Santa Monica-based SolarReserve, the developer of utility scale, solar thermal power plants, has raised $20M in a Series C funding round.

The funding was disclosed via a regulatory filing Thursday. Source of the new funding was not disclosed. The new funding brings SolarReserve’s total raised to over $160M. The firm has previously raised funds from Argonaut Private Equity, Citi, Credit Suisse, Good Energies, Nimes Capital, PCG Clean Energy & Technology Fund, and US Renewables Group.

SolarReserve was formed to solve two of the fundamental barriers of renewable energy: scalability and storage. Unlike hydroelectric, geothermal, biomass, and other renewable energy technologies that use limited renewable fuel sources, SolarReserve’s power plants draw their heat from the sun – earth’s ultimate source of clean energy. And unlike wind and photovoltaics, SolarReserve’s power plants can deliver power whenever it is needed, either 24 hours per day or only during "peak" demand. By overcoming these two key barriers, SolarReserve enables utility-scale, clean, renewable electricity generation.

One might guess that such revolutionary technology is an unproven, unrealistic concept dreamed up by optimistic scientists. Actually, this technology has been proven and demonstrated by one of the world’s leading technology conglomerates, United Technologies. United Technologies’ subsidiary, Rocketdyne, demonstrated the technology at the Solar One and Solar Two power plants in Southern California. United Technologies has granted SolarReserve the proprietary technology know-how and an exclusive worldwide license to develop power plants using this proven technology.

SolarReserve’s other founding partner is US Renewables Group, a $575 million private equity firm exclusively focused on renewable power and clean fuel projects. US Renewables Group has extensive experience developing successful renewable power projects, such as the Bottle Rock geothermal power plant and the Niagara biomass power plant. US Renewables Group will provide SolarReserve with the financing and development expertise to successfully implement this revolutionary technology worldwide.

With technology and engineering support from United Technologies and development and finance support from US Renewables Group, SolarReserve is poised to revolutionize the electricity industry. In addition to its backers, SolarReserve has assembled a strong team to achieve its objectives, including former executives at United Technologies, head engineers from Solar Two, leading renewable power developers, and the legal and financial experts required to build projects of such magnitude.

SolarReserve will build power plants designed as Solar Power Towers. This configuration captures and focuses the sun’s thermal energy with thousands of tracking mirrors (called heliostats) in a two square mile field. A tower resides in the center of the heliostat field. The heliostats focus concentrated sunlight on a receiver which sits on top of the tower. Within the receiver, the concentrated sunlight heats molten salt to over 1000 degrees Fahrenheit. The heated molten salt then flows into a thermal storage tank where it is stored, maintaining 98% thermal efficiency, and eventually pumped to a steam generator. The steam drives a standard turbine to generate electricity. This process, also known as the "Rankine cycle" is similar to a standard coal-fired power plant, except it is fueled by clean and free solar energy. Other than the few unique components noted below, SolarReserve’s power plants are comprised of available materials, such as mirrors, and established technologies, such as steam generators and turbines. This will enable SolarReserve to provide electricity at or below prices from traditional sources such as coal or natural gas.

The unique components in SolarReserve’s power towers are the molten salt storage loop and the power tower central receiver. The molten salt storage loop enables the plant to generate electricity whenever it is needed – 24 hours per day or during "peak demand" periods. Molten salt is an efficient and inexpensive medium to store energy. The salt used in the process is an environmentally friendly mixture of sodium and potassium nitrate, the same ingredients used in garden fertilizer. The other unique component is the power tower central receiver. This high heat flux hardware represents a unique blend of liquid rocket engine heat transfer technology and molten salt handling expertise. United Technologies has decades of experience with these technologies in both land-based and space applications, and its support will be invaluable to SolarReserve in developing power plants utilizing this revolutionary technology.

How big is the SolarReserve power plant?

