Differential power processing for increased solar array energy harvest

Abstract

The integration of power electronics in series-connected photovoltaics (PV) has provided a new approach to handling the well-known current mismatch problem. One such technique, known as differential power processing (DPP), has demonstrated high efficiency mismatch handling, as well as scalability, in PV applications. This thesis investigates the potential benefits of DPP in large-scale solar arrays. Mitigating mismatch is an important design parameter in the layout and orientation of solar arrays. To compare different designs, a solar simulator is developed which models annual energy production for arrays with and without DPP. Models for expected sources of loss are implemented to determine any improvement DPP offers over conventional methods. Two common and predictable sources of mismatch are self-shading and diffuse masking. Both these shading effects are influential in designing arrays. The simulation model is used to compare the impact of these two effects. Annual solar data, given in hourly measurements, is used to simulate the arrays. A test site is chosen to provide an in-depth analysis of DPP improvements. Results are then extended to sites across the United States to show the broader benefits of DPP. Analysis shows DPP improves the energy output per unit area of arrays, compared to conventional arrays. This is accomplished in two ways: array size can be reduced without sacrificing energy production, or energy production for identically sized arrays is increased. In addition to self-shading and diffuse masking, an analysis is performed on the effects of factory binning. Factory binning is assumed to be a static source of mismatch which will persist and worsen over the life of the array. Variations in panels are modeled using a bi-variate Gaussian distribution. A Monte Carlo simulation is used to quantify the impact of factory binning on an array's power output. With DPP, energy reduction due to factory binning is significantly decreased. Results indicate that arrays with DPP can handle wider ranges of binning mismatch than conventional arrays. This could ultimately decrease the installed price of installations, as both manufacturers and installers do not need to follow such stringent binning techniques