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 …
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.
We have a national grid that is shared by all power companies, and is open to all. Power companies just buy and sell power on the grid based on a spot pricing system. Because of this, we have very easy movement between power companies, and have dozens to choose from, leading to a lot of competition. Mine is a tiny company that specialises in solar, having sell to grid rates well above most companies.
The company that did our solar install had their top recommended companies, they worked out the best for us, and organised getting set up with them. Was I pretty nice experience to have everything taken care of like that!
We can’t, but we can do net metering, meaning we can offset costs but not get paid. So the best investment is to pay nothing through Dec. 31 and keep costs manageable at the start of the year (net metering ends with the calendar year).
Net metering is potentially better, as you are effectively getting free night usage based ob day generation. My setup pays me, but I get paid 20c per Kw (NZ dollar) and pay about 30c to buy, so there’s a 10c difference. Just as long as whatever you lose on 31st Dec is not too high, you’d be better off than me.
Only while there’s a surplus. Our net metering arrangement effectively forfeits any surplus at the end of the year. It obviously can vary by region and how much you’d get from surplus vs specifics of the net metering policy, but I think getting paid for surplus is simpler and easier to plan around.
I disagree, but in not in your situation so I can be wrong.
Unless you are producing way, way more electricity than you can use I think net metering is a great arrangement for the customer. (Not so much for the utility company)
The electricity is usually bought by the utility company at a much lower cost than what the customer is paying. Because the generation cost is only a percentage of the cost, there is taxes, maintenance of the grid …
For example in France we pay 0.1952€/kWh, but the utility is buying the solar electricity produced by household at 0.04€/kWh.
Meanwhile with net metering your electricity is virtually bought at the same price as what you are buying your electricity for.
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.
I’m feeling very lucky now!
We have a national grid that is shared by all power companies, and is open to all. Power companies just buy and sell power on the grid based on a spot pricing system. Because of this, we have very easy movement between power companies, and have dozens to choose from, leading to a lot of competition. Mine is a tiny company that specialises in solar, having sell to grid rates well above most companies.
The company that did our solar install had their top recommended companies, they worked out the best for us, and organised getting set up with them. Was I pretty nice experience to have everything taken care of like that!
We can’t, but we can do net metering, meaning we can offset costs but not get paid. So the best investment is to pay nothing through Dec. 31 and keep costs manageable at the start of the year (net metering ends with the calendar year).
Net metering is potentially better, as you are effectively getting free night usage based ob day generation. My setup pays me, but I get paid 20c per Kw (NZ dollar) and pay about 30c to buy, so there’s a 10c difference. Just as long as whatever you lose on 31st Dec is not too high, you’d be better off than me.
Net metering is great, much better than being paid for the surplus.
With net metering the grid is basically an free, infinite, 100% effective battery.
Only while there’s a surplus. Our net metering arrangement effectively forfeits any surplus at the end of the year. It obviously can vary by region and how much you’d get from surplus vs specifics of the net metering policy, but I think getting paid for surplus is simpler and easier to plan around.
I disagree, but in not in your situation so I can be wrong.
Unless you are producing way, way more electricity than you can use I think net metering is a great arrangement for the customer. (Not so much for the utility company)
The electricity is usually bought by the utility company at a much lower cost than what the customer is paying. Because the generation cost is only a percentage of the cost, there is taxes, maintenance of the grid …
For example in France we pay 0.1952€/kWh, but the utility is buying the solar electricity produced by household at 0.04€/kWh.
Meanwhile with net metering your electricity is virtually bought at the same price as what you are buying your electricity for.
Ah, I didn’t realize the payout was so low. If it was half the purchase price, it could be better than net metering.