Supply and Demand of Electricity

Electricity “cannot be stored.” Electric power companies adjust supply capacity (power generation) to demand (consumption) instantaneously (put on balance weights in response

to demand). It is impossible to supply electricity beyond the supply capacity of electric power companies (total number of balance weights in hand).

Supply side (power generation) Demand side (load)

Building

Supply

Supply capacity of

electric power companies

Add supply capacity (balance

weights) in response to demand

Supply capacity of

electric power

companies

Make full use of balance

weights in hand

In case “demand exceeds supply capacity,” an unpredictable major blackout may occur.

×

Factory House Store

Demand

Nuclear power

Hydroelectric power

Thermal power

In the world of electricity, the term kWh is used as a unit to represent a total amount (area) of generation or consumption of electricity. On the other hand, the term kW is used as a unit to represent an amount of electricity generated or consumed in a moment (height).

Peak hour supply capacity (kW) of electric power companies has been decreased, because power stations were damaged by the recent earthquake disaster.

Therefore, restriction will be needed at peak hours in terms of kW (height).

9:00 a.m.

kWh (area)

Electricity demand curve

(consumption pattern of a day)

Peak hour supply capacity before

the earthquake disaster

Peak hour supply capacity after

the earthquake disaster

Decrease of supply

capacity

Need to restrict kWs (height)

Electricity demand curve

(consumption pattern of a day)

(kW)

kWh (Represented by Area) and kW (Represented by Height)

Electricity demand curve

(consumption pattern of a day)

kW (height)

1:00 p.m.

5:00 p.m.

9:00 a.m.

1:00 p.m.

5:00 p.m.

9:00 a.m.

1:00 p.m.

5:00 p.m.

Largest power line (extra high-voltage transmission line)

○

×

During planned power outage

Both districts where power outages are conducted and

not conducted exist, even in the same municipality.

Electricity is sent from power stations by large capacity transmission lines, then branched into small capacity transmission lines at each substation and delivered to customers.

The recent planned power outages have been conducted by each primary substation. For this reason, outage and restoration works are to be carried out for all facilities that are connected to the same power line network. The scope of area served by a primary substation is not always identical to an area of a municipality. Therefore, both districts where power outages are conducted and not conducted exist, even in the same municipality.

Planned power outage is conducted

by each primary substation.

Mechanism of Electricity Service Delivery and Scope of Planned Power Outage

Second largest power line (extra high-voltage transmission line)

Slightly large power line (high-voltage distribution line)

Smallest power line (low-voltage distribution line)

Power station

Primary substation

Distribution substationPole transformer

General household

Small factory

General household

Store

Store

General household

Sewage treatment plant, etc.

Building and apartment house

Small and medium factories

Large factoryHospital

Same municipality

Primary substation Distribution substation Pole transformer