Concentrated solar energy in deserts

Deserts get a lot of sunlight and there is currently something of a race to develop and deploy the best technology to exploit this free energy.

Concentrating Solar Power (CSP) systems with mirrors, dishes or parabolic troughs focussing the sunlight to raise steam to run a turbines are currently in the lead. There have been some major developments in Spain and the USA, but also now in N Africa and the Middle East, with new projects opening in Morocco (the 470 MW Ain Beni Mathar hybrid project) and Egypt (the 150 MW Kuraymat hybrid project).

And more are planned. For example, the UAE is planning a 100MW project, and the Egyptian National Plan for 2012 -17 includes a 100MW Concentrated Solar Power  plant in South Egypt, while the follow-up National Plan for 2018-2022 has 2,550 MW of CSP. The German-led Desertec project seeks to build on the CSP option, making supergrid links back to the EU. It has plans for a €600m 150MW CSP plant in Morocco as a first stage.

It’s hard to know what the impact of the recent political convulsions in North Africa may be, but CSP does seem likely to continue to move ahead in the region, as well as elsewhere- the largest CSP array so far planned is the 1 GW Blythe project, being developed in California by Solar Millennium LLC, on which more later.

A solar industry roadmap, as outlined in a study by A.T. Kearney and the European Solar Thermal Electricity Association, ESTELA, sees solar thermal reaching 12 GW of installed capacity globally by 2015, 30 GW by 2020 and between 60 and 100 GW by 2025. But that may prove to be pessimistic- CSP is not just limited to desert areas. For example, South Africa has a plan for a 5GW solar park, with the initial 1000MW phase, aimed for 2012, incorporating an already planned Eskom 100 MW CSP plant, which has received part funding from the World Bank.

The Indian Ministry of New & Renewable Energy’s National Solar Mission aims to generate 20GW of grid linked solar power by 2022, 50% CSP. And in Australia a new ‘Zero Carbon Australia 2020’ report has 42.5 GW of CSP supplying 60% of total electricity there by 2020.

However a rival technology – Concentrating Photo Voltaic (CPV) power – may challenge CSP. CPV uses conventional solar cells but with large arrays and sunlight focussing arrangements, as with CSP. It may be too early to make longer-term policies on the basis of calculations like this, but PV and CSP do seem to be rivals. CSP has the major advantage of being able to store heat in molten salt heat stores, so that power production can be continued after the sun goes down, while most PV cell performance falls with time and rising temperature.

CSP and CPV both have similar environmental impacts in terms of their land use footprint, with some projects in the USA falling foul of local concerns about desert wildlife, and CSP’s need for water.

But there should be plenty of desert areas around the world where there are minimal land use conflicts, and some North African CSP projects have been seen as being used partly for desalination- with sea water piped in over perhaps long distances from the Mediterranean, possibly linked to Solar greenhouses projects.

New ideas may also emerge. It’s conceivable that CSP and CPV or PV arrays could be combined. There are some small-scale hybrid solar thermal-PV systems for domestic uses, the big advantage being that the solar heat absorbers keep the PV cells cooler, so they operate more efficiently, in tandem, with heat collectors in wafers in a sandwich with PV cells. Although it’s harder to see how this could be achieved with large scale focussing systems, it could be worth exploring in hot desert environments.

Hybrid CSP/PV systems were mentioned as a future option by the developer of the 1GW Blythe solar project in California mentioned earlier. Reflecting the changing fortunes of CSP and PV, it has now decided that the first 500-MW phase will be switched from CSP to PV technology because they say market conditions in the US now favour PV. But they also noted that CSP was a valuable ‘grid-stabilizing renewable energy source with storage capabilities,’ so a combination might prove to be the best option.