With renewable energy sources the electricity production becomes more variable and unpredictable, causing an imbalance between supply and demand. But balance is necessary. A possible solution to this is demand flexibility: making the electricity demand follow the supply, rather than the traditional way, the other way around. Such demand flexibility can be reached through demand response (DR) or energy storage. If these are combined, and complemented with a heat pump, they offer an interesting possibility for demand side flexibility in domestic settings.

Normally, the domestic electricity demand follows a pattern with peaks in the morning and in the evening. If this demand is to be met with for example photovoltaics (PV), there is a mismatch regarding the timing, as PV are most productive during mid-day. Introduction of DR measures means that the demand peaks are moved to better match the supply peak. The introduction of storage means that electricity can be stored and then used when there is a need. When combining demand response and storage, the peaks of the demand curve are shaved and moved to high-supply times, and at the same time the storage capacity can be reduced.

Using a heat pump as part of the DR measures is a realistic possibility. Then the heat pump is active during production peaks, and the resulting thermal energy is temporarily stored in the building construction. As heat pumps themselves use electricity they can thus become a part of the solution and not the problem concerning intermittent electricity production.

A lot of work has already been done proving what is possible in terms of DR with heat pumps, ranging from research to demonstration projects, and even commercial cases. In thuis article, a simulation study is carried out, showing the impact when heat pumps are used for DR, both on the building and and the system levels. At the building level, this shows that the heat pump operation is shifted towards (in this case) periods with lower energy prices. At system level, the most important impact of DR is the influence on the overall demand profile and the generation mix needed to cover this demand. The resulting combined effect of peak shaving and valley filling leads to a flattened demand profile and consequently a reduced need for expensive power plants to cover the peaks.

The concept is tested in a demonstration project in the Netherlands. A total of 203 households were equipped with smart appliances, smart meters and smart thermostats. Initial results imply that power outages can be avoided, and that power peaks can be reduced in both duration and height (power). There are also examples of commercial implementation. One of them is found in Switzerland, where more than 10,000 electric heating devices are connected, creating aggregated flexibility. This is done with a simple control strategy where the devices are being controlled in an on/off-manner.

The simulation, demonstration and commercial implementation together show that there is potential in using heat pumps for DR and grid stability. However, for this to happen at a larger scale, the use of heat pumps needs to be more wide-spread.
 
Anke Uytterhoeven, Belgium (KU Leuven, Department of Mechanical Engineering)

The text has been shortened by the HPC team

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