PhD - Karsten Hedegaard: Wind power integration with heat pumps, heat storages, and electric vehicles – Energy systems analysis and modelling, PhD thesis, DTU, Technical University of Denmark, 2013.


Wind power is in many countries considered a key renewable energy technology in achieving the goals of reducing greenhouse gas emissions and relieving the dependency on fossil fuels. However, the fluctuating and only partly predictable nature of wind challenges an effective integration of large wind penetrations. This PhD investigates to which extent heat pumps, heat storages, and electric vehicles can support the integration of wind power. Considering the gaps in existing research, the main focus is put on individual heat pumps in the residential sector (onefamily houses) and the possibilities for flexible operation, using the heat storage options available. Several energy systems analyses are performed using the energy system models, Balmorel, developed at the former TSO, ElkraftSystem, and, EnergyPLAN, developed at Aalborg University. The Danish energy system towards 2030, with wind power penetrations of up to 60 %, is used as a case study in most of the analyses.

Both models have been developed further, resulting in an improved representation of individual heat pumps and heat storages. An extensive model add-on for Balmorel renders it possible to optimise investment and operation of individual heat pumps and different types of heat storages, in integration with the energy system. Total costs of the energy system are minimised in the optimisation. The add-on incorporates thermal building dynamics and covers various different heat storage options: intelligent heat storage in the building structure for houses with radiator heating and floor heating, respectively, heat accumulation tanks on the space heating circuit, as well as hot water tanks. In EnergyPLAN, some of the heat storage options have been modelled in a technical optimisation that minimises fuel consumption of the energy system and utilises as much wind power as possible.

The energy systems analyses reveal that in terms of supporting wind power integration, the installation of individual heat pumps is an important step, while adding heat storages to the heat pumps is less influential. As such, the  installation of individual heat pumps can contribute significantly to facilitating larger wind power investments and reducing system costs, fuel consumption, and CO2 emissions. This is first due to the high energy-efficiency and economic competitiveness of the heat pumps. Moreover, their electricity demand profile is well suited for integrating wind power, even when not operated intelligently. The political phase out of coal in Denmark by 2030 furthermore creates particularly good conditions for utilising wind power in meeting the electricity demand for the heat pumps.

When equipping the heat pumps with heat storages, only moderate system benefits can be gained. Hereof, the main system benefit is that the need for peak/reserve capacity investments can be reduced through peak load shaving; in Denmark by about 300-600 MW, corresponding to the size of a large power plant. This can be achieved when investing in socio-economically feasible heat storages complementing the heat pumps. The potential for reducing the required investments in peak/reserve capacities is crucial for the feasibility of the heat storages.

Intelligent heat storage in the building structure is identified as socio-economically feasible in 20- 75 % of the houses with heat pump installations, depending on the cost of control equipment in particular. Investment in control equipment, enabling utilisation of existing hot water tanks for flexible heat pump operation, is found socio-economically feasible in about 20-70 % of the houses. In contrast, heat accumulation tanks are not competitive, due to their higher investments costs.

Further analyses investigate the system effects of a gradual large-scale implementation of battery electric vehicles (BEVs) and plug-in hybrid electric vehicles (PHEVs) in Denmark, Finland, Norway, Sweden, and Germany towards 2030. When charged/discharged intelligently, the electric vehicles can, in the long term, facilitate larger wind power investments, while they in the short term in many cases are likely to result in increased coal-based electricity generation. The electric vehicles can contribute significantly to reducing CO2 emissions, while system costs are generally increased, due to assumed investments in the costly BEVs. The need for peak/reserve capacities can be reduced through the use of vehicle-to-grid capability.

Flexible operation will be more important for electric vehicles than for individual heat pumps. The reason is that in the situation without flexible operation, the electricity demand for charging of electric vehicles will typically be concentrated in the hours, where conventional electricity demand peaks, while individual heat pumps will have a more distributed load profile.

Competing flexibility measures, such as large heat pumps, electric boilers, and thermal storages in the district heating system, have also been included in the energy systems analyses. These technologies can together facilitate increased wind power investments and reduce CO2 emissions in the same order of magnitude as a large-scale implementation of electric vehicles. The
connection between large heat pumps/electric boilers and the large district heating storages allows for storing electricity as heat during longer periods when needed. This is an advantage compared to individual heat pumps and electric vehicles, which will mainly be able to provide power balancing intra-day and intra-hour, due to smaller storage capacities.

Overall, it is concluded that individual heat pumps, flexibility measures in the district heating system, and PHEVs, can provide significant contributions to a cost-effective integration of wind power towards 2030. Heat storages complementing individual heat pumps can contribute only moderately in this regard.


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