Knockdown analysis of the performance of solar photovoltaic plants

This paper presents an efficiency map of a solar photovoltaic (SPV) plant through knock down analysis for the three major cell types monocrystalline silicon (C-Si), multicrystalline (M-Si) and amorphous silicon (A-Si). The highest efficiency achievable by a SPV cell is the Shockley-Queisser (SQ) limit which is the ultimate efficiency. When it comes to computing the working cell efficiency which can be treated as the SQ nominal conditions (after considering the cell losses) there is a drop. Moving up the organizational level, while at the module level, there is a further drop in the overall efficiency by 2-3 % points between the cell and the module. Further drop is seen when computing under Standard test conditions (STC) conditions and (PTC conditions PV-USA industrial test conditions). The STC module efficiency is taken as the reference or base condition for the SPV plant design. From the module to the array there is yet a drop of 3-4 % points. The performance drop of the plant from the STC conditions to the actually achieved conditions can be represented by the performance ratio (PR) which considers the stochastic efficiency of the plant site. The PR excludes excludes auxiliary power (2-4 % of the generated power), losses in battery (~20 %) due to storage component (if storage is present) and loss of energy generated due to non-availability of the grid (for grid tied systems). The stochastic incident radiation loss (~16-37 %) is already accounted in the PR. Automation helps to a large extent in tracking the component efficiencies and correcting the losses.

The paper also covers the sensitivity of SPV efficiency to positive factors such as incident angle variation, module tracking, Maximum Power Point Tracking (MPPT), concentration, etc., and negative factors such as environmental conditions (temperature, turbidity, water vapor), cell shunt resistance, initial and long term degradation, etc.