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Solar Power Plant Technology

Technology for Solar power plants

Solar power generation technologies can be broadly classified into two broad
categories:
• Solar Photovoltaic technologies
• Solar thermal power plants

Solar Photovoltaic (SPV) technologies
Photovoltaic converters are semiconductor devices that convert part of the incident
solar radiation directly into electrical energy. The most common PV cells are made
from single crystal silicon but there are many variations in cell material, design and
methods of manufacture. Solar PV cells are available as crystalline silicon,
amorphous silicon cells such as Cadmium Telluride (Cd-Te), Copper Indium
diselenide, and copper indium gallium diselenide (CIGS), dye sensitised solar cells
DSSC and other newer technologies such as silicon nano particle ink, carbon
nanotube CNT and quantum dots.

Crystalline silicon (c-Si) modules represent 85-90% of the global annual market
today. C-Si modules are subdivided in two main categories: i) single crystalline (scSi) and ii) multi-crystalline (mc-Si).

Thin films currently account for 10% to 15% of global PV module sales. They are
subdivided into three main families: i) amorphous (a-Si) and micromorph silicon (aSi/μc-Si), ii) Cadmium-Telluride (CdTe), and iii) Copper-Indium-Diselenide (CIS) and
Copper-Indium-Gallium-Diselenide (CIGS).
Emerging technologies encompass advanced thin films and organic cells. The latter
are about to enter the market via niche applications. Concentrator
technologies (CPV) use an optical concentrator system which focuses solar radiation
onto a small high-efficiency cell. CPV technology is currently being tested in pilot
applications.
The above technologies are mainly used on roof tops of commercial and residential
buildings, and as large scale grid connected power plants. For optimum output,
larger installations use tracking devices which change the orientation of the panels to
correspond with the trajectory of the sun to focus sunlight directly onto the panels.

Solar thermal power plants
Solar thermal power plants produce electricity by converting the solar radiation into
high temperature heat using mirrors and reflectors. The collectors are referred to as
the solar-field. This energy is used to heat a working fluid and produce steam. Steam
is then used to rotate a turbine or power an engine to drive a generator and produce
electricity
All CSP plants are based on four basic essential systems which are collector,
receiver (absorber), transport/storage and power conversion. Parabolic Trough,
Solar towers, Parabolic Dishes and Linear Fresnel Reflectors are the four main
technologies that are commercially available today

Parabolic trough
Parabolic trough shaped mirrors collect and reflect the solar energy onto receiver
tubes positioned along the focal line of parabolic mirrors. The troughs are usually
designed to track the Sun along one axis, predominantly north–south. Heat transfer
fluids, such as synthetic thermal oil suitable for temperatures up to 400 °C,
circulating through the tubes are used to generate steam through heat exchangers
and steam generators and drive turbine to generate electricity through a steam cycle.
This is a well established and proven CSP technology.
Solar Towers
A circular array of heliostats concentrates sunlight on to a central receiver mounted
at the top of a tower. The heliostats tack the sun on two axes. The central receiver
can achieve very high concentrations of solar irradiation thus resulting in extremely
high temperature for the operating fluid. A heat-transfer medium in this central
receiver absorbs the highly concentrated radiation reflected by the heliostats and
converts it into thermal energy, which is used to generate superheated steam for the
turbine through the Rankine cycle. Brayton cycle systems are also under testing
because of the higher efficiencies. Spain has several solar tower systems operating
or under construction, up to 20 MW capacity.
Parabolic Dish
The parabolic shaped dish tracks the sun, through a two axis movement, onto a
thermal receiver mounted at the focal point. The concentrated beam radiation is
absorbed into a receiver to heat a fluid or gas to approximately 750°C. This fluid or
gas is then used to generate electricity in a small piston or Stirling engine or a micro
turbine.
Dish technology produces relatively small amount of electricity compared to other
CSP technologies – typically in the range of 10 to 25 kW which results in high capital
costs.
Linear Fresnel Reflectors
Use reflectors made of several slices of mirrors with small curvature approximating a
parabola. Mirrors are mounted on trackers and configured to reflect sunlight onto
elevated linear reflectors. Water flows through the receivers and is converted into
steam and the intermediate heat transfer fluid is not required. These systems have
lower investment costs and also lower optical performance as compared to parabolic
trough collectors. This technology is still in the developmental stage.