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District Heating and Cooling

Annex XIV Project 04

The Research / IEA DHC Annexes / 2023-2026 / Annex XIV / Annex XIV Project 04

RE-PEAK - How to cover peak heat loads in DH networks with renewables?

Project summary

District heating networks (DHN) are still relying too much on fossil fuels, although the application of renewables is increasing. Today, many DHNs already use climate-neutral alternatives like geothermal and solar thermal energy, biomass, heat pumps with green power, waste heat and waste incineration for heat generation. These often fixed-cost-intensive systems usually require a certain number of full-load hours to be economic and are used to cover the base load. In most DHN, the challenge for full “decarbonization” is the supply of peak heat load.

Peak loads are about performance, not quantity. Peak heat load plants are only used for a few hours a year. They require having low investment costs. Due to their limited duration of operation, they may have higher operating costs. The demand for high performance can most easily be covered by combustion technologies. That explains why today, natural gas or heating oil are the dominant energy sources for providing peak heat load.

Many technologies that are expected to provide carbon-neutral peak heat load are mature. These include electricity generation (PV, wind) and transmission, electrolysis, fuel cells, combustion CHP, carbon capture. Nevertheless, there is no significant market for many of these technologies or their application in DHN. Although these markets currently appear to be forming, their medium-term development (i.e., availability for the parallel development of DHN towards climate neutrality) and their long-term shape (i.e., prices, quantities, security of supply) are not clear. Especially in winter, the “benchmark renewables” are green gas or green electricity, which need to be seasonally stored or imported. These high-exergy energy carriers are very expensive and scarce. The following questions arise: How big is the challenge of decarbonizing peak heat loads? What are the technical & economic options/limitations? Are there alternatives to the benchmarks? In which direction are the DHN operators planning?

The first goal of RE-PEAK is to provide a better understanding of the current problems of fossil-based peak heat load supply in DHNs and the possible challenges in the transition towards a climate-neutral provision. Therefore, a taxonomy of peak heat load will be created and the term will be classified according to certain criteria (e.g., temperature level, network size, maximum load etc.) using a model that will be developed in RE-PEAK. Based on this, it can be decided which alternative carbon-free energy sources are technically suitable and their economic feasibility can be elaborated.

The second goal is to obtain empirical data on the provision of the peak heat load through a comprehensive survey, which will be conducted to gain insight into the heat generation in DHNs, their internal definition of peak heat load, its reasons/occurrence and duration. We will then evaluate the answers statistically.

The third goal is to empirically analyze the perception of DHN operators regarding the transition to climate-neutral peak heat supply. The survey results will allow reflecting on the prevalent opinions on the various options and especially the “benchmark renewables”. In this context, the trends should also be clarified: How do the DHN operators expect that the climate-neutral provision will look like in their network; do they already have concrete plans or strategies?

The final goal of RE-PEAK is to merge the results and to derive recommendations. The aim is to prepare these in an application-oriented manner and make them usable: for DHN operators, we will develop a self-assessment tool. policymakers and branch organizations will benefit from an illustrative summary in a SWOT-like matrix that allows a direct comparison of the options and their strengths and weaknesses.

Thus, the transition of DHN must be supported by a better understanding of the challenges and options associated with peak heat loads.

Target audience and specific issues

  • DH industry representatives and utilities 
  • Authorities responsible for energy planning and regulation
  • National governments and international policymakers

Project aims

The aim of RE-PEAK is to

  • amplify the challenge associated with the decarbonization of peak heat loads,

  • derive empirical results about the DHN operators’ perception of climate-neutral options,

  • elaborate a technically sound decision support tool for DHN operators.

Project lead

Energieinstitut an der Johannes Kepler Universität Linz (EI-JKU)
Altenberger Straße 69
4040 Linz

Dr. Simon Moser
Phone: +43 676 4404755
Email: moser@energieinstitut-linz.at

Partner Organizations

  • Department of Energy Technology (DET), Estonia

  • Euroheat & Power (EHP), Belgium