Frequently asked questions on Solar Energy

Put simply, it is energy from the sun, which can be used to produce heat. For further details please check our Info section.

Active Solar Heating is one of the primary ways for buildings to use solar energy. This technology uses solar collectors to transform sunlight into heat to provide space and/or water heating. Solar water heating is the most common application of active solar thermal in Europe. A correctly sized solar water heating system can cover 50-60% of your hot water heating requirement with free solar energy.

A solar thermal system providing space and water heating is generally referred to as a solar combisystem. It is generally sized to cover 30 to 40% of the annual heating requirement of a house in Europe.

Photovoltaic means electricity from light. Photovoltaic systems use daylight to power ordinary electrical equipment, for example, household appliances, computers and lighting. The photovoltaic (PV) process converts free solar energy – the most abundant energy source on the planet – directly into electricity. Note that this is not the familiar solar thermal technology used for heating and hot water.

A PV cell consists of two or more thin layers of semi-conducting materials, most commonly silicon. When the silicon is exposed to light, electrical charges are generated and this can be conducted away by metal contacts as direct current (DC). The electrical output from a single cell is small, so multiple cells are connected together and encapsulated (usually behind glass) to form a module (sometimes referred to as a "panel"). The PV module is the principle building block of a PV system and any number of modules can be connected together to give the desired electrical output.

PV equipment has no moving parts and as a result requires minimal maintenance. It generates electricity without producing greenhouse emission or any other gases, and its operation is virtually silent.

Solar PV can also be used to provide free solar electricity to houses as well as for commercial and industrial applications. Recent developments in regulations mean that it will shortly be possible to connect solar PV systems to the grid, opening up a new era for solar PV in Ireland.

In general, it is probably safe to say that for a given absorber area, evacuated tubes are more likely to maintain their efficiency over a wide range of ambient temperatures and heating requirements. In constantly sunny climates flat plate collectors are more efficient whereas in more cloudy conditions their energy output drops off rapidly in comparison with evacuated tubes. 

Every situation is different and might be suited to one type of collector above the other. For example, where an “in-roof” installation is needed, a flat plate collector is used, and the lower yield can be compensated for by simply adding more collector area. In a situation where you have restricted roof space, then evacuated tubes would commonly be used to get the maximum yield from a smaller area.

Collectors facing south will receive the optimum amount of energy. Generally, anywhere between 30-45° is optimal for the tilt angle. Deviations from South to SE/SW will only affect output by approximately 5%, and even East/West systems are feasible. It is important to add the required amount of collector area to compensate for any expected reduction in energy due to mounting position, location, or for expected reductions due to possible sources of shading such a trees.

Rules of thumb for sizing a solar hot water system are as follows:

• 1-1.5m² of flat plate collector aperture area per person;
• 0.8-1.2m² of evacuated tube aperture area per person;
• Average hot water consumption per person = 40 litres per day (this informs the cylinder size)
• However to meet the technical specification of the grant, the solar water heating system installation must meet the 10kWh/m²/yr as calculated in the Building Energy Rating (BER) software DEAP version 3.1.0.

Solarhouse supplies two types of solar collectors: flat plate panels and evacuated tube collectors. Our WATT4000SU flat panel size is 1018mm (Width) x 2018mm (Height) x 90mm (Depth). And the vacuum tube collector sizes are as follows:
20Tube: 1610mm (Width) x 1980mm (Height)
15Tube: 1235mm (Width) x 1980mm (Height)
12Tube: 1010mm (Width) x 1980mm (Height)
Total collector area must not exceed 12m² or 50% of the total roof area.

The aperture area is the area through which light enters in m² should be used. Our WATT4000SU flat panel aperture area is 1.873m².  Aperture areas of the vacuum tube collector are as follows:
20Tube: 2.57m²
15Tube: 1.92m²
12Tube: 1.53m²

Yes, the Solar Keymark that is a European quality label for solar collectors. The flat plate licence number is 011-7S825F and vacuum tube:  011-7S297R. Further information can be found here

We offer a 5-year warranty on the panels and all other components against component failure and defects in workmanship and materials. Not covered is breakage after delivery, damage due to lightening strikes, storm damage etc.

Vacuum flasks have a design life of 20 to 25 years, after which the flasks themselves may lose their vacuum. However, these are relatively cheap to replace. Flat plate panel’s life span is 25 years.

The cylinder is a very important part of the system – its job is to provide efficient storage for the free heat the solar collectors have produced. The solar hot water cylinder is also sized for the hot water needs of the occupants. Average hot water consumption per person is 40 litres per day. Generally, for solar the cylinder should be sized to accommodate approx 1-2 days usage.

