Power-to-heat systems can be used both in the low-temperature range as well as in the high-temperature range (steam).
Immersion heaters or heating elements are used predominantly in the decentralised low-temperature range, while electrode steam boilers are used in the high-temperature range. The generation of process steam of up to 30 bar is technically possible by means of an electrode steam boiler. The saturated steam generated in this fashion can be superheated to higher temperatures by means of a downstream electrode flow heater and hence also fulfil higher requirements with regard to the steam generation.
The steam generation is based on the electrical resistance of the boiler water, whose electric conductivity should be analogously low (adjusted to 60 μS/cm). Efficient water conditioning is compulsory to achieve this. The efficiency of the electrode steam boiler is dependent in large part on the available water quality and is generally considerably higher than the efficiency of a steam boiler, as no thermal losses caused by hot waste gas occur.
Heat accumulators are not part of the standard outfit of a power-to-heat system, albeit they can enable a more flexible use. For instance, in the event of demand for balancing power, power-to-heat systems with heat accumulators can participate in the secondary and minute reserve market, without simultaneously being required to feed the heat into the district heating network (e.g. in the summer).
Investment costs for electric boilers used predominantly in the district heating network amount to approximately 75-100 euros per kilowatt. The costs vary depending on the field of application and the pre-existing infrastructure. In the high-temperature range, the system must fulfil higher requirements, and the investment costs may therefore be twice as high. They amount to approximately 100-200 euros per kilowatt. Large-scale systems are particularly lucrative; at the current performance prices in the balancing market, they can be amortised as early as after three to five years. Smaller, decentralised systems are less profitable from an economic point of view, as they are associated with higher specific costs, while the specific revenue is the same.
The annual maintenance costs amount to nearly 3% of the investment sum and are comparable to those of a natural gas boiler system. There are no classical wear parts. Still, a power-to-heat system requires two days of maintenance each year. The pumps, valves and water/steam/condensation mimicry etc. are subject to the same wear as a conventional steam boiler system.
With a central power-to-heat system, the heat converted by the power is fed into a supply grid. The district heating system of a municipal utility is a classic example of such a heat supply grid. With it, the produced heat is transferred to the consumer through an isolated pipe system.
CHP plants, such as for example a biogas CHP unit combined with a power-to-heat system have the advantage that this complex works very efficiently in conjunction, and there is often a connection with the subsequent utilisation of the heat. The control of the power-to-heat systems achieves a continuous operation of the CHP system, which can thus provide the full capacity.