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

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 is there a demand charge?

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

The rate you pay under your service contract is indicated on your bill.

Example – Rate D

Sample Rate D bill. The applicable rate is indicated under the line Billing date.

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 D

If you pay Rate D, you don’t use a lot of electricity and your rate doesn’t include a demand charge. For simplicity’s sake, Rate D, which generally applies to residential and farm customers with a power demand of less than 50 kW, is based solely on energy consumption, expressed in kilowatthours.

Details of Rate D

Rate DP

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

Details of Rate DP

Rate DM or DT

If you pay Rate DM or DT, it includes a charge for power demand above a certain threshold, which is the higher of these two values:

  • 50 kW
  • 4 kW times the multiplier

Details of Rate DM or DT

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

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

How to read a Rate G bill with billing demand

There is a demand charge only if your power demand exceeds 50 kW at any time during the consumption period. Here’s an example of a 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% × 76.4 = 68.8).
  5. Highest real power demand during the billed consumption period.
  6. Billing demand, which is the value at item 2 (50.3 kW), 4 (68.8 kW) or 5 (76.3 kW), whichever is highest.
  7. The cost of power, based on billing demand (item 6) greater than 50 kW (76.3 - 50.0 = 26.3).

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 (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 creates 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.