We hear a lot about the potential for using distributed solar power to send excess electricity back to the grid. But now the German power and gas company E.On says it has come up with a way for customers who produce heat using solar thermal systems to send heat itself back to the utility. What’s more, the customers still own the heat fed into E.On’s public Hanse Wärme heating grid in Hamburg. For example, if heat is fed into the grid during the summer, a customer can redeem that heat during the winter months, while a public storage unit handles the complexities of storing heat properly.
Heat storage can be somewhat esoteric – it’s not just hot air in a storage unit. Basically, salt hydrates such as magnesium sulfate are exposed to solar heat, which dehydrates them. The materials are kept insulated inside 20 cm of stainless steel. When exposed to water or water vapor, the materials release the stored heat that the solar energy imparted to them. This means customers can feed in solar heat, have the amount recorded, and then withdraw it when needed. It’s essentially a heat bank. (E.On Energy Research Center at Aachen University and the University of Technology in the Netherlands explain the process in more detail.)
The storage system itself is not a new idea; it came into being in Germany about 15 years ago. But now, hooked up to a larger grid, the system can store heat from not only households and businesses in Hamburg, but from other areas as well. The grid provides about 400,000 megawatt-hours of heat to customers each year, enough to heat 50,000 homes.
“The combination of point-of-use production and central storage will be an essential element of tomorrow’s energy supply,” said E.ON’s Dr. Dierk Paskert. The company’s project is the first of its kind to operate on such a large scale: the storage system in Hamburg’s Bramfeld district can store 4,000 cubic meters of heat. The project, which costs 7 million euros to implement, is being funded by Germany’s Federal Ministry of the Environment.