Source: S.O.L.I.D. Invest

Interconnected systems towards 100% renewable district heating & cooling

This Solution provides guidance on the integration of renewable energy sources in district energy production, both in new systems and in already existing ones, and can be of interest to both established and growing cities. While for new district energy systems cities should explore the opportunities to integrate local renewable energy from the early planning stage, for already existing systems the integration of renewables will be particularly interesting if coordinated with system expansion and/or the retrofitting plan of both production and network. These situations will offer opportunities to optimize the layout and design parameters such as reduction of the network temperature overall or in new subsystems. For already established and large systems, decentralized production using multiple renewable sources and technologies offers benefits in terms of reliability, operational flexibility and cost-effectiveness.

This Solution explores the different roles that local governments can play, including in creating an enabling framework in the context of urban and energy planning, facilitating stakeholder engagement and as owner and/or operator of a district energy utility.

It also zooms in on technical aspects such as specificities of different renewable energy sources (e.g.: biomass, solar thermal energy, waste heat from waste water, biogas or geothermal energy), thermal storage, lower operating temperatures and integration with the electricity grid.

This Solution builds on existing case studies and literature such as the flagship publication of the Global District Energy in Cities Initiative, led by UN Environment, and IRENA’s Renewable Energy in District Heating and Cooling, as well as on projects funded by the European Commission to promote the integration of renewable energy in modern district energy systems such as “SmartReflex – Renewable District Heating & Cooling” and “SDHp2m – solar district heating … from policy to market”.

It is assumed that the user has a good understanding of district energy concepts and processes. For additional information on those topics, please see the other Solutions included in this Package.

Video: Thisted - A Climate Friendly Region – the municipality has 100% renewable electricity and 85% renewable district heating supply, using multiple renewable energy resources such as wind, geothermal, biogas, straw. Source: Denmark State of Green.

Motivation / Relevance

More and more governments are recognizing the importance of renewable energy for security of supply and derive other socio-economic benefits, as demonstrated by the interest in the International Renewable Energy Agency (IRENA) which now has 150 Member States plus 28 States in the process of accession [1]. 

District energy has a high potential for enabling the integration of local renewable energy sources in the energy mix used for heat & cooling and electricity generation and thus contribute to reducing greenhouse gas emissions. However, in practice this potential is largely underutilized. The graphic below shows fuels used in global heat generation (IEA, 2016 in IRENA, 2017 [2]), showing that renewable sources represent 7-8% of the primary energy used in district heating [2][10]. For example in Spain only one third of the district energy networks consume renewable energy - the main renewable energy source used is biomass, in small district heating networks [3]. Only a few countries have taken advantage of their renewable resource potential for district energy or created policies to promote further uptake and renewable district energy still plays a modest role in most countries [2]. A study by IRENA [2] shows that renewables could theoretically satisfy all district energy demand in 2030. Realistically, taking into account technology costs, resource availability, land use and other criteria renewable energy could supply more than 20% of the energy needed for district energy within a few years, given the right policy and technology choices now. In a few countries, such as Denmark and Switzerland, renewable energy already provides more than 40% of district heat supply [2]. Geothermal, bioenergy, solar heat and free natural cooling are pointed as sources with great potential across different countries [2].

Source: IEA, 2016 [in 2]

The economic rationale for scaling up use of renewable sources in district energy becomes particularly compelling when the costs of pollution and carbon dioxide emissions are taken into account [2], although in the case of biomass good boiler standards should be enforced to ensure this statement holds unambiguously true [adapted from 31].

In Germany, an industrialized country that has set the ambitious target to reduce its greenhouse gas (GHG) emissions by 80% by 2050 in comparison with 1990 levels, the share of renewable energy in district heating systems is currently around 9% (including a considerable portion from waste incineration). The federal government`s energy concept to achieve the 80% GHG reduction target includes an increase an increase of renewable energy use in district heating generation to 47%, recognizing an important role for district energy [4].

Denmark is another country recognized for its leading role in the transition renewable energy. The country’s energy system evolved from a centralized production model in the 1980-90s to a decentralized production model with co-production of heat and electricity with around 415 decentralized plants being built in association with district heating [14]. Other advances include the integration of the electricity and heat networks and large-scale solar district heating systems - in 2013, the renewable energy share in Denmark’s energy mix was 27% compared with the EU average of 15% [5]. In Denmark approximately 55 district heating utilities (of more than 400 in total) are owned by municipalities and they deliver more than 60% of the district heating demand. Also where the utilities are not owned by the municipality, close cooperation exists and often representatives from the municipality are on the board of the utility [3] facilitating cooperation and planning coordination.

Main impacts

  • Reduce imports and dependency on fossil fuels
  • Protection against volatile and rising fossil fuels prices [6][15].
  • Development of local economy [5] - Drawing from local resources allows financial resources to keep circulating in the local economy, in contrast to the imports of fossil fuels [2].
  • Green business development
  • Potential improvement of air quality, contributing to better public health
  • Climate change mitigation

Benefits and Co-Benefits

  • Increased use of local renewable energy resources, such as solar thermal, geothermal and agriculture, urban and forest biomass, and waste heat [3]
  • Stable and secure heat/cooling supply [5][15]
  • Fixed, long-term energy prices [15]
  • Reduces costs for district energy consumers through the use of low cost local energy sources such as heat pumps and combined heat and power generation which are not always suitable for single-building energy systems [3]
  • Lower need for maintenance has been documented for geothermal and solar thermal plants compared to other conventional heat sources [13][15]
  • Increases local employment through the use of local energy resources and district energy [3]
  • Reduction of air pollutants associated with burning of fossil fuels, such as sulphur dioxide (SO2), nitrogen oxides (NOx) and particulates [3]. To ensure these benefits are confirmed in the case of biomass use, strict boiler standards and pollution controls should be in place [31].
  • Greenhouse gas (GHG) emissions reduction  


This Solution was jointly developed and peer-reviewed by ICLEI and the Global District Energy in Cities Initiative (DES Initiative) , which is coordinated by the United Nations Environment.

ICLEI acknowledges and recognizes all individual organizations and experts that kindly contributed their time and expertise to this Solution - for details please see the "Developer" section above and the "Supporters" webpage.

This Solution draws significantly upon the UN Environment publication: District Energy in Cities. For more information on the Global District Energy in Cities Initiative (DES Initiative) and to become a partner or learning city, please visit:

This initiative is the implementing mechanism for the SEforALL District Energy Accelerator.