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What a year of solar and batteries saved us in 2025

243 points by MattSayar 9mo ago

kccqzy 9mo ago
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.
- louwrentius 9mo ago
  From the article: "My wife and I both drive electric cars" That probably explains it.
  - kccqzy 9mo ago
    Yeah but they both work from home. The biggest reason for putting mileage on the car, commuting, is now out.
  - lostlogin 9mo ago
    A single extra charge in a month can really mess the stats up.
    - vel0city 9mo ago
      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.
      - metadat 9mo ago
        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).
      - lostlogin 9mo ago
        That percentage of total usage is tiny, I agree. 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.
- bryanrasmussen 9mo ago
  maybe saving money they used more - in other words Jevon's paradox https://en.wikipedia.org/wiki/Jevons_paradox https://en.wikipedia.org/wiki/Jevons_paradox thus perhaps leading to more global warming
- Aboutplants 9mo ago
  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.
  - lm28469 9mo ago
    The average household doesn't have two electric cars though
    - pixl97 9mo ago
      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.
      - KaiserPro 9mo ago
        I have an electric car, one powerwall (pre musk midlife crisis) and 5kw solar. we consumed 6mwhrs in 2025. Gas heating and hotwater, about 190w base because of networking, servers and shit left on.
      - Scott_Helme_ 9mo ago
        How did you know about my laser?!
        pixl97 9mo ago
        I saw your xkcd history...
- icehawk 9mo ago
  20MWh is around what my house used in both 2024 and 2025.
  - davely 9mo ago
    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.
- lostlogin 9mo ago
  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?
  - Scott_Helme_ 9mo ago
    Nah, there's no Bitcoin mining, honest!
- cptcobalt 9mo ago
  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.
  - lostlogin 9mo ago
    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.
    - sponaugle 9mo ago
      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.
    - lm28469 9mo ago
      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
      - lostlogin 9mo ago
        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. Yay for New Zealand housing.
      - MisterTea 9mo ago
        > All in one systems with water heating are way too complex and _will_ fail relatively quickly, ... Can you offer some evidence of this? I don't see how adding a refrigerant to water heat exchanger after the compressor, before the reversing valve, could possibly hurt the longevity of a system. > ... 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 Thing with mini-splits is you replace the entire unit so it doesn't matter.
- sponaugle 9mo ago
  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. ;)
- micromacrofoot 9mo ago
  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.
  - kccqzy 9mo ago
    They have no commutes. They both work from home. I don’t even understand why they need two cars for that.
- bz_bz_bz 9mo ago
  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.
  - UltraSane 9mo ago
    That is still an enormous amount of electricity for a single family to consume.
    - Dylan1312 9mo ago
      It's less than 50kwh a day, high but seems reasonable with 2 electric cars.
    - Aromasin 9mo ago
      He mentions that he has a server. It wouldn't surprise me if that consumes the majority of that.
      - port11 9mo ago
        People need to stop using the old Mac Pros for home servers, jeez.
        darknavi 9mo ago
        I had a old, cheap, used Dell R710 that I bought used in ~2016 until 2025. It only took a few months of running a new, much more efficient server to pay for its self.
        port11 9mo ago
        My EliteDesk G4 idles at 11W with 4 drives, so it’s not too bad. I really wish we could get something cooler, but it does the job beautifully. I see 150+ for the Dell, ouch.
- DamonHD 9mo ago
  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 https://www.earth.org.uk/saving-electricity.html
- lm28469 9mo ago
  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.
  - rokkamokka 9mo ago
    Heatpumps are not a gimmick - they're an excellent technology with lots of efficient and effective uses :)
    - lm28469 9mo ago
      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.
      - UltraSane 9mo ago
        Heat pumps are no more fragile than air conditioners.
        lm28469 9mo ago
        Yes, and that's why I have none.
        mrspuratic 9mo ago
