Heat is a crucial energy carrier, but considerable amounts are lost in homes, factories and thermal power plants. Recovering or producing this energy from renewable sources to heat domestic, collective or industrial sites would help cut down on the use of fossil fuels and reduce greenhouse gas emissions. That's the challenge being met by district heating systems. Some countries have developed these systems extensively, while others are just starting to look at them. This infographic gives an overview of the different ways to produce heat from renewable sources and outlines the advantages and disadvantages of each solution.