Seasonal pit heat storage: Cost benchmark of 30 EUR/m³
Date: 20/05/2019
Denmark has had a successful learning curve regarding to the cost and efficiency of seasonal pit heat storage, which is used to store sunlight in summer for heating purposes in winter. Take Sunstore 3, for example, a 60,000 m³ pit heat storage system built at a cost of 38 EUR/m³ of storage capacity in the town of Dronninglund in 2014: It has now reached a storage efficiency of more than 90 %. These are some of the numbers Jan Erik Nielsen, a solar district heating specialist who works at Danish consultancy PlanEnergi, highlighted during the webinar Task 55: Towards the Integration of Large SHC Systems into District Heating and Cooling (DHC) Networks.
“In Denmark, we have a wealth of experience in pit heat storage construction, which is fairly simple,” Nielsen said. “You dig a hole in the ground and put soil around the edges. Then, you add a watertight liner at the bottom of the pit, fill the pit with water and put an insulating and floating cover on top.”
An increase in the size of these systems has brought down costs considerably, as the following table shows. Denmark´s first big (10,000 m³) pit storage demonstration system, built in Marstal, came to 67 EUR/m³. This made it nearly three times as expensive as today’s biggest seasonal storage, which was put up in 2015 in Vojens and cost only 24 EUR/m³. Nielsen suggests using a benchmark of around 30 EUR/m³ when calculating the cost of pit heat storage with a capacity of 100,000 m³ or more.
Seasonal heat storage is a very cost-effective way to make use of surplus electric power generated by wind farms in Denmark. “Wind energy has already contributed up to 40 % to electricity generation in a year and we want to combine this rich intermittent energy source with seasonal storage via heat pumps,” Nielsen said.