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DESIGN AND OPTIMIZATION OF PARABOLIC TROUGH ORGANIC
RANKINE CYCLE POWERPLANTSAndrew C. McMahan
Sanford A. KleinDouglas T. Reindl
University of Wisconsin - MadisonSolar Energy Laboratory
July 12, 2006
Summary
• Optimal design of power cycles for solar-thermal applications requires techniques different from those used in traditional powerplant design
Background• Organic Rankine Cycles
– Organic working fluids (toluene, n-pentane)– Well suited for lower resource temperatures– Used extensively in geothermal applications– Compact, economical design relative to steam Rankine cycles
Österreichische 400 kW ORC
Power CycleResourceInlet Tin = Const.
= Const.
ResourceReturn
Optimal Powerplant Design: Traditional
Plant capital cost is a function of power cycle size (heat exchanger conductance, output)
W&m&
Power Cycle
Solar Field
Optimal Powerplant Design: Solar
• Solar Field and power cycle performance are coupled• Capital cost is a function of solar field and power cycle size• Solar “fuel” is a capital, rather than recurring, cost
W&
Typical capital cost break-down:• 75% Solar Field
• 25% Power Cycle
Solar Radiation
Case Study: Plant Description
• 1 MW Organic Rankine Cycle– n-pentane working fluid– Turbine exhaust recuperation
• Parabolic-trough solar field– Synthetic oil heat transfer fluid
Case Study: Process
Power Cycle Model*
Solar Field Model
Power Cycle Cost Model
$=f(size, output) Solar Field Cost Model
$=f(size)
IR
Boiler PressureHeat Exchanger AreaHeat Exchanger Allocation
*Power Output Fixed
Case Study: Results
• No Change in Power Output
• 5% Increase in total power plant heat exchanger size– 30% Increase in power cycle efficiency
– 24% Increase in solar-to-electric efficiency
– 23% Decrease in solar field area
– 17% Decrease in investment ratio ($/kWNET)
Conclusion
• Optimal design of power cycles for solar-thermal applications favors higher efficiency power cycle operation than traditional powerplants in order to mitigate solar field cost.