        No fridge? That's a heat pump.
- youngtaff 9mo ago
  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
  - KaiserPro 9mo ago
    external wall insulation and triples glazing first! We did it and made winter ~10 degress warmer, and summer 15 degrees cooler. its cheaper than the solar/battery install.
- HexPhantom 9mo ago
  It's more a stress test showing that even with unusually high consumption, solar + batteries + tariff optimisation can still materially change the cost curve
- GordonS 9mo ago
  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 :(
sounds 9mo ago
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-energy-credit 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.
- willis936 9mo ago
  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.
  - IAmBroom 9mo ago
    Assuming the entire used market is efficient, which I doubt. There will at least be a lag.
- toomuchtodo 9mo ago
  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-storage-technology https://www.energystar.gov/about/federal-tax-credits/battery...
lm28469 9mo ago
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.
- pja 9mo ago
  Brand trust? (Yes, yes: insert Musk related joke here.)
  - f1shy 9mo ago
    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.
- flakeoil 9mo ago
  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.
  - lm28469 9mo ago
    afaik it doesn't support bidirectional charging, I'd much rather cycle my standalone lifepo4 bank than my EV battery
    - flakeoil 9mo ago
      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.
      - 9mo ago
jstsch 9mo ago
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... :)
- j2kun 9mo ago
  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.
  - jstsch 9mo ago
    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! :)
    - rmcpherson 9mo ago
      I would appreciate this write up as well. Looking to do a DIY setup.
Havoc 9mo ago
Recently switched to octopus too because they have a proper api with 30min consumption updates
apercu 9mo ago
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.
- drak0n1c 9mo ago
  I had a good experience using EnergySage, a free marketplace that sources competitive detailed bids - it just needs your address and electric bill.
- toomuchtodo 9mo ago
  https://solarunitedneighbors.org/help-desk/ https://solarunitedneighbors.org/help-desk/
elAhmo 9mo ago
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.
- cptcobalt 9mo ago
  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.
  - DamonHD 9mo ago
    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/ https://octopus.energy/intelligent-flux-faqs/
- pixl97 9mo ago
  >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.
- icegreentea2 9mo ago
  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.
malchow 9mo ago
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 https://enphase.com/ev-chargers/bidirectional
boringg 9mo ago
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.
- toomuchtodo 9mo ago
  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.
  - systemtest 9mo ago
    -
    - toomuchtodo 9mo ago
      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.
      - systemtest 9mo ago
        Can you point out what part of what I said is factually inaccurate?
nasmorn 9mo ago
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.
j45 9mo ago
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 https://youtu.be/r7HwQdssbas
mbesto 9mo ago
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-bank 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.
- toomuchtodo 9mo ago
  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-recommending-some-tesla-powerwall-alternatives/ https://electrek.co/2025/12/28/opinion-its-time-to-start-rec...
  - latchkey 9mo ago
    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 https://www.youtube.com/@WillProwse
- dns_snek 9mo ago
  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.
  - scarecrowbob 9mo ago
    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.
andrewkittredge 9mo ago
[dead]
deadbabe 9mo ago
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.
dlcarrier 9mo ago
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.
- systemtest 9mo ago
  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.
  - dymk 9mo ago
    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
    - dlcarrier 9mo ago
      My provider wasn't PG&E, and I don't know if they do the same, but there's a fixed $30/mo service fee for connecting to the grid, regardless of how little power is used, even if its negative.
  - coryrc 9mo ago
    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.
