Section 4: - Solar Systems & Technologies

Section 4.1: - Roof Top Solar Water Tank Heaters

This is the most common form of solar heating in Northern Europe. For most people this is what Solar Heating means. The 2no. basic forms of of solar system are the "Pumped" and "Thermosyphon System". The Thermosyphon System operates in frost free climates so we will focus on the Pumped System type.

There are also two typical types of pumped solar collecters, Flat Panel & Tube System. The most efficient at the moment is said to be the tube system, although most domestic dwelling owners opt for the Flat Panel type as it is seen as less bulky and a neater finish on a pitched roof.

• A typical domestic panel pumped system consists of 3 fundamental elements; The Collector Panel, The Circulation Pump and the Hot Water Storage Tank.

  • The Collector Panel is positioned on the roof at a tilted angle. The panel itself consists of a back plate, a transparent top plate with copper tubes covered in black material between the plates. A temperature stat is also fitted to the panel pipe work to read the internal fluid temperature.

  • The Circulation Pump moves the fluid (Usually containing an anti-freeze element Glycol Mix) through the pipe work system, through the panel and through the primary coil with the hot water storage tank where the coil transfers its recovered heat to the domestic hot water within the tank.

  • The hot water storage tank (150 - 200 litres for a typical 3 bed domestic dwelling) usually consists of a primary heating coil and a secondary heating source known as an electric element, which acts as a back up heating source if the min required water temperature is not achieved through the solar due to the weather.

Vacuum Tubes

Advantages

• Higher solar yield than flat plate collectors with the same absorber area. 30% more effective

• Little thermal loss (only through some radiation)

• As the tube is sealed, dirt or moisture cannot get into the collector

• Works in cold, windy and humid conditions

• Individual tubes can be rotated to optimise ideal orientation

• High temperatures can be achieved

• Some people like the aesthetics of tubes

Disadvantages

• Cost

• Not easily integrated into the fabric of the building (e.g. roof or facade integrated)

• Some people do not like the aesthetics of the tubes

Flat Plates

Advantages

• Lower cost

• Can be more easily integrated with the fabric of the building (roof integrated / facade integrated)

Disadvantages

• Lower performance through conduction, convection and radiation, therefore you need more surface area of collector

• Higher wind load requirements (they act like a sail and catch the wind)

• Glass and absorber can get dirty and effect performance

• Needs more maintenance

• Higher volume content equated to larger component sizes. i.e. expansion vessel

• Isn't as efficient in lower light

In Ireland such a system, as discribed above can supply up to 40-50% of the hot water requirements for a typical 3bed house annually.

Section 4.2: - Glass

Most of the low temperature solar collection systems are dependent on Glass. This is probally the most important of all solar related properties. It is transparent to visible to light and short-wave infrared radiation, but however opaque to long wave infrared re-raiated from a solar collector.

Section 4.3: - Low Temperature Solar Energy Market Rivals

Although simple solar systems are in princple ideal for supplying low temperature heating, there are alternative competitors; These would include:

• District heating which could be fed by waste from existing convential power stations.

• Small CHP ( Combined Heat and Power ) generation plant.

• Small Heat Pump. ( Geothermal ).

All of the above alternatives have the advantage of being able to run more effectively & efficiently all year round.

Section 4.4 - Active Solar Heating

One of the primary ways of heating buildings is through Active Solar Solar Heating. The technology using solar collectors transform solar energy into heat, which provides either space or water heating, or both. Solar water heating is the most common application use in Ireland and indeed Europe. An efficiently designed Domestic Solar Water Heating System, as discribbed above can cover 50-60% of a users hot water needs for free, post installation costs.

The Solar thermal dual system mentioned above can providing space and water heating is commonly referred to as a solar combisystem. This type of system is commonly used throughout northern europe and is becomming more common in Ireland. Efficient design and installation of teh system can cover 30-40% of a users energy needs on an annual basis. Advantages include having both water and ventilation heating through the one system/appliance. This particular dual combi approach would suit the Irish Market. Although an energy efficient Natural Gas boiler may have to be used in conjunction during the winter and cold snaps.

Section 4.5 - Passive Solar Heating

The Passive Solar approach is manly focused on the design of a buildings fabric. Maximising solar gains through orientation, layout and window design. Avoiding heat losses through effective insulation installations and conducting air-tightness testing to check for leaks in the building fabric which may lead to heat loss.

As per the resent SEAI report, anyboby building a new house or refurbishing and existing one should apply the new solar passive princples to the design and build to reduce their heating requirements by up to 80%.

Section 4.6 - Solar Electrical Generation

Solar thermal electric systems use solar concentrators to focus solar radiation onto a heat transfer medium. The medium can be a thermal oil, capable of

withstanding high temperatures, or alternatively pressurised water. This is collected and passed through a heat exchanger/boiler where steam

is raised which is then used to drive a steam turbine producing electricity.

Climates like Ireland with cloudy/overcast conditions, where most of the radiation is diffuse, are unsuited to this.

Because this technology involves a thermal intermediary stage, systems

can be combined with a fossil-fuel combustion stage (a hybrid) or possibly

thermal storage to make them dispatchable (a big advantage).

Solar-to-electric efficiency is in the range 13-25%. Systems up to 150MW have been built.

Section 4.7: - Solar Heating System Varieties

Swimming Pool Heating

On previous projects i have worked on swimming pools usually and effectively are heated via a heat exchange plate, which in turn is heated from the solar system recirculating water heated by the array of solar collectors. Here the objective was to keep the swimming pools water temperature at a steady 28.5 degrees celcius. This was achieved through 1032 Solar tube Collectors, a recirculation pump, heat exchanger and cylon smart controls.

Essentially the system operates as follows;

Like a typical thermal solar system the collector tubes are heated via the suns radiation, the system is a closed circulating system. This evenly distributes the mean temperature throughout the system preventing hot and cold spots, and effective heat transfer to the exchange plate. It is a closed looped system, which prevents air intake, which is filled with glycol which prevents freezing.

Here the strategy employed to save money was to top up the heat to the swimming pool every morning using the high efficiency gas boilers. Once the temperature was achieved the Solar would top up and stabilise the pool temperature throughout the remainder of the day/evening, once the temperature was being achieved by the solar. This was done via a smart controls system. Once the temperature was there (45-65 degrees) within the closed looped solar system, the controls panel would activate a 3-port valve. This would islolate the heat exchange from the boilers and turn them off. It would also allow flow from the glycol filled solar pipe work system transfer its heat to the heat exchanger, which in turn would heat the recirculating pool water maintaining the desired pool temperature of 28.5 Degrees Celcius.

This Smart system is due to save the client up to €4,000.00 on an annual basis on their Gas Bill.

Trombe Wall

Named after the french inventor, Felix Tromhe. With the Trombe Wall the conservatory is replaced by a thin air space in front of a storage wall. This is a solar collector with the storage facility immediatley behind. Solar radiation warms the store and is radiated into the house in an evenly distrobuted fashion from its inner side.

Sunspace / Conservatory

A Conservatory on the south side of a building can be thought of as a habitual solar collector. With air being the heat tranfered, carrying its energy into the building. The energy store would be the building itself, especially the wall at the back of such a conservatory.