Living with solar hot water panels

Who should read this guide?

If you are living in a home with solar hot water panels, this guide will give you some general information about what to expect from them and how to get the best out of them. It isn't specific to any particular sort of panel, and it isn't about how to choose them. It does explain some things you should know if you move into a new home that has them.

What do solar hot water panels do?

Solar hot water panels use energy from the sun to heat the water in your hot water tank. Usually you will have a second heat source such as a gas boiler, heat pump or an immersion heater for use when needed. The idea is to use the solar panels to get as much free heat as possible and then top that up as necessary from the secondary source.

You should be able to get all or at least most of the heat you need from the panels in summer and there will be some heat even in winter. Overall you should get about half your hot water heating from the panels. However this depends on how much hot water you use, the size of your tank, the type and orientation of your panels, and of course the weather.

How do I know they are working?

The best way to check if they are working is to check the temperature of the tank at intervals during the day. After a sunny afternoon but before the secondary heating has had a chance to top up, the tank should be hotter than it was before. On a really sunny day it should be at least 60°C, assuming you haven't used a lot of water while it was heating. You should have some way to check the temperature, either on the tank itself or through your heating controller.

What do I need to do? Is there anything I shouldn't do?

diagram showing effect of timing

Heat your hot water tank in the
or evening to make the most of your free heat from the sun.

The main thing with solar panels is to allow the sun to do its work and heat up your hot water tank for free before you top up the heat from your secondary system. Most people use hot water in the evening and in the morning so it is best to set the secondary water heating to be in the early evening, after the sun has had its chance but before you need the hot water.

If your tank is properly insulated it should have no trouble keeping the water hot overnight until the morning. Unless the tank is very small, 50°C or even 45°C is plenty hot enough for a shower or a bath. However, if it isn't then you can heat the water in the morning instead, as long as the heating cuts out before you start to use the hot water. Otherwise, you will be using fuel to replace the heat which the sun might have given you for free.

Some people turn the secondary water heating off altogether during the summer. You can try this and see how you get on. However, you should make sure the tank is heated to 60°C at least once a week to kill off any bugs in it.

Why is it making that noise?

Your solar panels should run very quietly with just a a gentle hum when the pumps are going. If it is loud or graunchy it needs attention.

What maintenance does it need?

The main thing is to check it is working occasionally, as above. If there is a problem it could be due to air bubbles in the heating circuit, pump problems, leakage from the heating circuit or faults in the control system that manages the pump. This list is not exhaustive but it covers the most common issues.

The panel itself is normally very robust and should not need cleaning unless you are in a very dusty area or the slope is too shallow for the rain to run off cleanly.

It is also worth getting it serviced every few years, if only to to check that the glycol level in the heat transfer circuit is sufficient. Glycol is important as it acts as anti-freeze for the winter. However, it can break down at high temperatures so if your panels get very hot, for example if you go away for a while and aren't using any hot water, then the glycol levels may be affected.

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