Using Solar PV

Mixergy can use surplus solar PV to heat your hot water, helping you make better use of the energy your system generates. Solar heating only works when there is spare solar available, and behaviour can vary depending on weather, household demand, and how your system is configured. 

This guide explains how to confirm solar is working, why it may not heat the tank at certain times, and how Mixergy prioritises solar against other heat sources. 

How to Check Solar is Working 

The most reliable way to check whether solar is contributing to heating is through the Mixergy app. You can do this: 

• Viewing the graphs in the app and checking for solar related input 

• Looking for periods where hot water levels increase during daylight hours without grid or boiler use 

• Checking any clamps, sensors, or indicators fitted as part of your solar installation 

Solar heating only occurs when there is surplus generation after household electricity demand has been met. If solar generation is low or household demand is high, the tank may not receive any solar input. 

Why Solar Might Not Heat the Tank 

It is normal for solar not to heat the tank at all times. Common reasons include:

• Insufficient solar Generation due to weather or seasonal conditions 

• Household appliances using available solar before it can be diverted 

• The tank already being at or near its target hot water level 

• The solar diverter not detecting surplus energy 

• Another heat source being prioritised 

These situations do not indicate a fault and often resolve naturally as conditions change. 

How Mixergy Prioritises Solar Over Grid 

When solar is available, Mixergy may delay grid-powered heating to wait for surplus solar PV. This helps maximise self-consumption of solar energy but can make heating appear delayed. 

If solar does not provide enough energy within a reasonable window, the tank will fall back to another enabled heat source, such as: 

• The immersion heater using grid electricity 

• A boiler (if Electric and Indirect is selected) 

This balance between waiting for solar and ensuring hot water availability is intentional. 

Heat Source Settings for Solar Homes 

Correct heat source selection is essential for solar heating to work as expected. 

Most solar homes should use one of the following: 

• Electric: Use this if you only want to heat the tank using solar and grid electricity via the immersion heater. 

• Electric and Indirect: Use this if you want solar to be prioritised, with a boiler available as backup. 

If the wrong heat source is selected, the tank may rely on grid electricity instead of solar, even when solar is available. 

If you are unsure which setting is correct, check with your installer, developer, or housing provider. 

Solar Diverter Behaviour Explained 

Solar heating relies on a diverter to send surplus solar PV to the tank. 

Mixergy Solar X

If your tank includes Mixergy Solar X, the Solar Diverter is embedded in the tank itself. The Mixergy Solar X automatically monitors surplus solar PV and directs it to the immersion heater when available. 

If you are unsure whether this is working: 

• Check the solar-related information in the app 

• Confirm your solar system is generating electricity 

Mixergy PV Switch

If your setup uses a Mixergy PV Switch, a third-party diverter controls when surplus solar is sent to the tank. In this case: 

• Check the third-party diverter’s own settings and indicators 

• Ensure it is configured to prioritise the hot water tank 

• Confirm it is powered and operating normally 

If solar still does not appear to heat the tank, your original installer or solar provider should review the diverter configuration. 

When Solar Alone is Not Enough 

Solar heating is opportunistic. It depends on surplus generation and cannot be guaranteed every day. 

During periods of low sunlight or high demand, the tank will rely on another enabled heat source to ensure you still have hot water. This is expected behaviour and does not mean solar has stopped working.