Basic Research Needs for Solar Energy Utilization - Office of ...
Basic Research Needs for Solar Energy Utilization - Office of ...
Basic Research Needs for Solar Energy Utilization - Office of ...
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
BASIC RESEARCH CHALLENGES FOR SOLAR THERMAL<br />
UTILIZATION<br />
CURRENT STATUS<br />
<strong>Solar</strong> thermal utilization can be categorized into low-temperature solar thermal systems, which<br />
may not involve sunlight concentration, and high-temperature solar thermal systems, which<br />
require sunlight concentration. Concentrated photovoltaics (CPVs), although not a solar thermal<br />
process, crosscuts with solar thermal utilization through the use <strong>of</strong> concentrators.<br />
High-temperature <strong>Solar</strong> Thermal Systems<br />
High-temperature solar systems use various mirror configurations to concentrate the light and<br />
then convert the sun's energy into high-temperature heat. The heat can be converted into<br />
electricity through a generator, or it can be used to drive chemical reactions. A plant consists <strong>of</strong><br />
three parts: an optical system that collects and concentrates the light, a receiver or reactor that<br />
converts the light to heat, and an “engine” that converts heat to electricity or “reactor” that<br />
converts heat to chemical potential.<br />
We will survey the principles and state <strong>of</strong> the art <strong>of</strong> the optical systems used <strong>for</strong> concentration,<br />
discuss the engines or other components that convert the concentrated heat into electricity, and<br />
finally evaluate the state <strong>of</strong> the art <strong>for</strong> reactors that convert the heat into chemical fuels.<br />
<strong>Solar</strong> Concentrators<br />
The current status <strong>of</strong> solar concentrators, including current research directions, is treated in the<br />
<strong>Solar</strong> Thermal Technology Assessment, Appendix 1. We <strong>of</strong>fer a brief survey <strong>for</strong> the convenience<br />
<strong>of</strong> the reader.<br />
Line Focus Systems. In line focus systems, incident sunlight is “folded” from a plane to a line.<br />
In most cases, the optical configuration is that <strong>of</strong> a trough tracking the sun from east to west and<br />
a target that rotates accordingly (Figure 14a). The main inherent advantage <strong>of</strong> the system is its<br />
compatibility with large engines (i.e., steam turbines <strong>of</strong> hundreds <strong>of</strong> megawatts). The main<br />
inherent disadvantage is the low operating temperature, limited to less than 750K by the<br />
relatively low concentration and long tubular receiver configuration. Lower temperatures reduce<br />
the efficiency <strong>of</strong> the heat transfer to the fluid located in the tubular receiver; this fluid provides<br />
the thermal energy to drive electricity generation cycles. The current systems range from<br />
350 MWe to newer small-scale 1-MWe systems. Current installed cost is approximately $3/W;<br />
the short-term goal is to reduce this cost to $2/W.<br />
57