The potential of solar energy is ignored by the UK government in its decision to build a new generation of nuclear power stations. It is true that Solar energy currently generates a small amount of electricity worldwide compared with nuclear but it is growing at a phenominal rate. It is as if in the early 1980s, when personal computers were beginning to appear, the government decided to commit the country to using mechanical typwriters for the next 50 years.
An important use for solar energy is for heating buildings and hot water, however here we will look only at its use for generating electricity. There are two main ways in which solar energy can be used to generate electricity:
PhotoVoltaic Cells or Solar Cells (PV): Looking like black sheets of glass in a frame, PV solar panels directly generate electricity from light with no moving parts. PV installations can be just a few panels on the roof of a house, or a vast array of panels forming a power station.
Concentrating Solar Power (CSP): Large mirrors focus direct sunlight pipes or a boiler. The heat is used to generate steam and produce electricity via a traditional steam turbine coupled to a generator. This technology is only suited to areas with plentiful direct sunlight. However high voltage DC transmission lines could transmit the power from North Africa to Europe.
If you doubt solar's potential, the US Department of Energy listed some solar myths like: Myth 1: "Solar electricity cannot serve any significant fraction of U.S. or world electricity needs." Answer: "PV technology can meet electricity demand on any scale. The solar energy resource in a 100-mile-square area of Nevada could supply the United States with all its electricity (about 800 gigawatts) using modestly efficient (10%) commercial PV modules."
Generating electricity from solar PV is costs roughly twice the price of what a consumer would pay to buy the same energy from the grid (the exact ratio differs from country to country). Solar PV is taking off because some countries recognise its potential and are subsidising it to kick start the industry. The most notable is Germany where the operate a special 'feed in tariff' - they buy the solar generated electricity at a higher price. As a result, solar in Germany is growing at an astonishing rate of 20 to 25% a year.
But to understand explosive growth potential of solar PV, you have to look at what is happening to its price. Solar PV is a semiconductor technology; like computer microchips, its price have been falling steadily for decades. However PV's price hasn't fallen as fast as that of microchips because a PV panel can't get smaller and smaller in terms of area (it has to catch the sun) and because PV has not yet reached the point where it is cheaper than competing ways of generating electricity - but this day is fast approaching. The chief executive of the US General Electric Company says "I am convinced that in the next five years, the solar industry has the ability to take out half its [manufacturing] costs" (Financial Times 11.1.2008).
Solar PV is getting cheaper because solar panels are suited to the same sorts of mass production processes that in a few short decades have filled our world with TVs, cars, computers, CD players and the like. Once manufactured they are simple and safe to install. The 4GW of solar capacity installed worldwide during 2007, equates to something like 40 million panels. Contrast this to the nuclear dinosaurs of which there are only 400 odd worldwide with each taking up to 20 years to build.
When solar PV reaches and passes the point at which it undercuts the price of electricity from the grid, solar will really take off. Some experts expect a growth rate of 40% worldwide.
Where do such growth rates take you? Currently (2007) solar PV generates about 0.1% of electricity worldwide and about 0.5% in Germany (in 2010 it had risen to 2% in Germany).
- At a 20% growth rate, in 20 years time Germany would generate 19% of its electricity with PV, and the world 3.8%.
- At a 20% growth rate, in 25 years time Germany would reach 50% of electricity from PV, and the world would reach 50% in 34 years time.
- At a 40% growth rate, Germany would reach 50% in just 14 years and the world would reach 50% just 4 years later in 18 years time.
It is not suggested that solar will become such a large proportion of our electricity in so short a time. Electricity is not easy store economically and efficiently. Obviously solar is unavailable at night and much reduced in winter, so either the storage problem needs to be solved or another power source needs to be available. Also, initial growth rates may well slow. However the figures do show how quickly solar PV could go from being a negligible part of our electricity generation to being an important one.
Furthermore, current anticipated growth is based on just continuing the steady cost reduction of the existing PV technology. There is also a possibility that a breakthrough could occur, suddenly allowing much cheaper PV. "Figures released yesterday by the Earth Policy Institute in Washington showed that solar electricity generation was now the fastest-growing electricity source, doubling its output every two years. It is now attracting government and venture capital money on an unprecedented scale." ("Solar energy 'revolution' brings green power closer", The Guardian 19 Jan 2008). Some data on the progress of PV and other renewables in Germany: "New Record for German Renewable Energy in 2010"
Solar PV keeps getting better: (1) PV price falling - past and projected; (2) Cell efficiencies are rising. From: Scientific American: 'Does Moore’s law apply to solar cells?'. (3) Cost predictions from California Energy Commission - solar falls, nuclear rises.
Concentrating Solar Power (CSP) uses the suns heat to generate steam for a conventional turbine-generator set. The club of Rome and a study commissioned by the German government, argue that CSP can already compete with existing forms of generation - particularly when it is combined with desalination ( a valuable extra benefit in desert areas). But CSP is not likely to grow from thousands of small installations as solar PV has done. Firstly the technology is not suited to small household installations - a typical CSP plant will be tens to hundreds of Megawatts. Secondly CSP plants are best built in hot desert areas thus requiring investment in long low-loss transmission cables. In engineering terms however, CSP has some nice features:
It is a mature straightforward technology - some plants have already been running for over 20 years. Like PV, CSP is eminently suited to mass production since plants mainly consist of hundreds of identical units - mirrors mounted on metal frames.
CSP plants can store energy as heat (e.g. in hot salts) allowing them to continue operating through the night. As CSP plants supplying Europe would be located a long way south (ideally North Africa and the Middle East) they also still receive plenty of sun in winter.
Concentrating Solar Power (CSP): (1) In Seville; (2) A CSP Collector; (3) In Nevada. From sites of solar energy company Abengoa Solar and of REUK, whose website covers all aspects of Renewable Energy.
Read more about CSP:
Trans-Mediterranean Renewable Energy Cooperation - Concentrated Solar Power. The Club of Rome initiative.
Trans-Mediterranean Renewable Energy Cooperation - UK site. The TREC study can be downloaded from here.
The US Department of Energy's Solar CSP page and a document which though dated (2005) contains an overview of how it works with diagrams and photos. A Global Market Initiative to build 5,000 MW of CSP in 10 years was signed by 8 countries in Bonn.
Desertec Youtube film on Andasol III (English commentary over Spanish and German speakers). Andasol 3 has a gross electricity output of 50 megawatts (MWe), producing around 180 gigawatt-hours (GW·h) per year (21 MW·yr per year). It took just over 2 years to build, and has a thermal storage system which absorbs part of the heat produced in the solar field during the day, allowing the plant to continue to generate during the evening or when the sky is overcast.
Solar Millennium AG corporate film about Andasol plant in Spain and plants planned in China and USA and the Middle East.
Made in Germany: Desertec - Electricity from the Desert for Europe. A 2009 film, out of date but a useful introduction to DESERTEC, + nice camels.
Stunning solar towers light the way. This film discusses CSP and photovoltaics, and shows the PS10 solar tower CSP plant near Seville. It's a good video but the Guardian makes you see an advert first! (guardian.co.uk, Friday 11 February 2011).
SOLEIL - Sustainable On-Line Energy Information Listing. Maintained by the UK Solar Energy Society (UK-ISES), SOLEIL aims to be a sophisticated and comprehensive on-line resource guide for UK solar and renewable energy information on the World Wide Web.
Solarcentury. Solarcentury is the leading provider of solar photovoltaic (PV) solutions in the UK.
Energy Saving Trust. A description of domestic solar electricity (PV) and solar hot water (thermal).