Technologies

Key Technologies for DESERTEC

A large power network with very low electricity losses allows clean electricity to be generated from renewable sources at the most advantageous locations. The type of technology used on site depends on local circumstances, as well as on the wishes of the country concerned and the investors.

In desert regions near the coast, solar-thermal power plants can be combined with seawater desalination so that they not only produce electricity, but also drinking water. Air-cooled solar-thermal power plants combined with water-saving cleaning robots are particularly useful in desert locations inland. Many coastal areas are excellent locations for inexpensive wind power plants. Photovoltaic systems are useful for covering peak mid-day demand, for example from air conditioning systems. Solar-thermal power plants, as well as biomass, geothermal, hydroelectric and pumped storage plants, provide valuable, controllable electricity. This means they can be used to balance out the fluctuations of wind and photovoltaic power, so that more of these variable energy sources can be used in the future electricity mix.

youtube.com/desertecchannel

DESERTEC Foundation at Andasol 3

youtube.com/desertecchannel

The TuNur Plants in Tunisia

 

High-Voltage Direct Current (HVDC) transmission

HVDC transmission is a way of carrying clean electricity over long distances to the places in the world which consume large amounts of energy. Around 90% of the human population live less than 3000 kilometers from deserts and could be efficiently supplied with clean desert electricity. The line losses are very low – only around three percent per 1000 kilometers – and the extra cost is only one or two cents per kilowatt hour. This is more than compensated because solar power plants located in deserts are much more efficient due to the longer and more intensive solar irradiation and less winter months. The same is with wind power plants that benefit from stronger and more constant winds at optimum sites. An extended grid and connected backup power plants compensate for fluctuations in renewable energies and downtime in power plants and transmission lines.


There are dozens of lines up to 1700 km long (Inga-Shaba, Democratic Republic of Congo) with capacities of up to 5 gigawatts (Yunnan-Guangdong, China) already in operation around the world. HVDC lines are also used in Europe: Sardinia is connected to the mainland by undersea HVDC cable and there is a whole network of HVDC connections between central Europe and Scandinavia. HVDC lines take up less space than conventional AC power lines and can be laid over long distances underground. This increases public acceptance and means the network can be extended faster. A study by the DLR confirms the positive eco-balance of the transmission lines used for DESERTEC. Wikipedia contains a list of existing and planned lines around the world.

 

Concentrating Solar-thermal Power (CSP) plants

CSP plants are key to the DESERTEC Concept because they are ideal for utilizing the solar potential of the world’s deserts and supplying electricity on demand. A reflector area of just 20 square meters in a solar-thermal power plant is enough to supply all the electricity one person needs (including electromobility) day and night with no carbon emissions.


Solar-thermal power plants use mirrors to concentrate solar energy in order to heat water and produce steam. This creates pressure, which is used to drive a conventional steam turbine and generate electricity. Solar-thermal power plants can produce clean electricity from solar energy day and night, because heat, unlike electricity, can be stored in large quantities. Heat storage tanks supply energy to the steam cycle at night and especially during times of peak demand. This means that these power plants, when combined with other renewable energy sources, can compensate for the inherent fluctuations of photovoltaic and wind power and thus help stabilize the grid.

At sites near the coast, solar-thermal power plants can use sea water to cool the steam cycle. This way, a collector array designed for a 250 megawatt steam turbine can produce 200 megawatts of electricity and 4 million liters of drinking water every hour through thermal seawater desalination. This method is already used on a large scale at the fossil-fired plant at Jebel Ali in Dubai. At inland sites, air cooling is most suitable – which means that the ideal locations for solar energy can be used, regardless of whether there is a water source. Water-saving brush robots are already successfully used for cleaning the collectors.

Wikipedia contains a List of existing and planned power plants around the world.They use various methods of gathering solar energy:

  • Parabolic trough collectors have been used in the Mojave Desert in California since 1984. The power plants of the Solar Energy Generating Systems (SEGS) have a combined generating capacity of 354 MW. Despite the harsh conditions, the reflector arrays continue to function perfectly to the present day. During sandstorms, the swiveling mirrors are turned to a safe position. To produce electricity at night, the SEGS power plants are combined with gas combustion. The more recent Andasol power plants in Spain, on the other hand, use heat storage tanks containing molten salt. Work is currently in progress on developing even more efficient concrete heat storage tanks.
  • Fresnel collectors are the next stage on from the parabolic trough technology. The horizontally arranged flat mirrors do the same job as a parabolic trough, but are cheaper to make and allow water-saving cleaning robots to be used. These robots are already in use at the PE 1 pilot plant in Puerto Errado, Spain. The plant also uses dry cooling and direct evaporation of water without a heat exchanger fluid.
  • Solar towers have huge arrays of flat mirrors that concentrate all the sunlight towards a receiver at the top of a tower. This allows them to achieve very high temperatures and as a result, they are highly efficient.
  • Parabolic dishes concentrate the sunlight onto a Stirling engine. These comparatively small units can be used individually for decentralized power supply, or whole arrays can produce electricity on a large scale. However, heat storage tanks cannot be used with these systems.

It currently costs around a billion Euros to build a 250 megawatt power plant with air cooling and heat storage tanks. At first glance it seems that this investment is greater than that for a photovoltaic plant of the same capacity. But this holds true only for a few hours each day: while the sun shines the brightest. A solar-thermal plant, on the other hand, can supply electricity at its full capacity around the clock, such that the energy yield is three times higher and can be sold whenever there is demand. The more solar-thermal power plants are built in the coming years, the faster costs will decrease due to mass production, technological progress and competition. It is now up to politicians to provide the incentives for investment – if they act decisively, desert electricity could be as competitive as fossil energy in less than ten years.

 

 

Further information:

Answers to frequently asked questions (FAQ)
Brochures, papers and studies