Design of cooperative grid-tied photovoltaic systems



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Since 2009 there has been a discernable decrease in the price of solar photovoltaics (PV). In 2017 the average price per Watt installed was $1.50, which is 1/3rd what it cost in 2009, and the reduction in price has correlated with an increase in installed PV capacity in the United States and in Texas. While the majority of the growth in PV installations has been, and still is, in utility-scale photovoltaics, both residential and commercial installations have also grown and have done so at an increasing rate. Due to the nature of PV, this increased penetration of residential installations has created economic, social, and technical challenges for electric utilities and their customers in the United States. Although a consensus solution to these challenges does not yet exist, electric utilities have attempted to address them using a number of approaches within their sphere of control such as Rate Restructuring, Solar Cooperatives, and Subsidized PV Hosting. The upward trends in installed PV capacity, the utility’s ability to influence customer decisions through subsidized PV hosting programs, and the low additional cost of implementing these programs have combined to produce a great opportunity to apply creative problem-solving to the technical challenges associated with distributed residential PV. Empirical measurements of PV output variations caused by clouds are used in combination with detailed electrical distribution circuit models to determine the positive and negative effects of PV Distributed Energy Resources (DERs) on the electrical distribution system. Linear and quadratic optimization formulations are used to determine how to distribute PV DERs to minimize the negative effects from the perspective of the electric utility. When customer choice introduces uncertainty in the utility’s decision-making, stochastic optimization is applied to help deal with the uncertainty. This dissertation first identifies and quantifies the technical challenges that distributed PV generation creates on the electrical distribution grid resulting from PV’s distributed nature and variability of output. The dissertation then develops a methodology that electric utilities can apply to distributing PV DERs through the subsidized PV hosting programs, which they are already implementing, in a way that mitigates these technical challenges. This methodology can be applied in a present day scenario, where distributed PV is a small, yet considerable, and in a scenario likely to occur in the decades ahead – where continually increasing rates of PV installation result in extensive penetration of PV generation on the electrical distribution grid.


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