New Technology Bottles Up Summer Heat for Winter Use

A new method stores solar heat in the form of chemical energy and could mark a pivotal step toward increasing the use of renewable energy in homes and buildings.

For those living in winter's chill, summer's warmth is still a season away. But what if there was a way to bottle summer and use the heat to offset the cold during winter?

Researchers at the Swiss Federal Laboratories for Materials Science and Technology (Empa) have developed a new technology that does exactly that. Their storage method captures solar heat in the form of chemical energy and then releases it for use in colder months. Storing energy chemically gives it a longer shelf-life than other approaches, and because the system relies on common ingredients and equipment, the cost to implement it is relatively low.

Benjamin Fumey, a researcher on the project, told Seeker that this new method "will enable 100 percent solar heating for buildings by storing summer's heat for winter's demand."

It could mark a pivotal step toward increasing the use of renewable energy in homes and buildings, he said.

Currently, few people or business store heat energy for later use and for those that do, they tend to rely on large and particularly tall hot water tanks. But this approach comes with some obstacles. The tanks are so big, that buildings tend to be constructed around them and retrofitting older buildings is difficult and costly.

The stored water also suffers continuous heat loss and must be used within a few weeks or it cools down and goes to waste. Water tank systems usually require a backup system, too, like a wood furnace, to keep the water warm.

Empa's system is different because it stores heat in the form of chemical energy. The secret ingredient: chemical sodium hydroxide, also known as lye.

The setup consists of two main components, plastic storage tanks that hold the chemicals and a unit designed to charge and discharge the contained heat. The storage tanks contain the sodium hydroxide mixed with water. During the charging process, heat energy harvested from a renewable source, such as a solar thermal collector, is directed to the sodium hydroxide solution. As the solution absorbs the heat, the water evaporates.

The sodium hydroxide solution becomes more concentrated and can be stored like this for months or even years. What's more, it's heat storage capacity is five-times that of a hot water tank, which greatly reduces the space needed to contain the heat.

When water is added back into the condensed solution, the absorbed heat is released. That heat can be transported via pipes into the building's main heat system, delivering warmth to the rooms.

"We have succeeded in building an operational lab scale absorption heat storage system operating at the full potential," Fumey said. Empa has had a prototype of the solar-powered system running for about a year now.

Someday in the future, homeowners might be able to tap this new technology to save money on their winter heating bills.

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