environment. I'm not trying to claim that all rooftop solar projects are bad, but most of the residential ones I've seen make absolutely zero economic sense.
Large scale wind and solar projects are the best way forward. You get so much more bang for buck. I'd consider investing in these projects or their upstream suppliers and owners if you want to get involved financially in making the environment a better place.
I think you're mixing two very different things: the tech and the sales channel
This is indeed nice for a well-to-do home. But there is a tragedy of the commons issue here.
The grid needs to be up 24/7. And while peak usage is just that, the grid capacity still needs to support peak usage.
This can theoretically be done using batteries but not for an extended amount of time. To say we can have batteries for 2 weeks of normal consumption is highly improbable.
The metals do build those batteries do not exist. Or put in a worse way, the mines do not exist.
An off the cuff calculation of costs and the massive amount of batteries required in the context of Sweden can be found (you need to translate) here: https://www.tn.se/naringsliv/40181/utrakning-60-globen-batte...
In other words, 60 full scale Globen arenas of batteries to replace current Swedish nuclear production.
So for small houses these investments can make sense currently. But from a larger perspective it's not that interesting.
Residential solar with batteries greatly aids the grid and reduces costs for the entire system.
> The metals do build those batteries do not exist. Or put in a worse way, the mines do not exist.
Lithium and sodium, the two most promising battery metals, are not usually mined, though in Australia I hear there is mining. It's more of a brine process. All across the US, frackers are finding that all that water they are pulling out is a fairly rich lithium brine.
The amount of metal needed for 2 weeks of batteries is pretty trivial compared to the system we've built for extracting fossil fuels, and iron, etc. The bigger demands for electrification are acutally copper! Gotta wire everything....
Grid batteries on the GWh scale make a ton of sense financially and environmentally, and are revolutionizing the grid. Never before has the grid had a way to store electricity on a grand scale, which changes the entire nature of the beast. It's was one of the only massive systems we had where there wasn't buffering!
With storage, we can alleviate congested transmission without super costly transmission upgrades. On exist lines, we can the usage massively, reducing costs, because now we can buffer across time to shave off the peak demand.
Batteries are easy to build, environmentally friendly, and like a swiss army knife in their number of applications. We will be producing TWh of batteries a year in modern economies, and they last ~20 years, meaning that for the foreseeable economic growth in the coming decades, we'll easily have a peta-watthour of battery storage in use at a time.
What makes you think I need batteries for 2 weeks of normal consumption?
Nobody needs that, but from my point of view batteries will be so cheap and abundant that we will likely get to having 2 weeks of storage just sitting around the grid or rolling on wheels.
People always underestimate where exponential cost decreases will take us. Current battery production grows by 10x in a mere 5 years. In a decade, the time it takes to build a nuclear power plant, we will grow our battery production by 100x. Not enough people take this seriously, or even know that the trend exists.
Why do people still go for tesla powerwalls when you can get BYD batteries with 70%+ more capacity for cheaper ?
You can buy a BYD HVM 22.1 kWh for 6000 euros now (£5200) vs powerwall 2 13.5kwh for 7000 euros.
Or you can by a car instead. An MG4 costs less than 20000 euros with a 51kWh LFP battery. In addition to a good battery, it's a great car as well.
afaik it doesn't support bidirectional charging, I'd much rather cycle my standalone lifepo4 bank than my EV battery
Yes, it does. I haven't tried it as a do not have the cable for it, but the user interface for discharge is there and the manual also talks about this feature.
It's probably not ideal for running a full house (as it would require some other electronics and installations), but a couple of appliances should work.
In germany was (still is) illegal to use the car as battery… it is going to change soon though
Brand trust?
(Yes, yes: insert Musk related joke here.)
Those batteries must be connected to the internet to work, and the company could disable them anytime. Same for most of the inverters. I’m just hoping they don’t pull some nonsense like we have seen with other “cloud” devices. In that sense, I trust Tesla as much as BYD, and that is not at all.
Aren’t powerwalls overpriced?
this can be disallowed in the UK, depending on their agreement either their provider. the OP is exporting way more energy than they have ever produced through solar; in effect they’re selling back off-peak energy to the grid, which is making a profit
> Having our full costs returned in ~11 years is definitely something we're happy with
Except that after 11 years the equipment will have broken down or become obsolete, at which point you have to start over.
> we've also had protection against several power outages in our area along the way, which is a very nice bonus.
This seems to be the real benefit of the setup.
The equipment doesn’t have moving parts so I wouldn’t expect it to break down so quickly.
The real surprise for me was how much having solar panels on your roof adds to the cost of roofing work. Which is a problem because the roof is likely to need repairs more often than the solar panels.
