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Solar Parabolic Dish CSP

Page history last edited by Blake Langdon 13 years, 5 months ago

Parabolic Dish Concentrating Solar Power

Solar Parabolic dishes are two-axis tracking solar concentrators that use reflective, parabolic dishes to focus all collected direct sun radiation to a single focal point (instead of one line as with parabolic troughs). Typically this thermal energy is coupled with a Stirling engine where it is converted to mechanical energy which is then converted to electrical energy. Current manufactured parabolic dishes range in power from 3 to 25 kW. Multiple solar dishes are installed on one sight to produce a significant amount of energy. There is currently a 500 MW plant proposed in southern California which will consist of 20,000 (25 kW/unit) dish array.

The Stirling engine converts heat energy to mechanical work via the Rankine cycle with an appropriate working fluid. Hydrogen is commonly used as the working fluid but helium, nitrogen, air, and methane can be used as well. In a Stirling engine, ‘working fluid’ in gas form inside of a cylinder is heated via an external source (compared to an internal source in a combustion engine), in this case solar thermal energy. The heated gas expands forcing a cylinder to move and turns a shaft. The gas is then transferred to another cylinder where it is cooled (by ambient air) then pumped back into the original cylinder where it is heated and expanded again.

Advantages

High conversion efficiency

Parabolic dishes are the most efficient solar to electricity technology at >30%. This efficiency is achieved by a high concentration ratio (reflector area to thermal point area) resulting in high temperature and a greater heat energy to electricity conversion (higher T_high).

Scalable

Unlike central receiver systems and other large power plants, parabolic dishes are modular, allowing for many different size deployments from a single 10kW dish to a large field of dishes of 750 MW solar capacity (as planned in Imperial Valley California with Imperial Valley-Solar Two).

Low water use

Parabolic dish electricity generation requires no water consumption. This is very attractive for large desert installations where water is scarce. Water is only needed to wash mirrors.

Disadvantages

Expensive

High maintenance costs are required to upkeep Stirling engine moving parts. Two-axis tracking systems are required to control these moving dishes systems, which also include the heavy Stiriling engine. Parabolic mirrors are usually utilized rather than cheaper flat mirrors.