    - systemtest 9mo ago
      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.
domh 9mo ago
> 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/ 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?
- syncsynchalt 9mo ago
  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)?
  - coryrc 9mo ago
    Because of regulatory capture, only the big companies should be allowed to sell at retail and make profits.
- Perz1val 9mo ago
  Why wouldn't it be allowed? They're essentially renting their batteries and grids generally lack storage
  - domh 9mo ago
    Yeah not sure really. I thought these time of use tariffs were intended for charging EVs and using heat pumps, not charging batteries and selling the energy straight back to them later on in the day. But when you put it like that (decentralised grid storage) I guess it makes sense.
- dabeeeenster 9mo ago
  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/ 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!
oklahomasports 9mo ago
Aren’t powerwalls overpriced?
bstsb 9mo ago
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
- pornel 9mo ago
  Why would it be disallowed? That's a useful service to the grid – it's renting energy storage. UK off-peak energy is mostly surplus of wind, while the peak is burning natural gas. Feeding off-peak energy back to the grid at peak times makes it greener.
drnick1 9mo ago
> 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.
- kccqzy 9mo ago
  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.
  - Ensorceled 9mo ago
    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.
    - ishtanbul 9mo ago
      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.
      - Ensorceled 9mo ago
        /s is the sarcasm tag.
- IndrekR 9mo ago
  > 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.
lysace 9mo ago
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.
- pjc50 9mo ago
  Sweden is also extremely far north, so seasonality is a problem. Good synergy with Norway, though.
mikaeluman 9mo ago
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-batterier-kravs-for-att-ersatta-karnkraften/ 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.
- epistasis 9mo ago
  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.
bob1029 9mo ago
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.
- HexPhantom 9mo ago
  I think you're mixing two very different things: the tech and the sales channel
  - bob1029 9mo ago
    I was hoping to illustrate that without a hyper-aggressive sales campaign not as many people would have gone along with a bad installation.
    - toomuchtodo 9mo ago
      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). http://solarunitedneighbors.org/ http://solarunitedneighbors.org/ | https://solarunitedneighbors.org/locations/ https://solarunitedneighbors.org/locations/
HexPhantom 9mo ago
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
- Scott_Helme_ 9mo ago
  Absolutely — tariff choice, storage, and automation make a huge difference. The article isn’t claiming this setup is universally optimal, just showing what’s possible when those pieces are combined and used deliberately.
zackmorris 9mo ago
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: https://techcrunch.com/2026/01/12/trumps-epa-plans-to-ignore-health-effects-of-air-pollution/ https://techcrunch.com/2026/01/12/trumps-epa-plans-to-ignore... 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.
pier25 9mo ago
£3,632.86/year for electricity seems wild. 17,000kWh/year is about 46kWH/day. We consume less than 3kWh/day on average.
- coryrc 9mo ago
  Do you have electric heat? Do you have automobiles and do you fuel them with electricity?
  - pier25 9mo ago
    We do use electric heating from time to time but it's not constant. No electric cars. Still a 15x increase seems huge. Increasing electricity production 10x to electrify cars is not going to be achievable soon. Either via the power grid or home solar panels. Most people cannot afford to invest $40k in solar panels, batteries, etc.
    - coryrc 9mo ago
      Well, people who live somewhere where they need heating use more energy to stay alive than those who don't. Too bad California is so expensive because we could decarbonize the US significantly just by making it affordable for people to move there from Northern states.
dlisboa 9mo ago
It's crazy how power hungry UK homes are, or maybe it's UK power consumption habits in general. 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?
- jjice 9mo ago
  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".
- bradphipps 9mo ago
  They explain in the article.
- GordonS 9mo ago
