Here are a few key concepts to help us understand why water and wind are complementary.
The capacity to do work (in the field of electricity). The units of measure for power are the watt (W) and its multiples: kilowatt (kW), megawatt (MW), gigawatt (GW) and terawatt (TW).
Total generating capacity of the units in a facility (e.g., a wind farm or hydropower plant). Expressed in MW (millions of watts).
A hydropower plant with 2 generating units of 50 MW each has an installed capacity of 100 MW.
2 HYDRO GENERATING UNITS X 50 MW = 100 MW
This doesn't mean that the hydropower plant always has a maximum output of 100 MW. What it does mean is that if all the hydroelectric generating units were working to capacity at a given moment, the facility's output would be 100 MW.
A wind farm with 50 wind turbines of
2 MW each has an installed capacity of 100 MW.
50 WIND TURBINES X 2 MW = 100 MW
This doesn't mean that the wind farm always generates 100 MW. What it does mean is that if all the wind turbines were working to capacity at a given moment, the facility's output would be 100 MW.
The capacity that can be made available with a predetermined level of reliability. It's very important for an electric utility to be able to count on firm capacity, because electricity must be available just when the customer needs it.
The capacity of a hydropower plant can easily be guaranteed, because the quantity of water sent through the turbines can be controlled at all times.
A hydropower plant with an installed capacity of 100 MW has a firm capacity of nearly 100 MW, since generating units seldom break down.
100 MW HYDRO = 100 MW FIRM CAPACITY
In the case of a wind farm, there is no guarantee that the wind will blow when electricity is needed.
That is why Hydro-Québec has determined, based on statistical and meteorological studies, that during periods of peak demand, wind farms as a whole can contribute 35% of their installed capacity.
100 MW WIND = 35 MW FIRM CAPACITY
This is the power generated by a facility (e.g., a wind farm or hydropower plant) multiplied by the number of hours during which that power is delivered. The units of measure for energy are the watthour (Wh) and its multiples: kilowatthour (kWh), megawatthour (MWh), gigawatthour (GWh) and terawatthour (TWh).
Your electricity meter measures the energy or kilowatthours consumed, and this is what you are billed for.
Power X Number of hours = Energy
A wind farm that generates 100 MW for one hour on a continuous basis produces 100 MWh (megawatthours) of electrical energy.
No generating facility can operate at maximum capacity all the time, since allowances have to be made for maintenance, equipment failure and energy source availability. To determine a facility's real energy output, you need to consider its annual load factor, that is, the ratio between its actual energy output in a given year and the energy that would have been produced had the facility been operated continuously at maximum capacity throughout the year. This ratio is generally expressed as a percentage.
A hydropower plant with an installed capacity of 100 MW and a load factor of 65% (average load factor for Hydro-Québec's generating fleet) has an annual energy output of 569,400 MWh.
100 MW x 65 % x 8,760 h = 569,400 MWh
A wind farm with an installed capacity of 100 MW and a load factor of 35% (estimated average for all wind farms currently in operation) has an average annual energy output of 306,600 MWh.
100 MW X 35 % X 8,760 h = 306,600 MWh
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