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North East Renewable Energy Directory
Technology Variations
Type of Solar Panel
There are two main types of solar thermal panels/collectors – flat plate and evacuated tube. Flat plate panels are the most basic. They are based on a well insulated black painted radiator-like panel through which liquid is passed. As the sun shines on the panel, the liquid is heated. Their advantages are low capital cost and efficient heat transfer in the summer. Their main disadvantage is that they do not work well with low external temperatures so their harvest in the autumn/winter/spring is limited.
Evacuated tube panels enclose their collectors in glass evacuated tubes that provide good insulation. This means that they can operate even when it is sunny but the air temperature is below freezing. Their advantages are a higher annual harvest due to being able to operate at all times of year and their greater power per square metre. Their disadvantages are higher capital cost and risk of breakages.
A suitable site is required for the solar thermal panel, with the correct orientation and minimal shading. Solar thermal panels work better on south-facing pitched roofs but good results have been achieved on east- and west-facing roofs. The midseason/summer sun should be unobstructed for the majority of the day.
Solar thermal panels generally need a large hot water cylinder, preferably one that is designed for solar thermal panels as a primary heat source. This cylinder will typically have twin heating coils – one from the solar system and one from a conventional boiler (although in all-electric homes the second coil will be replaced by an immersion heater). You need to have space available for such a store. Solar panels do not work with most combi boilers, although there are a few solar-ready models available.
Flow and return pipes need to be routed between the panels and the thermal store. Shorter routes are of course less expensive and more efficient.
Evacuated tube panels enclose their collectors in glass evacuated tubes that provide good insulation. This means that they can operate even when it is sunny but the air temperature is below freezing. Their advantages are a higher annual harvest due to being able to operate at all times of year and their greater power per square metre. Their disadvantages are higher capital cost and risk of breakages.
A suitable site is required for the solar thermal panel, with the correct orientation and minimal shading. Solar thermal panels work better on south-facing pitched roofs but good results have been achieved on east- and west-facing roofs. The midseason/summer sun should be unobstructed for the majority of the day.
Solar thermal panels generally need a large hot water cylinder, preferably one that is designed for solar thermal panels as a primary heat source. This cylinder will typically have twin heating coils – one from the solar system and one from a conventional boiler (although in all-electric homes the second coil will be replaced by an immersion heater). You need to have space available for such a store. Solar panels do not work with most combi boilers, although there are a few solar-ready models available.
Flow and return pipes need to be routed between the panels and the thermal store. Shorter routes are of course less expensive and more efficient.
Active or Passive System
The fluid in the solar thermal system can either be moved by a pump or be allowed to flow naturally. In a passive system the water moves by natural convective flows. In an active system the heated fluid is transferred to the hot water cylinder by a pump. Active systems are usually easier to fit but are often more expensive due to the need to install a pump.
Open or Closed Loop
The collector panels can either directly heat the water that is used in the hot water system (i.e. comes out of the hot tap) or they can heat an intermediary fluid, which then transfers heat to the water.
Open systems heat the hot water directly whilst closed systems use an intermediary fluid and a heat exchange system. Closed systems are most suitable for areas that have periods of freezing weather, as the liquid in the external part of the system can contain anti-freeze.
