When you flip a light switch, the energy reaches your bulb almost instantly, but it may have started its trip at a nuclear station on Lake Huron, a waterfall at Niagara or a wind farm near Lake Erie. Most electrical energy has to be generated at the moment it is needed, from some other form of energy. Every way of doing that has benefits and costs, for your wallet, for nearby communities and for the climate. In this lesson you will see how generators work, weigh Ontario's energy sources, and plan real actions to use energy more wisely.
How a generator works
In 1831, Michael Faraday discovered that moving a magnet near a coil of wire (or moving a coil near a magnet) pushes the electrons in the wire and makes a current. This is called electromagnetic induction, and it is how almost all of our electricity is made. A generator spins a magnet inside coils of copper wire (or spins coils inside a magnet), transforming kinetic energy into electrical energy. Something has to do the spinning: a turbine, a set of blades on a shaft, pushed around by falling water, wind, or high-pressure steam. The steam comes from boiling water with heat from burning natural gas or biomass, or from nuclear fission. Solar panels are the main exception: they transform light directly into electrical energy with no moving parts.
Where Ontario's electricity comes from
Ontario gets most of its electricity from sources that release few greenhouse gases while running. In 2025, roughly 46% came from nuclear, about 22% from hydroelectric (waterpower), about 19% from natural gas, about 9% from wind, about 2% from solar and less than 1% from bioenergy. The share from natural gas was higher than in many recent years, when it was closer to a tenth, because demand grew and several nuclear reactors were offline in planned shutdowns, mostly for refurbishment. Ontario burned its last coal for electricity in 2014, and over the same years smog days in southern Ontario dropped to almost none. The exact shares change every year, but the pattern of roughly half nuclear and a fifth to a quarter hydro has held for a long time.
| Source | Renewable? | Benefits | Challenges |
|---|---|---|---|
| Nuclear (uranium) | No | Huge, steady output; almost no greenhouse gases while running; many skilled jobs | Radioactive waste that must be stored safely for a very long time; expensive and slow to build; uranium mining |
| Hydroelectric (falling water) | Yes | No fuel cost; no greenhouse gases while running; output can be adjusted quickly; dams last for decades | Dams flood land and change river ecosystems and fish habitat; past projects flooded First Nations lands; few good sites left in the south |
| Natural gas | No | Can be turned up or down quickly to match demand; plants are fairly cheap to build | Burning it releases carbon dioxide; gas leaks release methane; fuel prices change |
| Wind | Yes | No fuel and no emissions while running; farmers can earn rent for turbine sites | Only produces when the wind blows; some bird and bat deaths; noise and views concern some neighbours |
| Solar | Yes | No fuel, no moving parts; can go on rooftops close to users | No output at night and less in winter or cloudy weather; panels need mined materials and recycling |
| Bioenergy (wood waste, crops, landfill gas) | Yes, if the plants are regrown | Uses waste materials; can run whenever needed | Releases carbon dioxide and air pollutants when burned; needs land and fuel transport |
Impacts on communities, near and far
- Climate: burning fossil fuels releases carbon dioxide, the main greenhouse gas driving climate change, which affects communities around the world through heat waves, floods and wildfires.
- Air quality: coal plants caused smog and asthma attacks in southern Ontario. Closing them was one of the largest greenhouse-gas cuts in North America at the time.
- Land and water: large dams and reservoirs have flooded forests, hunting grounds and homes. Today, many new energy projects in Ontario are built as partnerships with First Nations, who share in decisions and profits.
- Long-term waste: Canada's used nuclear fuel is stored at reactor sites for now. In 2024, the Nuclear Waste Management Organization chose the area of Wabigoon Lake Ojibway Nation and Ignace in northwestern Ontario, with both communities willing, as the planned site for a deep underground repository.
- Global access: hundreds of millions of people worldwide still have no electricity at home, which limits schooling, health care and clean water. Low-cost solar panels and batteries are bringing power to many remote communities, including some in northern Canada that rely on diesel generators.
Emerging technologies: storage, smart grids and more
- Battery storage charges when there is extra electricity (for example, windy nights) and releases it at busy times. The Oneida Energy Storage project in Haldimand County, built in partnership with the Six Nations of the Grand River Development Corporation, began full operation in 2025 with 250 MW of lithium-ion batteries, at the time the largest battery facility in Canada.
- Pumped storage uses cheap night-time electricity to pump water uphill into a reservoir, then lets it flow back through turbines when demand is high. Ontario Power Generation has done this at its Sir Adam Beck station at Niagara Falls for decades.
- Smart grids use smart meters, sensors and two-way communication to match supply and demand, reroute power around problems and connect rooftop solar, batteries and electric vehicles.
- Heat pumps and electric vehicles replace burning fuel at home and on the road with efficient electric devices, which raises electricity demand but lowers total emissions when the grid is clean.
- Small modular reactors (SMRs) are smaller nuclear reactors designed to be built faster in standard pieces; Ontario Power Generation is building Canada's first one at its Darlington site.
Making a plan of action
- Pick the issue. For example: "Our home uses a lot of electricity at on-peak times" or "Our school leaves lights and computers on overnight."
- Gather data. Read the electricity bill or smart meter data, list devices with their power ratings and hours of use, and look for EnerGuide labels.
- Brainstorm actions. Conservation (using less: turning things off, air-drying laundry), efficiency (using better devices: LED bulbs, ENERGY STAR appliances, heat pumps) and shifting (moving use to off-peak hours).
- Choose and set a measurable goal. Use E = Pt and the price per kWh to estimate the savings of each action, then pick the best ones: for example "cut our monthly use by 10%."
- Act, measure and share. Carry out the plan, compare the new bills or meter readings with the old ones, and share what worked so others can try it.