March 12, 2012

DOE Sunshot Vision and Halotechnics Solar Thermal Storage

The US Dept of Energy SunShot Initiative aims to reduce the total installed cost of solar energy systems by 75%. (to 6 cents per kwh). This can be accomplished by reducing solar technology costs, reducing grid integration costs, and accelerating solar deployment nationwide.

Sunshot Vision Study provides an in-depth assessment of the potential for solar technologies to meet a significant share of electricity demand in the United States during the next several decades.

Key findings of the study include the following:

* Achieving the level of price reductions envisioned in the SunShot Initiative could result in solar energy meeting 14% of U.S. electricity needs by 2030 and 27% by 2050. However, realizing these price and installation targets will require a combination of evolutionary and revolutionary technological changes.
* Annual U.S. electricity-sector carbon dioxide (CO2) emissions are projected to be significantly lower in the SunShot scenario than in the reference scenario: 8%, or 181 million metric tons (MMT), lower in 2030, and 28%, or 760 MMT, lower in 2050.
* Achieving the SunShot scenario level of solar deployment could support 290,000 new solar jobs by 2030, and 390,000 new solar jobs by 2050.
* Across all market sectors, the lower electricity prices in the SunShot scenario translate into about $30 billion in annual cost savings by 2030 and $50 billion in annual savings by 2050 compared to the reference scenario.

Halotechnics (a new startup) will develop a high temperature thermal storage system utilizing a new low cost, earth abundant, and low melting point molten glass as the heat transfer material and thermal Energy storage. This new material will enable unprecedented efficiency with thermal energy storage and has the potential to reduce costs by a factor of ten when developed and deployed at commercial scale. Halotechnics will optimize the material in order to develop a complete system to pump, heat, store, and discharge the molten glass. If successful, this technology will enable low cost and efficient thermal energy storage for concentrating solar and nuclear power applications.

Technology Review coverage of Halotechnics.

The new salt and glass materials, which Halotechnics discovered by using a high-throughput screening process to sort through nearly 18,000 mixtures, could reduce the cost of solar-thermal power in several ways. They allow solar-thermal plants to operate at higher temperatures, thus improving their efficiency and reducing the size of the mirror array needed by up to about 25 percent. The materials store up to three times more energy than heat storage materials used now, reducing the cost of the storage system, and potentially increasing the number of thermal plants that can be equipped with storage (although the trend is to move toward storage even with existing materials). Better energy storage can reduce the
cost per kilowatt-hour of the electricity produced by a solar-thermal plant, because the turbines and generators can produce power day and night.

The materials could help lower the cost for solar power to six cents per kilowatt-hour, the goal of the U.S. Department of Energy's SunShot Initiative.

"The systems that are commercial today are limited to about 565 °C—that's the molten salt tower plants," says Mehos. "The tower and optics themselves can hit higher temperatures, but you're limited by the salt temperature right now." The new materials can work at temperatures up to 1,200 °C.

Improving the reliability of solar power will also be key to making solar power competitive with fossil fuels. Without storage, the amount of solar power that can be installed on the grid is limited, since utilities need to provide backup generation, or build extra transmission lines, to deliver power from other areas when solar power output drops. So far this isn't a problem, since solar power accounts for only a small part of the power on the grid. But it could be a serious issue within the decade in places such as California, where renewable energy requirements are leading utilities to install large amounts of solar power.

The first material Halotechnics plans to bring to market is designed for use in existing solar-thermal plant designs. It operates at the same temperature as the current molten salts, but will cost about 20 percent less. Salts currently cost about $1,000 a ton, and a typical plant uses 30,000 tons of salt, so this could save millions of dollars. Halotechnics plans to test the material in a pilot-scale plant for six months starting this summer and then license the formula for other companies to produce.

Two other materials—one an improved salt mixture, and the other a form of glass—can operate at greatly increased temperatures, reducing the amount of storage material needed and potentially improving efficiency.

While current materials limit solar-thermal plants to turbines that are about 42 percent efficient, this material could be paired with steam turbines that are 48 percent efficient. A storage system that will work with this material is being developed as part of an NREL project that's part of the SunShot Initiative.

The last material is a form of glass that melts at 400 °C (typical window glass melts at about 600 °C) and can operate up to 1,200 °C. It could be used to heat up air to drive a gas turbine, with the leftover heat used to drive a steam turbine, much as is done in a natural-gas combined-cycle plant. Such a system could be about 52 percent efficient using existing turbine designs. (Natural-gas combined-cycle plants can reach 60 percent efficiency, but the natural gas burns at temperatures higher than 1,200 °C.)

Operating at such high temperatures, however, will bring engineering challenges, including finding relatively inexpensive materials to contain the molten glass. Commercialization of this technology could be many years away.
Sunshot study analyzing solar technology, cost and performance

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