One of the challenges for network operators is to ensure the stability of the power system by using the available tools as cleverly and as frugally as possible. Various solutions come into the game here: incentive systems such as peak/off-peak hours, flexibility solutions such as shaving consumption in certain industries or programmable load management, and so on.
Heat pumps offer an interesting potential to activate for rapid self-regulation of consumption – fundamental behavior in grid stability – during events on the electricity network.RTE and the CEA have conducted studies to confirm this potential, check its feasibility and finally evaluate it on CEA experimental platform at INES.
Residential consumption has historically been sensitive to network conditions (voltage, frequency). Indeed, these loads (water heaters, electric ovens for example) often had a resistive behavior, or were operated with motors (as washing machines). With the increasing use of power electronics and the development of controls, this sensitivity is declining. However, certain common consumer devices can reintroduce this sensitivity, in a controlled way in order to ensure a non-perceptible impact for the consumer, while continuing to provide a significant service for the stability and operation of the network in real time.
The aim is to contribute to the power balance of the electricity network on a timescale of a few seconds, by reacting linearly to variations in voltage and frequency.
RTE and the CEA at INES have been jointly evaluating this approach for some time now. We have identified the technology roadblocks and the relevant devices to target in residential and tertiary buildings.
Heat pumps used for heating buildings, domestic hot water, or for air conditioning, emerged from this analysis as particularly interesting.
The total number of heat pumps installed in France is expected to reach around 11 millions by 2030, and most of them now have a power inverter for controlling modulation.
In the simulation study carried out on the total installed heat pump base estimated for France, the assumption is that the variable speed heat pump in operation would reduce the electrical power consumed by a maximum of 50%. This 50% factor is applied at each point in a typical year to assess the modulation potential at regional and national level.
The results confirmed the benefits of considering the introduction of grid-sensitive modulation in heat pumps as a tool for rapid self-regulation of consumption during events on the electric grid causing deviations from nominal frequency or nominal voltage, in an attempt to avoid reaching load-shedding thresholds.
Grid-sensitive power modulation potential of heat pumps used for heating/cooling are estimated in simulations, on a national basis, at a maximum drop of around -11GW in the early morning in winter and -7.5GW in the late afternoon in summer, and a minimum of -500MW in the late afternoon in the off-season and in summer.To this could be added -600MW for heat pumps used to heat domestic hot water, or Thermodynamic Water Heating Systems (TWS), assuming simultaneous heating start-up in the middle of the day.
The project then continued with an extended collaboration with heat pump manufacturers. This made it possible to verify experimentally the technical feasibility of artificially reintroduced sensitivity, using software programming, in 3 heat pumps representative of the European heat pump market. The sensitivity obtained was then evaluated in various realistic scenarii in terms of the conditions of the electrical network measured by the equipment at the power supply connection, and the thermal conditions at the heat pump terminals.
The experiment carried out on 3 heat pump models demonstrated the technical feasibility and the benefits of the solution in terms of contributing to the stability of the electricity grid, with no noticeable effect on user comfort in most scenarios.
These results have been brought to the attention of the European professional associations for heat pumps (EHPA and EHI) and electric grid operators (ENTSOE), as well as to the European coordination body for the European electric grid, ACER, to support the implementation of this type of solution.
Link to the publication:
https://cea.hal.science/cea-04738538
figure: theoretical/measured dynamic behaviour of the tested HPs in response
to large frequency drop event of the grid.
photo: view of part of the experiment - credit CEA.