As the fastest-growing generation in California, the exponential rise of solar will greatly increase the need for energy storage in the future.
Currently, the two renewables that are intermittent — solar and wind — together represent 15 percent of the California grid, which is now 25 percent renewable. But as we go forward into 30 percent by 2020 and on up to 50 percent, PV is expected to greatly increase its grid percentage relative to other renewables.
The non-variable renewables — hydro, geothermal, biofuels and biomass — with less benefit from the investment tax credit extension, are not growing at the rate of solar.
Shown, solar’s rise begins over the last four years.
Short Acting Storage
With more intermittent generation, fast-responding energy storage is becoming essential to maintaining grid reliability. PJM Interconnection was the first system operator in the U.S. to take advantage of FERC Order 755, which recognizes the value provided by resources that deliver fast-responding and accurate frequency regulation service.
PJM offered higher payments for fast-responding assets, such as batteries, flywheels and other quick-acting load control systems, compared to the fossil power plants that have traditionally performed the ramping up and ramping down to help stabilize frequency across the grid.
Sumitomo Corporation’s first storage venture in the U.S., with a 6-MW energy storage system, began in January providing supply-demand balancing services for the frequency regulation market operated by PJM. As well as PJM, Sumitomo plans to enter other frequency markets, including California and Texas.
“The battery has maximum output of 6 MW and capacity of 2 MWh, which means that it can deliver 6 MW continuously for 20 minutes,” Nick Hagiwara, director of the power and infrastructure group at New York-based Sumitomo Corp. of the Americas, told Renewable Energy World. “PJM sends the signal every two seconds, and the battery can respond to it in mil-sec scale. The price is decided by the bid made the prior day, and it is different hour to hour.”
There’s now about 110 MW of fast-responding assets online in the PJM frequency regulation market, with another 100 MW or so in the pipeline.
Batteries and flywheels can ramp to full power virtually instantaneously, so they respond faster to grid operator signals than coal or gas peaker plants, but they cannot last as long. Their fast response means batteries actually provide some real competition – but only to peaker plants.
Batteries Could kill Off Peaker Plants, But Can’t Slay Gas
The dirtiest peaker plants — combustion turbine (CT) plants — are able to ramp up in seconds, which is why they are currently used for up to the first half hour to balance intermittent renewables, while the less emitting gas plants, with combined-cycle (CC) turbines, ramp up in about 20 minutes.
Even the newest CC plants need, at best, 10 minutes to ramp up, which is why they are not able to be used as peaker plants. Both types of gas plants are used on the grid.
Those CC gas plants can ramp as fast as 100 MW per minute. Even if batteries can take care of the first few minutes, system operators and utilities would likely still favor gas to take over after batteries, switching to CC gas the same as they now do to take over after the CT peaker plants.
As a result, Black & Veatch actually foresees a great increase in CC gas plants in the future.
“You are still running gas plants — the older models of storage — not because you want them, but because you don’t have any other option,” Jim Baak, program director of grid integration with Vote Solar, said. “That’s all part of the assessment going on now — how to minimize the harm from lifecycle emissions. The benefits that you get from gas according to some studies, you make up for the difference in coal by methane leakage.”
Methane can leak not just from wells and pipelines, but also from where it must be stored, in readiness for demand, under ground near population centers. The Aliso Canyon leak in California has emitted as much greenhouse gases as burning billions of pounds of coal.
“The dilemma that the California [Independent System Operator] faces is should we keep some of these plants on or should we build a carbon-free option and get these associated carbon savings,” Baak said. “One of the storage options is [concentrating solar power (CSP)] with thermal storage.”
SolarReserve, a Platts Global Energy Rising Star award winner, holds permits for Crossroads, which is a 200 MW solar plant on the Arizona-California border that would combine 50 MW of PV with 12 hours of thermal energy storage from 150 MW of CSP, shaping production for stable solar power generation.
Already permitted in 2015 for the Chilean market, its previous combination PV/CSP 260 MW plant, Copiapó, will generate and stores solar thermal energy for 14 hours at well under 10 cents a kWh.
Utility-scale Renewables Could Provide Both Megawatts and “Negawatts”
Combining solar and wind with storage is another renewable/renewable hybrid that would utilize excess energy at night from wind and afternoon solar “spilled solar.”
Invenergy was the first to use this idea. It includes a small 1.5 MW battery in its 210 MW wind and 20 MW solar Grand Ridge project. Its next more ambitious 31.5 MW battery pairing with a 100 MW wind farm at Beech Ridge in West Virginia won the Renewable Energy World project of the year award.
Other solar firms are also looking at incorporating battery storage at the exit point of a solar or wind project so that its output can be ramped up (or down into onsite storage) on demand, avoiding intermittency in the first place. The combination avoids potential curtailments of PV output from bottlenecks at substations, by smoothing out generation to stay within the forecast window.
First Solar, as the top solar developer globally, with 10 GW already under its belt, will continue to build the majority of future solar due to its record-breaking prices.
First Solar spokesman Steve Krum noted that this kind of onsite storage is “the holy grail for large scale solar right now.”
“It’s not there yet but has great promise,” Krum said.
“While we have no current intent on including storage in our utility-scale projects, we do keep an eye on developments in storage technology,” he added. “It’s a natural complement to solar power, and we expect at some time in the future, a combination of PV and storage will create value for power plant operators.”
Sumitomo has also experienced the need for storage first hand. Its investment in First Solar’s 550 MW Desert Sunlight project marks the firm’s first U.S. solar project and expands its renewable portfolio to 2 GW in the U.S., previously all wind.
“All our projects have experienced curtailment to some extent, including quite heavy ones,” Hagiwara noted. Sumitomo sees onsite battery storage as a solution to the problem, if the cost goes down. But for now, Sumitomo’s battery business remains separate from its renewable investments.
“Technically, it is quite interesting to incorporate batteries in the operating renewable generation assets, but the economics need to be fully studied,” Hagiwara said.
Lead image credit: Sumitomo.