Running the home battery on the spot price

Running the home battery on the spot price means charging it when power is cheap and using it when it's expensive. The price changes hour by hour, and the battery shifts your consumption to the cheap hours without you noticing anything. Done right it happens automatically, around the clock, without you having to keep track.

The spot price is the variable electricity price set by the hour. Sometimes power is cheap, sometimes expensive, and the gap between the hours can be large within a single day. Running the battery on the spot price means charging it during the cheap hours and using the stored power during the expensive ones. You consume just as much, but you buy it when it costs less.

The point isn't to save electricity, but to move it in time. The battery becomes a buffer between when power is cheap and when you actually use it. Your morning coffee can run on power that was charged in at three in the morning.

Because power is priced on supply and demand, hour by hour. When many people use a lot at once, a cold morning when everyone wakes up, the price rises. When consumption is low and the wind is good, it falls. The weather, the season and what the rest of the country is doing decide, not you.

That movement is what the battery lives on. If the price were the same around the clock there would be nothing to shift and nothing to earn. The bigger the gap between cheap and expensive hours, the more there is to gain from steering it right.

It depends on how large the price gap is where you live, and that varies. If the difference between the day's cheapest and most expensive hours is small, there's little to gain. If it's large, every charge is worth more. No exact figure can be promised in advance, because it changes with the price.

If you have solar panels there's more to be had. Then the battery can store the day's surplus for the evening instead of you selling cheap and buying dear a few hours later. If you have a capacity tariff, the battery can also shave the peaks when consumption is at its highest. The spot price is one of several things to steer against, not the only one.

No. The spot price is the most visible part of the electricity bill, but not all of it. On top come the grid fee, taxes and, for many households, a capacity tariff that depends on how much you pull at most during a single hour. A battery that only chases the lowest spot price can miss that the most expensive hour to consume in is sometimes a different one.

Steering it right is therefore about weighing several things against each other at once, not about following a single curve. That's also why it's hard to do by hand.

In theory. The spot price for the next day is known in advance, so you could in principle sit down in the evening, look at tomorrow's prices and decide when the battery should charge and discharge. In practice that means replanning every day, all year round, while weighing in power peaks and solar production at the same time.

Most people can't be bothered, and don't need to. This is exactly the kind of nagging optimisation a computer does better than a human. It never gets tired and never misses a night.

Automatically, in the background. In an energy subscription Elvy owns the battery and handles the steering for you. We charge when power is cheap, use it when it's expensive, shave the power peaks and let the battery take part in support services that keep the grid stable, which Svenska kraftnät pays for. All of it fits inside a fixed monthly fee.

You notice nothing, and that's the whole point. Whatever the spot price gets up to tonight, you never need to know. The most boring thing about the battery should be that you forget it's there, doing the sums.