Abstract
A curve Fresnel lens is developed as secondary concentrator for solar parabolic troughs to reduce the number of photovoltaic cells. Specific measurements and optical tests are used to evaluate the optical features of manufactured samples. The cylindrical Fresnel lens transforms the focal line, produced by the primary mirror, into a series of focal points. The execution of special laboratory tests on some secondary concentrator samples is discussed in detail, illustrating the methodologies tailored to the specific case. Focusing tests are performed, illuminating different areas of the lens with solar divergence light and acquiring images on the plane of the photocell using a CMOS camera. Concentration measurements are carried out to select the best performing samples of curve Fresnel lens. The insertion of the secondary optics within the concentrating photovoltaic (CPV) trough doubles the solar concentration of the system. The mean concentration ratio is 1.73, 2.13, and 2.09 for the three tested lenses. The concentration ratio of the solar trough is 140 and approaches 300 after the introduction of the secondary lens.
Highlights
Optical characterization and practical experimentation on manufactured components are key elements to address and ameliorate the production process and to select the best performing samples
The value of C is circa two, so when the cylindrical Fresnel lens (CFL) is inserted inside the solar trough, the original concentration is doubled
The purpose was to develop a secondary optics for a concentrating photovoltaic trough that increases the solar concentration and reduces the photovoltaic cell number
Summary
The tested component is a novel secondary optics especially designed and implemented for an existing concentrating photovoltaic (CPV) trough It is a cylindrical prismatic lens of Fresnel type [1]. This secondary concentrator reduces the number of photovoltaic (PV) cells in the solar trough [2,3,4,5,6], which is used for the combined production of heat and electricity [7, 8]. The photocells directly exploit the concentrated sunlight providing electricity, while the cooling system of the cells furnishes heat In this concentration geometry, the curve Fresnel lens must be located inside the parabolic mirror around and near the absorber, constituted by a glass tube enclosing a row of photovoltaic cells placed over a rectangular tube.
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