Page 259 - Design of Solar Thermal Power Plants

242 4. DESIGN OF THE CONCENTRATION SYSTEM

2. The level-land requirement of a solar tower’s heliostat field is lower
than that of a parabolic trough as long as the adjacent rows of
heliostats satisfy no-shading and no-blocking conditions. In the
case where mountains are located south of the heliostat field,
construction costs for the heat-absorbing tower can be reducing the
building height of the tower. In the case where mountains are
located to the north, the blocking of front-and-back neighboring
heliostats in the heliostat field will be comparatively small.
3. The total mirror area of a solar tower heliostat field shall be
determined in accordance with the requirements of the design
point while satisfying the capacities of a steam turbine and thermal
energy storage system and the requests of time-dependent
grid-connected power generation.
4. The azimuth of the rotating axis of a parabolic trough concentrator
shall be determined by considering local longitude and latitude
and seasonally stepped grid-connected electricity prices. Generally,
the efficiency of a westeeast axis parabolic trough concentrator
during summer is higher than for one with a northesouth axis, and
the annual average efficiency of a northesouth axis concentrator is
higher than for one with a westeeast axis.
5. For the case of considering the growing of green plants within the
heliostat field during the local plant growing season (usually
AprileSeptember annually in northern areas), the sunshine
percentage on the land where plants grow should not be less than
70%, which can be designed using solar-concentrating field
optimization software.
6. When considering the growth of ground plants, the water used for
cleaning mirror surfaces shall be free of alkaline and grease
constituents. For a parabolic trough power plant using heat-
transfer oil as its medium, oil-unloading and firefighting channels
shall be designed within the solar field.
7. The solar-concentrating field layout should consider controller
grounding, lightning protection, and the intersection of the
communication cables with the high-temperature fluid pipeline.
The pipeline should be designed with consideration given to
cleaning vehicle access.
8. Maintenance space for concentrators should be reserved during
design. Major maintenance includes maintenance of the gearbox
and supporting frame deformation. Maintenance for mirror
damage and replacement requires a small space, and thus it is not
necessary to preserve additional space.
9. Due to the long length of the high-temperature, high-pressure
pipeline of a parabolic trough concentrator, leakage monitoring
and alarming facilities as well as solar field firefighting facilities