Demystifying solar energy

It is normal to regularly see cars covered in dust. What may seem abnormal is that this “dust” is likely to be a fine layer of sand from the Sahara Desert, hundreds of kilometres away.

Sand particles in the Sahara are disturbed by strong winds and drawn up into the atmosphere. These enormous plumes of dust are then carried off by the winds – often covering large areas of Southern Europe.

This almost invisible enemy can cause serious health problems, such as respiratory diseases, but it can also cause problems with solar energy production: an increasingly important clean and renewable alternative to oil.

Desert dust reduces the amount of radiation reaching the solar mirrors which transform sunlight into energy.

The European Monitoring Atmospheric Composition and Climate project (MACC-II) keeps power station managers informed of the frequency at which a certain location is affected by these large dust clouds. In the near future it is expected to provide daily updates and five-day forecasts to show the dust’s impact on solar radiation.

Florent Cassar, Project Head in the Solar Energy Division at Constructions Industrielles de la Mediterranée (CNIM), explained the importance of such forecasts.

“What we see on the mirrors are dust and aerosols from the desert. Those are harmful to our facilities because they reduce the incoming solar energy impacting on our system,” he said. “If we know a few days in advance that a dust storm is coming, we will store surplus energy so that it can be used on the days where there isn’t sufficient solar energy to operate the installation. At the moment, this storage works with pressurised water; so there are kinds of big cans that will store water at a very high pressure and a very high temperature. When we want to discharge this energy, we will use the steam present in these containers to power the electricity-production systems”

Data on solar irradiation is crucial when deciding the location of future solar power plants.

But how is it possible to foresee the movements of desert dust? At the University of Sophia Antipolis, close to Nice, researchers from Transvalor – a company specialising in solar energy research into
– are measuring the quantity of solar irradiation that reaches the ground.

Large screens follow the desert dust, as seen by satellites. Mathematical models and algorithms provided in the framework of the MACC-II project can then predict its movements.

Transvalor’s General Manager Etienne Wey expanded on this.

“Today weather forecasts have progressed greatly and are able to predict the desert sand that is raised and taken by the wind at high altitude to Europe, as seen here. These models are actually numerical. They run on very large computers and give us the transparency of the atmosphere, since the more sand there is the less the atmosphere is transparent. They also forecast what will become of the sand – how it will move in time in three, four or five days.”

Solar energy is becoming increasingly important as a source of renewable power generation. So, knowing in advance when a dust storm is coming from the desert is crucial.