  The OP is a significant outlier - the UK average is around 7.4kWh/household/day[0], or 11.2kWh specifically for large households. [0] https://www.britishgas.co.uk/energy/guides/average-bill.html https://www.britishgas.co.uk/energy/guides/average-bill.html
- Scott_Helme_ 9mo ago
  I did try to make it clear in the article. We're powering 2 x EVs, have two adults working from home full time, I have a server rack under the stairs, and we have a hot tub outside.
culebron21 9mo ago
How does a household use 1,500+ kWh per month? At my home, we sometimes get above 200, in summer with AC we may score 300 kWh, but how do you consume 5x of that? Is it heating?
- coryrc 9mo ago
  Is your heating electric and do you have two electric cars?
  - culebron21 9mo ago
    No, we either walk or use public transit, and we have central heating. Yes, this explains the difference.
testing22321 9mo ago
7.8kw on the roof here in Canada. 7.72MWh for the calendar year produced saving smack on $1000. $5000 gov grant (free money) Full remaining install cost covered by interest free loan, so we put that money onto the loan for the next 7 years, then get $1000 a year for the following 20 or more. Complete no brainer.
malshe 9mo ago
The payback calculation doesn't consider time value of money. They are paying down £40K today but the savings are realized over years in the future. But they implicitly assumed the discount rate on those savings to be 0.
- antisthenes 9mo ago
  Yes, if you want to be super precise you have to factor in both the time value of money on one hand and inflation & energy bill increases on the other. But very often these will roughly cancel each other out.
dreadsword 9mo ago
So TLDR: spend 40K up front to save 3K per year - could be cost effective depending on the functional lifetime of the tesla powerwall.
KaiserPro 9mo ago
I have 5kwp panels one tesla powerwall (bought before musk had a midlife crisis) and a single electric car. In 2025 we consumed 6Mwhr, imported 2.7 & produced from solar 5.1 I assume that OP must have electric heating to account for the extra power use, or just does huge amounts of miles. its about 54kwhr a day consumption.
NoLinkToMe 9mo ago
Great writeup! Tldr; their full costs of the system are returned in 11 years. Whether that's good depends on your perspective and assumptions, you can take a look at opportunity costs. Imagine you have 100k for say 30 years, and you have three choices: 1. put it in a UK government bond at 4.4% -> 100 * 1.044^30 = 363k 2. put it in the S&P500 (dividend reinvested) at nominal 10% rate -> 1.7 million 3. buy a system that can't be made liquid after 30 years, but returns 11k flat per year = 330k. 1 is very safe and virtually guaranteed. 2 is considered less safe, but over 30 years broad based stock indexes are far less risky than short-term stock investing. 3 is perhaps the most difficult to make assumptions, as its house-tied and operational. Switch houses for any personal reasons, and you'll not be able to fully make your investment liquid and recuperate it. Blow an inverter, see panels degrade and replacement costs must be factored in. This pushes down the final cash position of 330k. We could be generous and say that the 11k flat savings will increase, as electricity prices rise. Prices grew by 5% yearly in the UK, under that rate so the 11k savings today would grow to 47k annual savings in year 30, and total savings over 30 years would be 870k, pushing up the final cash position, but still not getting close to a long-term stock index investment. But even that's somewhat generous for two reasons: one is that the 5% inflation was unnaturally high due to the EU's energy crisis from the Russian invasion, and not necessarily indicative of the next 30 years. Various countries in the EU are also curtailing renewable production because there's too much of it (precisely during the moments solar systems were making their biggest profits < 2020, you since see curtailment growing), and with more storage coming online rapidly the profits from their battery system are expected to decline, not increase. -- generally speaking, solar energy producers were more profitable a few years ago, and are becoming less and less profitable over time as competition from cheap panels undercuts them. Many countries have begun to cut the reward from exporting back to the grid from the retail prices of €0.30 to the puny wholesale prices of €0.05 and all countries are expected to go down this road eventually. On the other hand, AI seems likely to push electricity prices higher for a long time... but it's the newest and biggest question mark compared to the other assumptions we've made above.

