this post was submitted on 17 Sep 2025
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O, god, it's going to be huge. You really can't do the off-grid thing unless you have enough power production to satiate you over any given 3-day moving window. Trying to store power from summer until winter is going to be too expensive, instead buy more panel.
This isn't even going into the fact batteries lose charge slowly. So any power generated in summer will be much diminished by winter, even if you have big enough batteries.
Seems to me his panel capacity is to small anyway.
We have 11 kWh panels, and yes in the summer we routinely produce 4 times more than we use, and we have a 7.5 kWh battery But November December and January it's not even close to enough.
In the Winter you can easily have a week with near zero production:
Our Import / export from grid last year:
November 215 / 59 kWh
December 300 15 kWh
January 268 / 34 kWh
Despite we have almost 3 times the capacity, and produce more than twice what we use per year, and we have a decent battery and believe it or not, even the shortest day we can produce enough power for a whole 24 hour day if it's a clear day! But we can also have clouds for 14 days!
But for those months we imported 783 kWh and exported 108 that could have been used with bigger battery. But the net import was still 675 kWh!! For those 3 months, and that's the minimum size battery we could have managed with, and then we even need 10% extra to compensate for charge/discharge losses.
TLDR:
Minimum 740 kWh battery in our case, and that's without heating, because we use wood pellets.
That means it would require at least the equivalent of 10 high end fully electric car batteries. But also a very hefty inverter, which AFAIK ads about 50% the price of the battery.
PS: Already in February we exported more than we imported.
(Author here) As I say in my post, our roof is full. We have 16x 320 Watt panels - 8 on each side of the roof.
OK I didn't see that, that's bigger than I expected, we make about 12.5 MWh per year on our 11.2 kWh panels = 1.1 MWh per kWh capacity.
Your system is 5.1 kWh but you only make 3.8 MWh per year = 0.75 MWh per kWh capacity.
Meaning we have 50% higher yield per kWh rated capacity!
So our production remains 3.3 times higher than yours, despite we only have twice the capacity.
But our panels are pretty optimally placed towards the south.
Considering you are further south compared to us, I'm surprised your yield is so low, despite London is infamous for being cloudy.
Damn, those winter numbers mean full off-grid is quite difficult with pure solar. A propane or diesel generator to occasionally top off the batteries would be required for winter.
It is not remotely close to economically viable to go off grid, and the exports of solar power to the grid pay for the connection anyway.
The reason to have a battery is that it lasts through the night, or even with a smaller system, it can handle dinner time, which is the most expensive time of day to buy electricity.
Now if you live in some remote area without a grid, a generator is a way better option than a huge battery.
Maybe if you live somewhere very sunny, like Spain and especially southern parts of USA you can probably do it with a modest battery that can handle a couple of days.
In the summer we can make enough electricity on by far the most cloudy days, but in the winter, the sun can't penetrate the clouds nearly as well.
Admittedly London is south of where I live, which is close to the most southern part of Denmark, but on the other hand London is infamous for grey weather with heavy clouds.
You could probably get by with a gas generator and only run it 2-3 times/year in many areas. It's not 100% green, but it could get you off grid for a fraction of the price.
Power the generator with vegetable oil. There are multi fuel generators that are designed to work well with that kind of fuel. You could also use them for heating which is very useful in Northern regions where you usually need heating and electricity during winter.
Diesel generatorsare significantly better on fuel consumption than a gas one and diesel takes alot longer to go bad than gasoline.
Diesel generators run fine on heating oil, which is cheaper since no fuel tax and has longer shelf life.
Stabil 360 additive to fuel.
Holy shit. I think we used that much last month, which is higher than average but not that high for August around here.
How ? Is it just AC ?
We oscillate between 300 and 800kwh per month and it's with an old water heater, an electric car charged at home, a dryer and electric oven.
Older house, poor insulation, 19 year old heat pump/AC, and hot summers.
You leave 5,278 LED light bulbs on 24/7?
...maybe.
I mean it's probably their kids doing that.
glad I'm not the only one that noticed that.
last time I checked I was using around 4600-5800kwh from May to August. the rest of the year its 3300-4200.
I live in a dual zoned 5200sqft home and my average power bill is around $900.
