Prof. Birgitta Martinkauppi
Geoenergy storage for cold
Energy is typically stored either as heat or as electricity. The heat can be stored in ground thermal storage using, for example, boreholes or water tank. Many heat storages are already constructed and their performance is investigated in many papers. There is not so much studies about storing cold or coolness on the ground although many industrial and residential places (factories, hospitals, shopping malls, blocks of flats etc,) use cooling. The need for cooling is predicted to increase in future because of more extreme temperatures. For example, there was a heat wave during this summer in Europe. Cold storages could be one of the solution to alleviate negative effects of heat waves. The cooling of industrial and residential buildings is usually produced using electricity part of which is generated using non-renewable sources. The usage of cooling naturally increases during heat waves which then increase the demand for electricity generation. Cold storages could be one of the solution which reduce the need of electricity for cooling and thus reduce carbon dioxide emissions from non-renewable sources. This is very relevant for energy systems since new methods are needed to local cooling and emission reduction. The production of cool or cold can be done ecofriendly for storing. In countries like Finland, the natural cold from outside air can be stored to the ground during winter. The cold can be produced using renewable electricity (e.g. wind or solar power) with less need for fossil fuels. The cold production can be even optimized in way that only excess renewable electricity is used in cold production while the rest is used for other purposes. The goal of this paper is to evaluate the use of naturally available, cheap materials for cold storages. The storage material should be available in large quantities, be relatively safe for humans and environmentally as well as easy to use. Since a storage requires a lot of material, big amounts are needed locally. These requirements limit materials suitable for storages. The material can be thus sand, water or different types of rocks which are easily available many places. Another option is use concrete crush. The concrete crush is viable option because concrete itself is quite safe and crush is available large quantities. This provides also a possibility for recycling the crush, which is EU’s largest waste stream in volume. The evaluation results include calculated available cold per volume for different material in five different temperatures (+5oC, 0 oC, -5 oC, -10 oC, and -20 oC). Based on this, the theoretical storage size is calculated for different cooling demands. The water has a phase change at 0 oC, which effect may have essential effect on heat storage and is thus discussed also here.