Patent Application
20230383995
The present invention generally relates to the field of solar collectors and solar concentrators. Specifically, embodiments of the present invention relate to novel solar collectors that utilize a wide-angle, nonimaging optical concentrator that is non-self-shading, thus eliminating the need for spacing between the collectors, and providing for efficient roof top and/or land use.
In the last two decades there have been two major solar energy success stories. The first is silicon photovoltaic collectors (PV), which has reached at least 700 GWel of installed capacity. The second is low temperature solar thermal collectors, which has reached at least 500 GWth, of installed capacity driven primarily by evacuated tube collectors (ETC) and flat plate collectors (FPC) for domestic hot water. These successes demonstrate how policy can trigger a self-reinforcing cycle of technology improvement and market expansion. Today PV is largely considered competitive with fossil fuels, and still reducing in cost.
Currently, about two thirds of the industrial process heat is consumed at temperatures below 250° C., which is ideally suited for solar thermal technologies. Despite this technical potential, solar thermal is not yet widely adopted because of the following key barriers to the use of the technology:
Achieving significant adoption of solar industrial process heat (SIPH) requires that technology overcome at least a majority of these barriers. The technologies which have become widely adopted worldwide, namely PV, flat-plate collectors (FPC) and evacuated tube collector (ETC) are simple to install and can be installed in small (as little as 1 KW) project sizes. Generally, large projects require significant upfront financing to provide cost reductions, and if financing fails to materialize, large projects may fail. Technologies that can enter the market at smaller scales have opportunities to demonstrate performance and learn with much lower risk, and can then rapidly scale up to achieve cost reductions.
The current U.S. Department of Energy, Solar Energy Technologies Office (SETO) goal for medium temperature process heat is $0.015/kWh compared to a natural gas price of $1/therm ($0.03/kWh), which provides for a 10 year payback time and a 294% 30 year internal rate of return (IRR). While the SETO goal provides a quicker payback time and higher IRR than residential PV technology, it is slightly less than commercial PV systems. Several technologies already offer quicker payback periods than PV. These other technologies, however, have not been adopted by the market on the same scale as PV because large industrial users often buy natural gas at a much lower wholesale price of $0.50/therm, thereby effectively doubling the solar payback times or halving the 30 year IRR. Additionally, the cost of land, permitting, or engineering is not factored in, which reduces returns. Thus, despite its potential, SIPH has yet to take hold in the market.
Therefore, it is desirable to provide modular (flexible), low cost, and high efficiency (as a function of land or roof area) solar thermal technologies.
The present invention advantageously provides a modular, low cost and efficient solar thermal collector with the capability to effectively utilize 100% of available roof or land area, and generate medium temperature (250° C. or less) process heat. The Non-tracking, Asymmetric, Shadeless (NASH) collector has the capability to generate heat at more than 200° C., where it can be used for approximately two-thirds of process heat applications. In preferred embodiments, wide-angle, nonimaging asymmetric optical reflectors have a solar acceptance angle of approximately 40 degrees, allowing for passive (stationary) solar tracking and the capture of a portion of the diffuse solar energy, which can be significant in cloudy or polluted regions. Additionally, in typical embodiments, an evacuated tube absorber provides efficient operation regardless of the external environmental conditions. The combination results in a lightweight and low-cost thermal collector that is easily roof or ground mounted. In typical embodiments, a flow-through piping design for the absorber assembly reduces the total pipe, insulation, fluid and installation costs, and reduces heat loss through the interconnection piping.
It is therefore an object of the invention to provide a highly efficient solar collector at operating temperatures from about 100° C. to about 250° C. where the thermal energy may be used to generate high-quality steam for industry.
It is also an object of the invention to provide a solar thermal collector with flexible installation and easy integration into industrial operations.
It is further an object of the invention to provide a modular solar collector that may be installed on a small or large scale, with the capability to deliver significant reduction in carbon emissions.
It is a further object of the invention to provide a low-cost thermal solar collector with a fast (less than 5-year) payback time.
It is a further object of the invention to provide a solar thermal collector with greater than a 50% thermal efficiency.
It is further an object of the invention to provide a thermal solar collector with an evacuated absorber having vacuum stability over a 30-year lifetime.
It is further an object of the invention to provide a solar collector that reduces the cost of solar heat below the SETO goal of $0.015 kWh.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, but not restrictive, of the invention. A more complete understanding of the improved solar thermal collector and the methods disclosed herein will be afforded to those skilled in the art.
Reference will now be made in detail to the preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the preferred embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications, and equivalents that may be included within the spirit and scope of the invention. Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will readily be apparent to one skilled in the art that the present invention may be practiced without these specific details.
Embodiments of the present invention advantageously provide a novel solar thermal collector that is low-cost and non-tracking (the collectors do not move with the movement of the sun), and maximizes land (or rooftop) use of the solar field by eliminating the need for collector tilting, and which may generate heat at more than 200° C., thereby providing heat necessary for approximately two thirds of the process heat applications.
