In a finding that could affect the outlook for renewables integration, solar facilities with smart inverter technology can provide key grid services at levels that are similar to, and in some cases better than, conventional power plants, according to a study by California's grid operator, the Department of Energy's National Renewable Energy Laboratory and First Solar.
"These findings mean renewable energy in the [California Independent System Operator] footprint -- and beyond -- could be integrated into power grids at a much higher level and faster pace than once believed," Clyde Loutan, ISO's senior adviser for renewable energy integration, said Wednesday.
The study comes amid concerns about how growing amounts of renewable generation will affect grid operations. The US has 25,000 MW of utility-scale photovoltaic capacity, plus 1,800 MW of concentrating solar, according to the report, titled "Using Renewables to Operate a Low-carbon Grid."
California is at the forefront in the shifting generation mix, with renewable requirements that climb to 50% by 2030. The ISO has more than 9,000 MW of grid-connected solar and expects rooftop solar to grow from about 5,000 MW to 9,000 MW by 2020. Also, the grid operator estimates an extra 20,000 MW of renewables may be needed to meet the state's renewable portfolio standard.
The ISO is being forced to curtail renewables during periods of growing oversupply, according to the report. The grid operator curtailed 2,000 MW of renewables on one day in April, it said.
"With increased frequency of curtailment, more opportunity is created if the industry can tap into the controllability of the renewable resources, and thus expand the carbon-free resources for such services," the report said.
Currently, utility-scale PV plants are typically not used by utilities or grid operators for electrical grid services, according to the report.
In August, the ISO and NREL tested a 300-MW solar plant in California owned by First Solar. The test aimed to show the plant's ability to follow signals from the ISO at sunrise, midday and sunset and how it performed in three key areas: frequency control voltage control and ramping capacity.
The data from the test show how with advanced power controls a photovoltaic plant can morph from being simply an intermittent energy resource to one also providing grid services ranging from spinning reserves, load following, voltage support, ramping, frequency response, variability smoothing and frequency regulation to power quality, the report said.
The ISO said the most unexpected and significant benefit from the tests was the "agile" voltage support the solar plant offered when it produced power during the day and at night when it could absorb a small amount of power from the grid.
The ISO, NREL and First Solar intend to explore economic and contractual incentives that could be used to encourage solar facilities to provide reliability services.
The ISO and NREL are also considering conducting simultaneous tests of ancillary service controls by solar PV and wind generation to understand how working in tandem they can provide various combinations of ancillary services.
