Basic Research Needs for Solar Energy Utilization

Figure 14 Three types of solar concentrators utilizing (a) linear collectors that focus on tubular receiver,
(b) central receiver (solar power tower) with heliostat field that tracks the sun, and (c) on-axis tracking
system with parabolic dish concentrator

On-axis Tracking Systems. On-axis systems, such as parabolic dish concentrators
(Figure 14c), provide the highest optical efficiency of all the concentrating solar systems. Their
main drawback is the concentrator size, which is limited by practical structural consideration.
Recent progress in the development of small Brayton engines provides the option of using a
dish/Brayton system as an alternative to the dish/Stirling system.

Estimates of large-scale (>50-MW) dish/Stirling facility costs are about $2.5/W (Stoddard et al.
2005), although the current costs, based on several demonstration systems, are three to four times
higher (Mancini et al. 2003). A recent study (Pitz-Paal et al. 2005) indicates that new
developments in current areas of research can reduce cost by more than $0.5/W. Other estimates,
by Stirling Energy Systems (Stoddard et al. 2005), suggest even a larger potential cost reduction.
The uncertainty in all of these estimates is considered to be large.

The development areas suggested in the Priority Research Directions should lead to the cost
reductions required to make this technology competitive with conventional electricity production
within five to ten years, assuming fossil fuels remain at present prices.

HeliostatField

Receiver & PowerConversion Unit

Heliostats

Solar Tower Reflected Light Beams

Structure

Direct Sunlight Tubular Receiver

Linear Collector

Concentrated

Sunlight

Rotational

Axis

Receiver & Power

Conversion Unit Parabolic

Dish

Concentrator

Concentrated

Sunlight

c

a b