Morten Jordt Duedahl, summarising a key point from a new report, “State of Green’s White Paper on District Energy”, published by the Danish Board of District Heating (DBDH), says that District energy allows for sustainability and flexibility. “A vast variety of energy sources can be used, including fluctuating renewable energy and surplus heat,” he elaborates.

Duedahl explains that District Heating is extremely flexible when it comes to choice of heat source, as it can accommodate all heat sources, even fluctuating sources like wind and solar and surplus heat from some industrial processes. In larger District Heating systems with several heat sources, he points out, District Heating makes it possible to switch from one fuel source to another, dependent on local situations, price signals and Green ambitions. So with a District Heating system, Duedahl underlines, one does not have to change all the small boilers in each and every house every time new fuel sources become viable and available.

In Denmark, almost 50% of District Heating was produced from renewable sources in 2014. The renewable sources are biomass (wood, waste, straw, bio-oil), biogas, solar, geothermal and electricity (heat pumps and electrical boilers).

Interconnectors and electrical storage can cushion some of the fluctuations in supply, but are not sufficient, and often do not represent the most economical and efficient choice, says Duedahl, and adds, integration of the electrical and thermal energy systems can be a part of the solution. If introducing electrical boilers and large industrial heat pumps in the production of heat for District Heating networks, the networks will act as large energy storages, he reiterates. Surplus renewable electricity can be used in heat production when the electricity price drops due to overcapacity from wind turbines and photovoltaic solar panels, he points out.

Surplus heating or cooling from, for example, industry, is often reportedly wasted. Where industrial or commercial buildings are in close proximity to a thermal grid, it can be beneficial to collaborate with the local utility company in utilising the surplus heat, thus replacing the use of fossil fuels in heat production, Duedahl says, citing the white paper.

According to the white paper, the waste which cannot be reduced, reused or recycled, can be used for energy recovery, and is increasingly being integrated into District Heating systems, and used for heating and cooling purposes in buildings in Denmark.