Prismatic Stationary Concentrators in the Photovoltaic Modules

This paper is about the researches conducted in the fields of development of prismatic stationary concentrators of solar energy and design of photovoltaic modules on their base. The developed concentrators and modules can be used with the silicon solar cells. The modules can be installed stationary without tracking systems. This paper shows the results of researching and development of the two classes V-shape stationary prismatic concentrators with the shapes of their edges’ sections as a straight line and the arcs of circles. The researches show the relations between the created mathematical models for these classes of concentrators. Basing on the conducted researches there are designed the schemes of the photovoltaic modules with the stationary prismatic concentrators, silicon solar cells and passive heat sink. The theoretical approach is supported by the experimental researches of the designed prototype of the stationary photovoltaic module with the V-shape prismatic concentrator. The paper is finished with the economical evaluation of the photovoltaic modules with the prismatic stationary concentrators and comparing them with the standard plain photovoltaic modules. The evaluations show the cost reduction for the photovoltaic modules up to 30% by using prismatic concentrators in them. 1. THE STATE OF ART. There are at least two reasons to use concentrators of solar energy in photovoltaic modules. The first one is to increase the efficiency of the photovoltaic modules, because efficiency of the PV transformation of solar energy increases as a logarithm of concentration. And, the second one is to reduce its cost and consequently the cost of the produced electrical energy reducing the number of expansive solar cells working with the concentrators. However, there is a tradeoff here, because high levels of concentrations demand precision tracking systems to keep the PV system in work and reliable in operation cooling systems to maintain the solar cells with the safety temperature conditions. These two factors can increase the cost of PV systems working with high levels of concentrations. The low concentration’s levels below 10 X could be successfully produced by stationary concentrators of solar energy. The advantages of this approach are using of concentrators to increase the efficiency and decrease the cost of PV systems and not using of the tracking systems at the same time. The first stationary concentrator was recognized the CPC (compound parabolic concentrator) concentrator invented independently by Prof. Winston in the USA [1] and Prof. Baranov in Russia [2]. Fig. 1. This concentrator has the Fig1. The CPC Concentrator. ( ) (1) ctg 2 sin α α ⋅ + = ⋅ = d D H D d field of view defined by its parametric angle and is able to focus radiation, which is falling on it with different angles less than the parametric. All parameters of this concentrator are directly dependent on its parametric angle. Formula 1. Today, this concentrator is successfully being used as the second concentrator in the high temperature solar thermochemical reactors, but it is seldom used in the photovoltaic with solar cells because of its highly non uniform energy distribution in the focal spot. The classical example of the stationary prismatic concentrator is the triangle prism. Fig. 2. This concentrator was invented and developed by Mills and Giutranich from Australia [3]. The solar radiation falls on the front edge, goes into the prism and reflects from the back reflective edge. After reflection radiation approaches the front edge with the angle bigger than full inner reflective angle for the prism material, catches by the prism and follows to the output edge of the prism. This classical prism can catch radiation from the different directions without tracking of itself and allows reaching up to 2 X concentration ratio for Fig.2. The triangle prism Concentrator. the stationary mode. Unfortunately for this concentrator’s design, the level of concentration falls fast when the sun changes its position during the year. The main advantage to use this type of stationary concentrators in the PV systems is its focal spot has very uniform energy distribution which is very suitable for the solar cells. 2. THE MODULE WITH THE PRISMATIC CONCENTRATORS. 2.1. The models of prismatic concentrators. To improve the characteristics of the prismatic concentrators, we developed two classes of symmetric V shaped prismatic stationary concentrators. The first one is the V-shaped prismatic concentrator with the linear edges [4]. Fig. 3. Fig.3. The linear V-shaped Concentrator. ( ) (2) 1 cos 1 arcsin sin sin 2 1 arcsin 2 sin + + ⋅       + ⋅       − + ⋅ = = γ β γ β π γ