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Understanding power and power demand

What’s the difference between energy and power?

Video: Power and energy

Learn about the difference between power and energy, two ways to measure the electricity used by a home or business.

Duration: 1 minute 59 seconds

View your consumption profile

Various ways of measuring power and power demand

Video: Real power

Learn about real power and
the underlying concepts.

Duration: 1 minute 12 seconds

Video: Apparent power

Learn about apparent power and
the underlying concepts.

Duration: 1 minute 47 seconds

Video: Minimum demand

Learn about minimum demand and
the underlying concepts.

Duration: 1 minute 53 seconds

Video : Billing demand

Learn about billing demand and
the underlying concepts.

Duration: 1 minute 22 seconds

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

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

Example – Rate DP

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

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 on Rate D

Rate DP

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

Details on 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, or
  • 4 kW times the multiplier

Details on Rate DM or DT.

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:

  • Real power
  • Apparent power

How to read a bill with billing demand

There is a demand charge only if your power demand exceeds 50 kW in the case of Rate DP contracts, or the greater of 50 kW or 4 kW times the multiplier in the case of Rate DM or DT contracts, at any time during the consumption period.

Here’s an example of a Rate DP bill, along with explanations.

  1. Electricity use data recorded by the meter for the consumption period.
  2. Total energy used, expressed in kWh.
  3. Minimum billing demand, which is 65% of the highest power demand during a period falling entirely within the winter period.
  4. Highest real power demand during the consumption period.
  5. Highest apparent power demand during the consumption period.
  6. 90% of the highest apparent power demand (90% × 76.5 kVA = 68.9 kW).
  7. The power factor is the ratio of real power to apparent power (76.1 kW ÷ 76.5 kVA = 99.5%).
  8. The load factor, which is the relationship between the energy (in kilowatthours) actually consumed and the amount of energy that can be consumed by using the entire maximum power demand* throughout the consumption period (26,560 kWh ÷ (76.1 kW x 744 hours) = 46.9%).
  9. Billing demand, which is the highest of the values at item 3 (49.5 kW), 4 (76.1 kW) or 6 (68.9 kW).
  10. The cost of power, based on billing demand (item 9) greater than 50 kW (76.1 kW - 50.0 kW = 26.1 kW).

* Real power (item 4) or 90% of apparent power (item 6), whichever is higher.

See also

  • Glossary

Multiplier

A factor that is applied to the system access charge, to the consumption at the various energy price tiers and to the base billing demand, as applicable depending on the rate.

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 amount of power billed. It is set automatically based on your previous winter consumption.

Energy

Power used by electrical equipment over a given period of time. Expressed in kilowatthours (kWh), energy is calculated as power, expressed in kilowatts (kW), multiplied by the time during which the power is used, expressed in hours (h).

The formula for energy is as follows: energy (in kilowatthours) is equal to power (in kilowatts) multiplied by duration of use (in hours).

Energy (kWh) = power (kW) x time used (h).

Maximum power demand

Maximum power measured during a given period. It is the higher of the following two values:

  • the highest real power demand, expressed in in kilowatts (kW)
  • 90% or 95% (depending on the rate applicable) of the highest apparent power demand in kilovoltamperes (kVA)

These power demands are determined for integration periods of 15 minutes.

Consumption period

Period during which electricity is delivered to the customer and which extends between the two dates used by Hydro-Québec for calculation of the bill.

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