Power systems with large shares of variable renewable electricity generation, i.e., wind and solar power, require high flexibility in both power generation and demand. Heat pumps and combined heat and power units within district heating systems and thermal storages have previously been studied for their potential to increase the flexibility of the energy system. When using these technologies for power balancing, they must be operated in a non-standard way with switched merit-order. This study hypothesizes that a residential area could form a locally operated entity, i.e., a virtual power plant, that provides power-balancing services to a national power system. The hypothesis is tested with a case study in Sweden where a combined heat and power unit, heat pumps, a local heat distribution system, and thermal storage constitute the local entity. A simulation of the energy balances in the system, with optimization of storage size, was performed. The results show that all power surpluses in the system are consumed by the heat pumps. 43% of the annual and 21% of the electricity peak load are covered by the combined heat and power unit. It is concluded that inter-seasonal thermal storage is crucial for the system’s flexibility. Also, large electricity surpluses, if converted to heat and stored, limit the ability of the virtual power plant to utilize the combined heat and power unit for power balancing at a later stage. Despite this, a local virtual power plant can provide increased flexibility by offering power-balancing services to the power system.

This study provides an analysis of the potential for a sub-energy system to provide an electricity balancing service to, in this case, a national energy system with a large share of variable renewable electricity generation. By comparing electricity balancing capacity, CO2, eq-emissions, and costs, three different local residential energy system setups are assessed. The setups contain different combinations of district heating, combined heat and power, thermal energy storage, electric battery storage, heat pumps, and electric boilers. The analysis focuses on system-level integration, heat and electricity cross-sectoral operations, and unconventional production strategies for district heating production. The results show that local sub-energy systems with heat pumps, combined heat and power, and thermal energy storage has the potential to reduce national electricity balancing demand in an economically feasible way, and with modest CO2, eq-emissions. It was also shown that electricity-based heat production without district heating is economically unfavourable, even in the most optimistic scenario; it is not likely to be feasible within a 30-year period.

The European Commission has, following the Paris Agreement, announced a “European Green Deal” to decarbonize energy sectors and increase renewable power. This study investigates to what extent district heating systems with biomass-fueled combined heat and power, electricity-driven compression heat pumps, and pit thermal energy storages, can contribute to power balancing capacity in a future Swedish power system with a high share of variable renewable electricity production. District heat production is, in this study, unconventionally controlled to primarily supply a power balancing demand, where co-produced heat is stored if not directly supplied to district heating users. The impact of this on biomass demand is also investigated. Simulations are made on an aggregated level for one part of the Swedish electricity market. The results show that district heating systems have the potential to reduce peak variable renewable power deficits by up to 52%. All power surpluses can potentially be used for heat production in heat pumps. A heat storage capacity of 17-18% of the heat demand is necessary. Fuel use is 11-12% higher for district heating production controlled for power balancing compared to conventional heat production, depending on the mix of renewable power generation technologies. For instance, a large share of solar power in relation to wind power reduces fuel use to a greater extent when compared to the opposite relation.

Large shares of variable renewable electricity (VRE) generation increase the demand for flexible power balancing capacities for handling both power surpluses and deficits. Within district heating (DH) production systems, electricity can be produced in combined heat and power plants, as well consumed in for example heat pumps. However, the power balancing (electricity production and consumption) potentials for DH production units are limited by the varying level of heat load. To improve these potentials, large-scale thermal energy storages (TES) can be used to increase heat-load flexibility. In Sweden, former rock cavern oil depots exist that can be converted to TESs. This study investigates the power balancing capacity of 58 DH systems with access to rock cavern TESs. A power balancing production strategy is applied for the heat and electricity production in the systems. The results show that Swedish DH, on a national scale, and with 60% wind power and 10% photovoltaic power covering the national load, potentially could reduce VRE power deficits by 9% and surpluses by 12%. Also, the results show that there will be competition for the heat load between heat pumps and CHP units. The fuel used in DH production is reduced by approximately 10%. The study highlights the impact of the temporal distribution and the annual shares of VRE sur-pluses and deficits on fuel use.

Large shares of variable renewable electricity (VRE) generation increase the demand for flexible power balancing capacities for handling power surpluses and deficits. Within district heating (DH) production systems, electricity can be produced in combined heat and power (CHP) plants but also consumed in heat pumps, and thus contribute with balancing capacity. However, this power balancing potential in DH production units is limited by heat load variations. To improve the potential, large-scale thermal energy storage (TES) can be used to increase heat-load flexibility. This study investigates the power balancing capacity of 85 existing Swedish DH systems, with hypothetical access to rock cavern oil depots assumed to have been converted into TES units. In the study, the Swedish power load is assumed to be covered by 60 % wind and 10 % solar power. The results show that Swedish DH systems, on a national scale, could reduce power deficits and surpluses by approximately 9 % respectively. There will be competition between heat pumps and CHP units for DH load supply while providing power balancing services. The use of heat pumps could also, on national level, yield a reduced fuel use in DH production by about 10 % when compared to conventional DH system operation. The study highlights the impact the temporal distribution and annual shares of VRE surpluses and deficits have on the fuel use.