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 …
Basically why the grid exists to begin with. You’re not supposed to be solving these engineering problems on a household budget inside a single home.
You’d be better off simply reducing your consumption or finding alternative methods of power (nat gas or maybe wind or geothermal) during the longer winter nights.
If you really want to go crazy, you should consider investing in a bigger home with better insulation and roommates. An apartment/condo block can at least leverage economies of scale, if you’re dead set on DIY. More people benefiting from the setup dilutes the cost per person.
I recently got a solar system and came to the conclusion that if you can sell power back to the grid (not everyone can) for some reasonable percentage of what it costs to buy it, then it will always be worth it to be connected (assuming you already are).
Quite simply, if you have enough solar capacity to get you through the winter (no house is going to have months of battery storage), then you will always be creating far more than you need in the summer. Selling this excess will easily cover any costs associated to being on the grid.
Also at current prices batteries are good for backup power only, it’s always cheaper to sell excess power to the grid in the day and buy it back at night than it is to have battery capacity to get through the night. I worked out it would take 40 years for our battery to pay for itself (assuming the battery kept a constant battery capacity for 40 years…) but less than 10 years for the rest of the system to pay for itself.
We pay a daily lines maintenance charge of 60c, then 29c/kWh during the day and a little under 27c for off peak night time. Then add 15% tax to these. These are in NZD, so almost halve them to get USD (e.g. 60cNZD is 35cUSD)
We also get about 17.5c for each kWh sold to the grid. So to sell it in the day and buy back at night is a 10c additional cost. A 10kWh battery can save a max of $1 per night, meaning it’s really hard to make your money back on a battery that’s $10-15k NZD on it’s own.
Basically why the grid exists to begin with. You’re not supposed to be solving these engineering problems on a household budget inside a single home.
You’d be better off simply reducing your consumption or finding alternative methods of power (nat gas or maybe wind or geothermal) during the longer winter nights.
If you really want to go crazy, you should consider investing in a bigger home with better insulation and roommates. An apartment/condo block can at least leverage economies of scale, if you’re dead set on DIY. More people benefiting from the setup dilutes the cost per person.
I recently got a solar system and came to the conclusion that if you can sell power back to the grid (not everyone can) for some reasonable percentage of what it costs to buy it, then it will always be worth it to be connected (assuming you already are).
Quite simply, if you have enough solar capacity to get you through the winter (no house is going to have months of battery storage), then you will always be creating far more than you need in the summer. Selling this excess will easily cover any costs associated to being on the grid.
Also at current prices batteries are good for backup power only, it’s always cheaper to sell excess power to the grid in the day and buy it back at night than it is to have battery capacity to get through the night. I worked out it would take 40 years for our battery to pay for itself (assuming the battery kept a constant battery capacity for 40 years…) but less than 10 years for the rest of the system to pay for itself.
I’m paying 50c per kWh for grid…its bad. And that’s if I don’t go over the limit. There’s 4 teirs so it gets more expensive per tier.
Wait, it gets more expensive when you use more?
Exceptionally. Yes.
What an odd pricing structure! I would normally expect higher usage to mean lower prices per unit.
I guess that gives you a large incentive to have at least a little solar, as there would be a big financial benefit.
Its pretty bad. They only show a couple of the tiers here. https://www.pge.com/assets/pge/docs/account/rate-plans/residential-electric-rate-plan-pricing.pdf
This is an old pdf but the only one they have on the website. They haven’t updated it in a while so its not counting the latest 2 rate increases.
Interesting! Your power seems super expensive.
We pay a daily lines maintenance charge of 60c, then 29c/kWh during the day and a little under 27c for off peak night time. Then add 15% tax to these. These are in NZD, so almost halve them to get USD (e.g. 60cNZD is 35cUSD)
We also get about 17.5c for each kWh sold to the grid. So to sell it in the day and buy back at night is a 10c additional cost. A 10kWh battery can save a max of $1 per night, meaning it’s really hard to make your money back on a battery that’s $10-15k NZD on it’s own.
4 years ago it was 18c per kwh. Which was nice.
Yours is very good. and selling back to the grid would be nice! Making me jealous lol.