Ultra high efficiency, high temperature solar collection and storage

Abstract

High-temperature solar trap collectors provide near ambient temperature solar entry surfaces and negligible thermal radiation losses by counterflowing low velocity transparent gases or liquids (fluids) to nullify internal thermal diffusion and radiative heat losses at the solar entry surface. Small steradian (sr) baffling plus wavelength-selective materials trap the entire 0.35 u to 2.7 u incoming solar spectrum and heat highly absorbing internal surfaces to high temperatures; only a small solid angle of the 2π steradians—on the order of 0.01 sr—of internal thermal radiation escapes. A nearly 100% efficient flat panel solar trapping embodiment exhibits alpha (α) absorption nearing 1.0 and radiant emission losses nearing 0.0 even at solar collection temperatures in excess of 1,000° K. Ultra high collection efficiency counterflow configurations are ideal for solar hot water, space heating, cooling, energy storage, and electric power generation applications.

1 . An exceptionally high efficiency, high temperature; solar energy collector, comprising:
 an enclosure having a front portion and a rear portion;   a solar entrance at said front portion to allow incoming solar radiation to enter said enclosure;   a fluid inlet at said front portion of said enclosure to receive a counterflowing working fluid at substantially ambient temperatures;   at least one baffle positioned laterally across said enclosure between said front and rear portions to guide the flow of said fluid through said enclosure toward said rear portion, said at least one baffle allowing said incoming radiation to be nearly fully absorbed and converted to heat within said enclosure;   a fluid exit at said rear portion,   wherein said at least one baffle further preventing radiation which is generated within the enclosure from escaping, whereby the fluid is heated and exits the enclosure at said fluid exit as a highly heated working fluid.   
     
     
         2 . The energy collector of  claim 1 , further comprising a solar spectrum absorption surface within the said enclosure, wherein said baffle permits an effective passage of said counterflowing fluid between said solar entrance surface and said absorption surface. 
     
     
         3 . The energy collector of  claim 2 , further comprising a plurality of baffles within said enclosure, each said baffle being gradually heated by reradiated and conductive energy within said enclosure and by incoming solar energy, as said working fluid flows from said front portion of the enclosure where it is at ambient temperature, toward said rear portion, whereby said fluid exits the enclosure as a very high temperature working fluid. 
     
     
         4 . The energy collector of  claim 3 , wherein said solar incoming radiation heats said fluid, said baffles, and said rear portion, wherein said heated fluid and heated baffles reradiate energy, and wherein each baffle is fabricated of, or is coated by, a material which exhibits selective wavelength absorption, whereby solar radiation passes through said baffle toward said rear portion and reradiated energy is substantially prevented from reaching said front surface. 
     
     
         5 . The energy collector of  claim 3 , wherein said baffles are honeycombs which exhibit angular selectivity to impinging radiation, wherein said incoming solar radiation heats said fluid, said baffles, and said rear portion and any reradiated energy from said heated fluid, said heated baffles, or said rear portion is substantially prevented from reaching said front portion. 
     
     
         6 . The energy collector of  claim 1 , wherein said at least one baffle produces substantially laminar fluid flow in said enclosure in a direction that is substantially perpendicular to the direction of said incoming solar radiation and also follows a serpentine counterflow path from said front portion to said rear portion. 
     
     
         7 . The energy collector of  claim 6 , wherein said at least one baffle is nonporous and transparent to incoming radiation and exhibits an index of refraction substantially the same as the working fluid flowing through the enclosure. 
     
     
         8 . The energy collector of  claim 7 , further comprising a plurality of baffles in said enclosure to produce said serpentine path, wherein said incoming radiation is solar energy to heat said fluid and said rear portion, wherein said heated fluid and said heated rear portion reradiate energy, and wherein each baffle exhibits selective wavelength absorption, whereby solar radiation passes through said baffles toward said rear portion and reradiated energy is substantially prevented from reaching said front surface. 
     
     
         9 . The energy collector of  claim 1 , wherein the rear portion of said enclosure incorporates a solar spectrum absorber. 
     
     
         10 . The energy collector of  claim 8 , wherein said solar entrance includes a transparent aperture for admitting said solar radiation. 
     
     
         11 . The energy collector of  claim 1 , wherein said solar entrance includes a transparent aperture for admitting said solar radiation. 
     
     
         12 . A method for collecting solar radiant energy, comprising the steps of:
 directing solar radiant energy through a front portion of an enclosure toward a solar spectral absorbing rear portion of the enclosure to trap heat in the enclosure;   supplying a counterflowing working fluid to said enclosure at a relatively low temperature;   causing said fluid to flow generally away from said front portion of the enclosure toward said rear portion of the enclosure to be heated by absorbed incoming solar radiant energy in said absorbing rear portion;   preventing heat from within said enclosure from exiting said enclosure while the fluid is still within said enclosure; and   directing heated fluid out of said enclosure.   
     
     
         13 . The method of  claim 12 , further including causing the working fluid to have a substantially laminar flow within said enclosure in a direction generally perpendicularly away from said front portion. 
     
     
         14 . The method of  claim 12 , wherein the step of preventing heat from within the enclosure from exiting includes wavelength-selectivity. 
     
     
         15 . The method of  claim 12 , wherein the step of preventing heat from within the enclosure from exiting includes angular-selectivity. 
     
     
         16 . The method of  claim 12 , further including thermally insulating the enclosure. 
     
     
         17 . The method of  claim 12 , wherein causing said fluid to flow generally away from said front portion of the enclosure toward said rear portion of the enclosure includes providing a plurality of wavelength selective or angle selective baffles. 
     
     
         18 . The method of  claim 12 , wherein causing said fluid to flow generally away from said front portion of the enclosure toward said rear portion of the enclosure includes a plurality of flow-direction baffles extending across said enclosure. 
     
     
         19 . The method for making a solar energy collector, comprising the steps of:
 providing an enclosure having a front portion and a rear portion;   providing a solar entrance at said front portion to allow incoming solar radiation to enter said enclosure;   providing a fluid inlet at said front portion of said enclosure to receive a counterflowing working fluid at substantially ambient temperatures;   providing at least one baffle positioned laterally across said enclosure between said front and rear portions to guide the flow of said fluid through said enclosure toward said rear portion, said at least one baffle allowing said incoming radiation to be nearly fully absorbed and converted to heat within said enclosure; and   providing a fluid exit at said rear portion,   wherein said at least one baffle further preventing radiation which is generated within the enclosure from escaping, whereby the fluid is heated and exits the enclosure at said fluid exit as a heated working fluid.   
     
     
         20 . The method of  claim 19 , wherein said baffles are honeycombs which exhibit angular selectivity to impinging radiation.