Solar Energy, Information on


		Solar Energy

		Solar is an ideal source of renewable energy. It's always there in abundance with no unwanted emissions.

		Introduction: There are three main, recognised ways of producing energy directly from the sun in most parts of the world including the UK (indirect methods such water, wind etc are discussed elsewhere, eg see the overview on the Alternative and Renewable Energy page). The first two, described as passive and active respectively, absorb the heat and store it to be used, for example, for space and water heating. The third method converts sunlight to electricity using photo-voltaic (pv) cells, a method which is flexible since electricity can be converted and used in many ways. Additionally, there are other methods for producing energy from the the sun's direct rays (eg the production of hydrogen from water) which are more applicable to warmer regions. The question which naturally arises in the UK is do we get enough sun to make solar energy a practical source? According to the modern view it appears that we do get sufficient, but in our changeable climate the sun's intensity varies from moment to moment, and from season to season. This implies a need for storage and for it to be used in conjunction with other energy sources, so that the necessary supply rate can be evened out. Like most, if not all, of the alternative energy sources in the UK the agenda has been influenced by the ready availability of cheap fossil fuels and government policies which have looked at short term expediencies. In the UK we have nearly always been able to extract energy from some forms of coal, oil and gas, easily and cheaply. Nuclear power has also entered the equation although maybe that was a different agenda altogether. It is now realised that nuclear was never a cheap option, quite the contrary. Nevertheless the availability of these alternatives and the notions of politicians, have suppressed the development and hence economic viability of alternative sources. The situation in the US has not been very different but at least there are now ongoing major projects to try to utilise solar energy. Practical ways of deriving benefit from the suns rays are briefly discussed below:

The Passive method:
this is quite basic and is implemented by designing residences in such a way as to trap heat, typically by using glassed areas just as a greenhouse does. It is not a self-sufficient measure in the UK but has the advantage that it can be done at little or no expense by using certain design principles for new constructions. For existing properties there is a moderate but significant cost in building glazed add-ons. For the best effects adjustable blinds can give some measure of control and appropriate wall insulation can maximise the benefits.

The Active method:
uses specially designed heat collectors where, commonly, the storage medium is water, then the heat can be transported by low-power electric pumps (sometimes by gravitation) to a main storage tank to supply the hot water (often seen on dwellings in southern Europe) or circulated to radiators for space heating. Once again this is not sufficient on its own for the UK but it can supply a significant proportion of the total demands for it to be incorporated into designs and also considered for the improvement of existing properties. Unfortunately in the latter case the capital outlays are substantial and it may take several years to recoup the costs.

Photo-voltaics (PVs):
this is perhaps the most exciting area because it is capable of supplying large amounts of energy both on a local and more central scale. It is also interesting because the devices (the cells, modules or arrays) are constantly being improved by research and development, and production costs are being reduced. Modern cells are capable of operating at relatively low lighting intensities and therefore providing energy when it is most needed. Currently available cell technology, in 2006, seems to be based largely, but not exclusively, on silicon in various fabrications which can be flexible sheets or replacement roof tiles for example. It is claimed that PVs can be incorporated into industrial, commercial, domestic and even mobile situations. Undoubtedly the range of applications is almost endless.
Most of us are familiar with the solar panels used in the space programme and the reality on the ground is similar. Normally a large array of cells is interconnected and positioned sensibly to expose the surface area to the sun as much as possible. Practical examples are south-facing roofs and walls and it is currently possible to incorporate such constructions now, although the installation costs seem to us to be so substantial as to make them unattractive on a purely economic basis. We have not noticed much said with regard to the life of the cells or maintenance costs, and would like to be better informed on this matter. For a definitive guide on the availability and cost of installing PVs, we suggest you select the link to Solar Century.
The UK law makes it so that electricity companies must let you install solar power and must also buy your surplus electricity. In the future it is hoped that they will pay you the same rate as they charge for their supply.
Once the electrical energy is generated it can be converted to ac (technically, inverted) and used in a variety of ways, it can even be fed into the national grid. These secondary, but important, enhancements can add significant cost and may reduce the reliability somewhat.

Photovoltaic Developments:
A main consideration with any power source is the cost of the generated power. In 2006 PVs don't do too well because with the available technology; they are not yet cheap to produce and work at low efficiencies. Practical, commercial crystalline silicon PV modules work at about 15% efficiency but efforts are concentrated on improving that figure. Research models can deliver more than double that efficiency.
Other research is aimed at producing larger PVs more cheaply while tolerating low efficiencies. Organic polymers feature in this pursuit because of the low cost of the base materials and the fabrication processes. Organic materials deteriorate with age but there is some hope that the organic processes can be reflected into inorganic materials which don't age so rapidly.
There are other research strands being pursued especially in the US and the main hope is that material science will be the key to success. There is some optimism that this branch of research will lead to a better and continually improving cost competitiveness.
[for more information on PV research in 2006 see the IEE Review, 'Let the Sun Shine In', February 2006]

In hot climates, there are other techniques:
often combined with mirror concentrators, the solar energy may be used to convert water into its constituent elements and the resulting hydrogen stored, piped and used as fuel. Hydrogen is regarded as one of the best and cleanest forms of fuel. Current practice is to use a thermal-catalytic process where the water is raised to several hundred degrees Celsius.
A further method, which in late 2005 is undergoing pilot tests in the Mojave desert, is to use mirror arrays to focus the sun's heat to drive Stirling engines*. The rotary engine is then coupled to an electrical generator. The pilot should expand to produce between 500 and 850 MW in the foreseeable future [ref: The IEE Review, September 2005].
Because of the nature of these methods they are economically practical only in reliably sunny climes such as the American deserts, but there are obviously other locations which would be suitable. In Europe the southern Mediterranean might offer satisfactory conditions (eg Italy and Spain). It seems to us (and we're making this up) that vast areas of Africa could be suitable thereby providing an improvement in the quality of life for some localities and also a potential export commodity.

[* Note; the Stirling engine was invented by Robert Stirling in the early 19th century, before the Internal Combustion engine, and relies on gas expanding when heated and contracting when cooled. It is an External Combustion engine, has the potential to be more efficient than the ic engine and does not involve explosions nor exhausting of gases, hence it is quiet in operation. It does not, however, allow rapid changes of energy output so is not as applicable to motor vehicles as the ic engine. For more information on the Stirling Engine see the reference page on 'Combined Heat and Power'; link is below]

Summary:
Solar energy certainly seems to be a practical possibility even in the UK. Although the suppliers of PV solar panels claim that the costs are already low, we have yet to be convinced. Nevertheless, as with some other forms of alternative energy, costs are falling and the technology is becoming more efficient at a steady rate so we are very optimistic, indeed excited, that solar energy could be at the forefront in meeting the Kyoto ideals, and maybe more than that.
The range of applications is enormous from micro generation to major energy production although we have to say that the emphasis is still on potential rather than commercially realisable. If only the UK government could channel a small fraction of the nations wealth into solar generation that is sucked into the nuclear sector we would feel a lot happier and sleep sounder.
With respect to other countries where there is a continuous abundance of sun then there is real potential for renewable energy production on a truly major, commercial scale.

To see the reference article on Combined Heat and Power, click this button