Solar Collector Designs

The best-developed method of solar electricity storage is to send it to an electrolyzer that splits water into Oz and H2. In this process, the 02 is released (used or sold), and the H2 is stored either as high-pressure gas or as a cryogenic liquid. This process will be described in the discussion of hydrogen processes after the forthcoming description of various solar collector designs in Section 1.5. 

In addition to the existing technologies, research is continuing on designs for new and more efficient converters. For example, researchers at Penn State University are working on new ways to harness the power of the sun by using highly ordered arrays of titania nanotubes for H2 production and increased solar cell efficiency. 

Another area of development is in lower-cost thin- and ultrathin-film designs. One such product is made by Nanosolar of copper indium gallium selenide (CIGS), which is claimed to achieve up to 19.5% efficiency and is as thin as a newspaper. This claim is yet to be proved. The collector cost is also reduced, because the substrate material on which the ink is printed is much less expensive than the stainless steel substrates that are often used in thin-film solar panels. The manufacturer claims a five- to tenfold reduction in the collector cost (about 1/W) compared to conventional PV cells. 

Thermal collectors on the roofs of private homes are usually flat and stationary units that serve to provide residences with heat and hot water. The 

Post-Oil Energy Technology After the Age of Fossil Fuels 

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Heat losses from solar collectors have been calculated by several investigators (3, 9, 13, 14). In this study the equation developed by Hottel (9) was used. The relationship, although somewhat complicated, can be solved directly and has been demonstrated by Hottel to give reliable values over the range commonly encountered in solar collector design. 

Figure 2. Performance of BNL solar collector design compared to that of commercial solar collectors.

The Insulation In the BNL solar collector design uses rigid Insulation as a structural member. This member Is presently made from glass reinforced polylsocyanurate with a aluminum foil facer (Thermax, Celotex). The sheet metal frame Is parametrically coupled to the rigid Insulation and Is under compression when the... 

The major key to low cost Is a solar collector design which has low material Intensity and Is capable of being produced at very high speed to reduce labor Intensity. The low material Intensity results from the use of polymer films and film laminates. The development of an efficient non-pressurlzed thin film absorb-er/heat exchanger also contributes to minimum material requirements. The use of a simple roll-formed sheet metal frame with a cost one third that of a conventional extruded frame further reduces the cost and can be produced as one piece to be bent around the Insulating substrate. The weather seals are Integrated Into the fllm/adheslve attachment for simplicity, reliability and very low additional material requirements. 

R. Rhodes, Thin-Film Thermosiphon Solar Collector Design, SPE-ANTEC Tech. Papers, Charlotte, NC (2006). 

Figure 10.8 Design of a fluorescent dye-based solar collector...

Sensitivity studies have shown that costs are likely to be contaminant specific and depend on plant size and location. The design of a commercial facility has not been finalized. Solar collectors are the largest cost component of solar detoxification systems, and some research indicates that a one-sun system (in a one-sun system, solar energy is not concentrated by reflectors or solar panels) that does not use a solar collector may be more efficient in accessing diffuse ultraviolet light. Another design concern that may impact process costs is the use of a fixed catalyst versus a slurry feed (D12953N, pp.190-203). 

Fig. 7. Section of solar-hcatcd building. Solar collector has an area of 3500 sqnaie feet (325 square meters) facing south ar an angle of 45 degrees. There are. about 8000 square feet (743 square meters) of working space. Estimates of heat loss indicate heat demand is in range of 40,000-70,000 Btu (10,080- ] 7,640 kcal) pei day. Locaied in die. northeastern United Stales, die building was designed to furnish between 65 and 75% of total seasonal heating load...

High-Temperature Collector A solar thermal collector designed to operate at a temperature of 180 degrees Fahrenheit or higher. 

The global total of installed solar collector capacity today (2008) is about 60 GW and according to Emerging Energy Research and the Prometheus Institute, it will reach about 300 GW by 2020. As to their size and design distribution, the small (10-100 kW) photovoltaic (PV) units will total 170 gW, the medium-sized (1-10 mW) concentrating PV (CPV) units about 6 gW, the... 

Thermal solar collectors are also available in so-called central concentrator or solar concentrator designs. In these configurations, a large number of independently movable flat mirrors (heliostats) are used to reflect the solar radiation onto a central receiver on the top of a tower. Each heliostat moves about two axes. The receiver typically is a vertical bundle of tubes in which the heat-transfer fluid (water or oil or molten salt) is heated by the reflected and concentrated insolation. The molten salt technology also provides thermal energy storage. 

A number of new solar power plants are under construction. In 2007, First Solar signed a contract to produce 685 mW of solar collectors over 5 years for 1.28 billion, or at a unit cost of 1.87/W. This might correspond to a 3/W installed cost. Southern California Edison is erecting a 500 mW plant designed by Solel Solar Systems of Beit Shemesh, Israel. It is scheduled to start up in 2009. 

Fresnel lens-type PV concentrators have operated at 26% efficiency (Amonix, Inc.). The efficiency of concentrating PV designs can reach 25-30%, and DSG thermal systems can also reach 30%. Similarly, the efficiency of dish concentrators using Stirling heat engines is also about 30%. Table 1.42 provides a summary of solar collector costs, efficiencies, and suppliers. 

The 12c/kwh electricity cost is based on 3,000/kW solar collector cost, 25 years of equipment life expectancy and 5% interest on investment. This price does not reflect that most of the electricity, is generated during peak periods, when the peak prices are often twice as high as the yearly average. This price does not consider either the drop in collector prices that will result from design advancements (nanosolar, etc.) and mass production. 

Example 8-3 (taken from Bolton et al, 2001a) A solar collector of an area of 4 m is used to treat a water containing 500 mg of 1,4-dioxane (C4Hg02) at an average solar irradiance of 850 W m . The total volume V of the batch system was 300 L and the substrate was degraded within 1.5 h by a zero order reaction kinetics to a final concentration of [C4Hg02] = 200 mg Calculate the appropriate design parameter. 

This chapter reviews some of the main topics involved in the design and modeling of solar photocatalytic reactors, with particular emphasis on the authors research experience. Solar photons are source of energy that initiates photocatalytic degradation. Thus, proper consideration of radiative processes is key to address this subject. The determination of the directional and spectral characteristics of solar UV radiation, the interaction of the catalyst with radiation inside reaction spaces, the optical design of solar collectors, and the optical properties of the materials involved are all subjects where these concepts are necessary. Therefore, developments in this area should be solidly grounded on the fields of solar collector optics and radiative transfer, besides the more traditional chemical engineering aspects involved. This requires a multidisciplinary approach. 

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