Cogeneration - Achieving Energy Savings
Ecoal, Vol. 74, Mary 2011
The recent economic slow-down has provided a new incentive to explore the energy saving potential of existing technologies. Combined Heat & Power (CHP) - which allows the simultaneous utilisation of heat and power - is one of the technologies that is receiving increasing attention.
CHP can achieve efficiency rates of up to 90% - almost double the current state-of-the-art coal-fired power plants. This is because the average global efficiency of traditional fossil fuelled power generation is around 35%-37% and the rest, or about two thirds of the primary energy input, is lost as waste heat.
CHP technology simultaneously utilises heat and power from a single fuel or energy source such as coal, natural gas, biomass or other renewable energy sources. CHP recovers energy which is normally wasted in conventional power generation. Heat recovered in this way can be used in a number of applications, including for heating, refrigeration or as process energy for industries.
Current Status
CHP power plants generate around 10% of the world's electricity. In OECD countries, almost one third of this is fuelled by coal and over 50% with natural gas. While natural gas is considered more appropriate in small CHP plants, coal is more extensively used in large CHP systems. CHP technology is most widespread in Europe. In Denmark, the share of CHP in total national power production is over 50%. Finland, Russia, Latvia and the Netherlands come next with a share of over 30%.
Mitigation Potential
The International Energy Agency (IEA) developed an energy scenario investigating the potential benefits from an accelerated deployment of CHP. The results show that, in comparison to the business-as-usual scenario, CO2 emissions arising from new generation plants can be reduced by more than 4% by 2015 and by 10% by 2030 due to CHP technology.
Denmark
Denmark obtains 51% of its electricity from coal and is home to some the most efficient coal-fired power plants in the world. With a 50% share of CHP in national power generation, Denmark is also the world's CHP leader and relies mainly on coal to power its CHP plants. In 2008 coal was used to generate 59% of electricity and 33% of heat produced in CHP plants in Denmark. In fact, the Avedore coal-fired CHP power plant is considered the most efficient fossil fuel power plant in the world. Its overall efficiency reaches 91% when heat demand is at its highest and in periods of lower heat demand, heating water is stored in tanks.
Developing Countries
According to the IEA, emerging economies represent some of the best opportunities to achieve benefits from CHP. India is considered to have significant potential in CHP generation. India is the world's largest producer of sugar and bagasse-based cogeneration is being particularly promoted.
Deployment of CHP in developing countries can be facilitated through the flexibility mechanisms under the Kyoto Protocol. CHP is part of the technology portfolio allowing supply side energy efficiency under the Clean Development Mechanism (CDM). India has hosted most of the CHP projects under the CDM - in 2007, 44% of all CHP projects registered under the CDM were in India.
Challenges
Despite its benefits, a number of barriers and challenges stop the wider deployment of CHP:
- Heat demand: CHP projects need to identify a relatively stable heat demand and rely on the availability of heat infrastructure. Although heat can be transformed into cooling during the summer, this adds to the overall cost of CHP.
- Regulatory barriers: there is no internationally agreed definition of CHP and its benefits are difficult to attribute between the heating and electricity sectors.
- Cost effectiveness: CHP projects require higher initial capital investment and smaller CHP projects often face cost effectiveness issues.
Future Perspectives
A number of countries have specific CHP targets and many have undertaken studies assessing their CHP potential. Germany intends to double its current share of CHP from 12.5% to 25% of national power generation. Japan has identified that around 11% of its power generation could come from CHP plants. In the USA, the share of CHP could rise from 8% to 12-21% by 2015. However, for CHP potential to be fully realised, government support will be needed to overcome the regulatory barriers and to facilitate the integration of CHP into existing energy markets.
