Give Me Sunshine  

A solar power plant in the Mojave dessert

Last Month we took a look at how wind turbines are being used to produce electricity and the target of providing 12% of power generation in the EU and 10% in the UK by 2010. We also listed other forms of renewable energy sources and so, following the theme, this month we will take a look in a bit more detail at probably the greatest potential renewable source – the Sun – and the means developed of capturing solar power.  

We all know that since the beginning of time the sun has played a major part in our development, being used for heat, plant growth and our general well being. But it is only during the last fifty years or so that we have been able to harness the sun’s energy to produce electricity as well as heat.  

In 1952 the Paley Commission prepared a report for the U.S. president of the day, Harry Truman, predicting that by the early 1970’s thirteen million solar homes would have been built. But this interest in solar power was lost as governments investigated instead ways of harnessing nuclear power to generate our electricity. But as time has gone by nuclear has not grown in its popularity and our attention has been drawn back again to solar.  

It has been calculated that the sun irradiates the earth’s landmasses with the equivalent of nineteen trillion tonnes of oil equivalent (toe) every year. Nine billion toe would satisfy the world’s current annual energy requirements.  

With this in mind, how can we harness this potential energy source in an efficient and effective way?  

Since the 1980’s, there has been a 350 megawatt solar power plant in the Mojave dessert in California, silently collecting solar rays and producing steam to run a power generator. There are many more power plants out there, and plans are being laid for a massive 20,000 dish power plant covering 4,500 acres in the Mojave dessert, which is expected to produce enough electricity to power over 270,000 homes every year. The expectation is that this should be up and running by 2011. These 37-foot-wide dishes, initially developed by McDonnell Douglas in the 1980s, act as mirrors that collect the sunlight and focus it on a liquid-filled chamber where its heat is used to drive the generator.  

The image below shows how this typically works. The solar field collects the heat from the sun, which heats the oil, which is then used to produce steam to drive the turbine. This in turn produces electricity, which feeds into the grid. The advantage of this sort of model is that if the sun doesn’t shine sufficiently then the oil can be heated by other means, as shown.

This isn’t the only way that solar can be used to produce electricity. Like wind turbines, solar can also be used in locations that are not connected to the grid. Solar also provides a means of providing power to many road signs and services. This is done with the use of photovoltaics (PV).  

Solar cells (pvs) convert energy from daylight into electricity using a semiconductor material such as silicon. When light hits the semiconductor, the energy in the light is absorbed, ‘exciting’ the electrons in the semiconductor so that they break free from their atoms. This allows the electrons to flow through the semiconductor material (in a similar manner to a normal electrical circuit) producing electricity.  

We also have passive solar design, which is by no means a new thing, whereby a building is sited and constructed in away that it makes full use of the sun for warmth as well as light. The next step was to use sunlight directly for interior lighting via lens collectors, reflective light-pipes, and fibre-optic bundles. The US Department of Energy have been working with Oak Ridge National Laboratory on Hybrid solar lighting (HSL). This is where sunlight is collected and routed through the building using optical fibres where it is then combined with electric light. Sensors maintain the light by adjusting the electric light according to the amount of sunlight. This helps to reduce the amount of power needed to light the building. A company called Sunlight Direct (http://www.sunlight-direct.com/index.html) are demonstrating hybrid solar lighting systems at the Department of Energy's American Museum of Science and Energy and several other locations across the US .  

We also have active solar water heating. Using the heat from the sun to heat up water in storage has in one form or another has been around for decades. Over the last ten years or so this process has become much more efficient and more buildings have incorporated it in their design.  

Even pvs can now be incorporated into roof tiles of a building to produce the power requirements for the occupants. Our architects and builders are coming under more pressure to produce energy efficient buildings, and using solar alone will make a large difference to the amount of power we will draw from the grid. But will this eventually make the grid obsolete?  

It is true that like wind, solar is being developed at an ever increasing rate. Our technology is improving, but still has a long way to go before solar becomes more economical than fossil fuel. Component parts are still very expensive, which is what makes potentially free energy expensive, but as governments offer financial incentives, to encourage use as well as development of renewable sources, so this market is destined to grow.  

But it is not always practical to erect a wind turbine in your garden or on top of your office, and it is certainly not a cost effective exercise to re-roof your building with pv tiles. So some utilities have come up with alternatives to encourage us to switch to using renewable energy in new and creative ways.  

One company in the UK , Scottish and Southern Energy, offer a concept called power2. It basically promises to replace every unit that you use with renewable power and if you buy gas from them also, to plant 5 trees a year per customer, which is sufficient to remove the co2 emissions, produced by the average household’s gas use. They currently supply 6.3 million UK customers and promise not to charge more than the local supplier. Take a look.  

Germany is one country that proves what a difference a government can make if it really wants to encourage the use of renewable energy and involve the population of its country. Starting with a small project called the 1000 roof project in 1991, the forward thinking Germans expanded it to the 100,000 roof project, which began in 1999. The aim was to install pvs into 100,000 rooftops by 2005; the project was completed in 2003. This brought Germany to second place in the use of pvs, with Japan in first. The increase of pv use in Germany has encouraged massive employment in this area, from the construction of pv units to their installation.  

Japan was, until the end of 2004, the world leader in solar production since 1995. The Japanese have a goal to reduce their dependence on oil and to be known for their lead in solar power generation. They had the largest total capacity at 1.13 million kilowatts, at the end of 2004, compared with Germany 's 790,000 kilowatts. But Germany , in 2004, became the world’s fastest producer, having installed enough equipment to produce 360,000 kilowatts compared to Japan ’s 270,000 kilowatts. As these two countries battle it out for first place, it can only be good for the environment as more power generated by solar means less CO2 in the atmosphere.  

This is just a snap shot of the race for solar power that is developing in the world around us. Solar, like wind has a downside, lack of shine, due to a cloudy day or of course at night. Long dark winter days will not generate loads of power, so we need to consider the other forms of renewable sources. Next month we intend to round this off by looking at the other sources of renewable energy and how all together renewables might just make a difference to our world and the generation of power that we have all come to rely so much on.  

Researched and compiled by Paul Cassar.