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 $5k and it's still cheaper and you wouldn't need an additional inverter every time you add a battery.
There's going to be a bloodbath in that market in the next years. There are a lot of battery producers and most of them are not producing at full capacity. At the same time, manufacturing cost is dropping as well.
Some battery makers are producing batteries at a cost level of around 60$ per kwh. At that cost, the 16kwh battery would come out below 1000$ (not the same obviously as the product price). Sodium ion might push those prices even lower. Below 50$ soonish and eventually closer to the 10-20$ range in maybe 5-10 years. At that point we're talking a few hundred dollars for a decent size domestic battery. You still need packaging, inverters, etc. of course.
But the ROI at anything close to those price levels is going to be pretty rapid. And it wouldn't break the bank for households across the world. Add a few kw of solar on roofs, balconies, etc. It won't solve everyone's problems and certainly not in every season. But it can help reduce energy bills in a meaningful enough way. Even in winter.
Also worth pointing out: most of the US is south of Cornwall. The Canadian border runs roughly at 49 degrees latitude. Cornwall is the most southern point in the UK sits at 50 degrees. If it can work there, most of the US has no excuse. Also, the UK isn't exactly well known for their clear blue skies. Even people in Scotland much further north manage to get positive ROIs out of their solar setups.
I installed a 16.5kWp ground-mount array a month ago. I live in the US Northeast, in a mountainous location that means we get late sunrises and early sunsets. Nevertheless, based on my one month of data, it looks like we can generate all the power we need for our household on a sunny winter day, excluding electric vehicles. Even on overcast days, we can sometimes offset a significant portion of our usage. My locale does not have time-of-use rates, so there’s no point trying to do arbitrage for electricity prices. So right now I just have our battery configured for backup. My hope is that during the summer months I can reconfigure the system to use the battery to reduce grid reliance instead.
The expiring tax credits were what forced my hand. I’m the kind of person who likes to install things himself, and I probably would have gone that route for solar too, because the materials costs (sans battery) aren’t even half of the total cost.
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.
> As of June 2024, Nio had installed 2,432 power swap stations in China, including 804 along highways, representing the largest battery swapping network in the country. Nio aims to expand to 4,000 stations globally by 2025. By February 2025, Nio had 3,106 battery swap stations in China, with 964 located along highways. In January 2025 alone, Nio added 111 swap stations and provided 2,949,969 battery swap services, averaging 95,160 daily.
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).
None of those things matter when your solar array is 4.5 kW and you have a standard 150A/200A grid in....
Like I said, they basically are not sold to scale like a normal household uses electricity.
EDIT: What the heck is in-rush and backfeed? Are you talking about AC input to charge the batteries? The 18k is 50A @ 240VAC (12kW) fyi. Also, why does the charge rate even matter there? For the AC output its also 12 kW...the family is average 48 kWh days, which is 2 kW hourly average...
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.
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.
How do you measure the depreciation? The panels deliver at least 70%, but probably closer to 80%, output after 25 years. The batteries need replacing after maybe 15 years. Assuming that knocks a couple percent points off the return (batteries can only get cheaper and cheaper) that's still a solid 7% long term yield with no default risk. Share your math if you disagree.
EDIT: Two more things that will juice the return
1. Grid electricity prices will go up over those 25 years, at the very least tracking inflation.
2. Unlike bond coupon payments, the "return" from a solar installation isn't taxable. Because you're saving money, not getting paid.
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.
im a systems engineer and cost analyst who has put together some modeling myself as well. as a personal investment on your house, i agree. The economic value of solar seems to be best applied as neighborhood or block purchases, like as part of a co-op or hoa. they would need dedicated infrastructure like a communal parking lot with solar overhead, or running them on the property line borders with an easement underneath for servicing, using property fencing as main support (with upgraded fencing)
basically, the way it really makes sense (to me) is to integrate it as part of a micro-grid system, possibly with generator backups and everything to also keep the lights on in the entire neighborhood if the main grid goes down.
its a higher upfront cost on paper, but way less variables with the roof and you are grouping multiple peoples needs together so the gamble goes down on repairs. the poles for ground-mounting can be used for 40 - 60 years, so you would get multiple panels out of them
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.
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.
> 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.
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.
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.
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.
I was really surprised too - our family (with electric car and a lot of tech) uses only a third of the energy used in TFA!
Still, even with our lower usage, solar still makes sense (especially with a South-facing roof) because electricity is so damned expensive in the UK :(
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
This makes me sad. I’m in a 1940s house where the lack of it being airtight is a key reason it’s still standing as it leaks and the airflow dries it. Water flows down the inside of the brickwork, and the cavity is well ventilated.
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...
