At its most basic, whether the source is nuclear, hydroelectric, fossil fuels or wind, electricity is generated by transforming one kind of energy into a flow of electrons. In order to determine how much generation capacity is needed, experts need to estimate the amount needed during peaks, which usually fall on hot summer days.

Total existing installed capacity was estimated to be 35,535 MW by the end of 2014. Last year saw an increase in wind and natural gas generation capacity compared to 2013. Hydroelectricity and nuclear power capacity have remained relatively unchanged over the last decade.

The amount of generation actually available at any one time is dependent on outages and the capacity factor at each facility. A key component of the cost of electricity is, the Hourly Ontario Energy Price, set in the wholesale power pool administered by the Independent Electricity System Operator.