Energy Superstore

Solar Thermal Water Heating

Solar water heating systems use heat from the sun to work alongside your conventional water heater. The technology is well developed with systems available to suit many applications.

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Benefits

	Can provide almost all of your hot water during the summer months and up to 60% throughout the year.

	Reduces your impact on the environment - the average domestic system reduces carbon dioxide emissions by around 400kg per year, depending on the fuel replaced.

Click to read - F.A.Q (Frequently Asked Questions)

Different types of system

There are two main types of solar collector, which can be used in Active Solar Heating systems. These are:

	Evacuated tubes
	Flat plate collectors

What best suits your needs depends on a range of factors, including the area of south facing roof, the existing water heating system (e.g. some combi boilers aren't suitable) and your budget. Energy Superstore can assess your situation and discuss with you the best configuration to meet your needs.

A typical flat-plate collector is an aluminium box with a glass or plastic cover on top and a dark-coloured absorber plate on the bottom. A copper pipe is laid out on top of the dark-coloured absorber, like a hose laid out on the ground; water is passed through this pipe and takes the absorbed heat to the domestic hot water storage cylinder. The sides and bottom of the collector are usually insulated to minimize heat loss. The collector is generally placed on a south-facing roof.

The Evacuated Tube Solar water heater uses exactly the same principle as the flat plate but uses some technical refinements to gather the heat.
The Evacuated Tube Solar water heater consists of two glass tubes, an inner tube and an outer tube, which are separated by a vacuum. The outside of the inner glass tube is coated with a special light absorbing coating. The outer tube is clear, allowing light to pass through unhindered. When the light hits the special absorbing coating it converts to heat. The vacuum protects the black area that absorbs the sunlight, so the harvested heat cannot escape and has to travel inward towards the heat pipe. This is a very important modification because it means that heat gathering can take place at very low temperature, as it is the sunlight that is converted, not the heat. This is why evacuated tube collectors work better than flat plate collectors in the marginal months.

When the heat is inside the glass tube it is transferred to the manifold by a heat pipe, another device that uses vacuum technology.

Inside the heat pipe is a special liquid, which when heated to 25 or 30 C0, starts to boil, converting to gas. The gas rises, bringing the heat to the highest part of the heat pipe, which is known as the condenser tip. There the heat is transferred to the water that circulates through the coil in the domestic cylinder.

This improvement means that all the collected heat is concentrated in a small area, where it can be transferred at a much higher temperature. This enables the evacuated tube solar collector to harvest more heat from sunlight than conventional methods.

Solar Radiation in the Ireland & UK

This map showing average solar radiation on a 30° incline facing due south.

shows the total average solar radiation falling on one square meter surface inclined at 30 degrees to the horizontal, measured in kilowatt hours.

These figures bring out the remarkable fact that the amount of solar energy falling on the total roof area of an average house is many times that required to provide all its heating and hot water.

However, we must note that there is a large difference between the radiation available in the summer and that available in winter; also Active Solar Heating systems will typically convert 40 to 50% of the solar energy falling on the solar collectors into useful heated water. These factors must be taken into account in determining the optimum size for a system.