It's more a stress test showing that even with unusually high consumption, solar + batteries + tariff optimisation can still materially change the cost curve
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
As long as you already have ductwork you lower complexity, instillation costs, and maintenance issues by also cooling or heating the air inside that ductwork rather than just using ductwork for heat recovery ventilation. Further moving air allows you to use dramatically less material for heat exchangers.
Net result higher efficiency, fewer things that can break, fewer locations something can break, and lower risks of water damage to your home.
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.
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.
The reason is that California has made their grid extremely vulnerable. The grid already heavily overproduces solar so it is reasonable to have negative prices. There is no sink available.
> 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?
I just had Solaredge battery installed in my house in the UK (Had a solaredge PV and inverter so made sense even tho it was more than other setups). If you are up for a challenge https://springfall2008.github.io/batpred/ is AMAZING and basically optimises when to charge and discharge your battery.
I've got a heat pump and think my paypack period is going to be about 6 years.
Hit me up on bluesky (in profile) if you want more info!
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.
For homes, solar car ports and pergulas look attractive if you are land constrained. No holes in your roof, and it is Texas, so more shade is always appreciated.
Find a solar coop if you can to avoid the sales pain. They will assemble a group of homeowners and bid the entire group install out to achieve cost efficiency. Ground installs are cheaper and easier, imho, whenever possible (but depends on land availability and favorable solar insolation).
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.
There are several types of bidirectional EV charging, the one most cars has is about a 1kW fused connection called "Vehicle to Load (V2L)" but the one you are discussing is what they call "Vehicle to Grid (V2G)" and in those cars it supports the full input and output of the vehicle inverter.
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.
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.
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.
Those prices are outdated now since practically all metals are surging.
There has indeed been great growth in battery capacity but it's as I said nowhere near able to supply a country like Sweden during the winter. It is off by orders of magnitude. We need 5TWh for that. It is not going to happen any time soon.
I understand California is different. Still, one would need to do these risk scenario calculations. Have they been made?
I know California has rotating blackouts already as it is. I really don't have any idea how people find that acceptable. If it happened in Sweden the government would be replaced on the day. It would be a real disaster.
I will be a bigger believer if a state like California can actually show its possible.
For sure I hope technology improves but the current ideas of solar+battery are simply highly unlikely.
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.
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
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.
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
This is totally wrong. I work in the industry. Solar panels should last for 30 years, but they degrade in capacity by 0.5 to 1% per year, depending on environmental conditions (temp, radiation, etc). Lithium batteries from tier 1 suppliers can last at least a decade of regular use. It depends on how their cycling and state of charge is managed. If you keep them between 20% and 80% charge, they can last incredibly long.
Are you commenting on this article? This person is in the UK. You can see it on their domain, their calculations using pounds, and then mention living in the UK multiple times in the "Our setup section".
I've been following a story where Elon Musk's xAI is building an 88 acre solar farm next to its Colossus data center near Memphis TN after public outrage due to running 35 methane gas turbines without a permit, which increased NOx emissions enough to allegedly impact health:
88 acres = 356,124 m2
4.56 kWh/m2 per day solar insolation (4.5 is typical for much of the US)
4.56 kWh/m2 per day \* 356,124 m2 = 1,623,924 kWh/day = 67,664 kW = 67.66 MW average
1000 W/m2 \* 356,124 m2 = 356 MW peak
They're estimating that they'll get 30 MW on average from that, but I'd estimate more like 15 MW at a solar panel efficiency just over 20%. Still, the total cost for that power should be less than for turbines, since solar is now the cheapest electricity other than hypothetical nuclear (assuming an ideal breeder or waste-consuming reactor and excluding mining/waste externalities/insurance).
30 MW is still only 10% of the the 300 MW used by the data center. But there's lots of land out there, so roughly 1000 acres per data center doesn't seem that extreme to me. That's a 4 km2 or 1.5 mile2 lot, or about 2 km or 1.25 miles on a side.
Basically every GPU server uses 1 kW (about 1 space heater), which puts into perspective just how much computing power is available at these data centers. Running a GPU continuously at home would need 24 kWh/day, so with > 20% efficiency panels that's 4.5*.2 = 0.9 kWh/m2 per day, so 26.67 m2, so at 2 m2 per commercial solar panel and assuming that my math is right: that's about 14 panels considering nights and seasons.
It's interesting to think just how many panels it takes to run a GPU or space heater continuously, even when they put out 500 W or 250 W/m2 peak. And how cheap that electricity really is when it's sold for on the order of $0.15 per kWh, or $3.60 per day.
I've found that the very best way to save on your electric bill is to have a few south-facing slider doors and windows, which is like running a space heater every square meter of window. There's just no way that any other form of power generation can compete with that. Also, I feel that we're doing it wrong with solar. This analysis shows just how much better alternatives like trough solar and concentrated solar (mirrors towards solar panels) might be cost-wise. On an ironic note, solar panels now cost less than windows by area, and probably mirrors.
