Operating regimes for second generation luminescent solar concentrators

Graphical Abstract

When they were first introduced, luminescent solar concentrators promised a cost reduction in the generation of solar energy. Here we show that if luminescent concentrators are to become a cost effective concentrator technology, then it must happen by a shift towards new second generation devices. These devices employ either molecular or optical methods to enhance the photon transport within the waveguide. The fundamental operating regimes that we identify provide a performance threshold that must be overcome by future devices if they are to significantly outperform the limits of the traditional technology.

ABSTRACT

In this paper, we introduce the concept of first and second generation luminescent solar concentrators. Traditional, first generation devices are characterised by their randomly oriented molecules that absorb sunlight and emit luminescence isotropically. By applying detailed balance to the absorbed and emitted photon fluxes we derive the Shockley–Queisser limit for these devices. It is found that they have inherently low efficiency due to optical losses (the well known reabsorption problem) and also that device performance is strongly affected by the areal ratio between the top and edge surfaces. This latter property makes it very difficult to achieve significant cost reductions because as the edge area is reduced (to lessen the amount of expensive photovoltaic material required for conversion), the efficiency of the system diminishes. First generation concentrators have now approached the fundamental limits which we predict here, thus to achieve a stand-alone luminescent concentrator that enables significant cost reductions, second generation approaches are now needed. New, second generation devices are characterised by either directional emitters or photonic filters which enhance the waveguiding mechanism, allowing high efficiency and large sizes to be achieved simultaneously. Here we define the fundamental operating regime in which second generation technology must reach to surpass the limit of first generation devices. Copyright © 2011 John Wiley & Sons, Ltd.