Solar Panels and Tubes

Solar Panels, also known as "collectors", can be fitted to a building’s roof. They use the sun’s heat to warm water, or another fluid, which passes through the panel. The fluid is then fed to a heat store (e.g. a hot water tank) and helps provide hot water or a source of hot water for the building’s central heating system.

Solar panels work throughout daylight hours, even if the sky is overcast and there is no direct sunshine, which means they can make a useful contribution even during the winter by pre-heating the water in the storage tank.  Your boiler or heat pump will boost the water temperature.

Are evacuated tube collectors more expensive than Flat panel collectors?
Until recently Evacuated Glass Tube Solar Collectors were considered to be more expensive than the Flat Panel Collector, but now with modern production methods and economies of scale, the Evacuated Glass Tube Solar Collectors have now become more affordable.The SEI grant now favours the Evacuated Glass Tube Solar Collectors.

Which type is most efficient?
Evacuated Glass Tube Solar Collectors are more efficient during the marginal months. Both types work well during long, bright mid summer days but during the months either side of summer, the Evacuated Glass Tube Solar Collector performs far better from, early morning till late evening ,and so increases the length of time that you can obtain free hot water. A Flat Panel Collector has a shorter maximum efficiency period, centred around midday when the sun is vertically overhead. Evacuated Glass Tube Solar Collectors are far more suitable for use in Northern Europe than the Flat Panel Type.

What is the Secret of the Vacuum?
The secret of the Evacuated Glass Tube Solar Collector lies with the vacuum which surrounds the absorber. This vacuum allows light to pass through and be absorbed by the absorber surface, here the absorbed light is converted to heat. Light will pass through a vacuum but heat cannot, so the heat that has been absorbed stays where we want it, and cannot escape by convection or conduction, back to the outside world.Flat plate collectors loose a significant amount of collected heat to convection and conduction. In other words, when the winds are cold, or it is raining, flat plates act like radiators and suffer from wind chill reducing the amount of heat harvested from the sun and are noticeably less efficient.The Evacuated Glass Tube Solar Panel is insulated by its inbuilt vacuum and does not suffer heat loss in this way.

Are Evacuated Glass Tube Solar collectors easy to install?
Because the Flat Panel Collector is larger it is considered to be more cumbersome to install whereas with the smaller size of the Evacuated Glass Tube Solar Collector, installation is easier as the component parts are smaller and lighter. This also means a reduction in the installation costs.

Who will install the collector for me? To avail of the grant opperated by Sustainable Energy Ireland you must use an SEI registered installer. SEI maintains an extensive list of registered installers . What does a roof mounted solar collector look like? Visually,when mounted on a roof both types look like a roof window, but the Evacuated Glass Tube Solar Collector is considerably smaller and more efficient. To obtain the same heat output, the Flat Panel variety would occupy a larger footprint on the roof than the Evacuated Glass Tube Solar Panel.

What size of pipe should be used?
On a normal domestic single collector installation ½ copper pipes is preferable as this reduces the amount of water in the solar loop. However if the installation is to be expanded it is wise to consider upgrading the pipe to allow for the addition of extra panels in the future. With any installation it is sensible to locate the collector as close to the domestic hot water cylinder as possible.

What type of pipe insulation should be used?
It is very important that the pipe insulation used can withstand the extremes of temperature that may occur in solar installations.A high temperature pipe insulation such as Armaflex HT should be used. Standard heating insulation could melt. On exposed external pipe work care should be to ensure the insulation is protected from the harmful effects of UV radiation. We have heard of insulation being robbed by resourceful birds, who obviously recognise the need for good home insulation! To guard against these we have found that if the insulation is covered with a good quality foil tape it is helpful with this problem.

What should I do about freezing?
The Solar collector manifold is extremely well insulated; however some installations will require frost protection. There are two types of frost protection in common use. If you live in a low frost area such as a costal area or other area which only receives occasional night-time frost the system controller has a frost protection circuit which can be enabled. With this system the sensor in the collector manifold registers when the temperature drops below 6 degrees. The controller then switches on the solar loop circulating pump until the temperature in the collector manifold reaches 10 degrees .This process continues until the threat of freezing is eliminated. If the solar collector is being installed in an area which is prone to prolonged periods of freezing your installer might suggest that you consider using a solar loop filled with an anti-freeze solution. This may requires the addition of a header tank, a pressurising pump and a pressure control unit. This system allows the addition of anti-freeze into the header tank which then replaces any occasional loss from the solar loop. Alternately anti-freeze may be added using a portable pumping unit which is disconnected when commissioning is completed, When anti-freeze is used it is important that it is checked regularly to ensure the effectiveness of the freeze protection it offers, and that the anti-freeze is suitable for use in a copper solar collector and will not damage the copper pipe work or component parts. What about overheating? The Dennen Bos Solar system is an extremely efficient and may overheat if the accumulated hot water is not used for a long time, during periods when you are on holiday for example. The most common way to deal this problem is to install a "heat dump circuit". This is a usually a radiator in the bathroom which uses up the unused excess heat. When the system becomes too hot, a thermostat opens a three way valve, which diverts the hot water from the cylinder to the radiator, thus venting the excess heat to the bathroom. Another method uses the fact that if the central heating pump is left on, (and the central heating turned off) the water circulating through the primary coil it will also dump heat. (A greener method is to invite your neighbours in to use your excess free hot water while you are away!) There is also the possibility that during normal use the water in the cylinder may overheat. This may present the problem of very hot water at the taps, this can be rectified by having a temperature regulating valve installed, and this can be set to ensure the hot water remains at a safe temperature.

Can I use a solar water heater for central heating?
Yes, but no! In theory a solar collector collects the sun's light and turns this into heat, so it would be possible to put together several collectors and heat a house. But, in Ireland we are blessed with long hours of daylight during the summer months and during winter we have short days and long nights, and in winter we need central heating more than we need central heating in the summer! The way we have sized the collector is to give almost all of a households domestic hot water from the sun during the summer, thus saving on conventional methods of heating (boiler or electricity), and during the winter the solar collector will assist your conventional method of heating water. If you were to size the collectors to heat a house, you would have too much hot water in the summer. The most cost effective method is to install a 20 or 30 tube collector and get nearly all of your hot water free from the sun during the summer and let the solar collector assist your conventional heating during the winter.

What direction should my solar collector face?
Optimally solar collectors should face directly south (only in the northern hemisphere!) , but they can face up to 45 degrees east or west of south without a significant decrease in performance. If this orientation is not available , we can supply an east / west controller which will regulate which collector is used depending on which collector is receiving sunshine. So in other words any direction except north (except if you live in the southern hemisphere!)