Decarbonisation Technology August 2022 issue

tested turbo-compressor with integrated expander at the heart of ETES is comparable to a conventional domestic fridge but represents a real advance in city-scale energy system management. Furthermore, while the ETES process not only allows heating and cooling to be distributed according to demand – as well as the option of converting this resource back into electricity – the process can be powered by renewable electricity such as wind or solar. This raises the possibility of using renewables and other carbon-free energy sources to provide the heat needed for previously tough- to-reach sectors. Recognising the advantages of this integrated energy management approach, DIN Forsyning – the Danish multi-utility company that operates the district heating network in the port city of Esbjerg, nearby Varde and part of the island of Fanø – is installing two large-scale ETES heat pump units. Using renewable electricity for heat was one of the big selling points for the ETES approach. “What we see from the major global trend is that renewable electrical power will be the basis of the whole energy system in some way. We see ETES as part of a transition,” said Claus Nielsen, Business Development Director at DIN Forsyning. “If we are to bring more renewable energy into the district energy system in Esbjerg then we have to find a smart way to integrate the network with the electricity system. The best method we have seen is the electrically driven heat pump,” he added. MAN Energy Solutions is developing a two- unit heat pump for the city with a total capacity of more than 50 MWth and is supplying the entire system, including the heat exchangers and all the associated electrical infrastructure. The turnkey project will supply around 235,000 MWh of heat annually and will largely replace an existing coal-fired thermal plant scheduled for decommissioning in 2023. Once completed in April 2023, the ETES project will form the backbone of a network of smaller and more sustainable heat sources for the city as part of its plans to become carbon neutral by 2030. It will be the largest CO₂-based heat-pump plant deployed to date. Energy to power the system will be supplied from nearby wind farms. However, as any heat

source can be recovered as usable energy through the ETES system, the Bay of Ho (Ho Bugt) in the Wadden Sea, a UNESCO World Heritage Site, will be employed as an energy resource. Nielsen explained: “Because we are close to the coast, we have a big heat sink. It’s at a low temperature, but it’s stable, and with eight million cubic metres of new water each tide, there is a huge and stable heat source accessible from the ocean.” The ETES system will extract heat energy from the bay by fractionally cooling the water. This heat will then be supplied to 100,000 of the city’s residents connected to the network as well as the company’s commercial and industrial customers. DIN Forsyning currently delivers around 1 million MWh to its district heating network. System-wide benefits of flexibility While the ETES system enables the use of renewable energy in normally unreachable heating and cooling applications, it also offers a number of associated benefits. The flexibility ETES provides allows energy to be stored or delivered depending on supply and demand. For example, when demand for electricity is high, ETES can convert energy in the heat store into usable power. When there is excess renewable generation, this can be stored as heat and cold. Furthermore, along with the energy storage capacity provided by the ETES, the district heating system itself can also act as a significant energy store. Additional capacity, and thus flexibility, can be achieved by temporarily adjusting the energy flows into the network to free up extra energy for other purposes, for instance as electricity. Nielsen explained: “The thing about a heating system is that a heat network is much better prepared for variability than the electricity system. The electricity system has to balance consumption and production at all times. With the heat system in Esbjerg, we can have up to 10 hours without any inputs and still meet demand using r esidual heat in the network, accumulated heat and moving around consumption at the consumer end. Even on the coldest day, we can supply heat to all customers for seven hours without any production.”