Solar Energy
By Brenda Shaw
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Solar EnergyBy Brenda Shaw
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Solar is an ideal source of renewable energy, always abundant with no unwanted emissions. |
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| 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 as water, wind etc are discussed elsewhere, e.g. 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 subsidiary 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.
Three Solar PV Panels on a small Roof: Click to Enlarge
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 renewable 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, historically, 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 renewable 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: |
| 1. 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. |
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| 2. 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. |
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| 3. 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 is based largely on silicon in various fabrications which can be flexible sheets or replacement roof tiles for example. These cells generate direct current which is then inverted to produce a 50 Hz alternating current at mains voltage. PVs can be incorporated into industrial, commercial, domestic and even mobile situations. Most of us are familiar with solar panels as we see them installed on house roofs and occasionally in larger arrays. Normally an array of cells is interconnected and positioned sensibly to expose the surface area to the sun as much as possible. South-facing roofs and walls at an angle of about 35% to the horizontal, with no shading are best. However surfaces with an easterly or westerly aspect can be quite practical and partial shading can be catered for by using micro-inverters. The cost of the panels and installation has fallen dramatically over recent years making solar PV installations attractive for domestic and commercial use. Solar panels come in three basic types which vary in cost and efficiency: first, monocrystalline, made of thin slices of silicon cut from a single crystal; second, polycrystalline, made from thin slices of silicon cut from a block of crystals; third, hybrid, combining crystalline cells with a thin layer of silicon on a glass or metal base. The most efficient type of solar cell tends to be hybrid. The UK law makes it so that electricity companies must let you install solar power and must also buy your surplus electricity. Once the electrical energy is generated it can be converted to ac (technically, inverted) and used in a variety of ways and surplus is fed into the national grid. |
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There are two UK Government initiatives to incentivise the above. The RHI scheme will be applicable to methods 1 and 2 and the existing FIT scheme applies to method 3. The funding sources are quite different for these two initiatives and be aware that Government programmes are always 'moving goal-post' schemes unless firmly tied down in law.
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| Photovoltaic Developments: A main consideration with any power source is the cost of the generated power. PV panels are becoming cheaper to produce and efficiencies are being improved. The highest efficiency recorded is about 40% efficiency using multiple layers of silicon but this is expensive and mainly used in Space applications (Solar-facts.com, 2012). 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 some of the organic processes are being reflected into inorganic materials which don't age so rapidly. Another method, of concentrating photovoltaic solar panels normally involving a lens or mirrors to concentrate more sunlight onto a photovoltaic cell, means that fewer cells are required for the same area of panel and efficiency is higher. The US site, renewableenergyfocus.com states '... last year (i.e. 2011) saw a plethora of company announcements from around the world featuring all manner of technology developments, from casting elimination; to N-type silicon; thinner wafers; ion implantation; electro-deposition and developments in organic materials and plastics to name a few… ' The web site solar-facts.com provides a wealth of information on solar power and panels, how they work, different types, construction, efficiency and much more. |
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| 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 was undergoing pilot tests in the Mojave desert, was 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 was expected to expand to produce between 500 and 850 MW in the foreseeable future [ref: The IEE Review, September 2005]. We cannot establish whether this was implemented. 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 (e.g. 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. See our Reference page for more information on the Stirling Engine] |
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| Summary: Solar energy certainly is a practical possibility even in the UK. Suppliers of PV solar panels are demonstrating that the costs are already low, and as with some other forms of alternative energy, costs are falling and the technology is becoming more efficient at a steady rate. The range of applications is enormous from micro generation to major energy production. At last the UK government recognised with its FITs and RHIs that solar energy is a good form of renewable energy but it has already reduced the payments from the FITs and RHIs payments are still to be finalised (expected possibly summer 2013). If only they could channel more of the nation's wealth into solar generation instead of it being 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 more potential for renewable energy production on a truly major, commercial scale. |
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