flexibilityDynamic TariffsElectric Storage Water HeatersHousehold Assets

Celebrating ESWH: The unsung flexibility champion

The flexibility of household assets can be harnessed to provide additional value for the household owner, the energy supplier, and the grid operator. This will be one of the pillars in the pan-European transition to a CO2 free energy ecosystem. In this transition, the electric storage water heaters (ESWH) are the proverbial uncut diamonds waiting to be cut and polished to their full brilliance.

Aby Chacko, tiko Energy Solutions
August 24, 2021

The InterConnect project aims to develop and demonstrate advanced solutions for connecting and integrating digital homes and buildings with the electricity sector. In the French pilot planned in the city of Toulon, one of the objectives is to help reduce the cost of electricity consumption by using household assets to consume during the best periods of the dynamic tariff (different hourly rates during the day) and to use the flexibility offered by household assets to support the grid. In this context, ESWH is one of the most promising assets to provide year-round flexibility.


As per the EDF position paper, in France there are about 15 million ESWH, which represent an installed capacity of more than 20 GW, an annual consumption of 25 TWh and a controllable daily storage capacity of more than 50 GWh ([1]). The average water storage capacity of EWSH in France is 258 Liters ([2]).


Today, the conventional technology of ripple control is employed to control ESWH. This however has the disadvantage that it cannot measure the instantaneous ESWH power consumption and is not suitable to implement use cases like 24 Hour Dynamic pricing and fast flexibility products like Frequency control. However, in combination with new smart control technologies, ESWH are ideally suited for these dynamic applications.


An ESWH has the advantage that there are no technical limitations on how often the power element can be switched nor does the life of the ESWH depends on the number of heating cycles performed. Hence it is logical to first utilize the flexibility offered by the ESWH before using the flexibility from other assets like battery storage, in which the number of charging cycles has an impact on the life of the asset due to chemical degradations. The lifetime of ESWH are 20-30 years. The fact that the number of switches does not degrade the lifetime of ESWH is an important argument to prioritize its use for flexibility offerings [2].


There are however interesting challenges when offering flexibility with ESWH.
The main challenge is that the temperature of the EWSH is not known to the control system. This means that the control algorithm for offering flexibility, must be designed intelligently to ensure customer comfort without having a feedback loop about the water temperature.


Since EWSH can switch instantaneously and there are no limitations on the number of switches, they are ideally suited for fast response grid services like Frequency Control Reserve and automatic Frequency Restoration Reserves. An EWSH typically consumes 1-3 hours a day. Hence for offering grid services it is ideally pooled with other household assets like direct heaters, electrical vehicles and with conventional generation units like hydro power plants.


The Figure 1 shows the control of an individual ESWH by tiko in Switzerland, in its pool of household heating assets, for the provision of automatic Frequency Restoration Reserve. In this solution a measurement and control device measure the instantaneous power consumption of the asset in seconds resolution and issues control commands via a potential free relay. This activates a contactor which in turn controls the asset.

Figure 1: Flexibility activation with ESWH. Blue curve : consumption of boiler, Red curve : Relay based control for  flexibility




It should be noted that to offer grid services the instantaneous power consumption of the EWSH must be measured. This continuous feedback of the power consumption and instantaneous control possibility is one major technical advantage of a smart control solution in comparison with the conventional ripple control technology.


From an asset perspective, the advantage of the ESWH in comparison with the room heating assets, is that it is in operation the year round and thus available to offer flexibility. For photo-voltaic self-consumption optimization and dynamic price optimization, ESWH is an ideal asset due to the previously mentioned reason.


In conclusion, it can be stated that the household asset, EWSH due to its high switching capability, the instantaneous reaction to control commands, and the year-round availability is an ideal source for flexibility. Hence the humble and simple ESWH, if controlled intelligently, will play a crucial role in the energy transition.


The author would like to thank his tiko colleagues Mr. Tim Ryan and Mr. Roberto Cersosimo for their support in preparing this article.



[1] EDF, «EDF Position paper for ecodesign and ecolabelling regulation for water heater and storage tanks,» EDF, Paris, 2020.
[2] Thema Consulting Group and Danish Technological Institute, “Value of flexibility from electrical storage water heaters,” Norwegian Water Resources and Energy Directorate , Oslo, 2021.

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