Solar Thermal Hot Water Explained

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Solar thermal systems don't generate electricity: they just heat water. This means that they'll never give you a net-zero or net-positive effect if they're used on their own. On the other hand, they're more efficient than renewable electrical systems, have fewer demands and can take care of pretty much all your domestic hot water needs.

The main criterion for installing a solar thermal system is to have a location that receives direct sunlight between 9:00 a.m. and 3:00 p.m. all year round. As you probably suspect, "direct sunlight" does not include cloudy days and other intemperate weather: solar thermal systems only produce hot water when the sun is shining.

Assuming you have enough sunlight, a solar thermal system operates extremely efficiently. Some systems can convert as much as 80% of solar energy into heat, compared with about 15% or 20% conversion for photovoltaic (PV) panels. They're often cheaper than other renewable systems (though that depends on what you install), don't take up much space and are less affected by equipment orientation.

You still need to consider your other renewable systems when installing a solar thermal setup, as you may need to prioritize the sunniest locations for PV panels to generate electricity.

Unless you're lucky enough to live in an area where the sun shines hot and clear almost every day, you'll also need to include insulated hot-water storage. The amount of storage depends very much on where you live and how much water you generally use: a couple living in an area which gets one cloudy day every two weeks will obviously a smaller tank than a large family living in a frequently rainy location.

Most solar thermal systems are installed as an extension of an existing, conventional water heater. This is because it's rare for a solar thermal system to provide enough heat for a home's use all the time. The conventional system acts as a sort of failover: the solar setup pre-heats water which feeds into the conventional system but, if there isn't enough hot water, the conventional setup kicks in and covers the shortfall.

Check out other articles on our site to discover the different types of solar thermal system and work out which one suits your circumstances best!