When Ivanpah's 392-megawatt concentrated solar power plant switched on in California's Mojave Desert in 2014, it was supposed to mark a new era for American renewable energy. Instead, the facility became a poster child for everything that could go wrong with early clean energy investments — or so it seemed. But a growing chorus of solar researchers now argue that Ivanpah isn't broken; it simply needs a better brain. And the fix they propose could reshape how we think about retrofittting aging renewable infrastructure across the country.
The plant's problem, according to a new Nature Briefing from researchers at the National Laboratory of the Rockies, was never its hardware. The thousands of computer-controlled mirrors, called heliostats, that track the sun across the desert sky performed with near-perfect precision, achieving 92 to 94 percent availability. What failed was the decision to use direct steam — a system that generates electricity the moment sunlight hits the collectors, with no way to store that heat for later use. In a market that rapidly came to reward electricity produced after sunset, Ivanpah was locked into selling power during the cheapest hours of the day, often the midday glut that has sent California electricity prices negative.
Now, the same federal laboratories that once helped design the plant are proposing a solution: rip out the direct steam system and replace it with molten salt — the same technology used at Spain's Solar Two plant in the 1990s, and at nearly every CSP tower built since. The researchers modeled a retrofit with 12 hours of thermal storage and found it would generate a 30 percent higher internal rate of return at today's grid prices than the original plant enjoyed in 2014. In other words, the very modification that everyone else building CSP towers adopted — and that Ivanpah's designers declined — would make the plant dramatically more profitable in the market it already operates within.
The timing matters. Pacific Gas & Electric and Southern California Edison have moved to exit their power purchase agreements for two of Ivanpah's three units, citing underperformance and high costs, years before the contracts expire in 2039. The California Public Utilities Commission rejected those exit proposals, citing the need to retain clean generation as electricity demand rises and as federal policy shifts make new renewable projects harder to permit. With solar panel prices dropping and simpler photovoltaic farms flooding the grid with midday power, the economic case for a plant that can store heat and dispatch electricity when prices peak has never been stronger.
"Without storage, Ivanpah became an expensive source of electricity during the lowest-cost time of day in California," the researchers noted. But a plant equipped with molten salt could run its turbines well into the evening hours, capturing the premium prices that come when millions of Californians return home and the sun disappears. The solar field — the heliostats that convert sunlight into heat — has already proven it works. What remains is the unlatching of a problem that was built into the original design: one that dozens of engineers at the National Laboratory of the Rockies believe they have now solved.