FLAT PLATE SOLAR COLLECTORS

Flat plate solar collectors consist of a thermally insulated case with a cover glass. The case contains an absorber, which absorbs the incident radiation, and which usually heats up a glycol mixture circulated in contact with it.

 

 

 

NEVADA SOLAR ONE

Nevada Solar One is one of the world’s largest CSP installations, with a nominal output power of 64 MW, and producing an annual energy output of 134 GWh/year.

 

 

 

POOL SOLAR COLLECTORS

A pool solar collector consists of an absorber made from UV resisting polymer that can withstand chlorinated water. As the collector heats up in the sun, it transfers its heat to a liquid circuit, which is often the pool water itself.

Solar energy technologies

 
There are several different ways of capturing solar energy, using appropriate collector technology. Some technologies are well developed, tried and tested, while others are still in process of development.
 

Solar electricity

Solar cells. Sunlight can be converted into electricity in solar cells – a technology that was developed as long ago as the 1950s in order to provide the first satellites with electricity. A solar cell consists of a thin layer of a semiconductor material, often silicon. When sunlight strikes the cell, it is polarised so that the front acquires a negative charge and the back acquires a positive charge. This creates a voltage difference, which can drive a current flow via metallic contacts on the front and back of the cell. The voltage of a single cell is only about 0.5 V, and so 30–36 cells are normally connected in series in a single module in order to supply a useful voltage that can be used to charge batteries or be connected to an inverter.
 
 Solceller
 
Silicon solar cells have an efficiency of about 15 %, and can produce a specific energy output of about 50–150 kWh of electrical energy per m² and year.
There are two different types of module: crystalline silicon solar cells and amorphous silicon solar cells, which are generally referred to as thin-film cells in everyday language. The crystalline solar cell module is the more common type, with about 80–90 % of the market. The thin-film modules consist of a film that is only a few μm thick, thus reducing the amount of semiconductor material required and so also reducing the cost of manufacture in comparison with that of crystalline cells.
Solar cells are today competitive for use in areas where it would be too expensive or complicated to provide a supply from the normal electricity mains. Common application areas are holiday cottages, on boats or in inaccessible areas. Another common application area is that of traffic monitoring equipment on roads.
It is also possible to create systems connected to the normal electricity mains, and several larger installations of this type have been built on public buildings in Sweden. One example of such a larger installation is that of the Ullevi sports arena in Göteborg, where 750 m² of solar cells produce about 65 000 kWh of electricity per year.
Electricity from solar cells is at present very much more expensive than electricity from, say, wind power, which is due mainly to the fact that solar cells are manufactured and used on a relatively small scale, and that wind power has a longer annual utilisation time. However, in actual capital cost in terms of SEK/kW, the cost of wind power is much the same as that of solar cells.
To assist the move towards a renewable energy system, and to create jobs and companies in the energy technology sector, the Swedish Government has introduced a grant for installation of all types of mains connected solar cell systems. The aim is to increase the use of solar cell systems, and the number of parties involved with them, in Sweden, in order to reduce system costs and increase annual electricity production from solar cells by at least 2.5 GWh over the period June 2009–December 2011, during which the grant is available.
 
A SOLAR CELL MODULE
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Concentrating solar energy

Concentrating solar power (CSP) is a system using mirrors to concentrate solar thermal insolation on to a particular point. The heat is used to produce steam to drive a turbine to produce electricity in the same way as in a traditional power station. There are also CSP installations that deliver energy using solar cell technology or other hybrid solutions.
 
 
 
Nevada Solar One is one of the world’s largest CSP installations, with a nominal output power of 64 MW, and producing an annual energy output of 134 GWh/year.  
 

