Use solar PV with your Mixergy tank
How your tank uses spare solar electricity and how to tell it's working.
If you have solar panels, a compatible Mixergy tank can use the electricity your panels are making that your home isn’t using. We call this spare solar electricity, and putting it into your hot water means less of it goes back to the grid unused.
How much spare electricity you have changes with the weather and with what you’re using at home, so solar heating will vary from day to day.
How solar heating works
Your home always uses the electricity from your solar panels first. When your panels make more than your home needs, a solar diverter sends some of the spare electricity to your tank’s electric heater, which heats your water directly.
How this works depends on your setup. Mixergy Solar X has a solar diverter built in, so the Mixergy app can show you more about your solar heating and give you more control over it. Other setups use a Mixergy PV Switch connected to a separate diverter made by another company. That diverter decides how much spare electricity goes to your tank, and the Mixergy app may not show it in the same way.
Solar X doesn’t rely on solar alone. It also works with your boiler, direct electric heating or a heat pump, so you’ll still have hot water on dull days.
How can I tell whether solar is heating my tank?
- Pick a bright part of the day, and check your solar system’s own app or display to see that your panels are generating electricity.
- Open the Mixergy app and select your tank. Look at your hot water level and any target shown. Solar heating stops once the tank reaches its solar limit or temperature target, even if your panels are still generating.
- Open Graphs and choose PV Power, if you can see it. If you have a separate diverter, check its own app or display too, because its solar input might not show up in Mixergy.
- Compare your hot water level before and after a sunny spell. If it’s gone up, solar is probably heating your tank, but bear in mind another heat source could also be running.
- Check again over a few bright days to get a clearer picture.
Appliances like kettles, ovens and washing machines can use up your spare electricity before it reaches the tank. On a dull day, or when you’re using a lot of electricity at home, there may be nothing left over for your hot water, and that’s completely normal.
Why might my tank wait before heating?
If your tank expects spare solar electricity later in the day, it may hold off heating from the grid so it can make the most of what your panels produce. It still keeps an eye on when you’ll need hot water. If there isn’t enough solar electricity in time, it finishes heating with its other heat source so you aren’t left short.
Keep the heat source setting your installer chose
The heat source setting tells the app how your water is heated. Electric is usually used when spare solar and grid electricity both heat the tank. Electric and Indirect is usually used when solar heating is backed up by a boiler.
Please leave this on the option chosen when your tank was installed. If a heat pump heats your water, follow Combine solar and a heat pump instead of choosing an electric or boiler option. If you’re not sure which setup you have, ask your installer.
SAFETY
Please leave electrical covers and wiring as they were installed, and don’t move the CT clamp (the sensor around a cable that measures electricity flow). If your panels don’t seem to be generating, or spare electricity isn’t reaching your tank, ask the installer who fitted your solar system to take a look.
For a step-by-step check, see Is solar PV working with your tank?.
[IMAGE – SOLAR ENERGY FLOW] Use: Solar panels powering the home first, with spare electricity passing through the diverter to the Mixergy tank. Caption: Your home uses the solar electricity it needs first, and the spare heats your water. Alt text: Diagram showing solar panels powering a home, with spare electricity going to a Mixergy tank.
Common questions
Do I need the app for solar heating to work?
No. Once your system is set up, solar heating works on its own. The app lets you see what’s happening and change settings where they’re available.
Will my tank use all my spare solar electricity?
Not always. It depends on how much spare electricity there is, how much hot water is already ready and the limits set for solar heating.
Why did my tank heat from the grid before the sun came out?
You may have needed hot water sooner than your panels could provide it. Your tank may also have used a cheaper time on your tariff so you weren’t left without enough hot water.
Why isn’t my hot water level going up?
Your tank may already have reached its solar limit, there may not be enough spare electricity, or another appliance may be using it. Try again during a longer spell of bright daylight.
Does nothing showing in the Mixergy graphs mean something’s wrong?
No. Some separate diverters don’t report to Mixergy, so check the diverter’s own display and your hot water level as well.
Can solar be my tank’s only heat source?
Solar changes with the weather, so Mixergy solar tanks are designed to work alongside another heat source, such as a boiler, direct electric heating or a heat pump. That way you still have hot water when the sun isn’t out.