Embodiments of the NASH collector typically comprise: (1) a wide-angle, non-imaging asymmetric optical reflector comprising a reflective film; and (2) an absorber assembly positioned within the optical reflector. The absorber assembly typically comprises: (a) a transparent tube evacuated to a vacuum or partial vacuum; and (b) at least two pipes inside the transparent tube, each of the at least two pipes having a fluid flowing through the pipe, wherein solar energy is transferred to the fluid in the form of heat, the optical reflector is non-shading (i.e., the reflector does not cast shadows on adjacent collectors/reflectors), and an aperture of the reflector is parallel to a surface on which the solar collector is mounted.
Because the NASH reflectors/collectors are non-shading, they may be placed adjacent to one another on a surface with little or no space between the collectors, thereby providing for efficient use (100% or nearly 100%) of the area designated for the solar collection.
Referring now to
The absorber assembly 102 is positioned within the optical reflector 101 and generally comprises a transparent tube, evacuated to a vacuum or partial vacuum, which allows light rays to penetrate to the interior of the housing. In some other embodiments, the interior of the housing may comprise an inert gases (e.g., argon, helium, radon, etc.) In these embodiments, the inert gas most typically is argon at atmospheric pressure (1 atm.), although other gases and pressures may also be utilized.
The absorber assembly may be glass, PLEXIGLASS, polycarbonate, acrylic and/or other plastic materials having a high degree of light transmission, clarity and strength at the operating temperatures of the solar collectors discussed herein. Two or more pipes run inside the transparent tube, which absorb the thermal energy to produce heat, typically in a “flow-through” design configuration (see e.g.,
Because of the novel shape of its reflectors, the accepted range of the sun's position is approximately 40 degrees. This wide-angle optical design allows the NASH collectors to remain stationary as the optics provide passive solar tracking. This eliminates capital, operating, and maintenance costs associated with active trackers (collectors that move with the movement of the sun). It also allows the collector to capture a portion of the diffuse solar energy, which can be significant in cloudy or polluted regions. It also reduces assembly, material, and installation requirements and enables operation in dusty conditions. The evacuated tube absorber provides thermal efficient operation regardless of external environmental conditions. The combination results in a lightweight and low-cost non-tracking solar thermal collector, which is easily roof mounted for flexible use of available roof space.
The wide-angle optical design also allows NASH collectors to be placed adjacent to each other, without the need for spacing the collectors, thereby utilizing one hundred or nearly one hundred percent (100%) of a roof's area. This is best seen in reference to
As illustrated in
The low-profile collector provides several additional benefits. Wind loading will be much lower than with tilted collectors, and the low-profile collector reduces costs associated with collector mounting and/or racking.
Second, vacuum tubes currently used in conventional solar thermal collector technologies have been traditionally manufactured with fluid pipes in a U-tube configuration. A U-tube configuration, however, results in excessive solar field plumbing and thermal efficiency reductions up to one-third due to piping heat losses and the additional heat capacity of materials, which must be heated to operating temperatures.
In contrast, the NASH collector typically utilizes a flow-through configuration that incorporates the solar field distribution piping into the active collecting area of the collector. This eliminates a significant amount of piping, which has the dual effect of reducing total pipe, insulation, fluid, and installation costs as well as increasing the solar field thermal efficiency by reducing heat losses. To accommodate the thermal expansion in the vacuum tube due to the flow-through piping design, flexible copper pipes and/or tubes, or stainless steel bellows are utilized.
Imaging optical systems (e.g., parabolic troughs) require high optical accuracy to provide solar concentration. Typical angular tolerance with such systems is +/−1 degree to provide solar concentration. This requires foundational and structural material costs to maintain optical accuracy during normal wind loading, and may account for nearly half of the installed system cost.
On the other hand, the NASH collector has a wide angular acceptance (+/−40 degrees) which reduces structural requirements and allows for tolerance in module assembly and installation. It also allows much lower cost semi-specular mirror materials to be used instead of the high specular mirror materials required by high accuracy systems.
Vacuum receiver tubes used in conventional solar industrial process heat (SIPH) collectors (e.g., parabolic troughs) are built using housekeeping seals with heavy bellows to accommodate thermal expansion resulting from a temperature rise of 400° C. to 550° C. during vacuum baking. The vacuum receiver (absorber) tubes utilized in the NASH collector may be customized for medium temperature applications (up to 250° C.), allowing for the use of lighter bellows and/or flexible copper piping. Optimization of the metal-to-glass seal and heat transfer enables an approximately 7-10 times cost reduction for the NASH collector's medium temperature vacuum absorbers per selective absorber area (see e.g., the metal to glass seal of WO 2020/159613 A1, published Aug. 6, 2020, incorporated herein by reference).
