Solar Energy is Becoming Mainstream
This issue of IEEE Power & Energy Magazine is the third in a series that addresses the integration issues associated with the large-scale deployment of solar energy. Solar power systems have come a long way since 2009, the year of our first issue on solar integration. Photovoltaic (PV) system prices have dropped by 50% over the last five years, which has led to remarkable growth in solar system installations. As of 2012, about 6 GW were installed in the United States and more than 90 GW worldwide. Many of these installed solar systems are accounted for by PV systems in Germany, which currently has more than 30 GW, mainly at the distribution level. In addition, Germany has 30 GW of wind on a system with a peak load of 80 GW. Germany can be seen as a harbinger of a future electrical power system that has a high penetration of variable-generation renewable energy.
In the United States, prices for installed PV systems at the utility scale (over 10 MW) average US$3 per watt. The U.S. Department of Energy (DOE) has targeted US$1 per watt for installed PV solar energy systems—equivalent to US$.05–.06/kWh—to make solar competitive, without additional subsidies, with the wholesale rate of electricity nearly everywhere in the United States. The DOE has initiated the SunShot Initiative to reach this goal by 2020.
Programs within the DOE are leading to diligent efforts with industry to make clean-energy technologies— such as solar, wind, electric vehicles, building-energy technologies, storage, and smart grid technologies—more commercially viable in the marketplace. However, cost reduction alone is a necessary but insufficient criterion for enabling large-scale deployment. As clean-energy and energy-efficient technologies become more prevalent, power systems must become more flexible and integrated to accommodate these technologies. This multisystems integration is critical to ensure that utilities can continue to operate the grid in a safe, reliable, and cost-effective manner. Developing a holistic approach that integrates these technologies into the distribution and transmission system is critical to ensure that solar and other renewable technologies are adopted by utilities and the marketplace at a relevant scale. To facilitate this work, the DOE has developed the Grid Tech Team (GTT) to create a holistic R&D approach that addresses grid-related issues.
We need to ready the electric power system for a time when variable generation of renewables is integrated at significant levels. This issue of IEEE Power & Energy Magazine examines some of the issues associated with the high penetration of solar energy into the electric power system. We also describe some intriguing future scenarios and real-world case studies in the United States and around the world.
The first article, “Bright Future,” describes the results of two recent studies that look at future electric power systems with a high penetration of solar energy. The first study, the SunShot Vision Study, was designed to examine the impacts and benefits of large-scale deployments of both PV and concentrating solar power (CSP) technologies as a result of significantly lower costs. Based on the Sunshot Initiative targets by 2020 of US$1.00/W for utility-scale PV systems, US$1.25/W for commercial rooftop PVs, $1.50/W for residential rooftop PVs, and US$3.60/W for CSP systems with up to 14 h of thermal energy storage capacity, this study shows a tremendous potential for increasing the amount of installed solar energy. The second study, the Renewable Energy Futures Study, investigated the extent to which renewable energy supply can meet the electricity demands of the contiguous United States. The analysis examined the implications and challenges of renewable electricity generation levels in 2050 with a focus on 80% of all U.S. electricity generation from renewable technologies. In this study, solar energy is one of many renewable energy technologies that could eventually be used to provide cost-effective electricity.
The second article, “PV Measures Up for Fleet Duty,” explores how PV systems will be measured against a utility’s existing fleet of generation. Operators do not consider individual solar plants to be dispatchable; rather, these plants are assumed to operate at a specific power output where all their energy must be accepted into the power system. The challenge is that solar plants vary in output due to weather conditions. This article develops new metrics for evaluating PV system performance in light of being a variable-generation source.
The third article, “Absorbing the Rays,” examines case studies of high penetrations (up to 80%) of PVs integrated into a distribution system in New Jersey. As penetration increases, several issues occur related to voltage, including elevated feeder voltage, caused by injecting real power at times of low load on the feeder, and voltage flicker, caused by fluctuating output power from the PV system due to cloud movement. This article also provides a detailed screening process for evaluating the impact of high-penetration PV scenarios on distribution circuits. This screening process moves beyond commonly used rules of thumb to better express how one can evaluate distribution circuits.
The fourth article, “Time in the Sun,” discusses the current situation of the high penetration of PVs in the German electrical power grid. This power system has 25% of its energy supplied by renewable energy resources, compared to 5% only 20 years ago. In particular, PV systems have greatly increased, with more than 1.2 million PV systems installed. These systems have a total installed peak capacity of 31 GW, and during clear days and low system load, they have contributed up to 40% of the peak power demand for the entire country. As the majority of the PV systems are integrated into the distribution system, this article focuses on the technical and economic consequences of operating distribution systems.
The final article, “A Good Fit,” examines the status of solar energy in Japan. PV systems have seen renewed interest in light of the March 2011 earthquake and tsunami and subsequent failures of the Fukushima Daiichi nuclear power plant. Japan recently evaluated its national energy program and is working to create an environment conducive to the expansion of renewable energy by identifying the appropriate mix of regulatory measures, public support, and private-sector voluntary efforts best suited to each energy source. This article describes the current status of the PV market in Japan; the new feed-in tariff program and its impacts on the PV market; and further institutional, technical, and R&D challenges for PV.