Demand for space heating in buildings and heat required for industrial processes accounts for more than half of the total energy demand in the Netherlands. Instead of converting fossil fuels or electricity into heat, it can also come from residual heat from power stations, incinerators and industrial processes, or renewable sources. Heat from renewable sources includes biomass, geothermal energy, ambient heat from water and air through the use of heat pumps (including aquathermal energy, thermal energy from mainly surface water and waste water), and solar thermal (extraction of solar heat). Recently, the attention for thermal energy from water has increased. According to the Unie van Waterschappen (the association of Dutch regional water authorities), it is estimated that aquathermal energy can potentially provide 25 to 40% of the heat demand in the Dutch household sector. To be able to use heat as an energy carrier, it is important to ensure that supply and demand are properly aligned in terms of capacity and location.
Heat from local heat networks can be used for heating buildings and for hot water, for processes in industry and in greenhouse horticulture. In the Netherlands, a large part of the heat networks are fed with residual heat from the industry. This heat is produced from fossil fuels (oil, gas, and coal). About half of the residual heat from waste incineration plants is renewable since roughly half of the waste used in incineration plants is of biogenic origin.
Residual heat, particularly when it comes from biogenic origin, prevents the use of fossil energy carriers for heat production and associated CO2 emissions. This also applies to combined heat and power that has a high combined efficiency in the production of electricity and heat. The use of heat and cold storage can save a lot of energy, for example, when summer heat is stored for the winter (that also happens with aquathermal energy) and cold for the summer. Various renewable heat sources are not weather dependent and can, therefore, offer a reliable potential for heat supply.
Heat as an energy carrier is now mainly used in production processes in industry (in view of the higher required temperatures, this usually involves steam) and in heat networks with a relatively high temperature (> 70 °C) for space heating and hot water in buildings. This often concerns residual heat that would otherwise be lost. Often, a great deal of heat is wasted due to poor insulation of industrial installations and buildings, so if energy saving measures are taken CO2 emissions will be avoided in the case of fossil fuels used for heat production. In well-insulated new buildings, heat with a low temperature (+/- 40 °C) can be used that comes from residual heat that cannot be used effectively in other situations.
The Dutch Climate Agreement (adopted in July 2019) aims to make heat supply to buildings more sustainable. Each district has its own characteristics and suitable sustainable heat source, i.e. high or low temperature heat networks with all kinds of different possible heat sources, renewable gas boilers or heat pumps (on renewable electricity). The aim is for the saved costs from natural gas to earn back the investment in the new heat supply. There is much to learn about how the market for heat networks can be organized from Denmark, where decades of experience with heat networks have existed. Transparency about the cost structure of heat from heat networks appears to be of great importance. Freedom of choice for consumers could also remain with heat networks.