Heat pumps can reduce the need for bought energy and contribute to a shift towards less carbon-intensive heating and cooling. But increased use of heat pumps also means increased load on the electricity grid, and might even lead to congestion. So, how to solve this? One alternative is through smart steering of heat pumps that are pooled together, allowing both power and cost peaks to be avoided. But there are challenges.

Pooling for increased flexibility
Pooling of heat pumps means that the flexibility of many heat pump installations are combined into one larger system. The individual flexibility is two-fold: the heat pump itself has fast reaction times and can change its electric consumption within seconds. Also, there is a flexibility in the building where heat can be stored both in accumulators and in the building itself. Integrated into a system with smart steering, this means that heat pumps can be switched on or off depending on e.g. electricity price and demand. This could also be used as a balancing system, providing the grid operator with storage in times of excess grid energy, and supply in times of shortage. Since this is a service to the grid operator, it is possible to find a business case in this strategy.

One problem with such smart steering of pooled heat pumps is that the flexibility influences the operation of the heat pump (e.g. operation cycles). Hence the trade-off between flexibility and an increase of shut off/on times as well as of dead times has to be found. Moreover, the impact of flexibility on the comfort of heating and hot water supply has to be limited.
Another challenge is that if several heat pumps in the same local grid area belong to one pool and react to the same market signal, they are prone to be switched on and off synchronously. This might cause grid congestion. One solution is to allow the grid operator to switch off the heat pumps at specific times each day. Another solution is to not send a market signal to all heat pumps in one pool, but to some heat pumps in a number of pools.

Case study: potential for business case
The potential contradiction between market optimization (low price) and grid optimization (avoid congestion) was analysed for a case study in Austria. Electrical power flow simulations were used to compare the different heat pump operation strategies and their impacts on the electrical grid, namely: thermal overload of assets (lines, transformers), grid voltages (levels and unbalance) and heat pump coincidence factors. The economic analysis showed that a business case for balancing can be interesting, if ICT costs for integration are low. Also, additional measures, e.g. an increase of PV self-consumption, improves the business case. The analysis further shows the importance of the flexibility potential of the building. For example, passive houses can be pre-heated but cannot cut energy costs much and have low balancing potential. The highest revenues could be gained with the existing buildings, since they have the highest heat demand.

In the Austrian case study, the impact of the heat-pump pool on the distribution grid was not very large. However, in countries with weak distribution grids this may still pose a problem in the future. Particularly the combination with other electrification trends, e.g. electric vehicles, can put further stress on the grids.

Johanna Spreitzhofer, Tara Esterl, Roman Schwalbe and Matthias Stifter, Austria
The text is shortened by HPC

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