Electricity Fuel Source Technical Papers

cogeneration

Cogeneration

Cogeneration Fast Facts

  • Cogeneration is the “simultaneous production of electrical and thermal energy from a single fuel.” 1
  • About seven per cent of electricity generation in Canada is through cogeneration. Alberta has 2.3 GW of cogeneration capacity, which is the largest in Canada. Ontario is second to Alberta, with 2.1 GW. These two provinces account for 67 per cent of the cogeneration capacity in Canada. Canadian utilities account for the most cogeneration capacity, at 45 per cent when classified by systems operator. This is followed by paper manufacturing, at 23 per cent.
  • There are five types of cogeneration systems. Condensing steam turbine engines are the most efficient, at 81 per cent, while diesel systems are the least efficient, at 41 per cent.

Cogeneration Basics

  • Cogeneration, combined heat and power (CHP), is the simultaneous production of electrical and thermal energy from one fuel source. The waste heat from electricity generation is recovered and used for applications such as space heating and cooling, water heating, and industrial process heat. By making use of the waste from one process in the production of the other, substantial gains in energy efficiency can be realized.
  • A cogeneration facility is comprised of two basic parts: a power generator and a heat recovery system. A range of technologies can be used to achieve cogeneration, including steam turbines, gas turbines, reciprocating engines, microturbines, fuel cells, and Sterling engines.
  • Cogeneration can be implemented at a range of scales, from large scale systems serving communities or large industrial complexes, to independent energy supplies for hospitals or universities. Since heat is not easily transported, facilities must be located near their “thermal hosts” or users of thermal energy.
  • System efficiency and heat output characteristics are important attributes of cogeneration. System efficiency is the percent of fuel converted to electricity plus the percent converted to useful thermal energy. Most cogeneration systems have overall efficiencies between 65 per cent and 85 per cent. Heat output from cogeneration systems varies depending on the system type. High pressure, high temperature steam is considered high quality thermal output and can be used to meet most industrial process needs. Hot water is considered low quality and can be used only for limited thermal applications.

Cogeneration in Canada

  • In 2011 there were 6.5 GW in electricity capacity in Canada. Alberta has the most cogeneration capacity in Canada, the majority of which serves the oil and gas industry. Cogeneration in Ontario serves a broader range of industries, including manufacturing, forest products, hospitals and universities. The majority of cogeneration capacity in British Columbia, Manitoba, Quebec and the Maritimes serves the forest products industry.
  • The technology has experienced two significant growth periods, the first of which occurred in the 1970s in response to rising energy prices and a perceived scarcity of energy resources. The second began in 1990 due to public protest over large-scale energy projects, smaller systems becoming more cost effective, and deregulation in Alberta stimulating the development of larger, grid-connected cogeneration systems.

Benefits of Cogeneration

  • By using outputs and waste from one process as inputs to other processes, cogeneration systems have the potential to increase fuel efficiency, reduce energy costs, reduce greenhouse gas (GHG) emissions, and reduce releases of ozone depleting chlorofluorocarbons (CFCs) from air conditioning units.
  • The benefits of cogeneration are maximized when the production of electricity is maximized and the thermal load requirements of the host are closely matched. If the thermal output is greater than necessary, excess thermal energy is produced that could have been used to generate more electricity.
  • Location of cogeneration near load for heat means electricity is produced closer to load than centralized power production. This “distributed” energy approach allows for geographically dispersed generating plants, reduces transmission losses, and provides spare and process heating / cooling for buildings.
  • Most of the world’s electricity is generated by rotating machinery that is driven by the combustion of fuels. As a result, cogeneration systems have enormous potential for growth.

Challenges to Development

  • Siting of cogeneration can be challenging, as facilities must be located near their thermal hosts, as well as near an area of the grid that requires additional capacity in order to maximize efficiency. In addition, integrating distributed energy sources into the electricity grid may require transmission and distribution system upgrades.
  • Many players must work together in the development and operation of a cogeneration facility, including the electricity generator, the utility that distributes the electricity, and the thermal host. The distribution utility must be willing to purchase power from the generator, and may put restrictions or costs on connecting to the grid. In addition, the thermal host may have fluctuating heat requirements which are difficult for the system to follow.
  1. Natural Resources Canada, RETScreen International, www.retscreen.net

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