Category Solar Collectors and Panels, Theory and Applications

Other concepts

In order to maximize the conversion efficiency of the solar cells and of the complete concentrating system, some CPV designs act onto the spectral properties of the light together with the geometrical ones. Each photovoltaic materials has the best photovoltaic performances for wavelengths with energy slightly higher than the semiconductor bandgap. A splitting of the incoming light or the wavelength shifts are tricks used in dichroic and luminescent concentrators to try to increase the PV conversion efficiency.

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Design methods

The design of solar concentrators has different drivers respect to imaging optical elements. Indeed, the design goal here is to maximize the flux density, i. e. the irradiance, at the receiver. Different methods can be implemented to achieve this result (Winston et al., 2005); one of the most commons is the edge ray method. This is based on the assumption that the edge rays in the phase space, i. e. with higher incidence angle at the entrance boundaries of the concentrator, correspond at the extreme rays, in term of positions as well as angles, at the receiver too; the rays between the edge rays are collected to the receiver as well, supposing smoothing and optical active surfaces in continuous media for the concentrator...

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Optics for concentrators

The optics for the Sun concentrators have been mostly developed during the last 30 years; the non-imaging optics, a branch of geometrical optics, has given a great contribution to the

evolution of the shapes for solar light concentrators. For this application there isn’t the concern to reconstruct images avoiding distortions, but the aim is to maximize the transfer of light flux from the first intercepting area of the concentrator, to the photovoltaic receiver. In this application, the light can be represented with sunrays, so the geometric optics is suitable to describe the optical properties of the concentrators.

Some optical parameters cover a substantial role in photovoltaic concentrators; the parameter are both geometrical, related to the ideal design of the parts, and physical, rela...

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Photovoltaic Concentrators – Fundamentals, Applications, Market & Prospective

Andrea Antonini

CPower Srl Italy

1. Introduction

The main obstacles for the photovoltaic energy to be competitive with standard energy sources are 3: the low efficiency, intended as low density of energy production for occupied area, the high cost of the constituting materials and the variability of the production which is correlated to the meteorological conditions.

While for the last point the solutions are related to technologies external to the PV, touching issues of grid management and distribution of solar plants, the first two issues are the aims of the PV research...

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Installation and validation of the museum plant demonstrator

A demonstrator of our solar collection system was installed in a prestigious museum in Florence to provide illumination inside several large showcases. The width of the showcases can be 5m or 2m, while the height is 3m. The photos of Fig. 21 present two 5m X 3m showcases: the pictures show the showcases before (left) and after (right) the installation of the solar lighting plant. The installation of the lighting terminations within the showcases was realised in the occasion of a re-styling of the exposition showcases, with displacement



Fig. 21. Two museum showcases without (left) and with (right) the internal lighting supplied by the installed solar plant.

of the shelves and consequent new arrangement of the exhibit items (particularly evident in the lower pictures)...

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Light level and colour suitable for museum illumination

The museum demonstrator employed a combination of solar light and other sources, represented by white LED with high emission levels at low supplying power (DGA product number 700001.31 "1W fixed LED gem", ref. www. dga. it). Museum object illumination has specific requirements on illuminance levels, light colour and light distribution uniformity. The first task was to reach a mean illuminance of 100+120 lx, with the uniformity of light distribution being maximised within the showcases. The second task was the colorimetric equivalence between LED and fibre illumination. The third task was to obtain a yellow – orange colour. This section is devoted to photometric analyses and colour studies on the three light categories: sunlight guided by glass and plastic fibres and LED emission...

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Fibre selection and tests for the museum installation

The optical coupling between solar lens and fibre bundle was one of the major causes of energy losses in the whole optical system of the museum demonstrator. The focused light should be received by the fibre with the maximum optical coupling obtained in the best alignment condition. As regards the core diameter, we finally chose the value of 1.5mm, to take into account the spot enlargement and to facilitate the alignment.

Another important cause of losses was the absorption in the optical fibre, which basically depends on material, diameter and length of the fibre. The fibre bundles should be characterised by high performance as regards spectral transmission. Typical materials for optical fibre production are quartz, glass and plastic...

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Plastic lens exposure to atmospheric agents and UV irradiation

The solar lens with anti-reflection coating was tested in various atmospheric conditions to estimate the endurance of the treatment. An obvious negative effect was the deposit of raindrops or dust on the upper lens surface. However, the most disturbing effect appeared to be water condensation on the lower lens surface, occurring in sunny weather or raining conditions, because it is basically due to moisture presence and thermal changes between night and day. The collection efficiency E was monitored during the first ten weeks of exposure to the atmosphere. E was measured every week before and after cleaning the lens, since there were water droplets on one or both lens surfaces...

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