Several concentrating solar thermal power (CSP) plants around the world, either online or in line to be approved and built, will go a long way toward addressing a major hiccup for utility-scale solar power: intermittency.

Solar energy has advantages over other renewables, such as wind power, because we know when it will rise and how long it will shine each day, and we can tailor our solar power systems to maximize energy potential. Yet solar has issues when compared to fossil-fuel plants, namely coal, which can run 24 hours per day with no wavering in power output.

Photo Credit: SaravK

Many new solar thermal power plants, however, are being equipped with molten salt storage tanks that can store solar heat into the evening or night, heat which can be used to create electricity long past sunset and hopefully, up to 24 hours in the near future.

The Spanish Connection

Molten salt storage is still a fairly young technology, and its ability to consistently and affordably deliver power into the night is not certain. There are some plants already online which can deliver power for several hours into the evening.

The 50 MW Andasol 1 plant in Spain, built by German company Solar Millennium, is a prime example. It went online last year. Reportedly, the plant can produce electricity for 7.5 hours after dark using concentrated solar energy to heat a fluid which transfers some of that heat to a molten salt storage tank (the rest is sent directly to a turbine to create on-demand electricity).

In the United States, two Spanish companies, Albiasa Solar and Abengoa Solar, have announced plans to build the world’s largest CSP plants with storage abilities in Arizona. The Albiasa plant will provide 200 MW of power, while the Abengoa plant will soar to a whopping 280 MW of concentrated solar power. Both plants will use molten salt storage tanks to hold some energy over for after dark.

Spain has seen a massive upsurge of solar thermal power plants in recent years thanks to a very generous feed-in tariff which pays solar power producers for their power several times what the power is actually worth. This tariff helped Spain become the world’s leading solar energy producer in 2008.

DOE To Fund Storage Technology

Here in the United States, the Department of Energy shows an interest in molten salt storage and full-time solar power. The DOE announced that it will dole out over $52 million in funding for the “research, development, and demonstration of concentrating solar power systems that can deliver power 24/7.”

The feds will give out money for the research and development of CSP plants that can produce power at least 18 hours per day. They may even chip in to help build a subsequent demonstration plant. Several U.S. companies could qualify for the funding, including Cool Earth Solar and BrightSource Energy out of the Bay Area. Solar Millennium has their U.S. headquarters in Berkeley as well.

How Close Are We?

It is difficult to predict how far we actually are from 24/7 solar power. It would appear that molten salt storage can definitely get us close, with Spanish plants already able to produce for about 18 hours per day. Yet even those plants remain unproven in the long term and must dedicate a portion of the power created during the day to storage rather than the grid.

“Power Towers” could be a key. Instead of using solar troughs, power tower designs concentrate solar radiation onto a central tower that is filled with molten salts. These heat to higher temperatures than the other designs, enabling more energy to be stored as heat in less space.

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Posted on August 20th in Solar News by Dan.