Is solar PV working with your tank?

Solar PV panels generate electricity from daylight. If your Mixergy tank has a compatible solar setup, it can use the electricity your panels generate that the rest of your home isn’t using. We call this spare solar electricity.

Solar heating depends on the weather and on what else your home is using, so it won’t happen every day. Using another heat source on dull days or when you need lots of hot water is normal and doesn’t mean anything is wrong.

1. Is your tank set up to use solar electricity?

Having solar panels doesn’t automatically mean they supply your tank. Your tank can use spare solar electricity in one of two ways.

With Mixergy Solar X, the solar diverter is built into the tank. It sends spare solar electricity to the tank’s electric heater.

With a Mixergy PV Switch, a separate diverter decides where spare solar electricity goes, and it can send it to your tank. See [PV Switch article] for more information.

If your installer has confirmed you have one of these setups, carry on to step 2. If you’re not sure, ask the installer who fitted your tank or solar system. If you rent or live in a new build home, ask your landlord, housing provider or developer. They’ll need to confirm the setup is compatible and switched on before you can check whether it’s working.

2. How your tank uses solar

Your tank tries to use solar electricity first. It may hold off heating from the grid for a while in case spare solar electricity becomes available. If there isn’t enough within a reasonable time, it uses its other heat source so you aren’t left without hot water.

Which other heat source it uses depends on its setting in the Mixergy app. On Electric, the tank heats using spare solar electricity, then electricity from the grid. On Electric and Indirect, it uses spare solar electricity first, with your boiler as backup.

If you’re not sure which setting is right for your home, ask your installer before changing it.

3. Choose a good time to check

Check during a bright part of the day, when your panels are likely to be generating plenty of electricity.

Your tank might not get any solar electricity even on a sunny day. If the oven, an electric shower or other appliances are on, your home may be using everything your panels make, so check again when you’re using less. If your tank already has the hot water it needs, it won’t take any more, so check again after you’ve used some hot water.

4. Check whether solar electricity is reaching the tank

In the Mixergy app, look at the graphs for solar electricity going to your tank. This is different from how much electricity your panels generate overall.

If the app shows solar electricity going to the tank, the solar connection is working.

If the app shows nothing, check again during another bright period when you’re using less electricity and the tank needs more hot water. If there’s still nothing, carry on to step 5.

If you can’t find the solar information, that doesn’t mean solar heating isn’t working. Ask your installer or whoever manages your tank to show you where to find it.

Another good sign is your hot water level going up during daylight while your boiler and grid electricity aren’t heating the tank.

5. If you have a PV Switch

Because a separate diverter controls where spare solar electricity goes, check that it’s switched on and that its settings send spare electricity to your tank first. If you’re not sure how, contact the installer or solar provider who fitted it.

6. Ask for a setup check if there’s still nothing

If you’ve checked during more than one bright period and still can’t see any solar electricity going to the tank, contact your installer. If you rent or live in a new build home, contact your landlord, housing provider or developer.

Tell them when you checked, whether it was bright, how much hot water you had, and whether anything was using lots of electricity at the time. If you have the app, send a screenshot of the solar information.

Ask them to check that solar water heating is switched on and that the diverter is picking up your spare solar electricity. Please don’t open electrical equipment, move sensors or touch solar cables. Your installer may need to check a CT clamp, which is a sensor fitted around a cable to measure electricity flow, and they should do that check themselves.

Common questions

Does having solar panels mean they heat my tank?
No. Your tank needs a compatible setup, either Mixergy Solar X or a Mixergy PV Switch, configured to use spare solar electricity. Ask your installer, landlord, housing provider or developer if you’re not sure.

Why is there no solar heating on a sunny day?
Your home may be using all the electricity your panels make, or your tank may already have enough hot water. Check again during another bright period before assuming something’s wrong.

Why did my tank heat from the grid or boiler when it was sunny?
If there wasn’t enough spare solar electricity within a reasonable time, your tank used its other heat source so you still have hot water. That’s normal.

Can I check without the app?
Yes. Ask your installer, landlord, housing provider or developer to check the solar setup. You don’t need to download the app just to report a problem.

Can I still have hot water when there’s no spare solar electricity?
Yes. Your tank heats using its other heat source. If you have no hot water at all, follow No hot water instead of these solar checks.