243 points by MattSayar 9mo ago

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.

louwrentius 9mo ago
From the article: "My wife and I both drive electric cars" That probably explains it.
- kccqzy 9mo ago
  Yeah but they both work from home. The biggest reason for putting mileage on the car, commuting, is now out.
- lostlogin 9mo ago
  A single extra charge in a month can really mess the stats up.
  - vel0city 9mo ago
    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.
    - metadat 9mo ago
      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).
    - lostlogin 9mo ago
      That percentage of total usage is tiny, I agree. 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.
bryanrasmussen 9mo ago
maybe saving money they used more - in other words Jevon's paradox https://en.wikipedia.org/wiki/Jevons_paradox https://en.wikipedia.org/wiki/Jevons_paradox thus perhaps leading to more global warming
Aboutplants 9mo ago
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.
- lm28469 9mo ago
  The average household doesn't have two electric cars though
  - pixl97 9mo ago
    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.
    - KaiserPro 9mo ago
      I have an electric car, one powerwall (pre musk midlife crisis) and 5kw solar. we consumed 6mwhrs in 2025. Gas heating and hotwater, about 190w base because of networking, servers and shit left on.
    - Scott_Helme_ 9mo ago
      How did you know about my laser?!
      - pixl97 9mo ago
        I saw your xkcd history...
icehawk 9mo ago
20MWh is around what my house used in both 2024 and 2025.
- davely 9mo ago
  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.
lostlogin 9mo ago
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?
- Scott_Helme_ 9mo ago
  Nah, there's no Bitcoin mining, honest!
cptcobalt 9mo ago
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.
- lostlogin 9mo ago
  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.
  - sponaugle 9mo ago
    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.
  - lm28469 9mo ago
    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
    - lostlogin 9mo ago
      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. Yay for New Zealand housing.
    - MisterTea 9mo ago
      > All in one systems with water heating are way too complex and _will_ fail relatively quickly, ... Can you offer some evidence of this? I don't see how adding a refrigerant to water heat exchanger after the compressor, before the reversing valve, could possibly hurt the longevity of a system. > ... 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 Thing with mini-splits is you replace the entire unit so it doesn't matter.
sponaugle 9mo ago
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. ;)
micromacrofoot 9mo ago
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.
- kccqzy 9mo ago
  They have no commutes. They both work from home. I don’t even understand why they need two cars for that.
bz_bz_bz 9mo ago
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.
- UltraSane 9mo ago
  That is still an enormous amount of electricity for a single family to consume.
  - Dylan1312 9mo ago
    It's less than 50kwh a day, high but seems reasonable with 2 electric cars.
  - Aromasin 9mo ago
    He mentions that he has a server. It wouldn't surprise me if that consumes the majority of that.
    - port11 9mo ago
      People need to stop using the old Mac Pros for home servers, jeez.
      - darknavi 9mo ago
        I had a old, cheap, used Dell R710 that I bought used in ~2016 until 2025. It only took a few months of running a new, much more efficient server to pay for its self.
        port11 9mo ago
        My EliteDesk G4 idles at 11W with 4 drives, so it’s not too bad. I really wish we could get something cooler, but it does the job beautifully. I see 150+ for the Dell, ouch.
DamonHD 9mo ago
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 https://www.earth.org.uk/saving-electricity.html
lm28469 9mo ago
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.
- rokkamokka 9mo ago
  Heatpumps are not a gimmick - they're an excellent technology with lots of efficient and effective uses :)
  - lm28469 9mo ago
    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.
    - UltraSane 9mo ago
      Heat pumps are no more fragile than air conditioners.
      - lm28469 9mo ago
        Yes, and that's why I have none.
        mrspuratic 9mo ago
        No fridge? That's a heat pump.
youngtaff 9mo ago
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
- KaiserPro 9mo ago
  external wall insulation and triples glazing first! We did it and made winter ~10 degress warmer, and summer 15 degrees cooler. its cheaper than the solar/battery install.
HexPhantom 9mo ago
It's more a stress test showing that even with unusually high consumption, solar + batteries + tariff optimisation can still materially change the cost curve
GordonS 9mo ago
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 :(

sounds 9mo ago

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-energy-credit 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.

willis936 9mo ago
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.
- IAmBroom 9mo ago
  Assuming the entire used market is efficient, which I doubt. There will at least be a lag.
toomuchtodo 9mo ago
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-storage-technology https://www.energystar.gov/about/federal-tax-credits/battery...

lm28469 9mo ago

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.

pja 9mo ago
Brand trust? (Yes, yes: insert Musk related joke here.)
- f1shy 9mo ago
  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.
flakeoil 9mo ago
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.
- lm28469 9mo ago
  afaik it doesn't support bidirectional charging, I'd much rather cycle my standalone lifepo4 bank than my EV battery
  - flakeoil 9mo ago
    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.
    - 9mo ago

jstsch 9mo ago

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... :)

j2kun 9mo ago
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.
- jstsch 9mo ago
  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! :)
  - rmcpherson 9mo ago
    I would appreciate this write up as well. Looking to do a DIY setup.

Havoc 9mo ago

Recently switched to octopus too because they have a proper api with 30min consumption updates

apercu 9mo ago

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.

drak0n1c 9mo ago
I had a good experience using EnergySage, a free marketplace that sources competitive detailed bids - it just needs your address and electric bill.
toomuchtodo 9mo ago
https://solarunitedneighbors.org/help-desk/ https://solarunitedneighbors.org/help-desk/

elAhmo 9mo ago

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.

cptcobalt 9mo ago
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.
- DamonHD 9mo ago
  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/ https://octopus.energy/intelligent-flux-faqs/
pixl97 9mo ago
>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.
icegreentea2 9mo ago
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.

malchow 9mo ago

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 https://enphase.com/ev-chargers/bidirectional

boringg 9mo ago

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.

toomuchtodo 9mo ago
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.
- systemtest 9mo ago
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  - toomuchtodo 9mo ago
    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.
    - systemtest 9mo ago
      Can you point out what part of what I said is factually inaccurate?

nasmorn 9mo ago

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.

