Efficient Energy Production through Cogeneration and Trigeneration

Cogeneration is the simultaneous production of useful heat and electricity from the same fuel (IEA, 2009), also known as Combined Heat and Power generation (CHP). It is much more efficient than separate power generation through the combustion of fuels and usually a good choice for large consumers of both heat/cool and electricity such as certain types of industry and hospitals. Cogeneration is ideally suited for constant load profiles of heat and electricity. Its viability is also enhanced by the possibility to feed excess electricity into the public grid and heat into a district heating network.

Taking this one step further to integrate cogeneration with chillers in one process and thus generate cooling from waste heat is called trigeneration or Combined Cooling, Heating and Power (CCHP). Absorption chillers are typically used. By using the fuel in sequential steps, higher primary energy efficiency and cost-effectiveness can be achieved.

This Solution looks at the framework conditions and determinants that are relevant for project viability and implementation. It also looks at the relevance of district cooling in complementing and strengthening the business model for district heating when cogeneration is used.

Some of the roles local governments can play include: acting as role model by contributing to demonstration projects, policy, planning, regulation, stakeholder engagement and coordination for systems-integration across urban utilities and matchmaking between waste heat supply and demand.

Motivation / Relevance

Cogeneration is a well-established and proven technology that contributes to a more decentralized and reliable electricity and thermal energy supply.

Secure, reliable and affordable energy supplies are fundamental to economic stability and development. In emerging economy countries in particular, rapid population and economic growth result in fast growing electricity demand, often leading to a constrained power grid that hampers industrial and economic development.

The demand for higher indoor comfort level as well as the misalignment between energy demand and supply have major consequences on energy prices, energy security and climate change, posing a major challenge for decision makers. Cogeneration can help address these challenges by enabling a more efficient use of primary energy sources (International Energy Agency, 2011 in [1]). As a result many industrialized countries developed explicit objectives and policies to promote cogeneration although these can change over time, for example, European policy priority has shifted from cogeneration to renewable energy recently.

The efficiency gain of cogenerated heat and power (which is typically in the range 75-90%) in comparison with the traditional separate provision of electricity for the grid (which is typically in the range 35-40%) is more than 30% [1]. For example Helsinki’s CHP plants often operate at 93% primary energy efficiency, in connection with district energy [18]. This translated into direct savings of primary energy (fuel) and has an even greater impact on climate change mitigation, as cogeneration often also implies a fuel switch, for example from coal (with a greenhouse gas emission factor of 101 t CO2/TJ)  to gas (55-56 t CO2/TJ) reducing the carbon intensity of electricity generation [2]. Cogeneration projects are usually smaller than conventional power plants and thus have lesser financing challenges and shorter lead times to be implemented [1].

Nevertheless, there are also very large cogeneration plants, for example in Warsaw, where two large combined heat and power plants of Siekierki (622 MWel and 1966 MWth) and CHP Żerań (334 MWel and 1435 MWth) are the basis of the energy system. Warsaw also has the largest district heating system in the European Union. The total length of the double heating pipes is 1763 km, supplying 18 600 buildings and covering 78% of the demand of the city inhabitants. Economies of scale of such large systems enable the price of heat to be very cheap. The use of large cogeneration plants to produce electricity near or inside the city is also very important for energy security [25].

Trigeneration can also be used as a substitute for diesel generators in the education and health sectors in particular, providing heat, steam and cooling energy for operations, hygiene and medication.

 

Maabjerg cogeneration plant fired with biomass and biogas. Source: Denmark, State of Green

Main impacts

  • Increased energy security
  • Reduced imports and dependency on fossil fuels
  • Resilience of energy supply, for example in 2003 the New York blackout 58 hospitals lost power, whereas hospitals with cogeneration were able to operate as normal, prompting the New York State to become a strong proponent of CHP at critical infrastructure facilities (Hampson et al., 2013; Hedman, 2006 in [1]).
  • Increased local and regional manufacturing and value added, particularly in developing and emerging economy countries where industrial development and production is being hampered by lack of grid capacity and power outages with consumers having to invest heavily on standby diesel generators.
  • Reduced strain in the power grid and avoidance or delay of investments in power grid infrastructure, namely trigeneration in connection with district cooling, waste heat use or free cooling sources.
  • Increase resilience of industry and the service economy to energy prices fluctuations
  • Increased competitiveness of small and medium-sized enterprises due to lower energy costs
  • Economic development and job creation.
  • Contribution to climate protection and decarbonisation strategies: reducing primary energy consumption and promoting the use of lower carbon intensity fuels. This is the case in Copenhagen, Denmark, and Frankfurt, Germany, where cogeneration and district energy systems are a cornerstone of the climate and energy policies [18]. 
  • Contribution to Sustainable Development Goal 7: Ensure access to affordable, reliable, sustainable and modern energy for all
  • Lower the heat island effect. By step usage of the primary energy, less heat is dumped into the outdoor environment.

Benefits and Co-Benefits

  • Decreased use of primary energy by 30 to 40% compared to separate electricity and heating/cooling generation.
  • Increased security of supply due to increased energy efficiency and additional decentralized electricity generation
  • Decreased transmission and distribution (T&D) distances and corresponding energy losses. This can be particularly relevant in developing countries: while the T&D losses corresponded to 6% in the European Union and OECD countries in 2013, they amounted to 14% in Mexico and 18% in India [19]. 
  • Reduced burden of fossil fuel import on public budget, balance of payments and currency
  • Reduced peak electricity consumption and strain on the power grid in the summer through the use of trigeneration and connection with district cooling
  • Lowering the energy bill to consumers – Here are a few examples The Aberdeen City Council identified that district heating connected with cogeneration was the technical solution best able to deliver low-cost heating to residents for the implementation of the Affordable Warmth Strategy approved by the Council. In Velenje, Slovenia a pilot project utilizing waste heat through absorption chiller technology achieved significant electricity savings relative to normal cooling technologies, at a production cost that is 70 per cent that of normal cooling technologies [18].
  • Potential to enhance private investment in energy efficiency on the supply side
  • By integrating CHP with district energy networks, there is a more steady demand, making the system more cost-effective.

Acknowledgements

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: www.districtenergyinitiative.org.

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