The cylinder usually has a volume greater than a standard domestic hot water cylinder. This additional capacity allows the solar system to work more efficiently and stores water from the day to use later that night and the following morning and beyond. The volume of your hot water cylinder is related to the maximum cylinder temperature. It is recommended that at a maximum cylinder temperature of 60ºC, 70 litres per square metre of aperture area is supplied and at a maximum cylinder temperature of 80-90ºC, 50 litres per square metre of aperture area is supplied. Smaller capacities will limit the benefit from the system and may lead to frequent overheating of the solar circuit. For this reason the cylinder is insulated with 50mm thickness of blow-moulded foam; this helps retain heat longer than standard insulated cylinders. Generally Dual Coil cylinders should be used, having the coils at the top and bottom of the cylinder. The solar collector circuit should be connected to the bottom coil and the auxiliary circuit to the top coil, which will enable the solar system to pre-heat in bad weather.

This depends on the size of the cylinder you chose, and the amount of water you use. A smaller cylinder will be heated to higher temperatures, whereas a larger cylinder will heat more water, but not to the same extent. Systems are generally designed to heat water to 65ºC or so, although during the winter, it may be necessary to ‘top-up’ the heat on less sunny days. Large arrays, running high temperature solar antifreeze at high pressures can be designed to achieve temperatures of 170ºC or more!

Panels should be sited on a south facing wall or roof. In fact, anywhere between South-West and South East will give good results. If you are limited to an East-West facing system, then you will need two panels to provide the same amount of hot water as a single south-facing roof slope. The most frequent solution to this problem is normally to mount one panel on the east slope and a second panel on the west slope. A special controller is available for East/West facing installations.

The panels should be mounted at the angle of your latitude. In Ireland, this is approximately 52 degrees. This is the AVERAGE optimum angle. In fact, in winter the optimum angle is 15 degrees steeper, whereas in the summer it is 15 degrees shallower. The panels will function anywhere between 15 and 90 degrees angle of inclination. This is actually academic, a variation of 15 degrees will make very little difference to the output, so most people simply settle for whatever angle their roof slope is. The extra cost of trying to stand panels off the roof to achieve better efficiency would probably be better spent on purchasing a second panel!

Yes, spares are always available, should you need them. With no moving parts, it is very unlikely that you will need to replace anything, but occasionally customers break tubes during the installation process, in which case you can purchase a modestly priced replacement. However, it is not possible to post a replacement tube, so you will need to collect it. The tubes are made of borosilicate glass (aka ‘pyrex’) so they are actually very tough.

Many houses end up with a pressurised system because the panel has been located higher than any attic tank can be positioned. With a pressurised system, the plumbing is simpler, and by running the system at 1-2bar, it is possible to increase the boiling point of the water to 120ºC or higher - allowing greater safety margins, and lower chance of fluid loss. However, if you place your panels lower on your roof, it is possible to feed them from an open-vented attic tank, and this is more fail-safe in the event of a power-cut.

Very little maintenance is required for solar water heating systems. If you have a pressurised system, you should occasionally check the system pressure, to make sure there has been no water loss and to check for any air in the system. The only other requirement is to ensure that there is an electricity supply connected at all times, otherwise without pump circulation, in strong sunshine, the panel could overheat, and start to boil off water.

Yes. There are two ways to achieve this. You can either purchase a mains pressure unvented water cylinder (check our Ultrasteel Albion Unvented Solar Cylinders). Please note that you will have to have a pressure vessel certificate to install these. Alternatively, you can fit a ’solar store’ cylinder (see below).

A thermal store is a tank which has an additional large surface area high efficiency coil fitted. The mains cold water is fed into this coil, thus heating the water on its way through. The mains water exits the tank as hot as the hottest water in the tank, but without losing any pressure - thus providing mains pressure hot water to the household taps.

An €800 grant is now available through the SEAI Better Energy scheme to help you reduce your energy bills using solar hot water heating system. For more details please check our Grants & BER section.

• Is the product on SEAI’s list of registered products? (Remember, if it is not listed you will not receive a grant under the Better Energy scheme).
• Is the solar collector certified by the European Solar Keymark?
• Are all the flashing and fixing components for the panels provided?
• Do all the materials used conform to the solar system manufacturer’s specifications?
• Is the solar hot water cylinder sufficiently large (minimum 50 litres per person to 40 litres per person in the household)?
• Is the cylinder sufficiently insulated (minimum 3 inches thick insulation, more at the top)?
• Is the solar heat exchanger area large enough (minimum 0.25 m2 per 100 litres of cylinder volume)?
• Is the system protected against overheating, freezing and excessive pressure?
• What is the performance rating of the solar collectors under expected operating conditions?
• Is pipe work thoroughly insulated?
• How do the controls work and are they suitable for my requirements?