Thermal solar energy

The principle behind all thermal solar energy systems is simple. Insolation is capture by a surface, raising its temperature, with the heat being transferred to a medium, which can be either a liquid or a gas. The heated medium can then be used either directly, as for heating swimming pools, or indirectly via a heat exchanger. Thermal solar collectors can deliver heat for a wide range of applications, such as for heating domestic hot water, space heating or the drying of timber. Another interesting application is to use thermal solar energy for producing cooling: this application is particularly attractive, as about 15–20 % of all world electricity is used for various types of cooling or heat pump systems, and because it is particularly in areas where insolation is high that cooling requirements are likely to be greatest. Under Swedish conditions, a thermal solar collector can deliver 350–700 kWh/m² and year.
Thermal solar collectors can be divided up into glazed and unglazed collectors.
Schematic arrangement of a flat plate solar collector
 
Ett annat intressant område är att använda termisk solenergi för att producera kyla. Området är extra intressant genom det faktum att cirka 15–20 procent av all el i världen går åt till olika kyl- och värmepumpssystem och att solinstrålning och kylbehov nästan alltid sammanfaller. En solfångare producerar värme och ger mellan 350–700 kWh/m2 och år under svenska förhållanden. 
De termiska solfångarna kan delas upp i glasade och oglasade solfångare.


Glazed solar collectors

There are two types of glazed solar collectors: Flat plate solar collectors and Vacuum tube solar collectors. 
 
Flat plate solar collectors. Flat plate solar collectors consist of a thermally insulated case with a cover glass. The case contains an absorber, which absorbs the incident radiation, and which usually heats up a glycol mixture circulated in contact with it. The cover sheet and thermal insulation behind the absorber minimise heat losses to the surroundings. The heat is transported in a closed circuit to a heat store, which might be, for example, a domestic hot water tank or a hot water tank for space heating purposes, forming part of the solar energy system.
 
 
 
Vacuum tube solar collectors. Vacuum solar collectors consist of various types of vacuum tubes. The commonest of these is the Sydney type, which is double glazed, with the outer tube being transparent and the inner forming the actual absorber. There are two ways of converting the incident solar radiation into heat in vacuum collectors: either through the use of an absorber, as in a flat plate solar collector, or through the use of a heat pipe. A medium in the pipe collects the heat from the absorber by evaporation, and then delivers it by condensation in a heat exchanger at the top of the tube.
 
 Vakuumrörsolfångare
 
A vacuum tube solar collector
  

Unglazed solar collectors

There are two types of unglazed solar collectors: Pool solar collectors and Air solar collectors/Ventilation solar collectors. 
 
Pool solar collectors. A pool solar collector consists of an absorber made from UV resisting polymer that can withstand chlorinated water. As the collector heats up in the sun, it transfers its heat to a liquid circuit, which is often the pool water itself. These collectors are uninsulated and have poor efficiency due to being considerably warmer than their surroundings. However, as a result of their low price, they are very suitable for low temperature applications such as heating swimming pools.
 
 
Poolsolfångare
 
Air solar collectors/ventilation solar collectors. An air solar collector provides a simple means of ventilating and drying buildings such as holiday cottages or barns. Heat from the sun is absorbed by a dark back panel, behind which an air gap with ducting provides a passage through the collector from one end to the other, warming the air as it passes. The warm air can them be discharged through a thermostatically controlled fan, either directly into the building or into its ventilation system.

Air solar collector/ventilation solar collector
 
 
 

Solar energy systems

When considering solar energy applications, it is important to concentrate on the entire energy system, and not solely on the solar collectors or solar cell modules. A solar energy system can be built up in essentially the same way as all other energy systems, involving the main stages of energy production, energy distribution and energy use.
 

Local and large scale energy system
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Go to next chapter: Market development >

 

Duplication of this publication (in full or in part) without S-Solar AB's (reg. No. 556233-7617) prior consent is prohibited according to the Swedish Copyright Act (1960:729) (Sw. Lag (1960:729) om upphovsrätt till litterära och konstnärliga verk). The foregoing limitation applies to all forms of copying.
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