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SOLAR THERMAL POWER systems use concentrated solar
radiation as a high temperature energy source to produce electrical power.
These clean energy technologies are appropriate for applications where direct solar radiation
is high. The first commercial plants have been in operation in California since the mid-1980s,
providing 354 MW of solar power.The many types of systems under development (including
parabolic troughs, power towers,and dish/engine systems) for different markets vary
according to the concentration devices,energy conversion methods, storage options and other
design variables. Solar radiation can also drive chemical reactions for the production of fuels
and chemicals. Additional uses include environmentally benign technologies in fields such
as detoxification of chemical wastes and energy storage which are aimed at the medium to
long term.
1. Parabolic troughs solar collector system
A parabolic trough solar collector is part of a solar
collector field, designed to collect heat from the sun. Solar radiation is concentrated via
parabolic curved solar reflectors to a heat collecting element (HCE) located in the optical focal line
of the collector. The solar collectors are continuously tracked to direct to the sun. A heat
transfer fluid is circulated inside the HCE tubes and transports the absorbed energy to a conventional
power block where electricity is generated (see figure 1). The smallest subunits of the
collector field, the so-called solar collector ele ments (SCE) are shown in figure 2. They are
made up of a steel space frame structure of approx. 12 m length. 28 curved solar
reflectors are attached to the steel structure in 4 rows, forming the parabolic collector with approx. 12
m length and 5.76 m width. The absorber or HCE is fixed to the steel structure by means
of steel supports, one at every 4 m.Each SCE is supported at its end by pylons. They are
provided with plain bearings, allowing for rotation along the collector longitudinal axis. 12
SCES form the solar collector assembly (SCA) with a length of approx. 150 m. All collectors of
the SCA are connected by means of torque transfer units to permit joint movement. Therefore
the pylon in the middle of the 12 SCES is equipped with a hydraulic drive unit. 4 SCAs are
combined to a so-called solar collector loop. Within the loop all absorbers (HCEs) are
connected, the heat transfer fluid flows through all of them, heating up in every collector.
2. Solar power tower systems
A short description of the major Solar
Power Tower (SPT) System Elements follows. In figure 3, an image of a SPT
plant and figure 4 its main components and their relationship are shown.
2.1. Collector System (CS)
The CS contains the collector field and heliostats that redirect and
focuses sunlight on the receiver. The major system elements are two-axis
tracking mirrors (heliostats), heliostat controllers (HCs), heliostat
array controller (HAC), and communications link between the HCs and the
HAC. The number of heliostats will vary for a particular receiver thermal
duty and a specific heliostat design.
2.2. Receiver System (RS)
The RS converts the redirected solar flux into thermal energy. The
receiver is a cylindrical tube wall heat exchanger that heats molten
nitrate salt from 290°C (550°F) to 565°C (1050°F) and includes the
associated piping, valves and controls and unique RS control system
2.3. Steam Generation System (SGS)
The SGS uses thermal energy from the hot nitrate salt to produce
superheated steam at the conditions required by the turbine-generator and
auxiliary steam systems.
2.4 Thermal Storage System (TSS)
The TSS stores high temperature nitrate salt 565°C (1050°F) from the
receiver for use by the steam generator, and stores low temperature
nitrate salt 290°C (550°F) from the steam generator for use by the
receiver. The TSS system components are the: cold nitrate salt tank;hot
nitrate salt tank; pressure relief valves (over- and under- pressure
relief); tank foundations;nitrate salt inventory; tank immersion heaters
and tank insulation system.
2.5 Master Control System (MCS)
The MCS controls and monitors all SPT process functions for all system
equipment through all states and transitions in response to operator
commands. The MCS is comprised of the following major subsystems: a
Distributed Control System (DCS), Heliostat Array Controller (HAC) and
Administrative and Data Analysis System.
2.6 Electric Heat Tracing System (EHTS)
The EHTS provides nitrate salt freeze protection to all process equipment
and components;thermal conditioning of all process equipment and
components for plant startup, and protects equipment from extreme thermal
gradients and excessive thermal stresses
2.7 Electric Power Generation System (EPGS)*
The electric power generation system converts the energy in the main steam
into electric power for delivery to the electric grid. The EPGS consists
of the turbine-generator and asociated equipment.
2.8. Balance of Plant (BOP)
The BOP supports all other plant systems and includes, among other: Switch
yard / main power distribution system, emergency and uninterruptible power
supply system, RS tower cranes. |
