Abstract:
The most common type of concentrating solar power (CSP) plant in operation today
is the parabolic trough plant. In recent years molten salt power tower plants have
demonstrated the benefit of using molten salt as heat transfer fluid and a storage
medium. New research has shown that molten salt can be used in parabolic trough
technology in a similar manner. This thesis documents an investigation into both
technologies in order to compare them on a qualitative and quantitative basis.
South Africa has become a hotspot for the development of CSP thanks to the
abundant solar resource and the implementation of the Renewable Energy
Independent Power Producer Procurement Program (REIPPPP) in the country.
South Africa therefore provides a realistic backdrop for the comparison of the two
CSP technologies.
Parabolic trough and a power tower simulation models are constructed for the
comparison of the two technologies. Meteorological data for six selected sites in
South Africa are used to simulate the performance of both of the technologies, while
operating under a flat feed in tariff and a two-tiered feed in tariff.
Results of plant simulations show that molten salt can be used effectively as heat
transfer fluid in parabolic trough technology. Parabolic troughs are shown to have
higher annual optical efficiency compared to power towers. The main drawback of
the parabolic trough technology is the thermal losses experienced in the field during
overnight recirculation of the hot molten salt.
Parabolic trough solar fields show a large seasonal variation in efficiency while
power tower plants are shown to benefit from relatively consistent solar field
efficiency throughout the year. The seasonal variation in solar field efficiency results
in substantially higher thermal energy being available in the summer than in the
winter, thereby resulting in storages being filled and the subsequent dumping of
solar energy in parabolic trough plants.
A simple cost model is built to compare the financial performance of the two
technologies and allow for the optimization of the plants according to levelized cost
of electricity (LCOE). At a site near Springbok in the Northern Cape Province
optimization of both plant types resulted in an estimated LCOE of 0.127 USD/kWhe
and 0.129 USD/kWhe for parabolic trough and power tower plants respectively.
This study demonstrates that both parabolic trough and power tower plants require
careful consideration when selecting the most appropriate CSP technology for a
given location. Depending on the available solar resource and the tariff structure
under implementation, this thesis finds that both parabolic trough and power tower
plants can offer competitive CSP solutions with their own set of strengths and
weaknesses.
