Simulation and Performance Evaluation of Parabolic Trough Solar Power Plants
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- University of Wisconsin-Madison
- Patnode, A.M. (2006). Simulation and Performance Evaluation of Parabolic Trough Solar Power Plants. Master's Thesis, University of Wisconsin-Madison.
Thesis (M.S.)--University of Wisconsin--Madison, 2006.; Dissertations Academic Mechanical Engineering.; University of Wisconsin--Madison. College of Engineering.
- Nine Solar Electric Generation Systems (SEGS) built in southern California between 1984
and 1990 continue to produce 14-80 [MWe] of utility-scale electric power each from solar
thermal energy input. The systems collect energy using a synthetic heat transfer fluid
pumped through absorber tubes in the focal line of parabolic trough collectors. The heated
fluid provides the thermal resource to drive a Rankine steam power cycle.
A model for the solar field was developed using the TRNSYS simulation program. The
Rankine power cycle was separately modeled with a simultaneous equation solving software
(EES). The steady-state power cycle performance was regressed in terms of the heat transfer
fluid temperature, heat transfer fluid mass flow rate, and condensing pressure, and
implemented in TRNSYS. TRNSYS component models for the steam condenser and cooling
tower were implemented in the simulation as well. Both the solar field and power cycle
models were validated with measured temperature and flow rate data from the SEGS VI plant
from 1998 and 2005. The combined solar field and power cycle models have been used to
evaluate effects of solar field collector degradation, flow rate control strategies, and
alternative condenser designs on plant performance.
Comparisons of measured solar field outlet temperatures between 1998 and 2005 indicate
some degradation in field performance. The degradation in performance over time may be
attributed, in part, to loss of vacuum in the annulus surrounding the absorber tube. Another
potential contributor to solar field degradation is hydrogen accumulation in the annular
space; hydrogen may dissociate from the synthetic heat transfer fluid and permeate through
the absorber tube into the annulus. The thermal losses and resultant outlet temperatures are
modeled assuming 50% of collectors experience some loss of vacuum and/or hydrogen
permeation. The loss in electric power from the cycle is quantified as a function of the
prevalence of vacuum loss and hydrogen accumulation in the field.
The electric power output from the system at a given incident radiation depends on the
system efficiency, defined as the product of the solar field efficiency and the power cycle
efficiency. The solar field efficiency will decrease with increasing outlet temperature, while
the power cycle efficiency will increase with increasing outlet temperature. The magnitude
of these competing trends is such that the net change in system efficiency with outlet
temperature is small.
The SEGS plants use induced draft cooling towers for heat rejection. Cooling towers provide
an effective means of heat rejection, but require makeup water to compensate for evaporative
losses. The use of air cooled condensers can reduce plant water consumption; however,
system efficiency suffers with the higher condensing pressure. The optimal size of an air
cooled condenser unit is evaluated, and its performance assessed and compared to that of the
current condenser/cooling tower system.
- Under the supervision of Professor Sanford A. Klein
- Sponsored by the National Renewable Energy Laboratory under
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