j45 9mo ago

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 https://youtu.be/r7HwQdssbas

mbesto 9mo ago

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-bank 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.

toomuchtodo 9mo ago
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-recommending-some-tesla-powerwall-alternatives/ https://electrek.co/2025/12/28/opinion-its-time-to-start-rec...
- latchkey 9mo ago
  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 https://www.youtube.com/@WillProwse
dns_snek 9mo ago
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.
- scarecrowbob 9mo ago
  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.

andrewkittredge 9mo ago

[dead]

deadbabe 9mo ago

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.

dlcarrier 9mo ago

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.

systemtest 9mo ago
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.
- dymk 9mo ago
  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
  - dlcarrier 9mo ago
    My provider wasn't PG&E, and I don't know if they do the same, but there's a fixed $30/mo service fee for connecting to the grid, regardless of how little power is used, even if its negative.
- coryrc 9mo ago
  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.
  - systemtest 9mo ago
    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.

domh 9mo ago

> 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/ 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?

syncsynchalt 9mo ago
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)?
- coryrc 9mo ago
  Because of regulatory capture, only the big companies should be allowed to sell at retail and make profits.
Perz1val 9mo ago
Why wouldn't it be allowed? They're essentially renting their batteries and grids generally lack storage
- domh 9mo ago
  Yeah not sure really. I thought these time of use tariffs were intended for charging EVs and using heat pumps, not charging batteries and selling the energy straight back to them later on in the day. But when you put it like that (decentralised grid storage) I guess it makes sense.
dabeeeenster 9mo ago
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/ 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!

oklahomasports 9mo ago

Aren’t powerwalls overpriced?

bstsb 9mo ago

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

pornel 9mo ago
Why would it be disallowed? That's a useful service to the grid – it's renting energy storage. UK off-peak energy is mostly surplus of wind, while the peak is burning natural gas. Feeding off-peak energy back to the grid at peak times makes it greener.

drnick1 9mo ago

> 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.

kccqzy 9mo ago
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.
- Ensorceled 9mo ago
  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.
  - ishtanbul 9mo ago
    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.
    - Ensorceled 9mo ago
      /s is the sarcasm tag.
IndrekR 9mo ago
> 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.

lysace 9mo ago

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.

pjc50 9mo ago
Sweden is also extremely far north, so seasonality is a problem. Good synergy with Norway, though.

mikaeluman 9mo ago

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-batterier-kravs-for-att-ersatta-karnkraften/ 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.

epistasis 9mo ago
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.

bob1029 9mo ago

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.

HexPhantom 9mo ago
I think you're mixing two very different things: the tech and the sales channel
- bob1029 9mo ago
  I was hoping to illustrate that without a hyper-aggressive sales campaign not as many people would have gone along with a bad installation.
  - toomuchtodo 9mo ago
    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). http://solarunitedneighbors.org/ http://solarunitedneighbors.org/ | https://solarunitedneighbors.org/locations/ https://solarunitedneighbors.org/locations/

HexPhantom 9mo ago

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

Scott_Helme_ 9mo ago
Absolutely — tariff choice, storage, and automation make a huge difference. The article isn’t claiming this setup is universally optimal, just showing what’s possible when those pieces are combined and used deliberately.

zackmorris 9mo ago

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: https://techcrunch.com/2026/01/12/trumps-epa-plans-to-ignore-health-effects-of-air-pollution/ https://techcrunch.com/2026/01/12/trumps-epa-plans-to-ignore... 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.

pier25 9mo ago

£3,632.86/year for electricity seems wild. 17,000kWh/year is about 46kWH/day. We consume less than 3kWh/day on average.

coryrc 9mo ago
Do you have electric heat? Do you have automobiles and do you fuel them with electricity?
- pier25 9mo ago
  We do use electric heating from time to time but it's not constant. No electric cars. Still a 15x increase seems huge. Increasing electricity production 10x to electrify cars is not going to be achievable soon. Either via the power grid or home solar panels. Most people cannot afford to invest $40k in solar panels, batteries, etc.
  - coryrc 9mo ago
    Well, people who live somewhere where they need heating use more energy to stay alive than those who don't. Too bad California is so expensive because we could decarbonize the US significantly just by making it affordable for people to move there from Northern states.

