Heat Supply in Future Energy Systems

27 system in Denmark. Each of these will enable the

different energy sectors to integrate more effectively and allow the systems to utilise high amounts of intermittent renewable energy sources. The transition to a more flexible and energy efficient power production should be developed in the whole country for both decentralised and centralised plants, since the same power system covers the whole country, in contrast to DH systems for example. The centralised plants in the large cities play an important role because they account for a large share of the production capacity. Therefore, decisions relating to these plants have a large impact on the flexibility of the total system. A large share of the centralised power plants in Denmark is located in the Greater Copenhagen Area, which means that the development here is important in terms of shaping the future energy system in Denmark.

Planning and operation of CHP plants today is to a large extent determined by the heat demands and cost of supplying heat, also in the Greater Copenhagen Area. If this perspective continues to influence the planning, this will be a challenge to the implementation of Smart Energy Systems, which focuses on the overall feasibility of the energy system, rather than planning a cheap heat supply alone. This problem may not be solved by the local authorities alone, but attention should be paid to the fact that heat supply planning should not be done independently from energy system planning.

4.2 Heat Supply in Future Energy

28 systems, but it is seen as an important parameter

that the transmission system contributes to

system flexibility and the accommodation of low temperature heat sources.

Figure 31: Development of district heating in the past (1^st and 2^nd Generation), current district heating technology (3^rd Generation), and the future of district heating (4^th Generation) [53].

At the same time as this development, the heat demand on the consumer side will increase and decrease in different ways between now and 2050. It will increase in absolute terms as the district heating network expands [54], but it will decrease for the individual consumer as more heat savings are added to the buildings. Therefore, the heat density in district heating areas will be reduced, but the length of district heating networks will increase in Denmark and in the Greater Copenhagen Area. To enable this transition, new district heating components, installation techniques, and planning tools will need to be developed, which is the focus in the

4DH (4^th Generation District Heating) research centre [55].

..Production from waste incineration will decrease, while industrial and other

surplus heat sources will increase..

The heat production from the waste incineration CHP of today will be reduced as more combustible waste fractions are sorted out of the municipal waste for reuse or recycling. In a 100% renewable energy system, the fractions of fossil based materials like plastics will also be replaced or sorted out. The remaining waste fractions for incineration will be available in lower quantities

29 and are expected to have a lower calorific value;

thus, a lower energy output from incineration is expected. The surplus heat from industries may be lower than today because of increased energy efficiency measures, but large amounts of heat that could be recovered for DH are still wasted today because of DH temperature levels and the lack of suitable regulations for waste heat recovery.

More surplus heat should be recovered from industries in future energy systems but potential new sources should also be utilised. Some are already used in a few places today, e.g., geothermal and large electric heat pumps, which both have much larger potential. Also sources that are not relevant in the actual energy system may come to play important roles in the future heat supply, e.g., biomass gasification units or electrolysers. These technologies play central roles in the CEESA scenario and they may have surplus heat that can be recovered in DH systems.

In the CEESA scenarios, only some surplus heat from gasification is included for DH supply and none from electrolysis, because of the uncertainties about the technologies in future large-scale systems.

. .There is a balance between heat supply

and heat savings in both existing buildings and in new buildings..

To reach a 100% renewable energy system, substantial heat savings in the building stock will be necessary. The consumption of heating in buildings accounts for about one third of the energy consumption in Denmark and reductions in the heating demand in buildings in a future energy system will both imply reduced fuel and energy consumption, but also a reduced need for conversion capacities to supply the heating. But to which extent will it be feasible to refurbish houses and invest in energy savings? And to which geographical extent will it be feasible to develop

the district heating systems in the future energy system?

There is a balance in the feasibility between heat savings and the supply of heating. There are costs connected to both heat supply and heat savings, but from a societal perspective, focus should be to find the long-term optimum between investments in heat supply and heat savings. In some cases, mainly new buildings, it will be relevant to consider low energy or passive houses with a very small heat demand. In other cases, mainly older existing buildings, the costs of heat savings per energy unit will be higher than the cost of supplying the remaining heat demand at some point. In most existing buildings, a substantial amount of heat savings will be feasible though.

District heating systems will need to be extended to convert some of the present natural gas areas or areas with individual boilers to district heating, which will improve the overall energy efficiency.

The development of DH systems requires substantial investments in infrastructure and, in some cases, it will be more socio-economically feasible to invest in a new individual heat supply solution such as heat pumps and solar thermal combined with heat savings. This will depend on the efficiency of the DH system, the amount of waste heat sources in the local area, and the heat demand density of the area.

4.2.1 Importance to the Energy System in the Greater Copenhagen Area

The points outlined in this section; i.e., requirement of reduction of temperature level in DH systems, change in heat sources for DH supply, and the balance between heat supply and heat savings, are important because the infrastructure should be dimensioned for the future demand situation and for the integration of new renewable heat sources into the supply. Large investments in technologies that do not suit a future 100%

renewable energy system may result in an

30 inefficient system where low marginal prices keep

renewable and more efficient alternatives out of competition. This points to the importance of energy savings in buildings and assessments of the potentials and the feasibility of investing in heat savings, to avoid an over-dimensioned supply system. The Greater Copenhagen Area includes Denmark’s largest DH system and it is also the most densely populated area of Denmark. This means that the planning of the development of the DH systems in Copenhagen is very important.

Here initiatives for heat demand reductions should be planned together with initiatives for the supply systems, including low temperature DH.

Heat savings in particular – and thereby lower demand - are also important because the low-cost base load heat sources can be supplied to other areas through the DH transmission system in the Greater Copenhagen Area and thus enable cheaper replacement of for example natural gas boilers. Heat savings in the City of Copenhagen may therefore lower heating costs in other municipalities. This should be considered in connection to a strategic energy plan.

4.3 Biomass, Electricity and Gas for