Halotechnics creates molten salt heat transfer and thermal storage materials for applications in concentrating solar power plants.
The solar thermal power plant business is all about big: Square miles of mirrors in the desert that surround 600-foot-tall towers to generate massive megawatts of electricity for multibillion- dollar price tags. Big Solar’s ability to compete against fossil fuels, though, could come down to grains of salt.
In a small lab in the San Francisco Bay Area biotech hub of Emeryville, scientists at a startup called Halotechnics are sifting through thousands of mixtures of molten salt. They’re searching for the right combinations that will allow solar thermal energy to be stored cheaply and efficiently so it can be dispatched to generate electricity after the sun sets. In other words, the 24/7 solar power plant.
Molten salt storage has been around since the 1990s, when United Technologies’ Rocketdyne division developed it for Solar Two, a prototype “power tower” station built by the U.S. Department of Energy in the Mojave Desert. Arrays of mirrors called heliostats focus the sun on a boiler filled with salt that liquefies at high temperatures. The heat released by the molten salt is used to create steam that drives an electricity-generating turbine. Some of that heat can be held in tanks of molten salt and released when needed to produce electricity.
But as oil prices plunged in the Clinton era, the U.S. abandoned its grand solar experiment, and molten salt technology got shoved into cold storage. “There hasn’t been a heck of a lot of innovation in the technology,” says Mark Mehos, a veteran solar program manager at the National Renewable Energy Laboratory in Golden, Colo.
Now salt is back on the table as states such as California green-light big solar thermal power projects to meet ambitious renewable energy mandates. Utilities want those power plants to store solar energy so it can be used to balance a power grid increasingly supplied by intermittent sources of electricity like wind farms. GTM Research estimates solar energy storage will be a $3.7 billion market by 2015.
Justin Raade, Halotechnics’ 34-yearold founder and chief executive, saw an opportunity. A newly minted Ph.D. in mechanical engineering, Raade was working at a Silicon Valley materials science company called Symyx in 2009. “I was looking for a big problem to tackle in renewables, and the more I read about concentrated solar power the more I realized that energy storage was a bottleneck that kept it from being cheaper than fossil fuel,” he says.
His idea: a better molten salt mixture that would store heat at higher temperatures to boost electricity production but that would remain liquid at lower temperatures so less energy would be diverted to keep it from solidifying.
Raade secured a $1.5 million Department of Energy grant and in 2009 began screening 5,000 different salt combinations at Symyx. Raade started Halotechnics with an investment from Symyx and a license to its intellectual property. The startup tapped another $4.5 million in government research grants to develop its first molten salt product as well as begin work on a novel liquid glass storage system. “We’ve developed a new oxide-based chemistry that has a much lower viscosity and a much lower melting point than other glass materials. You can actually pump it like a liquid and store it in a big tank like you do with molten salt. But it’s stable at a much higher temperature.”
Higher as in 1,200 degrees Celsius, which would heat air hot enough to run a high efficiency turbine like those used in fossil fuel power plants. In the lab Raade picks up paper cups containing globs of green and black glass, two promising mixtures that Halotechnics hopes eventually to use in a prototype energy storage system the company plans to bring online in 2015.
Elsewhere in the lab, Halotechnics continues to sift through nearly 100 salt combinations a day—some 14,000 so far. Current molten salt mixes are typically 60% sodium nitrate and 40% potassium nitrate. Halotechnics aims to replace 80% of the increasingly costly potassium nitrate with materials it will describe only as “abundant, low-cost salt components.”
The startup’s proprietary software identifies likely candidates based on melting point, heat absorption and cost. Its lab machines measure, mix and dispense 96 different combinations at a time. The quarter-gram mixes are baked in a furnace and put into a device that slowly heats them, shooting lasers through the materials to pinpoint their melting point. “These machines were literally in a corner of the lab at Symyx collecting dust,” says Raade.
Halotechnics’ frugality—engineers designing storage tanks and pumping systems sit cheek by jowl in the office’s foyer—means the company expects to have to raise only an initial $2 million in funding to build a pilot molten salt storage system and another $5 million to $7 million to enter commercial sales.
The company is already in preliminary discussions with solar thermal power plant builders such as eSolar, Sener and BrightSource Energy, all of which are looking to energy storage to give them a competitive edge over photovoltaic farms. While the price of photovoltaic modules has plunged 75% in the past three years, the only option to store electricity generated from solar panels are prohibitively costly batteries.
Halotechnics claims its first product, called Saltstream 565, will be at least 20% cheaper than existing storage systems because it uses less expensive salts to obtain the same operating temperatures – 565 degrees Celsius – as those used by SolarReserve, a solar power plant builder that licenses its technology from United Technologies. But Halotechnics has also filed patents for salt mixes that could operate at 700 degrees Celsius. Higher temperatures mean solar power plants could deploy the latest, most efficient turbines.
Craig Tyner worked on molten salt storage at Sandia National Laboratories and now plans long-term technology strategy for eSolar, a Pasadena, Calif. solar power plant builder. “If there was a salt that would allow us to go 50 C higher than we currently can go, it would be very advantageous for us, as you could store more energy in the same salt and could cut the cost of a storage system 10% or 15%,” he says.
Spanish solar power builder Sener has developed its own molten salt storage system but sees Halotechnics as a potential collaborator, according to Mercedes Sierra, chief executive of Sener’s U.S. division in San Francisco. “We’ve been exploring the possibility of testing their products in our plants,” she says. “We need a high-quality salt and would be ready to buy.” Says Raade: “Storage at 565 degrees is a proven technology, but at higher temperatures it’s a wide-open market.”