Cavity Receivers for Parabolic Solar Troughs
A tubular heat-absorbing element partly enclosed in an insulating layer or jacket, has absorbing surface that is accessible to solar radiation. The thermal insulation is designed to provide entry to solar radiation by way of a cavity. The absorbing surface can be substantially planar.
1 . A system for generating energy from solar radiation as part of a solar power system, said system comprising:
a plurality of linear receivers, each of said plurality of linear receivers including at least a solar radiation absorbing element designed to absorb an incident flux of solar radiation and transfer an absorbed flux of energy to a heat transfer medium, said heat transfer medium designed to receive and transport at least a portion of said absorbed flux of energy, at least a portion of said radiation absorbing element being covered with a solar selective absorber, said solar selective absorber having a thermal emittance value and an optical absorptance value, said optical absorptance value being different from said thermal emittance value;
a parabolic trough mirror collector for concentrating solar radiation onto said plurality of linear receivers;
a control system for directing said parabolic trough mirror at the sun,
wherein said heat transfer medium circulating in a first receiver in said plurality of linear receivers is heated by solar radiation from a first elevated temperature T 1 to a second elevated temperature T 2 over a first distance corresponding to a length of said first receiver and said heat transfer medium circulating in a second receiver in said plurality of linear receivers is heated by solar radiation from a third elevated temperature T 3 to a fourth elevated temperature T 4 over a second distance corresponding to a length of said second receiver, where T 4 >T 3 ≧T 2 >T 1 , said first receiver and said second receiver having structures designed for operation in different temperature ranges.
2 . The linear solar receiver of claim 1 , wherein the portion of the radiation absorbing element being covered with the solar selective absorber for said first receiver is greater than the portion of the radiation absorbing element being covered with the solar selective absorber for said second receiver.
3 . The linear solar receiver of claim 1 , wherein said first portion of said outer surface of said solar radiation absorbing element is substantially planar.
4 . The linear solar receiver of claim 1 , wherein said first portion of said outer surface of said solar radiation absorbing element comprises a fraction in the range of 0.50 to 0.20 of an area of said outer surface of said solar radiation absorbing element determined on a per unit length basis.
5 . The linear solar receiver of claim 1 further comprising a glass cover enclosing the solar radiation admitting region.
6 . The linear solar receiver of claim 5 wherein an inert gas is introduced into the radiation admitting region.
7 . The linear solar receiver of claim 1 , wherein said interior surface of said solar radiation admitting region forms a compound parabolic collector.
8 . The linear solar receiver of claim 1 , wherein said interior surface of said solar radiation admitting region is a reflective surface.
9 . The linear solar receiver of claim 1 , wherein said heat transfer medium is selected from the group consisting of a molten solar salt, a molecular silicone based fluid, and steam.
10 . The linear solar receiver of claim 1 , wherein said linear receiver has a thermal efficiency, said thermal efficiency selected from the group consisting of 94 percent at 450 degrees Celsius and 92 percent at 500 degrees Celsius, 89 percent at 550 degrees Celsius, 85 percent at 600 degrees Celsius, 80 percent at 650 degrees Celsius.
11 . The linear solar receiver of claim 1 in combination with an energy collection system configured to operate a Carnot cycle energy recovery machine.
12 . The linear solar receiver of claim 1 in combination with a plurality linear solar receivers, said linear solar receivers each including at least solar radiation absorbing elements, adjacent solar radiation absorbing elements forming a nearly continuous absorbing surface.
13 . The linear solar receiver of claim 1 in combination with a plurality linear solar receivers, a first one of said plurality of receivers operating at a first temperature and a second one of said plurality of receivers operating at a second temperature, said first receiver and said second of said plurality of receivers having different designs, said first and said second temperatures being different.
14 . The linear solar receiver of claim 1 , further comprising a symmetric parabolic trough collector mirror structure having a rim angle of less than 75 degrees, said symmetric parabolic trough collector mirror structure focusing said incident flux of solar radiation on said solar radiation absorbing element, said linear solar receiver disposed between said symmetric parabolic trough collector mirror structure and the sun.
15 . The linear solar receiver of claim 1 , further comprising a symmetric parabolic trough collector mirror structure, said symmetric parabolic trough collector mirror structure being held in a substantially rigid form with cable suspension.
16 . The linear solar receiver of claim 1 , wherein at least a portion of said absorbed flux of absorbed energy is used to perform an action chosen from the group consisting of generating electricity and completing an industrial process.
17 . The linear solar receiver of claim 1 , wherein said solar selective absorber is a plasmonic nanochain cermet structure.