07
JAN
2015

## Understanding Energy Demand and Consumption

First, let’s start by looking at the units of measure

## Consumption = KWh

Now, let’s illustrate that with an example:
One 100-watt light bulb burning for 10 hours consumes 1,000 watt-hours or 1 kWh. The entire time it is on, it requires a “demand” of 100 watts or 0.1 kW from the utility.
That means the utility must have that 0.1 kW ready whenever the customer turns the lamp on.

Similarly, 10 x 100-watt light bulbs burning for 1 hour consume 1,000 watt-hours or 1 kWh. Because all 10 lamps are only on for 1 hour they require the entire demand of 1000 watts or 1 kW at the same time. That means the utility has to make 1kW available to that company at all times because it doesn’t really know when that one hour will be when the lights are on.

Note that in both examples, the consumption is 1 kWh, however, the serving utility must be prepared to provide ten times as much ‘capacity’ in response to the “demand” of the 10 light bulbs operating all at once compared to the 1 light bulb for 10 hours.

Electricity demand and consumption visualized

If both of these customers are billed for their consumption only, both will get the same bill for 1 kWh of energy. And that is the way most residential customers are billed. But the requirement for the utility to meet this energy requirement is very different. In the second case, the utility has to have 10 times more generating ‘capacity’ to provide the second customer’s brief high demand for power compared to the first case.

Commercial and industrial customers are often billed for their hourly consumption patterns and their peak demand for energy. These customers often have special meters that measure both, unlike residential meters that just record total consumption in a time period, usually one month.

Residential consumers usually don’t get billed for demand because their use patterns are much more predictable and the meters to measure demand are much more expensive than the simple residential units.

Let’s summarize: electric power use is metered in two ways: on maximum kilowatt use during a given time period (i.e., kW demand typically measured in 15-minute or 30-minute intervals) and on total cumulative consumption in kilowatt hours (kWh). A customer’s electric rate is set using a complex process of tracking cost of services and often seeking regulatory approvals.

The general theory is that demand charges reflect the utilities’ fixed costs of providing a given level of power availability to the customer, and energy charges reflect the variable portion of those costs as the customer actually uses that power availability.

Power companies often use a meter that records the power use during either a 15- or 30-minute time window. The average power used during that window is used to calculate the kW demand. The peak demand used for billing purposes in any month can be

1. Time of Day: Dependent on the time of day (i.e., on-peak {usually during the day} and off-peak
{usually at night time periods) and/or the day of the week (e.g., Monday through Friday and separately for weekends):
The metering system tracks the highest usage anytime during the month under the appropriate time windows. These pricing schedules are generally referred to as Time of Use (TOU) rates.
2. Seasonally Differentiated: For example, the demand charge might be higher during the summer than during the winter, or vice versa.
3. Declining Blocks: This is where the demand charge up to a given level is at one price with the price declining above that level. For example, the demand charge might be \$10 per kW up to 10,000 kW demand, and drop to \$6 per kW for demands in excess of 10,000 kW.
4. Interruptible Blocks: The demand charge depends upon whether the customer can reduce electrical demand to a given level if it is notified in advance by the utility. The price reduction often varies with the time of notice (i.e., the discount is higher if shorter notice is given). Some utilities also offer direct load control for air conditioning and water heating equipment, the utility itself can cycle this equipment on and off for brief periods.
5. Ratchet: Certain rate designs incorporate minimum billing demands based upon historical peak demands. For example, if the peak demand last summer was 500 kW and the rate design has a 50% ratchet, the minimum billing demand would be 250kW (500 kW times 50%) for the following eleven months, regardless of whether the actual demands were lower.

The meter recording kWh power use during either a 15- or 30-minute time window also tallies total kWh use. This meter is read at roughly monthly intervals and total power use is billed according to applicable pricing schedules.

Average Retail Price of Electricity in Ohio