Finding the chase and cutting to it

A few suppliers in the UK are allowing people to use their home battery storage to buy electricity when it is cheap and sell it when it is expensive. The homes doing this often don’t get to say how this works, it is managed for them, but it varies from network to network. That process is called energy arbitrage.

So, how come we’re not doing that?

The short answer is two fold:

1. That’s not the aim of our installation, we’re looking to cut our usage/emissions.
2. Most of the suppliers doing this have much higher standing charges than our current tariff.

When I looked into this for us, I worked out that we would be marginally worse off. Especially during the summer. Our electricity for June was £18.03, which was the standing charge for 30 days, £1.15 in usage charges and the VAT. Hard to do that with the higher standing charges on the variable tariffs.

We might make up the difference during the winter, but it’s marginal on whether that would actually be the case. We tend to use our battery to cook our evening meal and avoid using peak-time electricity. I did several simulations and instead we do this during the working week.

Set a reasonable ‘backup reserve’ and run self-powered.

During non-peak times our backup reserve (the emergency rations for if there is a power cut), our reserve is set to 20-25%. We use solar to charge up the battery and the rest of our solar power is used to run the home. We do our washing during this time, cycle the dishwasher, charge our phones and laptops, work.

During peak times, we drop it down to 10-15% and tell the battery to ‘save money’. This means the battery software chooses battery and solar energy instead of the grid. As soon as peak time is over, it switches back again to ‘self-powered’ and a higher reserve. I could tweak this further during the winter but I am doing other things to keep our peak usage down.

Use the house as a heat battery.

During the summer, the goal is to get as little solar gain as possible. During the winter it is all about getting that lovely infrared free power into our home!

We heat the house and our hot water once the sun gets high enough. The sun warms the air, the air is sucked in through the heat pumps propellers, and our heat pump gets an easy time of it. Easier to do during the spring and autumn. Harder during the deep mid-winter, though it provides benefit then too.

Even during the winter, a clear sunny day gives two benefits. Plenty of solar power, and precious amounts of infrared radiation. Double glazing in our two main rooms provides a harvesting mechanism second to none. Triple glazing is great for insulation, poorer at solar gain. Double glazing is the opposite, although miles better than single glazing for insulation.

The rest of our insulation makes this work well. Even the best insulated houses lose heat. Having a warm home to come in after work without having to pay anything to heat again is invaluable. More importantly, it means we’re not using electricity during peak demand. Nor are we using cold air as the basis for heating our radiators.

It’s like economy 7, only the heat is available for us when we want it, the early evening. It’s a win-win situation. Our air sourced heat pump is more efficient, and our electricity bills are lower.

Does that really work?

Yes, it really does. I do use a little energy between 6:30 and 8:00 to ensure the chill is off our bathrooms. Yet, we typically use 3-4kWh of electricity to get 27kWh of heat this year (COP of 27/3=9).

Compared to last year, when we spent 31.2kWh of electricity to get 109kWh of heat (COP of 109/31.2=3.494). The ‘low performance’ was due to the fact we were doing the majority of the heating during the evening and early morning. This meant the heat pump was trying to extract heat from the air when the air was cold. Changing how we use the heat pump and the thermostats has given us a real advantage, even as it has got significantly colder. Of course, that is just looking at one day: 18^th November 2025 and 18^th October 2026, both had highs of 11˚C and overnight temperatures of 8˚C.

Setting up the heat pump.

When we had standard double glazing throughout, a heating curve slope of 0.7–1.0 kept us comfortable. The heating curve dictates the weather-compensated flow temperature: on mild days, the inverter compressor quietly ticks along at low power to supply lukewarm water; on freezing days, it ramps up compressor speed to push higher water temperatures into our system.

Of course, last winter we couldn’t evaluate the full impact of our triple glazing and building upgrades because fresh plaster and building materials were still drying out, absorbing a lot of latent heat. This year, with everything dry and settled, we’ve noticed our old heating curve is no longer matching our needs and keeping the heat pump running well.

Our ‘wet’ underfloor heating and radiators work by transferring heat from circulating water into the building’s thermal mass and air. If your heating curve is set too high for a well-insulated home, the water returns to the heat pump nearly as hot as it left because the rooms simply can’t absorb any more of the generated heat. Detecting this high return temperature, the heat pump shuts off prematurely, causing ‘short cycling’, where the unit repeatedly turns on and off in brief bursts, even while the outdoor sensor reports that it’s freezing outside!

Getting the heat curve tuned to your house is one of the things your heating engineer can help you do. Do not accept the default settings either, if you are getting new units installed. Most heating engineers will love to pass on their hard won knowledge and help you get the most out of your system.

It’s not just about having the equipment, but about making the most of it.

It really is. No point having great insulation and not modifying your heating settings. The heat pump is an amazing piece of kit. But tuning it to fit your home and life is what really saves the energy. And that gives us more than arbitrage can this winter.