Here’s a couple of great ideas for maximizing the efficiency of CHP-based district heating systems. On the energy input side, add a bioenergy plant so that food and sewage wastes can be used as carbon-neutral fuels; and on the output side, add the capability for surplus power generated both to be stored and used to charge electric vehicles locally. These are the aims of a two-year project just started in the city of Birmingham, UK.

Birmingham already has a series of modern district heating networks fed by gas-fired CHP plants. The network supplies heat and electricity to many buildings including the City Council HQ, the main railway station, the City Library, and Aston University, which is home to the European Bioenergy Research Institute (EBRI). The plan is to connect EBRI’s 1 MW gasification waste-to-energy plant to a district heating network, making at least some of the heat sent to consumers to be from a renewable resource.

On the electrical front, the system will be controlled to allow surplus power to be stored for future use, or to power new electric vehicle charging points in the city. And the whole system is to be controlled to optimize revenue generation for those putting energy into the system, maximize carbon savings, and help National Grid to balance local electricity systems.

The intention is to develop techniques that can be transferred to other district energy systems around the UK. Each of these will be different, of course, but an established district energy (DE) network is the key to making full use of local renewable energy resources in any town or city. In this Birmingham example an existing biomass-to-energy facility is to be connected to the DE system, but this could just as well be a municipal waste-to-energy facility, ‘waste’ heat from local industrial processes or wastewater treatment facilities, or any of a number of lower-grade waste heat streams now being recognised as valuable.

For example, in London local energy specialists are working to incorporate waste heat from electricity transformers and warm air emanating from the underground rail system into DE systems, although for these lower-grade sources a heat pump may be required to raise their temperature.

District energy networks really are fundamental to local energy, providing a set of client buildings for generated power and heat, and opening up opportunities to recover and make use of  ‘free’ heat’ from a variety of sources locally