To mark the mid-point of the U.S. Department of Energys (DOE) SunShot program, which aims to make solar PV cost-competitive with conventional generation by 2020, the agency has published eight reports detailing progress to date and the challenges that lie ahead.
These On the Path to SunShot reports come five years after the program was launched in 2011, and while DOE says that it is now 70% of the way towards reaching its goal, new challenges and opportunities have emerged.
Chief among these is that in areas with high levels of solar and wind combined with inflexible baseload generation can lead to overproduction, negative electricity prices and ultimately curtailment.
As the proportion of solar energy on the grid reaches unprecedented levels, the systems that manage U.S. electricity generation, transmission, distribution, and consumption must evolve to maintain grid reliability and cost-effective solar integration, notes DOE.
The first report of the eight, authored by the National Renewable Energy Laboratories (NREL), finds that curtailment could affect the economics of solar generation and erase the progress made under SunShot goals when solar is meeting 20% of annual electricity demand.
However, it also finds that with the replacement of baseload with flexible generation, utilizing advanced inverter capabilities and other measures, solar PV can remain cost-competitive while meeting 25% or more of annual demand without any major intervention.
In most of the United States this is a distant concern, as the nation only meets around 1% of annual electricity demand with solar PV. However, California is currently meeting more than 5% of demand with solar PV and has experienced moments of negative electricity prices, as high solar and wind output conflict with the inability of the states sole remaining nuclear power plant and coal generation to cost-effectively ramp.
The report notes that making changes to grid scheduling and dispatching does not require new technology and is often the least-cost option to integrating more variable renewable energy such as wind and solar PV.
However it also found that more flexible generation, provision of reserves and grid stability features using wind and solar plants with advanced inverters and balancing supply and demand over larger areas were important components. Additionally, NREL says that the implementation of measures to make demand more flexible, such as demand response, will assist with integration.
In terms of energy storage, the reports assumptions are limited. NREL looked at California as its base model, and the figure that assumes that 25% of annual demand can be met with solar PV includes only the energy storage which is currently planned for construction by 2020.
The report also found that deployment of concentrating solar power (CSP) with thermal energy storage could allow the cost-effective integration of much higher levels of solar PV. NREL has been studying CSP for years, however the technology has fallen out of favor as its cost reduction has not kept pace with solar PV.
While this report did not specifically address the ability of battery storage to assist with the integration of more solar PV, NREL says that it expects to publish more reports this year on that topic.
Were doing a lot of work on how storage integrates with solar PV, both at the transmission and distribution system level, Dr. Margolis of NRELs Strategic Energy Analysis Center told pv magazine.
The other seven reports examined a variety of topics, including integrating high levels of solar PV on the distribution system, advancements in PV efficiency, reliability and costs, challenges for U.S. solar manufacturing, and the role of finance in bringing down solar costs.
In terms of cost reduction, NREL notes that while PV system costs have fallen 65% since 2011, they must fall another 40-50% to reach SunShot goals. And while this may require more significant changes to technology than are currently being considered for mainstream technologies, DOE SunShot Program Director Dr. Lidija Sekaric says she is confident that we will reach these goals.