How will the role of cogeneration develop as we head towards a low carbon and decentralized energy future? The quick answer is that it will depend, eventually, largely on the fuel used to generate heat and power; the current favourite, natural gas, or various bioenergy options (I’m assuming that the role for coal-fired CHP will end quite soon).
I’ve been looking at an analysis of the economic and environmental case for cogeneration in the US both now, and in a future in which generators have to pay significant carbon taxes. For the moment, a well-designed gas-fired cogeneration installation demonstrates significant environmental (ie carbon) advantages in most parts of the US, but not necessarily in those where zero carbon hydropower is the dominant grid-supplied alternative.
On the economic front, in today’s US of plentiful gas supplies and high electricity costs, cogeneration also tends to be a winner – carbon costs are all but insignificant. But, looking to a future with much more renewable electricity on the system and with hefty charges for carbon emissions levelled on generators, that starts to change – both the economic and environmental advantages of cogeneration start to reduce.
In the UK, it used to be easy to contrast high efficiency, predominantly gas-fired CHP with what was predominantly coal-fired power generation, with a distinctly low efficiency of 33–34%. The quantity of heat discarded at coal power stations was often quoted as equivalent to the total heat requirements of the country – a disgraceful waste.
The arrival of more efficient combined cycle gas-fired plants onto the system started to reduce the carbon advantages of CHP, and the subsequent arrival of significant amounts of wind power reduced them a little further. Cost advantages are more difficult to quantify, but we can expect both environmental and economic benefits with CHP to persist for many years yet, as coal-fired power stations continue to throw away vast quantities of heat in both the US and the UK.
Meanwhile, an increasing number of waste, biomass and biofuel CHP systems will combine renewable fuels with CHP’s particular advantage – high efficiency operation. Eventually a wider move to decentralized energy systems – where fossil and renewable CHP plants, waste and biomass-fuelled boilers, waste heat from local industries, heat pumps and solar electric and thermal units, all working with flexible district energy systems, will prove the winning combination.