Concentrated solar power – CSP – has the potential to bring energy to remote areas of the world. The heat of the sun is reflected off rows of mirrors onto a central tower, transforming water into steam and turning a turbine which then generates electricity. But these plants have a fatal flaw – they are extremely thirsty.
This type of solar energy is perfectly suited to deserts with their strong sunlight, but desert sand and dust mean all the mirrors need regular cleaning – using precious water.
At the Plataforma Solar de Almería (PSA) scientists are working on water-saving experiments, among the barriers to stop the dust from reaching the mirrors in the first place.
Aránzazu Fernández-García is a researcher at CIEMAT-PSA. She tells us what they’ve noticed about the tests barriers so far: “The barrier that is working best so far is the one with a flat geometry. Compared with the curved one, we get slightly better results and if we compare it with the natural barrier, the results are spectacular. With the artificial barrier, we can block up to 50% of the particles and stop them from entering the solar field.”
Cleaning the gigantic mirrors also uses lots of liquid. Researchers are testing an ultrasonic cleaning system, which uses less water, as part of an EU project.
Aránzazu Fernández-García says: “We are using a manual system to perform the experiments for a year, in which we will obtain results on water consumption, electricity consumption, etc., and the next step will be to ‘scale up’ the device in a working solar plant using an automated system.”
Special coatings to stop dirt sticking are being tested, measurements taken by hand show when surfaces need cleaning but a new sensor does the work automatically, and a hybrid water cooler prototype, with both wet and dry cooling towers, has just been installed.
Steam cycle plants require cooling to function – to condense the steam back into water and complete the cycle – but this is the most water-intensive part of any CSP plant.
In France, researchers are working on a different type of cooler – using jets of water mist. Concentrated Solar Power has one big advantage over the better-known solar panels – heat produced can be stored and used long after the sun has set, so it’s a technology well worth refining via smart cooling and cleaning.
A storage tank for cool night air
Delphine Bourdon is the co-ordinator of the European WASCOP project. She explains: “We’re adding a water mist system which will cool the air before it gets to the heat exchangers so we will have a much more effective cooling system. We should be able to reduce water consumption by more than 90 per cent, compared to a traditional wet cooler.”
The team is also working on an innovative device to store cold air – this tank, which is filled with layers of rock and water.
In effect, it stores the fresher night air which can then be used to cool the turbine condenser, using no water at all.
Christophe Dumas, head of the Cadarache Solar Thermal Group, explains why this matters: “CSP power stations have an important role to play in the coming years. The irregularity of renewable energies is quite a problem and CSP allows us to store energy and produce electricity 24/7, with costs which can be very attractive.”
Many of these experiments will soon be tested in working power plants in Spain as part of a further European Union project – SOLWATT, and could be commercially available within three years.