How does a home battery shave the power fee?

A power fee charges for your highest power peak, the moment when the most things in the house draw electricity at once. A home battery shaves that peak: when everything comes on together, the battery covers part of the load instead of it all being pulled from the grid at once. The measured peak drops, and the fee with it.

And the battery does it without you changing a single habit. Below we cover what a power peak actually is, how the battery shaves it, why power matters and not just size, and when the shaving actually pays off.

The highest power you draw during the measuring window, usually an hour or a quarter-hour. Power is measured in kilowatts and tells you how much electricity you're drawing right now, not how much you've used over time. Run the oven, EV charger, washing machine and a heat pump working hard all at once and the power gets high, even if it only lasts a short while.

The power fee only cares about the worst moment. A single quarter-hour with everything running can set the price for the whole month, no matter how sparing you were the rest of the time. That's the moment the battery is there to handle.

By stepping in and covering part of the load right when it's highest. When several things start at once, the house normally pulls it all from the grid together, and that's when the meter maxes out. A battery can instead give off electricity in the same moment, so part of the load comes from there and less from the grid. The measured peak drops.

The point is that the battery doesn't reduce how much electricity you use, only where it comes from at the instant that counts. The oven gets its power, the EV gets its, but some of it passes through the battery instead of through the meter. The grid company sees a flatter curve than the one you actually run.

To shave a peak, the battery has to be able to give off a lot at once, not just hold a lot. The size, measured in kilowatt-hours, tells you how long the battery lasts. The power, measured in kilowatts, tells you how hard it can deliver in the moment. A large battery that can only give a little at a time does poorly against a short, high peak.

So a battery meant to shave power peaks is judged on both measures. It has to be strong enough to meet the peak while it lasts, and last until it's over. Which combination fits depends on how high and how long your peaks are, and that only shows once you look at the house.

No. The alternative to a battery is spreading out your usage by hand: charging the EV at night, running the wash when nothing else heavy is on, and never starting everything in the same quarter-hour. It works, but it means keeping track of it every day, all year round. The cold evening when you really want the heat is also the one where the peak is most expensive to avoid by hand.

A battery takes over that planning. The optimisation knows when the EV is charging and when the heat pump is working hardest, and discharges the battery at the right moment to flatten the curve. You notice nothing, and you don't have to schedule your life around a tariff.

It depends on two things: whether your grid company charges a power fee, and how spiky your usage is. If you have no big, simultaneous peaks, there's little to shave. If you have an EV and a heat pump that often draw at the same time in the evening, there's all the more, because those are exactly the peaks the fee charges for.

The shaving is rarely the whole reason to get a battery, but it's one of the returns added to the others: moving electricity to cheap hours, saving solar power for the evening, taking part in support services. How much the peak-shaving alone gives varies with how your tariff is built, and it's not something you can read your way to in an article.

You don't have to think about it. Elvy sizes the battery to your house, so it both holds and is strong enough for what you need, and puts it together with solar panels and a heat pump as one whole. Elvy owns the equipment and runs the optimisation against spot price, power peaks and support services in the background.

The peak-shaving happens automatically and is part of the fixed monthly cost. If the grid company changes its tariff, it's our job to adjust, not yours. What you pay for power is something you never have to do the arithmetic on.