Mediterranean Solar

We’ve reported before on TREC, “The Trans-Mediterranean Renewable Energy Cooperation,” an initiative that campaigns for the transmission of clean power from deserts throughout Europe, the Middle East and North Africa.”

The mission of this group, affiliated with the Club of Rome, is to promote the construction of high voltage direct current (HVDC) transmission lines throughout Europe, the nations ringing the Mediterranean, and the Middle East. At the same time, they are calling for the construction of solar thermal power stations in the Sahara Desert to produce electricity that can be efficiently transmitted to European markets via the HVDC cables.

This is an ambitious project, to put it mildly. We reported on HVDC transmission technologies in our post “Life in the Electric Age,” describing the attempt to bring HVDC to the west coast of North America. HVDC has several advantages over typical high voltage AC transmission lines. Most importantly, HVDC experiences far less power loss over long distances, and the lines can be buried underground. We have also covered TREC’s work in the past, in our posts “Mega Solar Concentrators,” and “Saharan Solar Power.”

A solar field and power tower.
(Photo: Bright Source Energy)

One of the questions with solar thermal power, particularly if you are going to operate these plants in the desert, is how to access an adequate water supply for the steam turbine. Clearly these plants would have to recycle nearly all of the water if they were to be practical. The solution to this may lie in using the “power tower” design, vs. the various parabolic trough designs. The reason for this is because the temperature in the power tower, where a solar field of mirrors all focus on a single boiler, gets quite a bit hotter than vs. competing designs, up to 550 degrees centigrade.

This advantage is realized when it is time to recycle the water back into the solar field. Because the water is being reused, the steam that moves the turbine that turns the generator cannot simply be blown into the atmosphere. Instead the steam has to be condensed, meaning the condensor has to shrink the steam back into water at the same rate as the hot steam is being released into the turbine, to avoid back pressure that will undermine the efficiency of the turbine.

Because a power tower design can achieve temperatures of 550 degrees centigrade, vs. approximately 325 degrees centigrade for a parabolic trough design, it is possible to efficiently air cool the water exiting the turbine for recirculation back into the solar field – even in the Sahara Desert. With a parabolic trough design, there simply may not be enough differential in temperature between the steam entering the turbine and the ambient temperature to allow cost effective water cooling. For more on this read “Bright Source’s Power Tower.”

TREC’s goal of replacing literally terawatts of power output throughout Europe, the Mediterranean and the Middle East with solar thermal power stations may never happen at the scale they envision, but the technologies they are advocating are being explored around the world. Solar thermal power combined with HVDC electricial transmission technology are innovations that should be explored further. It is also encouraging that the solar thermal cycle of boiling and condensing water may conceivably be integrated with desalination. TREC’s vision is an example of a comprehensive potential solution to many challenges – efficient energy transmission, renewable energy production, and alleviating water scarcity.

One Response to “Mediterranean Solar”
  1. Gerry Wolff says:

    This is a good article but there is just one detail that I believe is not right. Where you say “… the steam that moves the turbine that turns the generator cannot simply be blown into the atmosphere …” it suggests that some thermal power plants do blow the steam from the turbines into the atmosphere — and I don’t believe that is ever done. All thermal power stations need cooling and, quite often, water is used for cooling leading to clouds of steam in the atmosphere. But the water going through the turbine is always recycled, as shown on this page: .

    With the plants in California, quite a lot of water is used for washing the mirrors but this is not strictly necessary — there are methods of cleaning the mirrors without using water.

    If necessary, a CSP plant can be run with little or water, except for an initial supply of water for the steam cycle (and this can be constantly recycled). We have a page about how water usage can be minimised here: .


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