Concentrated Solar Power
Concentrated Solar Power (CSP) means generating electricity by means of solar thermal power stations. The unique characteristics of CSP solar thermal power stations are the concentrating collectors (of various specific technologies, forms, and designs) used to concentrate solar radiation. The mirrors of the collectors concentrate solar energy on a receiver, which heats up a heat transfer fluid. Solar energy can then be used to generate electricity, heating, cooling, solar fuels or be used for water purification. Solar power plants have been successfully installed and operate economically on several continents. The optimum sites for CSP are in regions with high direct solar radiation along the Earth’s sunbelt.
Mirrors with line focus or spot focus
Concentrated collectors can be distinguished by the layout of their concentrating mirrors. Line focussing systems such as parabolic trough collectors or linear Fresnel technology follow the sun in one axis. They concentrate the radiation on an absorber tube that transfers the energy to a heat transfer fluid (e.g. water, thermal oil, or liquid salt). In practice, the sunlight can be concentrated 100x. Numerous concepts exist in which the heat transfer fluid is used directly in the power plant circulation, e.g. in steam, or where it circulates in a secondary circulation (e.g. thermal oil). Spot focussing systems such as power tower plants use a number of single focussed collector mirrors (heliostats) to concentrate the radiation on one single receiver on the peak of the central tower. They can concentrate the sun’s radiation 500x.
Thermal energy storage and use of fuels
Solar power plants have the advantage that thermal energy storage (e.g. storage tanks with hot, melted salt) can be integrated. This is significantly easier, more efficient and cost effective than directly storing electricity. Heat storage keeps the plant in operation when clouds pass overhead or after sunset. In addition, heat generation can be adjusted to the use of fossil or biogenic fuels as required. At large scale, using high temperature heat to generate electricity is of special importance. This means that a collector system is transferring the high temperatures collected to a conventional power plant. In combination with a water reservoir and/or combustion of fuels, more cost-efficient energy can be provided as required without reserve power plants for times without sunshine.
Storage for liquid salt – solar power station Andasol-3
Solar power plants with steam circulation operate – like all steam power plants – on water; in particular to cool the circulation. Since water is scarce in the regions where this technology is used, the water consumption of cooling systems needs to be as low as possible. Instead, using ambient air for cooling, water consumption decreases significantly (90-95% reduction in overall water consumption). Alternatively, in close proximity to the sea, sea water cooling systems or the operation of sea water desalination plants are an option.