Module mismatch loss and recoverable power in unshaded PV installations

Distributed electronics which optimize power in PV systems have the potential to improve energy production even under unshaded conditions. This work investigates the extent to which mismatch in the unshaded electrical characteristics of PV panels causes system-level power losses, which can be recovered in arrays employing power optimizers. Of particular interest is how this potential for power recovery is affected by factors such as available light, cell temperature, panel technology, and field degradation. A system for simultaneous collection of panel-level I-V curves over an entire array is designed. This system is used to acquire high and low light module performance data for a variety of arrays at the National Renewable Energy Laboratory (NREL) test facility. The measured data show moderately low variation in module maximum power and maximum power producing current in all of the arrays. As a group, the tested arrays do not show any strong correlations between this variation and array age, technology type, or operating conditions. The measured data are used to create individual panel performance models for high and low light conditions. These models are then incorporated in annual hourly energy simulations for each array. Annual mismatch loss (and thus potential for increased energy capture using power optimizers) is found to be minimal, <;1 % for all of the sampled arrays. Due to the nature of the tested arrays, these results may or may not be indicative of typical PV array behavior; further investigation is planned over a larger group of PV installations to determine the general applicability of this study's results.