The NASH design greatly simplifies installation, which may be as simple as laying down a module flat on a roof and tying together the plumbing connections (which, for example, may be quickly installed copper flare fittings, or other types of quick pipe and/or tube connectors or couplings). A typical installation speed of approximately 4 to 6 m 2 per man hour reduces installation costs. The labor required for assembly of the module is also reduced compared to conventional SIPH collectors.
The NASH collector design is a horizontal aperture solar thermal collector that is easily installed in a bolt-on scenario on a building roof. While not integrated into the building envelope, in typical embodiments, the NASH collector is approximately 1 foot tall and has a flat top which is much more “integrated” into a building than, for example, a parabolic trough. Therefore, the NASH collector provides an option for consumers not interested in a solar energy system that is visible on the roof.
Referring now to
In some embodiments, the absorber assembly may comprise a circular cross-section. In other embodiments, the absorber may be conical, parabolic, diamond, hexagonal, decagonal, oval, square, rectangular or other polygonal or geometric-shaped cross-section, and having a high transparency and low thermal expansion rate. The absorber assembly also comprises at least two pipes, which are typically copper. The outer diameter of the absorber assembly, if circular, may range from 25 mm to about 125 mm. Other types of absorbers may also be utilized. For example, in some embodiments, a copper absorber may be utilized, having two copper channels within the absorber. The copper channels may range from about 3 mm to about 12.5 mm inner diameter (typically about 6.5 mm), and about 4.0 mm to 17 mm outer diameter (typically about 8 mm) and may be attached (e.g., by ultrasonic welding) to the absorber. In other embodiments, the absorber may be a metal pipe absorber.
The cross-sectional shape of the reflector may also vary. Particularly those embodiments having an absorber with a non-circular cross-section, the cross-sectional shape of the reflector may comprise arcs of varying lengths and radii, connected at endpoints. In some embodiments, the cross-sectional shape of the reflector may also comprise one or more irregularly shaped portions. In any case, the reflector has a wide acceptance angle, and generally has a flat aperture.
In some embodiments, the ribs 403 may be aluminum and/or an aluminum alloy, a polymer (e.g., polyethylene, polypropylene, polystyrene, polycarbonate, polyvinyl chloride (PVC), or a combination thereof) and/or fiberglass. The ribs may be coated with a mirror film having a high reflectance across the solar spectrum (e.g., REFLECTECH®, or other reflective film with a high reflectance value). In embodiments not having ribs, the reflector film and substrate on which the film is applied, if any, are formed to an asymmetric shape (see e.g., the reflector cross-section of
In some embodiments, the absorber assembly will comprise glass, PLEXIGLASS, polycarbonate, acrylic and/or other plastic materials having a high degree of light transmission, clarity and strength at the operating temperatures discussed herein. Most typically, the absorber assembly will comprise borosilicate and/or soda lime glass. Borosilicate (also called PYREX) glass is a low iron glass with a high transparency (91.8% transmissivity) and low thermal expansion rate (3.3e-6 m/m ° C.). Because of these properties, borosilicate glass may be used in preferred embodiments.
In typical embodiments, the NASH collector may be about 2 meters long, by about 0.5 meters wide by about 1 meter tall. On other embodiments, however, the NASH collector may be between about 1 meter to about 3 meters long, from about 0.2 meters to 1.0 meter wide, and from about 0.16 meters to about 1.00 meters tall.
Perspective views of the various deformed shapes of
A plurality of NASH collectors may also be arranged into a solar collection system. A typical NASH solar collection comprises a plurality of solar collectors, each solar collector comprising (1) a wide-angle, non-imaging asymmetric optical reflector comprising a reflective film; and (2) an absorber assembly positioned within the optical reflector, the absorber comprising: (a) a transparent tube evacuated to a vacuum or partial vacuum; and (b) at least two pipes inside the transparent tube, each of the at least two pipes having a fluid flowing through the pipe, wherein solar energy is transferred to the fluid in the form of heat, and each solar collector is non-shading and is placed adjacent to one or more other solar collectors with little or no space between the collectors.
As with each NASH collector, the aperture of the optical reflector may be parallel to a surface on which the solar collector is mounted, and the optical reflector's acceptance angle may be approximately 40 degrees. Other properties/characteristics of each NASH collector may be as described above for an individual NASH collector.
Thus, the NASH collector advantageously provides modular, low cost and efficient solar thermal collectors with the capability to effectively utilize 100% of available roof or land area, and efficiently generate medium temperature process heat up to 250° C.
The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.
Pursuant to 35 U.S.C. § 371, this application is a U.S. National Phase application of PCT/US2021/053816 filed Oct. 6, 2021, which claims priority pursuant to U.S.C. § 119(e) to U.S. provisional patent application No. 63/088,392, filed Oct. 6, 2020, which applications are specifically incorporated herein, in their entireties, by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2021/053816 | 10/6/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63088392 | Oct 2020 | US |
