As we wait for a clear picture of the impact of Ivanpah Solar Electric Generating System on the energy portfolio and environment, one thing is clear: The world of solar power has changed since that project was conceived nearly a decade ago. So much so that if Ivanpah were being developed today, there’s a good chance it would look quite different than it does.
“A few years ago, there was absolutely no comparison,” says Robert Boehm, director of UNLV’s Center for Energy Research. “Thermal [energy] was a great deal more efficient.” But the cost of photovoltaic panels has dropped about 70 to 80 percent in the past five years [see related story, Page 26]. And PV systems can now incorporate high-performance cells that Boehm says have essentially leveled the playing field.
There are other factors to consider, Boehm says. For example, thermal projects require a huge capital investment up front, with the need for the towers and entire field of mirrors to be in place before operations can begin. With a PV project, developers can start small, adding panels as more money comes in and demand increases. That’s likely a big reason why two other solar projects under construction now in the Ivanpah Valley—Stateline Solar Farm (a 300-megawatt project just north of Ivanpah) and Silver State South Solar (a 250-megawatt project east of Interstate 15, just across the Nevada border)—will both use traditional PV solar technology.
Then there’s the question of whether the federal government will extend a 30 percent tax credit for solar projects that’s set to be reduced to 10 percent at the end of 2016.
And while the Mojave is known for its abundance of sun, that sun eventually sets and storms do come, rendering these billion-dollar projects temporarily useless. But if solar plants could efficiently store their energy for those nights and rainy days, they could produce power around the clock. “The thing that’s really crucial to all of this is storage,” Boehm says.
With PV panels, the way to store energy is through batteries. However, doing so is extremely expensive, which is why companies like Tesla are working to lower the cost.
With thermal solar plants, Jeff Holland, spokesman for Ivanpah developer NRG Renew, says there’s a bit of power still produced after the sun goes down, since super-heated boilers still generate some steam as they cool. Depending on how hot and steady the sun shines on a given day, Holland says residual production could last up to 30 minutes.
The main option for extending storage in thermal solar projects today is to circulate molten salt (rather than water) through the power towers, Boehm says. The liquid salt mixture holds more heat, allowing the plant to continue producing energy for hours after sundown.
That’s why the Crescent Dunes project near Tonopah uses molten salt in its power tower. That 110-megawatt project a few hours north of Las Vegas came online in March and is generating electricity for NV Energy, with developer SolarReserve touting the plant’s ability to store energy for up to 10 hours. Like the NRG plant at Ivanpah, however, Crescent Dunes has drawn criticism from environmental groups for bulldozing the project site and impacting local birds.
Rather than pick the project with the fewest negative impacts, Kevin Emmerich with Basin and Range Watch says many environmental groups would like to see solar panels relegated to the roofs of buildings and parking structures. NRG is doing those projects, too, Holland notes, recently finishing its largest rooftop installation to date at the Mandalay Bay Convention Center.