I have a modest set of solar panels on an entirely ordinary house in suburban London. On average they generate about 3,800kWh per year. We also use about 3,800kWh of electricity each year. Obviously, we can't use all the power produced over summer and we need to buy power in winter. So here's my question: How big a battery would we need in order to be completely self-sufficient? Background …
they generate about 3,800kWh per year. We also use about 3,800kWh of electricity each year
Obviously, we can’t use all the power produced over summer and we need to buy power in winter. So here’s my question: How big a battery would we need in order to be completely self-sufficient?
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.
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.
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.
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.
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.
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.
Holy shit. I think we used that much last month, which is higher than average but not that high for August around here.
You leave 5,278 LED light bulbs on 24/7?
…maybe.
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.
That house sounds like a terrible investment.