18 May 2017

O.2.3.3 Thermal storage improves flexibility of residential heating systems for smart grids

Renewables energies such as photovoltaics are often available when there is little energy demand for space heating. One major strategy to enable this flexibility in heat pump operation is the short-term storage of thermal energy.
In our contribution, we explore the boundaries of flexibility achievable by the combination of heat pumps and thermal storage systems in residential heating. Flexibility is quantified based on the average fraction of hours per day with blocked heat pump and the costs for the consumed electricity on the German EPEX-Spot day-ahead market. The impact of different system designs (heating capacity of the heat pump and storage capacity), and control algorithms is examined with an experimentally verified model for the complete residential heating system. As an example for a typical old building in Switzerland, a single family house (SFH) with 100 kWh/m2 annual heating energy consumption adopted from the IEA Annex task 44 is considered.
The integration of a thermal storage system together with scaling the heat pump power increases the flexibility (fraction of the day with blocked heat pump) by up to 43 %. Furthermore, the number of blocking periods longer than 12 hours increases by a factor up to 16. With the EPEX-Spot prices, the annual energy costs can be reduced by up to 28 %. In selected periods of the year, cost reductions of up to 30 % can be achieved with only 6 % reduction of efficiency. Future incentives for flexibility will help to increase the financial benefits, compensate for the costs of the required additional installations and thereby improve the integration of heat pumps into smart grids.