Yeah it's a tradeoff on the roof. The panels also increase the lifetime of the roof.
Solar panels are incredibly durable, there's a thriving secondary market for used panels, and we're likely to see 30-50 years of usage out of any panel created today.
Cracking the problem of making the roof out of solar panels seems like a fantastic engineering challenge. But not one with small tiles, make the roof out of the bigger cheap large panels. I would love to see startups working on that. Asphalt roofs look like crap anyway, changing to shiny panels would be a huge improvement IMHO
What breaks in 11 years? Solar panels and batteries both last longer than that.
As for your other point of becoming obsolete, why care about chasing latest fads for home appliances.
Are you sure? Lots of people are telling me that batteries only last 4-5 years tops and solar panels usually burn out before 10 years /s
I particularly love when they are telling me that my 11 year old Prius' batteries will only last 5 years before they are junk.
> Except that after 11 years the equipment will have broken down or be obsolete, at which point you have to start over.
If my calculations are correct, that setup probably lasts at least 30 years. This is not a cell phone battery and panels do not degrade that fast.
Great read!
I am just wondering would stacking up batteries, charging them off-peak and using/selling back during peak usage be as good as this, or even better? Seems like this shouldn't be a viable scenario, but given the prices and idle capacity, it seems just investing in batteries and charging them at night, to be used/sold to the grid during the day would be as good as a solar installation.
The author pays £0.07/kWh off peak, but can export at £0.15/kWh. The author paid ~£7500 per powerwall which has ~13.5kWh capacity. Assuming full charge/discharge every night, you can make ~£1.08 per day, which works out to about 19 years to pay back.
Utilities normally consider disincentivizing this type of behavior from residential customers as one of the factors when setting their export pricing.
You can usually save more by generating solar locally and using it to power the home and charge the battery, then discharging the battery during peak hours (usually around and just after sunset) to earn the most. Obviously higher upfront capex.
Pure grid cycling is also frowned on by some utilities.
Octopus in the UK has tariffs where it basically takes over your system (ie the batteries in particular) and subsumes them into its wider activities, eg:
https://octopus.energy/intelligent-flux-faqs/
>it seems just investing in batteries and charging
I mean a lot of companies already do this with megawatt/gigawatt installations.
The key is peaking and grid stabilization. If you're a huge provider you can pay for all your batteries in a year or two if there is some large grid emergency and rates skyrocket.
If you're a non-commercial user, it's going to be hard because the provider rates you pay/get paid are much more likely to be fixed at a pretty low rate.
The US clean energy tax credit is only available for equipment installed on or before Dec 31, 2025 https://www.irs.gov/credits-deductions/residential-clean-ene...
As a result, more used solar should become available on ebay. I'm excited to see what I can do on a shoe string budget.
Don't be surprised when the answer is "not much". Apply supply and demand to electric power generation. If your grid rate is getting hiked then so is the market price of used solar.
Assuming the entire used market is efficient, which I doubt.
There will at least be a lag.
Battery storage tax credit (30%) runs through 2032, must have at least 3kwh capacity. IRS Form 5695.
https://www.energystar.gov/about/federal-tax-credits/battery...
So what I take away is that he is using approx 3x electricity, that I do and that is including my electric car. I use an additional 5-7MWh of heat but on a heat pump that would still only be a max of 2MWh which doesn’t even bring me to half of his usage, for a family of 4.
You can add your car to your whole-house AC bus using the Enphase bi-di EVSE, releasing this year:
https://enphase.com/ev-chargers/bidirectional
Recently switched to octopus too because they have a proper api with 30min consumption updates
Solar panel investment has slowed down substantially in Sweden. Basically, when the sun is shining, electricity is close to free. Similar situation with wind power.
Neither technology can move forward until there's a 100x leap in electricity storage costs. Like a bunch of us said 10 years ago, because we remembered high school physics.
Sweden is also extremely far north, so seasonality is a problem. Good synergy with Norway, though.
My electric bill was up 35% year over year from 2024 to 2025 - only two of us live here and there were no infra changes or new appliances.
I really need a solar solution but I feel so far out of my wheelhouse.
https://solarunitedneighbors.org/help-desk/
I had a good experience using EnergySage, a free marketplace that sources competitive detailed bids - it just needs your address and electric bill.
Heat Pump water heater running in heat pump only mode is a way better ROI if you’re looking to save some money on electricity.
Interesting breakdown for the UK where sunshine isn’t always plenty. If you have more sun this will be different.
Solar tracking trees seem to be an interesting way to get wintertime solar way up.
https://youtu.be/r7HwQdssbas