High Solar Fraction with Pit Heat Storages
Abstract
In the latest years solar district heating has been common as a supplement to the heat production from Danish CHP plants using natural gas. In 2010 has been implemented 45,000 m2 new solar collectors in connection to natural gas fired CHP plants and more than 100,000 m2 are expected to be implemented in 2011. But the typical yearly solar fraction is 10-20% and the district heating utilities ask for solutions with higher solar fraction and solutions with 100% renewable energy. In the projects SUNSTORE 3 and SUNSTORE 4 pit heat storages are used as seasonal storage to extend the solar fraction. The first pit heat storage (1,500 m3) was build in Denmark in 1996 and a 10,000 m3 pilot sto- rage was built by Marstal District Heating in 2004 as a part of the project SUNSTORE 2 supported by EU and the Danish Energy Agency. The two new storages represent a further development of the pilot storage in SUNSTORE 2. They are situated in Dronninglund, DK, as part of a new project, SUNSTORE 3, with 50% fraction of renewable energy and 50% fraction of heat from a natural gas fired CHD plant and in Marstal, DK, as a part of another new project, SUNSTORE 4, with 100% renewable energy.