dlisboa 9mo ago

It's crazy how power hungry UK homes are, or maybe it's UK power consumption habits in general. 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?

jjice 9mo ago
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".
bradphipps 9mo ago
They explain in the article.
GordonS 9mo ago
The OP is a significant outlier - the UK average is around 7.4kWh/household/day[0], or 11.2kWh specifically for large households. [0] https://www.britishgas.co.uk/energy/guides/average-bill.html https://www.britishgas.co.uk/energy/guides/average-bill.html
Scott_Helme_ 9mo ago
I did try to make it clear in the article. We're powering 2 x EVs, have two adults working from home full time, I have a server rack under the stairs, and we have a hot tub outside.

culebron21 9mo ago

How does a household use 1,500+ kWh per month? At my home, we sometimes get above 200, in summer with AC we may score 300 kWh, but how do you consume 5x of that? Is it heating?

coryrc 9mo ago
Is your heating electric and do you have two electric cars?
- culebron21 9mo ago
  No, we either walk or use public transit, and we have central heating. Yes, this explains the difference.

testing22321 9mo ago

7.8kw on the roof here in Canada. 7.72MWh for the calendar year produced saving smack on $1000. $5000 gov grant (free money) Full remaining install cost covered by interest free loan, so we put that money onto the loan for the next 7 years, then get $1000 a year for the following 20 or more. Complete no brainer.

malshe 9mo ago

The payback calculation doesn't consider time value of money. They are paying down £40K today but the savings are realized over years in the future. But they implicitly assumed the discount rate on those savings to be 0.

antisthenes 9mo ago
Yes, if you want to be super precise you have to factor in both the time value of money on one hand and inflation & energy bill increases on the other. But very often these will roughly cancel each other out.

dreadsword 9mo ago

So TLDR: spend 40K up front to save 3K per year - could be cost effective depending on the functional lifetime of the tesla powerwall.

KaiserPro 9mo ago

I have 5kwp panels one tesla powerwall (bought before musk had a midlife crisis) and a single electric car. In 2025 we consumed 6Mwhr, imported 2.7 & produced from solar 5.1 I assume that OP must have electric heating to account for the extra power use, or just does huge amounts of miles. its about 54kwhr a day consumption.

NoLinkToMe 9mo ago

Great writeup! Tldr; their full costs of the system are returned in 11 years. Whether that's good depends on your perspective and assumptions, you can take a look at opportunity costs. Imagine you have 100k for say 30 years, and you have three choices: 1. put it in a UK government bond at 4.4% -> 100 * 1.044^30 = 363k 2. put it in the S&P500 (dividend reinvested) at nominal 10% rate -> 1.7 million 3. buy a system that can't be made liquid after 30 years, but returns 11k flat per year = 330k. 1 is very safe and virtually guaranteed. 2 is considered less safe, but over 30 years broad based stock indexes are far less risky than short-term stock investing. 3 is perhaps the most difficult to make assumptions, as its house-tied and operational. Switch houses for any personal reasons, and you'll not be able to fully make your investment liquid and recuperate it. Blow an inverter, see panels degrade and replacement costs must be factored in. This pushes down the final cash position of 330k. We could be generous and say that the 11k flat savings will increase, as electricity prices rise. Prices grew by 5% yearly in the UK, under that rate so the 11k savings today would grow to 47k annual savings in year 30, and total savings over 30 years would be 870k, pushing up the final cash position, but still not getting close to a long-term stock index investment. But even that's somewhat generous for two reasons: one is that the 5% inflation was unnaturally high due to the EU's energy crisis from the Russian invasion, and not necessarily indicative of the next 30 years. Various countries in the EU are also curtailing renewable production because there's too much of it (precisely during the moments solar systems were making their biggest profits < 2020, you since see curtailment growing), and with more storage coming online rapidly the profits from their battery system are expected to decline, not increase. -- generally speaking, solar energy producers were more profitable a few years ago, and are becoming less and less profitable over time as competition from cheap panels undercuts them. Many countries have begun to cut the reward from exporting back to the grid from the retail prices of €0.30 to the puny wholesale prices of €0.05 and all countries are expected to go down this road eventually. On the other hand, AI seems likely to push electricity prices higher for a long time... but it's the newest and biggest question mark compared to the other assumptions we've made above.