T J Rogers, CEO Cypress Semiconductor
Solar energy is by far the most abundant source of power we have available: enough solar energy hits the earth every day to meet our energy needs for 27 years. The challenge lies in capturing this free bonanza of 3,850,000 exajoules annually and converting it into electricity at a reasonable cost. Current solar energy technologies fall into two main groups, solar photovoltaic (PV) and solar thermal power.
Solar Photovoltaic (PV)
Solar PV uses photovoltaic cells to generate electricity: the PV industry has evolved rapidly over the last 20 years and is now worth around $50 billion annually. As with all renewables, the global recession has taken its toll but some analysts believe that this may have a beneficial effect, speeding up a shake-out in the industry. Consolidations will create stronger, more dominant players on the global stage.
Most traditional panels use PV cells made from crystalline silicon, which is ‘grown’ in ingots and then sliced into very thin wafers before being baked at high temperatures. Since 2005 there has been an acute shortage of refined silicon worldwide, a situation which is changing rapidly as new production capacity comes on-line. Wholesale prices are forecast to drop by up to 40% in 2009, with the price of solar modules (the finished product) also freocast to drop by 30-40% (so if you’re a consumer thinking of installing PV panels this year, hold back until these reductions feed through into retail prices).
Thin Film PV
Shortages of crystalline PV have also led to the development of a whole new generation of solar technology known as thin film photovoltaics. Using nanotechnology or other advanced processes, a mixture of elements is applied in a thin layer on to backing material. This substrate can either be glass or, more commonly, some sort of flexible membrane. This makes it relatively easy to mass produce on a continuous roll, bringing down costs dramatically. The downside is that it’s not as efficient at converting sunlight into electricity: thin-film panels on the market today generally convert 7-12% of sunlight to electricity whilst conventional panels can reach 22%. However, thin-film is growing incredibly fast and is expected to make up around 25-30% of solar production capacity by 2010.
Building Integrated Photovoltaics (BIPV)
A huge growth area for thin-film technologies is in Building Integrated Photovoltaics (BIPV). This incorporates PV modules directly onto roofs and other surfaces, doing away with the need for a separate panel altogether. This has aesthetic as well as cost advantages, and BIPV applications range from single solar roof tiles for domestic houses to industrial-scale applications.
Thermal Solar Power
The second main category is thermal solar power, which uses the sun’s energy to heat fluid or air, which is then used to provide hot water or heat to buildings. The most basic and inexpensive type of solar water heating is domestic solar thermal. Concentrating solar power is the utility-scale version.
Concentrating Solar Power (CSP)
CSP is a utility-scale application (plants are usually in the 50 to 250 MW range). There are several different technologies. Concentrating systems focus the sunlight using reflectors such as parabolic troughs, Fresnel reflector power plants, tower power plants or solar dishes. The captured heat is fed into a steam cycle at high temperature, and the steam is used in a turbine or Stirling engine to generate electricity just like a conventional power plant. There are also non-concentrating systems which don’t use reflectors, such as solar chimney power plants.Because heat is easier to store than electricity, these plants can be combined with heat storage units (generally filled with ‘molten salt’, a combination of sodium and potassion nitrate) which release the heat later on in the day (or at night) to keep the turbines turning.
One way to increase the efficiency of silicone cells is to use a mirror or advanced optics to focus sunlight onto small, highly-efficient solar cells. Although these high performance cells tend to be expensive, far fewer of them are needed since the sunlight is concentrated some 500 times onto each cell. Most CPV panels use advance tracking systems in order to maximise solar radiation. CPV systems can reach conversion rates of between 25-30% efficiency.
Concentrating Photovoltaic Thermal (CPVT)
CPVT uses a layer of PV material over a thermal collector to heat water or air. The advantage of this is that the thermal collector not only produces hot water or air but helps cool the PV cells, which operate at higher efficiencies when they’re kept cooler.
The solar future
New ways of harnessing solar power are being explored in research labs and universities all over the world. Organic PV cells and windows which generate electricity are just two of the ideas which have cropped up recently. Undoubtedly there are many more exciting innovations and commercial opportunites to come. Whatever the ups and downs in the near future, solar power will continue to show substantial growth in the decades ahead.
Print Page
By Nick Hanna
Format: Paperback
Pages: 196
Edition: 1st
RRP: £14.99
Due for publication: 24th May 2010
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