Solar power plants – Concentrated
solar energy results in heat first, then electricity
According to the Fraunhofer-Gesellschaft
(FhG), the sun sends as much energy to earth in less
than one hour as we humans consume in a year1). At a time when
fossil raw materials are both scarce and expensive, it is important to make
greater use of this renewable energy source, for instance by operating solar
power plants based on Concentrated Solar Power (CSP) technology.
While photovoltaics is a technology designed for local use of solar energy, the
strength of the solar power plant lies in its centralized generation of
electricity. According to the calculations of the Fraunhofer
Institute for Solar Energy Systems (FhG ISE), the
unpopulated deserts of North Africa alone are capable of generating enough
energy to cover Europe’s needs many times over2). This makes solar
power stations a significant technology option for the sustainable energy mix
of the future. It is more than likely that these will contribute directly to
the European Union’s CO2 reduction strategy. According to a study conducted by
Greenpeace, every kilowatt hour of solar energy saves
around 0.6 kg of CO2. This means that the use of solar power plants on a
worldwide basis could prevent the emission of approximately 154 million tons of
CO23).
Simple mode of operation and
proven technology
Solar power stations with parabolic trough technology
are steam-driven power stations that generate electricity from heat. Here, the
sun provides the energy that is needed to drive the turbines. Inside the solar
field of a solar power station with parabolic trough technology, parabolic
mirrors arranged in long rows concentrate the incident solar radiation by a
factor of up to 80 onto an absorber tube, inside which a heat carrier is heated
to around 400 degrees Celsius. The steam necessary to drive a conventional
turbine is generated by a heat exchanger located in the central block of the
power station. Modern storage technology even makes the solar energy available
in inclement weather and at night: The heat carrier that circulates through the
solar field is a heat accumulator that can bridge cloudy phases for a short
period. Salt reservoirs additionally provide a reliable supply of electricity
for several hours if the sun is not shining. This makes this technology
attractive for continuous generation of electrical power. Due to the use of
storage techniques, the turbines are also able to operate for long periods of
time under full load and therefore at a higher degree of efficiency.
New standards for solar power
plants
The quality of the absorber tube is the crucial factor
in how efficiently a solar power plant runs. The absorber tube must be capable
of absorbing as much sunlight as possible and yet emit hardly any heat. Future
solar fields will either generate steam directly or use molten salt instead of
a heat transfer oil as the heat carrier in order to be able to operate the
power plant process at at least 500 degrees Celsius
and thus much more efficiently. This would allow for solar electricity to be
produced even more cost-effectively.
Good prospects
Solar power stations are particularly efficient when
there is a high level of solar radiation. Therefore, they offer good
opportunities for development not only in the more southerly EU states, but
also in many economically disadvantaged regions across the earth’s sunbelt. Given the threat of climate change, solar power
stations open up the possibility of considerably increasing the proportion of
renewable sources used to produce energy, especially in these regions. Since
they are steam-driven, solar power plants can also be combined with fossil or
biomass sources of energy. Parabolic trough solar fields can even be linked
with conventional power stations. Particularly inside the earth’s sunbelt, this would allow for a secure supply of energy to
be realized, a large share of which can be attributed to solar.
Sources: 1) FHG Magazin,
2/2008; 2) FhG ISE, Solar Thermal Power Generation,
7/2003; 3) Greenpeace, Solar Generation II, 10/2004
