Civil Engineering Reference
In-Depth Information
Insulated water-storage tanks are always installed; the average capacity is at
least 100 L/m
2
of collector (2.4 gallon/ft
2
). If an intermediate fluid is used, heat
exchangers with high effectiveness must be installed.
With hot-air systems, thermal storage with rock bed can be used, if necessary.
Generally, these systems are difficult to justify from the economic and technical
points of view for use in factories and in buildings.
4.3.2 Photovoltaic Systems
Electric energy can be produced from solar energy by using photovoltaic silicon
cells. As a general indication, the voltage across one cell is 0.5 V and it is
independent of the solar energy rate to which the electric current fed to the load
is linearly related. In practice, cells are mounted on a module and the modules are
arranged in panels or arrays in series, in parallel, or in combined series/parallel.
The efficiency, that is the ratio between the electric power generated and
the solar energy rate, is not more than roughly 15 % for standard
applications. That means that 1 m
2
of cells will produce not more than
75 W with an average solar energy rate of 500 W/m
2
.
The electric energy produced by a series of cells must be stored in an accumulator
storage system.
The equivalent operating hours at the peak power range from 1,000 to 2,000 h/
years depending on the geographical location.
4.3.3 Solar Concentrated Solar Power Systems
Solarenergyisusedtoheatafluidathightemperatures by means of concentrator
systems like parabolic collectors (concentration factor less than 100), solar
tower (concentration factor 300-1,000), or parabolic concentrators (concentration
factor 1,000-3,000). The greater the concentration factor is, the higher the
temperatures of the heated fluid (water and steam), in most cases from 300 to
600
Candmore.
A classical thermodynamic cycle is then used to produce electricity.
Solar concentration systems are suitable for utility plants, with an electric
output power higher than 10-20 MW (the surface of concentrator is 50,000-
100,000 m
2
) and a total efficiency, the ratio between input solar and output
electrical energy, about 30 %. Notice that in case of solar tower and parabolic
concentrators heat storage is possible before entering the electric power section of
the plant.
