Figure 2 Illustration of flexibility divided into flexible and non‐flexible production and demand. Figure 2 shows that the variability in production (from wind power, solar power, outages, etc.) and in demand must be balanced by flexible demand and flexible production. Electricity demand and production can be local but it can also originate from other regions through the transmission lines to the surrounding countries. The electricity demand can either be for traditional electricity consumption or by the coupling to the heat, gas or transport sectors, or even storage facilities. 1.2. District Heating-Electricity Interface Fundamentals This study focuses on the interface between DH and electricity. DH is centrally produced heat, distributed to consumers through pipes, across an area (the district) in the vicinity of the heat producer. The concept of DH was introduced commercially in Europe in the early 20th century (Frederiksen & Werner 2013), while the concept of circulating hot water from a central source for heating purposes was already seen in ancient Rome (Skov & Petersen 2007). Just as with electricity, transport of heat is affected by losses. Losses in transmission of DH are relatively higher than for transmission of electricity, and DH is thus only relevant in areas with a certain density of consumers and heat demand, to ensure relatively short transmission distances. Heat sources for DH are multiple, since hot water can be generated in many different ways, including combustion in CHP and electricity in electric boilers and heat pumps. The different options are explained in what follows. CHP, combined heat and power, generates electricity and heat at the same time. This enables a high energy efficiency, since both electricity and heat are generated, instead of either one or the other. P2H, power-to-heat, generates heat in two different ways. For electric boilers, the heat is generated as electric resistance, much like in an electric tea-kettle. For heat pumps the heat is, in simple terms, generated by pumping fluids in a circuit with different levels of pressure, allowing a concentration of heat from a low-quality heat source (e.g. sea water) to DH temperature. In the present study, these two P2H technologies are considered. Figure 3 displays an example of a Danish DH plant with a gas boiler, heat pump and CHP gas engine. The vertical axis corresponds to the marginal cost of producing 1 MWh of heat, and the horizontal axis shows the day ahead electricity price. 3
WP2 DH report
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