100% renewable district heating

Why a R&D project?

One of the huge problems when talking about solar heat and renewable energy sources in general, is storage technologies. Provided that energy systems in the future should consist of windmills, solar collectors, solar cells or wave energy operated with high long term efficiency, the seasonal storing will become a necessity.

This is not least the case in North European countries, where the solar energy production capacity and the heat storage capacity have to be high, because of the relatively short period of high solar energy production. Facing these barriers of overheating and at the same time keeping down costs is a big challenge.

The SUNSTORE4 plant, which concept is being developed in the framework of this project, is the first of its kind. Therefore, the team had almost to start from scratch and to implement innovative solutions.

The unique about the SUNSTORE concept is its flexibility

The concept makes it possible

  • To use all types of renewable heat and waste heat, because of the storage and the heat pump (solar thermal, geothermal, biomass, waste heat from incineration, excess heat from industries).
  • To provide consumers with district heat from 100% RES, also without use of biomass.
  • To consume and to produce electricity when needed in the electricity system and thus to integrate fluctuating electricity production from wind and solar.
  • The concept can be built up gradually.

Challenges to be taken into account when developing a 100% Renewable District Heating:

  • Overall cost efficiency, not only for long term heat storage;
  • Technical and functional reliability of the long term heat storage, avoiding problems with liners and cover;
  • System integration between the elements of the solar thermal, heat pump, biomass CHP plant and the long term heat storage;
  • Low efficiency of the solar absorbers, e.g. due to condensation problems or overheating problems during summer time;
  • Increasing the energy efficiency in the biomass boiler and reduce especially the NOx- and particle emissions considering the utilisation of wet biomass fuels;
  • Increasing running hours for electricity production from biomass CHP based on ORC;
  • Flexibility in the system concept making it possible to adapt the core parts of the system concept to different conditions in different regions of Europe, e.g. including cooling as a part of the concept being important in southern Europe with overheating climate conditions;
  • High solar fractions mean higher solar panel temperatures in summer and higher heat loss from the storage and thus lower utilised heat production. This makes it important to reduce investment costs for solar panels and storage;
  • High solar fractions mean high temperatures in 4-5 summer months in the storage. This will reduce the lifetime of plastic liners.

The projects SUNSTORE2 and SUNSTORE4 were intended to tackle these challenges.