Producing Electrical Energy: Efficiency and Environmental Impact

Where does your electricity come from?

When you charge your phone in Ontario, the energy most likely came from a nuclear station such as Bruce, Darlington or Pickering, or from a hydroelectric station on a river like the Niagara or the Ottawa, with some from natural gas, wind, solar and bioenergy. Not long ago, Ontario also burned a lot of coal. Every source has a different efficiency and a different environmental footprint. In this unit you have learned how generators and transformers work; now you will judge the systems they are part of.

Efficiency of a generating station

Efficiency = (useful electrical energy out ÷ total energy in) × 100%, and the same with power.

In any thermal station (coal, natural gas, oil, biomass or nuclear), heat boils water, the steam spins a turbine, and the steam must then be cooled and condensed back to water before it returns to the boiler. That cooling step dumps a large amount of waste heat into a lake, river or the air. It is a basic limit of heat engines, not just poor engineering. Rough typical efficiencies:

• coal: about 33% to 40%
• nuclear: about 33%
• natural gas, combined-cycle (a gas turbine plus a steam turbine using its hot exhaust): about 50% to 60%
• hydroelectric: about 85% to 90% of the water's gravitational potential energy becomes electrical energy
• wind turbines: a large share of the wind's energy passes through unused; physics limits any turbine to at most 59%, and real turbines capture less
• solar photovoltaic panels: about 15% to 22% of the sunlight

Low efficiency is not the whole story. Wind and sunlight are free and do not run out, so the environmental impact also matters.

Analysing one source in depth: coal

How it works: coal is burned in a boiler; the steam drives a turbine and generator; the steam is condensed with cooling water.

Efficiency: only about a third of the coal's energy becomes electricity.

Environmental impact:

• Carbon dioxide: coal releases more CO₂ per kilowatt-hour than any other common source, contributing to climate change.
• Air pollutants: sulfur dioxide and nitrogen oxides (acid precipitation and smog), fine particles (lung and heart disease) and mercury (which builds up in fish).
• Mining and waste: land disturbance from mining, and large amounts of ash to store.
• Thermal pollution: warm cooling water returned to lakes and rivers.

Ontario's decision: Ontario phased out coal-fired electricity generation; its last coal-fired station stopped burning coal in 2014. Most of the replaced energy came from refurbished nuclear capacity, natural gas and new wind and solar, together with conservation. Ontario's electricity is now one of the lower-carbon supplies in North America, although natural gas use (and its emissions) has varied from year to year.

Comparing sources

• Nuclear: very low greenhouse-gas emissions during operation and a steady supply, but long-lived radioactive waste that must be stored safely, high construction and refurbishment costs, and uranium mining impacts.
• Hydroelectric: very efficient, renewable and flexible, but dams flood land and change rivers, fish habitat and the traditional lands of First Nations communities. Newer projects in Ontario include partnerships in which First Nations co-own the station, such as the Peter Sutherland Sr. Generating Station, built by Ontario Power Generation with Taykwa Tagamou Nation.
• Natural gas: more efficient and cleaner than coal and can be switched on quickly when demand rises, but it still emits CO₂ and methane can leak during extraction and transport.
• Wind and solar: no fuel and no emissions while operating, but they produce power only when the wind blows or the sun shines, so they need backup or storage, and they use land and materials.

Ways to make production more sustainable

• Conservation and efficiency at home: the cheapest, cleanest kilowatt-hour is the one not used.
• Cogeneration: use a thermal station's waste heat for district heating or industry.
• Storage (batteries, pumped hydro) to make wind and solar more useful.
• Choosing low-emission sources, and capturing emissions where fossil fuels are still used.
• Better transmission (high voltage, as you saw) to reduce losses.
• Planning with the communities affected, including First Nations, Métis and Inuit communities, through meaningful consultation and partnerships.