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What a year of solar and batteries saved us in 2025

scotthelme.co.uk

161–170 of 368 posts

Re: What a year of solar and batteries saved us in 2025

#161

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 d…

What makes you think I need batteries for 2 weeks of normal consumption?

Nobody needs that, but from my point of view batteries will be so cheap and abundant that we will likely get to having 2 weeks of storage just sitting around the grid or rolling on wheels.

People always underestimate where exponential cost decreases will take us. Current battery production grows by 10x in a mere 5 years. In a decade, the time it takes to build a nuclear power plant, we will grow our battery production by 100x. Not enough people take this seriously, or even know that the trend exists.

Re: What a year of solar and batteries saved us in 2025

#162
post #2

Good analysis. And kudos to the author for saving money. But still 21.6MWh per year excluding solar production seems too high for a household. I use electric heating and drive an electric vehicle, and my household annual energy consumption is about one fifth of that.

It's more a stress test showing that even with unusually high consumption, solar + batteries + tariff optimisation can still materially change the cost curve

Re: What a year of solar and batteries saved us in 2025

#163
post #124

Earlier quoted context omitted.

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.

That's fair. Better comparison: Author's config: 3x Powerwalls + inverters = 40 kWh 4.2 kW array £39,360 = $53k USD Alternative: EG4 18kPV Hybrid Inverter = $5000 3x RIUXU = $9600 10x Trina Solar 435w panels = $1580 Cabling, installations, etc. = $5000 Total = $21k It's not even close...

This is still not an accurate comparison. I'm not a Tesla fanboy but of all of the major players in the non-diy game (Enphase, Franklin, Tesla, Sol-Ark) they provide the best value for money, and are impressive pieces of equipment.

The EG4 18k has 11.5 kw backfeed capability, with a rather pathetic 65ish amp in-rush. Obviously 18kw usable solar capacity(they technically let you land up to 21kw, but only 18 is usable).

The Powerwall system you outlined can take 60kw of usable solar input, has 34kw standing backfeed capability, and a whopping 555 amp in-rush (not a typo, it's 185 amps per unit).

Not to get in to warranties, etc.

Re: What a year of solar and batteries saved us in 2025

#164
post #43

Earlier quoted context omitted.

Overly complex and fragile in the long run, the savings are meaningless if you're already self sufficient. I'd much rather spend the money in insulation and self sufficiency than these voodoo appliances. That's my reasoning my new build house with plenty of land. In other scenarios it might be more beneficial to go for them.

Heat pumps are no more fragile than air conditioners.

Which are famously reliable and cheap to service...

Re: What a year of solar and batteries saved us in 2025

#165
post #52

It's wild how overpriced Tesla Powerwalls are. 16 kWh battery with all of the UL supported listings etc = $3300 [0] 13.5 kWh Tesla Powerwall is $12k~$15k You would get your return way back quicker. [0] - https://www.ruixubattery.com/product-page/lithi2-16-battery-... EDIT: As others have pointed out, powerwalls have inverters built in so it's not totally apples to apples. You can get a beefy inverter for $5k and it's…

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.

Re: What a year of solar and batteries saved us in 2025

#166

Earlier quoted context omitted.

Well, the math still maths, right? I am writing this off grid, using about 15kwh of batteries and a $1200 (6kw) inverter. My entire system puls panels and racking those panels, plus wiring some un-powered shacks was about $10k, though I did the work myself (which would probably hae been another 3-5k if I could have found someone to do it.

> which would probably hae been another 3-5k if I could have found someone to do it. Yo. If you can find an electrician to stop by my house and turn a light switch off for less than 1000$, please inform me. I got a quote for 25k$ to install a system that size, and that price. City code has me by the balls: I can't modify my main panel without inspection, the inspector won't show up without a licensed electrician, and…

For 2500$ maybe you can pass the exam to become licensed yourself. Like do it over the weekends.

Re: What a year of solar and batteries saved us in 2025

#167
post #29

Earlier quoted context omitted.

That’s an awful lot of power. I’m waiting on a quote for an hvac that uses its waste heat for the home hot water. Im irritated that I’m cooling the house, pushing out hot air, and heating water at the same time.

Get a basic heat recovery unit, it basically has no moving parts (just a few fans) and good ones recover 90%+ of the heat going out of your house. It's almost useless if you don't have an airtight envelope though. All in one systems with water heating are way too complex and _will_ fail relatively quickly, mini heat pumps won't last 10 years, and by the time it dies you won't be able to find a replacement for your sp…

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.

Re: What a year of solar and batteries saved us in 2025

#168

Earlier quoted context omitted.

Any idea why swapping didn't pan out for Tesla? My understanding is they are doing that in China.

Probably because the economics just don't make sense here. You'd have to have so many compatible cars on the road, driving all day with no opportunity to charge. I'm having a hard time imagining a place I've been to in North America where that'd seem logical. > they are doing that in China Are they actually doing that at scale?

A little out of date now but:

> 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...

Re: What a year of solar and batteries saved us in 2025

#169
post #35

Earlier quoted context omitted.

afaik it doesn't support bidirectional charging, I'd much rather cycle my standalone lifepo4 bank than my EV battery

Yes, it does. I haven't tried it as a do not have the cable for it, but the user interface for discharge is there and the manual also talks about this feature. It's probably not ideal for running a full house (as it would require some other electronics and installations), but a couple of appliances should work.

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.

Re: What a year of solar and batteries saved us in 2025

#170
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...

  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.

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