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.
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 $5k and it's still cheaper and you wouldn't need an additional inverter every time you add a battery.
Some battery makers are producing batteries at a cost level of around 60$ per kwh. At that cost, the 16kwh battery would come out below 1000$ (not the same obviously as the product price). Sodium ion might push those prices even lower. Below 50$ soonish and eventually closer to the 10-20$ range in maybe 5-10 years. At that point we're talking a few hundred dollars for a decent size domestic battery. You still need packaging, inverters, etc. of course.
But the ROI at anything close to those price levels is going to be pretty rapid. And it wouldn't break the bank for households across the world. Add a few kw of solar on roofs, balconies, etc. It won't solve everyone's problems and certainly not in every season. But it can help reduce energy bills in a meaningful enough way. Even in winter.
Also worth pointing out: most of the US is south of Cornwall. The Canadian border runs roughly at 49 degrees latitude. Cornwall is the most southern point in the UK sits at 50 degrees. If it can work there, most of the US has no excuse. Also, the UK isn't exactly well known for their clear blue skies. Even people in Scotland much further north manage to get positive ROIs out of their solar setups.
The expiring tax credits were what forced my hand. I’m the kind of person who likes to install things himself, and I probably would have gone that route for solar too, because the materials costs (sans battery) aren’t even half of the total cost.
This is the company that owns APC so its not like theyre new or untested. They just don't bother with brand awareness
Alternatives: https://electrek.co/2025/12/28/opinion-its-time-to-start-rec...
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.
As far as I can tell if your battery isn't air cooled, it can go a very long way
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)
> they are doing that in China
Are they actually doing that at scale?
> As of June 2024, Nio had installed 2,432 power swap stations in China, including 804 along highways, representing the largest battery swapping network in the country. Nio aims to expand to 4,000 stations globally by 2025. By February 2025, Nio had 3,106 battery swap stations in China, with 964 located along highways. In January 2025 alone, Nio added 111 swap stations and provided 2,949,969 battery swap services, averaging 95,160 daily.
https://enertherm-engineering.com/chinas-battery-swap-revolu...
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 $10k, though I did the work myself (which would probably hae been another 3-5k if I could have found someone to do it.
Yo. If you can find an electrician to stop by my house and turn a light switch off for less than 1000$, 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.
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...
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.
Like I said, they basically are not sold to scale like a normal household uses electricity.
EDIT: What the heck is in-rush and backfeed? Are you talking about AC input to charge the batteries? The 18k is 50A @ 240VAC (12kW) fyi. Also, why does the charge rate even matter there? For the AC output its also 12 kW...the family is average 48 kWh days, which is 2 kW hourly average...
Your point that they are overpriced still stands though.
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.
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.
As long as the bond issuer remains solvent. How much do you trust bonds that yield 9% to retain their full value for 25 years?
"Another way to look at this is that the investment is returning ~9%/year."
EDIT: Two more things that will juice the return
1. Grid electricity prices will go up over those 25 years, at the very least tracking inflation.
2. Unlike bond coupon payments, the "return" from a solar installation isn't taxable. Because you're saving money, not getting paid.
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.
LiFePO4 generally degrades to 80% capacity after 10 years, that's it. Safety isn't an issue.
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.
basically, the way it really makes sense (to me) is to integrate it as part of a micro-grid system, possibly with generator backups and everything to also keep the lights on in the entire neighborhood if the main grid goes down.
its a higher upfront cost on paper, but way less variables with the roof and you are grouping multiple peoples needs together so the gamble goes down on repairs. the poles for ground-mounting can be used for 40 - 60 years, so you would get multiple panels out of them
probably a bureaucratic nightmare though
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.
[edit: yes, I assume you also get batteries, I know that solar alone doesn't magically power your house.]
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.
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.
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.
Maybe, but that power is typically generated far from where it's consumed and so you have significant transmission losses.
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... :)
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.
Willing and allowed. In some countries it can only be done by certified electricians.
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.
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]
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...)
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.
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.
It’s been crazy seeing the western home storage market selling systems with the €/kWh being more expensive than buying a BEV. And that includes a car.
https://www.docanpower.com/eu-stock/zz-48kwh-50kwh-51-2v-942...
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.
Still, even with our lower usage, solar still makes sense (especially with a South-facing roof) because electricity is so damned expensive in the UK :(
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.
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
Yay for New Zealand housing.
https://www.earth.org.uk/saving-electricity.html
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?
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.
Some of this extra is certainly my 6kw homelab + HVAC for that. ;)
thus perhaps leading to more global warming
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.
