How Does Solar Water Heating Work Exactly?

A free resource that’s available all over the planet, solar energy is a great alternative to other types of power and what’s better; it’s free and environmentally friendly too!

Solar water heating has become much more popular in recent years, particularly as a result of the government subsidy, and now the familiar sight of solar roof panels can be seen dotted around every town.

But how exactly is the energy from the sun harnessed and transformed into hot water? We take a more detailed look at exactly how solar water heating works.

The components

A solar water heating system is made up of several parts, each of which performs a vital role in the process. We will examine each part in turn, looking at its role in providing heating.


This is the official name for the parts that you have seen before. The big black solar panels which squat on roofs gathering the solar energy are known as collectors.

Homes which are either smaller, or in a very hot climate, tend to have smaller collectors than this in larger dwellings or colder climates. Collectors are split into two types: flat plate and evacuated tubes.

The flat plates are the simplest system as they are essentially no more than water pipes which are run through a shallow metal box, which is coated with thick black glass. Working just like a green house, the heat becomes trapped inside and runs through the water in the pipe and transfers to the hot water tank.

Evacuated tubes are slightly more complex, and work in a similar way to vacuum flasks. Totally empty, the heat is collected which then travels to a device at the top known as a manifold, which has either water or another type of fluid running through it. This in turn takes the heat to the hot water tank.

The latter system is more efficient as it doesn’t let heat escape but it is also more expensive.

Hot water tank

This is the part of the system which stores the hot water as it comes off the roof. If you have a combo boiler you will need to have a tank fitted too to store the solar heated water.

If you have a large family you’ll need a bigger tank; a typical family tank will normally be around 100-200 litres.

Heat exchanger

This is the device which moves the hot water from the collector and into the hot water tank, flowing through a separate system and exchanger.

The water that has been heated by the sun never actually finds its way into a tap; instead it moves from the collector into copper coils or piping inside the hot water tank where the heat is used to warm up the waiting water. The then-cooled water (or other fluid) is returned back to the collector to go and pick up more heat from the roof once more.


To facilitate the flow of water between the collector and the tank a pump is needed to provide power.

Your pump can either be run on traditional electricity or more cleverly, use solar electricity instead, making the set up entirely run on renewable energy. For most people, the latter is the preferable option.

Control system

To provide that little bit of control to the process, there’s a system which allows you to switch off the water circuit if you want to. As an example, if your roof is icy cold, you wouldn’t want the water flowing into your lovely hot water tank. A control system normally incorporates a pump, flowmeter, thermometer, pressure gauge and thermostat.


Solar water heating sounds like almost a mystical process but when each part is examined it’s actually quite a straight forward system which is easy for everyone to understand. Increasingly common and expect to continue to gain momentum, these type of systems require plumbers who are familiar with how to maintain and repair solar heated water so make sure you check this before booking one, should the need arise.