The renewable-power sector in California is facing a problem: Solar power is becoming so plentiful, generators have to sometimes pay other states to take the juice off their hands.
When this overproduction occurs, pricing for power can go negative. In this case, generators can voluntarily decide to pay utilities to take their energy. Doing so can be cheaper than shutting down their whole operation, only to start it back up a short time later.
According to the California Independent System Operator (Cal ISO), as of June 19, 29 percent of California’s power comes from renewable sources — and of that, 48 percent comes from solar energy. However, the state’s solar plants are producing so much energy at times that generators have had to pay utilities to take the power to avoid overloading power lines.
Solar and wind energy production was ordered to stop 15 percent of the time in 2015, 21 percent in 2016 and 31 percent for the beginning of 2017, according to an article last month in the Los Angeles Times.
This can become a problem particularly in spring and fall, when people aren’t using a lot of electricity for air conditioning, but the solar panels are still producing a lot of power in midday.
“Even though generators may be paying utilities to take their power, the generators are not necessarily paying at a total loss because while it is generating, it still receives production tax credits, etc.,” Steven Greenlee of Cal ISO told Techwire via email.
Negative pricing of solar power occurs in intervals of five or 15 minutes. In 2016, generators experienced negative pricing in 2.6 percent of 15-minute intervals and 5.5 percent of five-minute intervals. In the first quarter of 2017, negative pricing reached approximately 10 percent of 15-minute intervals and 13 percent of five-minute intervals.
To put this in monetary values, generators spent $3.6 million on negative selling in 2016, which is about .04 percent of the overall cost. For the first half of 2017, $3.84 million has been spent, which is about 0.1 percent of the estimated overall cost.
Producing too much power can overload the power grid and cause complications. However, the solar grid’s power market platform balances the supply and demand automatically. According to Greenlee, Cal ISO is required to ensure the balance of supply and demand at all times, but it steps in only if the automatic market platform fails to do so on its own.
Negative selling occurs because there is not enough energy storage to make a big difference. Cal ISO has a capacity for approximately 119 megawatts of storage connected to the grid, which is a relatively insignificant amount when taking into account California’s daily energy consumption.
Although it doesn’t occur often, the Los Angeles Department of Water and Power has figured out a solution for its solar overproduction. According to Joseph Ramallo, the assistant general manager of LADWP, it uses its generating units at the Castaic Pumped-Storage Plant to absorb the overproduction. This acts as a battery for the excess solar power.
If Castaic is at its 1,175 MW capacity, LADWP sells the power, but this rarely happens, and it has never had to negative-sell its energy.
Greenlee said on behalf of Cal ISO, “As storage technology is refined and the cost comes down, we look forward to the time when (power) storage is a common asset on the grid.”
The LADWP already has several energy storage projects in the works. It plans to have 178 MW of storage by 2021 and 404 MW by 2025. This is the equivalent of 10 percent of LA’s daily energy demand. A 20-MW Battery Energy Storage System (BESS) at Beacon Solar Plant in the Mojave Desert is expected to be completed by next year. It also has a pilot energy storage project at a Los Angeles fire station that will be unveiled in August.
Additionally, the California Energy Commission has approved six large grants intended to develop and advance deployment and grid integration of solar energy. These advancements will include energy storage technology and advanced forecasting and modeling techniques. The grants will total almost $7.5 million.
The Public Utilities Commission is working on ways to incentivize people to use electricity during mid-morning hours when use is low and production is high. It is considering time of use rates and the possibility of expanding the ISO day-ahead market to the rest of the West.
Another aid in managing power oversupply is the western Energy Imbalance Market, which is “a real-time market in which non-ISO utilities can elect to participate,” Greenlee said.
Despite the overproduction of solar energy, it is not an issue for everyone. Sacramento Municipal Utility District (SMUD), a large community-owned electricity provider, has about 290 MW of solar power in its load-serving capability, of which a little over half is customer-owned solar generation. “Considering that (solar) is such a small part of our daily capability, managing it presents no challenges,” Christopher Capra, a public information specialist from SMUD, told Techwire in an email.
California still relies heavily on non-renewable power plants, like natural gas, in more populous areas, which don’t have enough space for solar plants or other renewable energy plants.