That's my reasoning my new build house with plenty of land. In other scenarios it might be more beneficial to go for them.
Anecdotally, two of the smartest people I know love heat pumps—doesn’t Technology Connections too?
Was probably this:
https://youtube.com/watch?v=7J52mDjZztoNo 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.
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
Net result higher efficiency, fewer things that can break, fewer locations something can break, and lower risks of water damage to your home.
I am, and I am not an american, lol.
I do think more people should consider mini-split reversible AC in the UK, but the subsidy system specifically excludes it.
https://www.gov.uk/government/news/discounts-for-families-to...
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.
That probably explains it.
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.
We have one car and charge it quite often.
I just checked last month: 184kwh went into the Leaf. We used 557kwh in total (excluding the car charging).
We generated 1170kwh.
The key thing for me is the wild energy usage from the house. It’s a lot.
Edit: Your car energy usage calculation works out awfully close to what we use.
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
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.
Depending on when you signed up for NEM you may have a guaranteed floor like 4¢/kWh or even much more.
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?
I've got a heat pump and think my paypack period is going to be about 6 years.
Hit me up on bluesky (in profile) if you want more info!
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.
http://solarunitedneighbors.org/ | https://solarunitedneighbors.org/locations/
You can buy a BYD HVM 22.1 kWh for 6000 euros now (£5200) vs powerwall 2 13.5kwh for 7000 euros.
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.
(Yes, yes: insert Musk related joke here.)
https://enphase.com/ev-chargers/bidirectional
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.
> 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.
Those prices are outdated now since practically all metals are surging.
There has indeed been great growth in battery capacity but it's as I said nowhere near able to supply a country like Sweden during the winter. It is off by orders of magnitude. We need 5TWh for that. It is not going to happen any time soon.
I understand California is different. Still, one would need to do these risk scenario calculations. Have they been made?
I know California has rotating blackouts already as it is. I really don't have any idea how people find that acceptable. If it happened in Sweden the government would be replaced on the day. It would be a real disaster.
I will be a bigger believer if a state like California can actually show its possible.
For sure I hope technology improves but the current ideas of solar+battery are simply highly unlikely.
I consider 2 weeks of supply a bare minimum.
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.
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.
Utilities normally consider disincentivizing this type of behavior from residential customers as one of the factors when setting their export pricing.
Pure grid cycling is also frowned on by some utilities.
https://octopus.energy/intelligent-flux-faqs/
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.
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.
There will at least be a lag.
https://www.energystar.gov/about/federal-tax-credits/battery...
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 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.
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
As for your other point of becoming obsolete, why care about chasing latest fads for home appliances.
I particularly love when they are telling me that my 11 year old Prius' batteries will only last 5 years before they are junk.
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.
I use about ~300 kWh/month. A little bit more with AC some times of the year. What are you even powering with 15000 kWh?
[0] https://www.britishgas.co.uk/energy/guides/average-bill.html
https://techcrunch.com/2026/01/12/trumps-epa-plans-to-ignore...
They're estimating that they'll get 30 MW on average from that, but I'd estimate more like 15 MW at a solar panel efficiency just over 20%. Still, the total cost for that power should be less than for turbines, since solar is now the cheapest electricity other than hypothetical nuclear (assuming an ideal breeder or waste-consuming reactor and excluding mining/waste externalities/insurance).30 MW is still only 10% of the the 300 MW used by the data center. But there's lots of land out there, so roughly 1000 acres per data center doesn't seem that extreme to me. That's a 4 km2 or 1.5 mile2 lot, or about 2 km or 1.25 miles on a side.
Basically every GPU server uses 1 kW (about 1 space heater), which puts into perspective just how much computing power is available at these data centers. Running a GPU continuously at home would need 24 kWh/day, so with > 20% efficiency panels that's 4.5*.2 = 0.9 kWh/m2 per day, so 26.67 m2, so at 2 m2 per commercial solar panel and assuming that my math is right: that's about 14 panels considering nights and seasons.
It's interesting to think just how many panels it takes to run a GPU or space heater continuously, even when they put out 500 W or 250 W/m2 peak. And how cheap that electricity really is when it's sold for on the order of $0.15 per kWh, or $3.60 per day.
I've found that the very best way to save on your electric bill is to have a few south-facing slider doors and windows, which is like running a space heater every square meter of window. There's just no way that any other form of power generation can compete with that. Also, I feel that we're doing it wrong with solar. This analysis shows just how much better alternatives like trough solar and concentrated solar (mirrors towards solar panels) might be cost-wise. On an ironic note, solar panels now cost less than windows by area, and probably mirrors.
I really need a solar solution but I feel so far out of my wheelhouse.
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.
Solar tracking trees seem to be an interesting way to get wintertime solar way up.
https://youtu.be/r7HwQdssbas