Differential Processing for Improvements in Solar Array Energy Harvest
MS student Jason Galtieri with advisor P. T. Krein
Mismatch among PV cells accounts for a significant proportion of annual energy reduction in solar arrays. Sources of mismatch include cell degradation, poor factory binning, and non-uniform irradiance due to shading. Differential power processing (DPP) has the capability to mitigate all three of these sources by reducing the dependence between neighboring PV cells. The focus of this research has been developing models for the various sources of loss in arrays, as well as DPP operation. With these models we can quantify the improvements DPP offers in annual energy production.
Results from self-shading simulations have shown that DPP allows rows in an array to be spaced closer together and yield the same energy output as traditional arrays. In Figure 17, the annual energy harvest of a single row of panels experiencing self-shading is shown. We can see, for each tilt angle, that rows with DPP outperform rows without DPP when row spacing is close. Reductions in array size range from 5-10%. Alternatively, for identical row spacing, arrays equipped with DPP achieve better annual energy harvest due to localized maximum power-point tracking and efficient power management. Another promising result is reduced dependence on factory binning. Currently PV manufacturers have to bin panels to minimize the effects of production variations. With DPP, binning tolerances can be lessened or completely removed by allowing the converters to handle the mismatch. Without the need for factory binning, the cost of producing panels can be reduced.
This research is supported by U.S. Department of Energy grant DOE Sub SB DE-AR0000217.