UPDATE: Footnotes have been added to elaborate on a few of these items, most notably the comparative price of energy between Ivanpah and Crescent Dunes.
It uses mirrors and a giant tower, like the Ivanpah Solar Electric Generating System in California, and molten salt like Solana Generating Station in Arizona. But SolarReserve’s Crescent Dunes, now in “full commercial operation” [PDF], is different from any large-scale power plant that came before it in several important ways.
1. Unlike Ivanpah, Crescent Dunes, in Nevada, was built with the ability to store energy and dispatch power when needed.
At Crescent Dunes, giant mirrors focus the sun’s energy at the top of a tower, heating a mixture of sodium and potassium nitrate. This molten salt can be used immediately to superheat water and produce electricity in the manner of any other thermal power plant. Or it can be stored in insulated tanks to drive the thermal-power process during periods of cloudy weather or at night.
At Ivanpah, the “heliostats” focus the sun’s energy atop towers to heat water, which won’t hold the heat for long. That means the vast bulk of Ivanpah’s production comes at the same time the California grid is being fed large and rapidly increasing amounts of power from solar PV plants. Ivanpah can provide a smoother flow of electricity than a PV plant, but its value is still limited by immediate reliance on the sun.
2. Solana can store energy, too, but Crescent Dunes claims an advantage over the Arizona plant.
As SolarReserve CEO Kevin Smith told me last year: “We’re using molten salt directly,” giving Crescent Dunes the ability to drive the temperature of the heat-holding salts 300 degrees higher than at Solana, where long rows of parabolic mirrors are used to first heat a transfer fluid. “They need two or three times the salt we have to get the same amount of heat storage,” Smith said. That leads to a bigger, more expensive footprint – “a whole lot more tanks, pumps and salt.” In sum, Smith said, the multistep nature of the Solana process results in less efficient operation.
3. Unlike Ivanpah, Crescent Dunes doesn’t burn fossil fuels.
In 2014, Ivanpah used 867 million cubic feet (mmcf) of natural gas. It helps jump start the system in the morning, mostly, and to get through some cloudy periods. At a typical gas-fired power plant, that would produce around 85 gigawatt-hours of electricity. Ivanpah produced 420 GWh in 2014 – so you could say natural gas use was equal to about 20 percent of the plant’s output. This is way over the 5 percent allowed by California regulations, but a California Energy Commission spokesman said much of the natural gas Ivanpah uses isn’t held against it.
“(N)atural gas used between the end of daily generation and the start of generation the next day is not considered as contributing to electricity generation and therefore, not included in calculating the percent of non-renewable fuel used at the facility,” the CEC’s Michael Ward said in an email earlier this month.
Ivanpah’s output jumped up to 652 GWh in 2015, so if natural gas use held steady, the plant’s generation-to-gas-use ratio would have improved substantially. But while we won’t know exactly how much gas Ivanpah used in 2015 for a few months, some hints are available: Between August and November in 2015, gas consumption at one of its three units was double what it was in 2014.
4. Crescent Dunes should break out of the gate faster than Ivanpah.
Ivanpah went into full commercial operation in February 2014, not even three and a half years after construction began. Despite being one-third the size of Ivanpah, Crescent Dunes took at least four years to achieve that status.NOTE A One reason Crescent Dunes was slower to start up: SolarReserve saw what happened when Ivanpah’s early production fell dramatically short of ultimate expectations.
“We certainly recognized that Ivanpah got hammered,” Smith told me. “From a management perspective, that led us to want to be more cautious.” That was a year ago, when Crescent Dunes seemed on the precipice of startup, but it wasn’t until today that SolarReserve heralded the plant’s opening.
After the fact, Ivanpah’s operators said they expected all along that it would take up to five years to hit long-term performance targets. But they didn’t make that clear at the plant’s grand opening.NOTE B And, as my reporting has revealed, performance has even fallen short of contractual obligations that anticipated a slow start.
After taking extra time to dial in performance, SolarReserve was confident enough to say today that “Consistent with the rollout plan, the facility will ramp up to its full annual output over the coming year.” The target number: 500 GWh/year beginning in Year 2. Yes, we will be watching.
5. Crescent Dunes electricity is less expensive than Ivanpah electricity.
Crescent Dunes is selling its output to NV Energy for 13.5 cents per kilowatt-hour, rising 1 percent a year during the life of the 25-year power purchase agreement. Ivanpah’s contracts with PG&E and Southern California Edison are confidential, but filings with the Federal Energy Regulatory Commission show that during the high-demand July-September period last year, the utilities paid between 20 and 22 cents per kWh for Ivanpah electricity.NOTE C During the same period, Solana sold electricity to Arizona Public Service at 12.8 cents/kWh.