The sun provides an abundant, free source of clean energy which can be used to heat 50-60% of your household hot water. Hot water systems will produce some hot water throughout the whole year even in winter, but obviously it is necessary to top up the system so that you can obtain the temperature that you want, when you want it. This is done easily by using your existing hot water system ‿boiler or immersion ‿to automatically increase the water temperature to meet your requirements.
Systems can be designed to fit into most existing heating systems, although they are not usually compatible with combination boilers. All that is needed is the space for a suitably sized hot water cylinder and a sufficient area, usually on the roof to fit the panels.
Roof Space/Area
Solar thermal collectors are normally positioned on the roof of your house although they can be free standing if this is not an option.
The roof needs to face between south east and south west, although if your home faces east-west it is possible to place panels on both sides to collect both the morning and evening sun. The space must be unobstructed as the shadows from trees, chimney stacks and other buildings will significantly reduce the amount of heat obtained from the collector. This would of course make the system less cost effective.
The panels are usually pitched at between 30º and 45º although mounting frame kits are available for flat roofs. A minimum of 1.5 square metres is needed but of course the larger the area covered the more efficient the system and the greater the benefit.
Solar Thermal Collectors
We all know from everyday experience that when the sun shines on something, it gets warm. Part of this solar radiation will be absorbed, and part will be reflected. We need to maximise the part that is absorbed. When something is warmer than its surroundings, it will radiate heat away from itself. We want to minimise this. These two requirements, together with a need to transport the heat (in the form of hot water) to where we want it, constitute the basic design criteria for a solar collector.
There are two types of solar thermal collectors ‿flat plate collectors which contain metal tubing, and evacuated tube collectors which are made up of a series of glass tubes containing a liquid that heats up.
Flat Plate Collectors
These collectors have a glazed, flat, dark surface which contains metal tubing. The tubing has a liquid circulating through it which is heated up by the sun. These tend to be less effective than evacuated tube collectors and need a larger surface area, but they are less expensive.
Evacuated Tube Collectors
These consist of parallel rows of double walled glass tubes with a vacuum in the space between the walls. A liquid inside the collector passes the heat through a series of pipes which warms the water which is fed into the hot water tank. They are more effective and efficient throughout the whole year than flat plate.
Hot Water Storage
A standard hot water cylinder contains a single metal coil connected to the boiler which heats the water. A solar system has a dual coil cylinder, the top coil being connected to the boiler, the bottom one to the solar collector. This means that most standard hot water cylinders will need to be replaced with a larger one when the solar system is installed.
Ideally the boiler, or immersion heater, is timed to top up the heat early in the evening after the solar system has worked for the day. This way the hot water can be used later that evening or the following morning.
