What’s the difference between energy and power?

Video: Power and energy

Learn about the difference between power and energy, two ways to measure electricity.

View your consumption profile

Various ways of measuring power and power demand

Video: Real power

Learn about real power and
the underlying concepts.

Video: Apparent power

Learn about apparent power and
the underlying concepts.

Video: Minimum demand

Learn about minimum demand and
the underlying concepts.

Video : Billing demand

Learn about billing demand and
the underlying concepts.

Why bill for power demand?

Power demand is one of the main components of electricity rates, because rates reflect the costs actually incurred by Hydro‑Québec to deliver electricity.

As the example below shows, basing billing solely on kilowatthours (energy) used wouldn’t be fair: it wouldn’t take into account the cost of supplying electricity to meet power demands that can vary in size and duration from customer to customer.

Customer 1 – Power demand of 24 kW for 1 hour
Customer 2 – Power demand of 1 kW for 24 hours

In this example, Hydro‑Québec has to have equipment with a capacity 24 times greater for Customer 1 than for Customer 2. Not only is the equipment more expensive, it will be used only 1 hour out of 24.

Do you pay for power demand?

That depends on your service contract rate, which takes into account your power needs.

Checking the rate on your electricity bill

Example – Rate G

Sample Rate G bill. The applicable rate is indicated under the line At General Rate G for Small Power.

How the rate applies to power demand

Rate G

If you pay Rate G, it includes a charge for power demand greater than 50 kW.

Details of Rate G

Rate M, L or LG

If you pay Rate M, L or LG, it includes a charge for power demand, for every single kilowatt of power that you use.

Details of Rates M, L and LG

How billing demand is determined

Various ways to measure power and power demand

To determine billing demand, Hydro‑Québec measures your power two ways using your facility’s electricity meter:

How to read a Rate G bill with billing demand

Rate G has a demand charge only when your power demand exceeds 50 kilowatts. For medium‑power rates, the demand charge is billed from the first kilowatt.

Here’s an example of Rate G bill along with explanations.

  1. Consumption data recorded by the meter for the consumption period.
  2. Minimum billing demand, which is 65% of the highest power demand during a period falling entirely within the winter period.
  3. Highest apparent power demand during the consumption period.
  4. 90% of the highest apparent power demand (90% × 67.0 = 60.3).
  5. Highest real power demand during the consumption period.
  6. Billing demand, which is the highest of the values in item 2 (42.7 kW), item 4 (60.3 kW) or item 5 (65.8 kW).
  7. The cost of power, based on billing demand (item 6) greater than 50 kW (65.8 kW - 50.0 kW = 15.8 kW).

See also

Real power

Amount of electricity consumed in a useful manner to operate equipment, such as a motor or a heating or lighting system. Real power is expressed in kilowatts (kW).

Apparent power

Amount of electricity that Hydro-Québec supplies to a customer, expressed in kilovoltamperes (kVA). When it is used, apparent power breaks down into real power (kW), which runs devices, and reactive power (kVAR), which produces magnetic fields and which is not useful power for the customer.

Minimum demand

Minimum demand is 65% or 75% of your highest power demand during a period falling entirely within the winter period.