Thermal Solar Power Booming in Spain

The Spanish thermal solar power race is on. In Spain, a company called Solucar has a 11 MW solar tower power project under construction, two more 20 MW towers being financed and permitted and 300 MW of parabolic trough plants under development.  ACS Cobra has three 50 MW of parabolic trough plants due to start construction soon. In addition Spain's largest utility, Iberdrola, has announced that it has ten parabolic trough trough projects totaling 500 MW underdevelopment. An array of smaller projects brings Spain's total pipeline of solar projects to near 1,000 MW. 

All this activity results from a 2004 ministerial ruling, Royal Decree 436, which "establishes two alternative payment schemes, both guaranteed over the 25 year life-cycle of thermal solar plants, and diminishing thereafter. The first is a fixed, guaranteed payment of 300% of the Average Reference Tariff (ART) for electricity. The second induces operators to compete on the national wholesale electricity market. Here, CSP generation receives 250% of the ART plus a 10% additional incentive."  This is further explained in the referenced article.

The solar tower technology involves a high central tower, around which a series of reflectors, or heliostats, are situated in concentric arcs at ground level. The heliostats track the sun's position and concentrate radiation on a thermal receiver, mounted at the top of the tower. The heat, at a temperature in excess of 1100 ºF (600ºC), is used to generate the steam that drives the turbine.

The solar towers will use water to store some of the thermal energy produced by the tower. Water is  pumped from a 'cold' tank through the tower receiver, which heats the water to around 480-490ºF (250-255ºC).  The hot water is pumped to a hot tank where it is stored and subsequently released to generate steam when the sun does not shine. Storage enables the plant to generate higher earnings not only from increased production but also from more predictable production. That allows the plant to produce for about an hour, at half load, without sunlight, which is enough to avoid penalization for bad scheduling on the electricity system. Solucar will use the same thermal storage technology in its solar trough plants.

Solar trough technology uses troughs, approximately 230 feet (70 meter) long, lined with concave mirrors which concentrate the sun's rays on a circuit of tubes running along their focal point. Synthetic oil flowing through the tubes is heated to around 750ºF (400 ºC ) and then passes through a heat exchange unit to generate the steam for the turbines.

Molten salt storage will be used in nearly all of the solar trough plants.  The concept is similar to using water for heat storage, except that the latent heat of the salt is utilized, which makes the storage volume less, for the same quantity of heat stored.  However, the molten salt solution is more corrosive than water and thus the system must be constructed of more expensive materials.  The first two ACS Cobra plants, Andasol I And Andasol II will have have seven hours of storage and Andasol III will have 12 hours of storage.  Iberdola will also use molten salt, but the size of the systems will be determined on a case by case basis.  An Iberdola spokesperson was quoted as saying, "With storage the investment is higher and the technology is more complicated but profitability also goes up."

Material for this post was abstracted from "Mirrored sunshine" by Mike Stirzaker that appeared in the March/April online edition of the UK magazine Renewable Energy World. The article uses the acronym CSP, which stands for concentrating solar power, the same technology that I refer to as thermal solar power which I use to avoid confusion with concentrating PV technology.  I believe my terminology is more widely used.

Technorati tags: solar, solar power, thermal solar, solar troughs, solar towers, energy, technology

The Energy Blog: Thermal Solar Power Booming in Spain

Comments

[JN2]

Costs: Anyone know what the approximate installed cost per MW?

[solar power]

Check out this introduction article on solar power:
http://www.articleworld.org/Solar_power
Contents
1.Methods of harnessing the sun's energy
* 1.1 Direct solar power
* 1.2 Indirect solar power
2.Forms of solar power - either passive or active