UNDERSTANDING ELECTRIC DEMAND　電力デマンドの理解のために 　Information to help you make cost-saving energy-use decisions.

Defining Our Terms

kW Rate of using electricity (Demand).
Example: Ten 100-watt lamps consume electricity at the rate of 1,000 watts, or 1 kilowatt.

kWh Electrical energy actually used (Energy).
Example: Ten 100-watt lamps, when on for one hour, consume 1 kilowatt-hour (kWh).
[10 lamps x 100 watts x 1 hour = 1 kilowatt-hour]

A measure of energy use equal to the ratio of total kilowatt-hours used in a given time period divided by the peak kilowatt use during that time, multiplied by the hours in the time period.

Load factor expresses how well or poorly a given electric system is being utilized. Electricity users strive for a better load factor, or the most efficient usage of their installed electric equipment. The closer to 1 a given load factor, the better is the system's efficiency.

The rock crusher who has high electric demand for small periods of time and is not a big overall electricity user usually will have a very low, or poor, load factor. The energy-efficient process line, which takes advantage of electrotechnologies and state-of-the-art controls, will likely have a much better load factor.

While often used to measure monthly billing cycles, a load factor's time variable can be any desired length.

What Is This Thing Called Demand?
Every electricity consumer's service bill contains both consumption and demand charges, which can be compared to a business's overhead costs for doing business. Residential customers pay one rate of charges for electricity service, covering both consumption of electricity and demand. This simple, combined charge is possible because there is relatively little variation in electricity use from home to home.

This is not the case among commercial and industrial energy users, whose electricity use-both consumption and demand-varies greatly. Some need large amounts of electricity once in a while-others, almost constantly. Complicating this variable usage and demand is the fact that electricity cannot be stored. It must be generated and supplied to each customer as it is called for-instantly, day or night, in extremely variable quantities. Meeting these customers needs requires keeping a vast array of expensive equipment-transformers, wires, substations and even generating stations-on constant standby. The amount and size of this equipment must be large enough to meet peak consumption periods, i.e., when the need for electricity is highest.

Utilities and public service commissions around the country have determined that the most equitable way to cover the cost of this equipment is to have those customers who create this demand and the need for power during these peaks pay for its availability. For this reason, utilities spread the costs of this extra equipment among all commercial and industrial customers as a separate charge for demand.

Defining Demand Customers
Niagara Mohawk installs a demand meter whenever a customer's energy consumption has exceeded 2,000 kilowatt hours (kWh) per month for four consecutive months. Once demand billing begins, it remains in effect unless the monthly energy consumption decreases to less than 2,000 kWh and remains under that amount for 12 consecutive months.

Comparing Demand and Consumption
For demand customers, charges for consumption and demand are separate. This exaggerated example illustrates how the two work: Suppose you have a commercial building with lighting, cooling, machinery, and miscellaneous electric equipment. Its fully installed load totals 15 kW. You are not using the building and have no employees. On the first day of each month, you come into the building and turn on all electrical equipment and leave it on for 15 minutes. Then you shut everything off again and lock up the building until the following month. What would your electric bill look like? It would show very little consumption; in fact, only 4 kWh, at a cost of about 30 cents. (Added to Niagara Mohawk's basic service charge of $27.35 which includes maintenance of electric lines, metering and other costs such as meter reading and billing, the total is $27.65.)

But what about your demand charge? At an average cost of $8.32 per kW and the meter reading at 15 kW (8.32 x 15), the demand charge would be $124.80* (for customers in Service Classification No. 2, Small General Service-Demand).

The prices in this example became effective February 12, 1999 and exclude applicable surcharges and taxes.

Niagara Mohawk customers billed on the demand price who provide the transformers required to take service, as designated by Niagara Mohawk, have their charges reduced by $ .90 per kW billed.

Understanding Demand Metering
Much like your car's odometer records accumulated mileage, electric meters record consumption (kWh). Electric demand meters function like your speedometer-with an important difference.

A demand meter's needle advances as electricity consumption increases, just as your speedometer needle advances as your speed increases in a car. When you stop the car, the needle moves back to zero, regardless of the highest miles per hour reached on the trip. Unlike a speedometer needle, demand meters record the highest average kilowatts reached and maintained in a 15-minute interval within the billing period.

If within one billing cycle your usage reaches 50 kW, for example, and stays there for 15 minutes, the meter needle remains at 50 kW unless or until your usage exceeds that level. If your usage later reaches 55 kW and stays there for 15 minutes, the needle will then stay at 55. The new index point is maintained, even when you are using electricity at below 55 kW, until the meter reader comes to record the demand and resets the meter back to zero.

For example, suppose you have a 10 kW motor in one part of the building and a 15 kW motor in another. If you operate both units simultaneously, the demand meter will record 25 kW. However, if you can use the motors alternately, operating the 10 kW unit only when the 15 kW unit is off, the maximum demand reading will be only 15 kW. The 10 kW saved would save about $82 per month, or $984 per year.

Some intermittently used equipment can be operated using various interlocks and automatic controlling devices. Since each kW demand saved is worth $8.32 per month (at current demand prices), looking into these types of devices makes good sense.

Saving Energy with Demand Control
There are many ways to manage demand, ranging from manual controls and timeclocks to sophisticated automatic units that program buildings and processes. For the average commercial building, the best control over electrical demand may not be in the electric system, but in the building itself. Good thermal design-tight construction, good window design, and appropriately sized ventilation systems-is the key to limiting demand and avoiding demand charges. It creates less need for heat and cooling, allowing you to select smaller, more cost-effective equipment.

The Demand "Ratchet" Clause（デマンド料金制度はラチェット条項を前提にしている）
The demand "ratchet" clause applies only to Niagara Mohawk customers on Large General Service Classifications receiving service under 15,000 volts whose monthly measured demand equals or exceeds 100 kW. At times, there will be a difference between these customers recorded demand as taken from the meter by our meter reader and the billing demand that the customer pays. For example, suppose a building with heating reaches a peak of 300 kW during one winter month. For the next 11 months, the minimum demand will be 150 kW per month for billing purposes, even though the recorded demand may have been less than 150 kW. This is because our pricing structure's ratchet clause stipulates that the minimum billed demand will be not less than one-half of the maximum demand recorded during the previous 11 months. When the ratchet clause is applied to your electric service account, both the meter-recorded demand and the billing demand are indicated on your bill.

　日本では最大需要電力がでた月の値は、次の１１ヶ月間基本料金対象として保持されるが、制度としては問題がある。ここに説明があるように、最大値の２分の１を歯止めとして、月々の最大需要電力をもとにして、基本料金は毎月変動し、２分の１以下の時は基本料金を２分の１としている。つまり、ラチェットのように最大値の２分の１を下限に基本料金は変動しているのである。