The field of mirrors, called heliostats, is roughly two square miles or 1,280 acres. The power tower is roughly 600 feet tall. The plant will generate between 100-600 megawatts of electricity, depending on the configuration of power load that the utility or customer requires. One megawatt is enough power to supply approximately 1,000 US households.
Why do electric utilities favor SolarReserve’s solution?
The molten salt storage technology enables SolarReserve to deploy electricity whenever the utility demands it. SolarReserve’s power plants can generate electricity 24 hours per day, or only when electricity demand is at its highest. Other renewable technologies, such as wind and traditional solar power, offer no or limited thermal storage, and therefore can only generate electricity when the wind blows or when the sun shines.
 Does this technology actually exist, or is this just a concept?
Rocketdyne successfully demonstrated the molten salt power tower technology at Solar Two, a plant that operated in the 1990s in Daggett, California. The technology has continued to evolve since Solar Two; and recently the U.S. Department of Energy, who co-funded Solar Two, awarded Rocketdyne with another grant continue development of the technology. With this significant support, SolarReserve’s technology is ready for utility-scale development today.
What are the plant’s emissions?
An operating SolarReserve power plant is 100% clean. No fossil fuels are required to to operate the plant.
Does electricity from SolarReserve cost more than electricity from traditional sources such as natural gas and coal?
At full scale, we anticipate our power prices to be competitive with modern fossil fuel-based generation facilities. And as the costs of fossil fuels rise, as most forecasts predict, electricity from these sources will rise accordingly. SolarReserve, which fuels its plant from free sunlight, will not be affected by fossil fuel prices, and therefore will produce comparatively cheaper electricity in the future.
Is this the same technology as the photovoltaic panels that I see on rooftops?
No, the only similarity to photovoltaic panels is that both technologies use sunlight as fuel. SolarReserve’s technology is similar to using a magnifying glass to focus sunlight generate heat, but at a much larger scale. SolarReserve technology uses the sun’s thermal energy to heat molten salt. Molten salt is a very efficient heat carrier and storage medium. The stored molten salt can be called upon at any time to generate steam which will then spin a turbine to create electricity. The latter half of this process, also called a steam cycle, is identical to the process used in traditional coal or nuclear power plants, except it is 100% renewable and 100% clean.
How does SolarReserve technology differ from other concentrated solar power technologies such as troughs and other power towers?
There are fundamentally two types of concentrated solar thermal technologies: troughs and power towers. The trough configuration has been proven at the SEGS plants in Southern California. However, incorporating storage technology with troughs is inherently difficult. They operate at lower temperatures, have hundreds of miles of receiver tubing, and use oil as a working fluid, which is less efficient than molten salt. Power towers are more conducive to storage technology, however other operational power towers use direct steam technology, which does not offer the enhanced storage capability of SolarReserve’s molten salt power tower. Molten salt is the ideal storage medium for concentrated solar power, offering 98% thermal efficiency. SolarReserve molten salt power towers operate at high temperatures (over 1000 degrees Fahrenheit) to generate superheated steam and drive a standard steam turbine at peak efficiency. Other lower-temperature solar thermal technologies require a customized steam turbine that is less efficient.
What is molten salt?
Molten salt, which is used as a heat storage medium in the SolarReserve power plant, is an entirely and environmentally friendly mixture of sodium and potassium nitrate. If fact, in solid form, it is traditionally used as garden fertilizer.
Where do you envision future SolarReserve plants being built?
The Southwestern United States has some of the best high sunlight incidence regions for a SolarReserve plant. Other regions that have good sunlight characteristics include southern Europe, Australia, and northern and southern Africa.
Who are United Technologies and US Renewables Group, and what is your affiliation with them?
United Technologies is a $70 billion Dow 30 component and one of the world’s leading advanced technology companies. Its many products include Hamilton Sundstrand aerospace systems, Pratt & Whitney aircraft engines, Sikorsky helicopters, Carrier climate systems, Otis elevators and escalators, UTC Fire & Security systems and UTC Power fuel cells. United Technologies has been developing power systems and molten salt technology for 30 years in both terrestrial and space applications. United Technologies provided SolarReserve with an exclusive worldwide license to develop projects using the proprietary molten salt power tower technology, which has been in development for nearly three decades.
US Renewables Group is an investment firm focused exclusively on renewable power and clean fuel projects. US Renewables Group teamed with SolarReserve to provide capital and development and financing expertise to build projects worldwide.
I want to help build this revolutionary technology – is SolarReserve hiring?
Keep an eye out for a "career" page on this website in the near future. SolarReserve is growing rapidly and anticipates hiring a team of passionate, brilliant people to manage this growth.

SolarReserve is building utility-scale solar power projects around the world, which includes development of Concentrated Solar Power (CSP) and Photovoltaic (PV). The company has a geographically diverse portfolio of more than 3,000 MW of CSP. SolarReserve currently has three lead projects that are fully permitted, two projects in the United States and one in Spain, which total 300 MW of CSP development. SolarReserve has more than 600 MW of CSP projects in late stages of development across the US, with international activities in Southern Europe, Africa, Middle East, China, India and Australia. SolarReserve’s Photovoltaic development pipeline includes more than 1,100 MW in various stages of permitting across the Southwest US.