I've had solar sales try to talk me into solar panels but once they see my consumption they stop answering my calls lol. could be because I told them I'll buy once I can get net zero.
I'm not following your logic. You aren't willing to accept any savings unless you can completely zero out your power bill? Judging from your consumption I'm assuming a good chunk of that is for cooling your home? If so that means you're likely in a pretty great place to harvest solar power. You'd reach payback of your investment on your array much faster than most, and be saving money for probably 35 years or more with little to no additional investment.
Making some guesses for how much your electricity rates are, and how much you're consuming (assuming much from cooling), you might be a full payback in less than 7 years if you took advantage of the tax credit. Then, every month after that you'd be gaining money back.
my house is over 120 years old. it still has knob and tube in half the house. I have even found gas lines for the old sconces, that were "conveniently" used as grounds for said knob and tube in some places. the house is a nightmare, electrically speaking. the only new-ish electrical are the HVAC systems, the 200amp panel, and the basement (where the rack lives).
for me to get proper solar installed, it would cost more than the house cost to buy. For me to find it in any way cost effective, I would need my $900 a month power bill to pay for the $200k loan on top of my mortgage.
As someone who electrically renovated houses without beeing an electrician. If you find an electrician who is willing to work with you: do a full planning of the house. (What lines go where etc) ask them to go over this, and pay them for their time. If all goes well this will cost them an evening or three (depending how many flaws they find in your design). Do the wiring and drilling raw sockets yourself. Buy the top sockets wholesale, then have the electrician make a fixed price for installing sockets and wiring your fuse box , it will be much cheaper.
appreciate the sound advice. I've rewired plenty of houses that I'm comfortable with DIMS and know most of the NEC.
the problem is time and effort. I'm getting older and just don't have the drive I used to have 20 years ago. the biggest problem is the house is still mostly original plaster lathe which is a huge pita for running new electrical across four floors. add to that the other litany of projects I have to do plus daily life/work. it's a lot.
if I was 10 years younger I'd probably start one room at a time, but I'm old enough now that I look forward to taking my daily naps before bedtime.
I reserved myself to a modest retirement when I bought this house because I knew the risks going in.
That house sounds like a terrible investment.
lol. all houses are terrible investments, too volatile.
Wtf?? Are you running a crypto farm or something?? $900 is insane
that's an average btw. last months bill was $1100.
this month is already at $960 and we're only halfway through the month.
this year has been lower than previous. I had new insulation installed last November.
highest bill I have ever seen was around $2200 which is over my monthly mortgage.
no crypto farm. though it would probably be higher if I was.
Thats awful, im so sorry. Our entire house is usually $200ish but it jumped to $400ish because they put in a data center nearby and are using residents to subsidize it
I have personally never seen a bill of more than 60€ per month. I have some friends living in bigger houses, not apartments, and they tell they can get over 100 fairly frequently, the bigger ones more in the North can get over 200 in the winters, but even still, I’ve never even heard of anything reaching 300.
But I’m in my thirties and don’t really know anyone from beyond upper middle class. That might help explain my experience if it happens to be the outlier, but just reading the responses to this, I might not be the outlier here.
Anything four figures is just crazy surreal to me. I can not even imagine what it takes to reach that kind of electric usage. Or maybe it’s just extremely expensive, not the usage itself being crazy? I would think living in a place where sustaining one’s existence requires that kind of resource usage would be very hostile against settling and building in general?
But if it’s just personal usage rather than the regional climate or whatever, and an insane price of electricity isn’t the main reason, then I don’t even know what to say. That’s crazy.
it's kind of a mix of everything.
I grew up poor. like, "take a nap for dinner" poor. I was afforded great opportunities that allowed me to become comfortably wealthy, as in I can freely go to the store and just buy groceries without concern. This is important because I always promised myself that when I grew up I would live comfortably.
I keep my house between 68F-72F year round. I don't open my windows because I have terrible allergies (that my kids have also inherited). at least half of my bill is just heating and cooling. the other half is likely a mix of the servers and the regular appliances.
I have family ranging from 30-60 years old. when I told them how much I spend on power their eyes popped out. they don't run their hvacs as much as I do, and actually use their windows and attic fans. they also don't have the allergic reactions I have either so 🤷.
in my old home, 1600sqft, our highest bill was around $300, and that was still high for the area. our neighbors were average between $100-$150. they were in their 70s though, so likely they didn't use their hvac as much either, nor the technology I was running.
