3.3.5 ELECTRIC POWER

The generation of electricity from solar thermal energy requires higher temperatures than for heating, and therefore some kind of concentrating collector is required. Three techniques have been applied: trough type parabolic collectors, parabolic dishes and a power tower. They all require an array of collectors, each of which must be capable of tracking the sun in a coordinated manner. These technologies are still at the demonstration stage, and rely mainly on work at just two research centres in the world: the Solar Electricity Generating Station (SEGS) in California and Plataforma Solar de Almeria (PSA) in Spain.

3.3.5.1 Solar farms

Trough type collectors heat a tube containing liquid, which is normally then pumped to a high temperature heat exchanger to generate steam for a conventional power cycle. European companies have a lead with this technique; German and Israeli companies contributed basic components at the SEGS plants. Direct generation of steam in the absorber tubes, thus dispensing with thermo oil, has also been tested in Europe. With the participation of Siemens, the hybrid operation mode, which combines solar thermal with the combined cycle gas technology, has been investigated. A consortium of European firms is offering a parabolic trough system for application on the Greek island of Crete.

3.3.5.2 Parabolic dishes

Dish collectors may be used in the same way as troughs, but an alternative is to place a Stirling engine at the focus of each receiver (see fig 3.3), which will generate electricity directly with maximum efficiency. EU (German) industry still holds a leading position compared to the US industry for dish/stirling systems. Particularly the 16,000 hours operational experience from the three PSA plants has provided valuable results.

3.3.5.3 Solar towers

A power tower works in a similar way to a very large dish, but the reflective surface is split up and distributed as individual mirrors over a large area of ground, each of which independently tracks the sun in order to deliver radiation to the central tower (fig 3.14). By putting into operation SOLAR TWO, the American industry will gain operational experience, particularly in the use of salt as the heat transfer medium. European companies have operated an open volumetric air receiver at PSA. Currently EU industry can offer a 30 MWe solar power tower.

 

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source: NREL
Fig 3.14 Solar Power Tower