Fair enough, that’d explain it. I did expect air conditioning to be a big part of it, kind of makes a lot of sense that you do run servers as well.
Still, that’s a huge bill to eat each month.
don't I know it 😭
is that per-month, or for the whole span?
per month.
I assume that's HVAC. Makes more sense to fix that before solar.
You also lose some energy to heat while charging and discharging. And depending on load profiles, you might not be able to load all of your excess solar power at once (depends on how many Watts the battery can be charged at) or fulfill your power requirement with battery alone (depends on how many Watts your battery can deliver).
I’m a fan of small scale wind, if there’s climate and space for it. 20hrs a day of a (small) 500w adds up really quickly compared to more panels, especially in grey winter weather. The problem is that there’s a bigger difference between megawatt scale solar vs homeowner scale, and megawatt scale wind vs homeowner scale, so there’s limited investment.
Wind isn’t great small scale. You rarely can get high enough for constant wind energy. They are noisy. They don’t produce a lot. In many or even most cases solar will be better than wind.
I’d go so far as building both sun oriented and a solar “fence” line going north/south to get more non-peak solar before putting up small-scale wind.
As is mentioned in the article 😉 What is also mentioned is the fact that battery prices are going down. Soon it seems they’ll be down to $10/kWh!
There's also alot of new battery tech on the way.
There will be a market for batteries at home, and they will exist with the best suitable tech for it - and it's probably not lithium.
How many years, I dont know. What will it be, and who will do it, no clue. Otherwise my stock portfolio would look better if I knew these things haha.
I wish the second-hand battery market were more lively. Using half-worn car battery packs seems optimal for home use.
I'm not putting cobalt based (NMC or NCA) batteries bolted to the inside my house. Thats nearly exclusively what car battery packs are. Thermal runaway is too great a risk to bolt that much energy to a wall in the house. I am comfortable with LFP in the house though.
It is. Some of them are getting snapped up to help with powering factories.
I think this is car companies using the incoming battery packs from replacing worn out packs. Time to look it up...
https://www.autoblog.com/news/toyota-just-found-a-clever-new-use-for-old-ev-batteries
This is the article I was thinking of. It's more of an idea than a common use case to use old packs to help power factories.
Sodium batteries?
BTW that's the wish for trend line, $10/kWh right?
I mean.. they are at ~$16/ kwh right now, so...
https://www.alibaba.com/product-detail/CATL-75AH-220Ah-Grade-a-Sodium_1600972483761.html
No?
I have seen some wild priced on Ali, in your link the 75Ah and the 210Ah are priced the same, so I guess it's for the smaller one, 30€ for ~0.225kWh or 133€/kWh.
Could be wrong ofc, but it sort of fits what I thought it would roughly be.
I mean even ~133/kWh..
Whats an average, perhaps even gratuitous, level of consumption per household? 24kwh if you are running a clothes drier and an AC nonstop? Lets go nuts, say you are a DIY enthusiast and hosting your own servers, so 36kwh daily.
3192€-4788€ to be and you can be effectively energy independent with a small solar system.
Triple that and you are truly energy independent are any where south of the English channel. I mean obviously its money out of pocket, but its a fixed cost that you pay now, instead of a variable cost that continuously goes up. It just seems basic.
Sure, but at 16€/kWh well that's a whole other ballpark. Buy one 36kWh for < 600€, put it in your car, charge at work 😋 style of different.
Exactly. Haven't read all details of the link,so I react your comment, and have immersed myself a bit in this earlier.
You need to change your way of thinking and energy usage. Start with your daily energy supply and then change your energy consumption pattern to day time use Then, with for example a dynamic energy contract or if you can spare solar energy, buy or store cheap electricity in your storage ( battery ). The energy management system ( charge / uncharge and which cells) is very important.
Also, realize that battery life is tied to charge cycles and need replacing like every 10 years when talking about the better quality Lithium battery . Sodium systems could and maybe should be used in parallel, if you want more storage, safety and longevity (20 years).
It is yet all quite expensive, though imo having a half day reserve like 5 - 10 kwh, battery, would already create more independence (at around € 3K to € 10 K in Europe) .