Rolling blackout refers to an intentionally-engineered electrical power outage, caused by insufficient available resources to meet prevailing demand for electricity.

In many African countries – e.g. Cameroon, Democratic Republic of the Congo, and Nigeria – a combination of aging electricity generation infrastructure, and the inadequacy of the supply of electricity to the ever expanding demand, has made rolling blackouts a staple of daily life.

Other developing countries, particularly Asian countries like India and Pakistan have daily blackouts of up to 8 hours daily in even the capital and major cities. Rural areas receive power for as little as 1 hour a day. This can be attributed, apart from the shortage of fuel, old equipment and so on, to high incidence of power theft. Indeed, Delhi power distribution companies reported that 40% of their power was being stolen during summer 2006. Practically no effort is being made to curb theft as corruption in law enforcement agencies makes it exceedingly easy to escape punishment and fines. Another cause is the free electricity (among other subsidies) being provided to farmers in India; large amounts of wastage is seen here, and the subsidy will continue as long as farmers constitute a significant voting bloc.

United States

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Texas

In April of 2006, parts of Texas experienced rolling blackouts due to excessive air conditioner use because of unexpectedly high temperatures. The longest power outage so far, lasted for a period of five hours, affecting areas in the Middle to the South of Texas. The Texas power system runs on a system similar to the one in California.

California

Though the term did not enter popular use in the United States until the California electricity crisis of the early 2000s, such outages had occurred previously, almost always triggered by unusually hot temperatures during the summer, which cause a surge in demand due to heavy use of air conditioning. Rolling blackouts were again imposed in late August 2005 in Southern California due to the loss of a key transmission line; the transmission line shut itself off because of a faulty sensor.

Most of California is divided into 14 power grids, each containing approximately 7% of electricity customers in the state, creating a total of 98%. The remaining 2% are placed on a separate grid, where users such as hospitals and police stations are exempt from ever having their power deliberately cut off.

In a Stage 1 emergency only a general call for voluntary conservation is issued, while a Stage 2 emergency results in power being temporarily cut off to certain large users, primarily industrial concerns, who have agreed to this arrangement in exchange for lower rates. When a Stage 3 power emergency is declared, electricity to one of the grids is shut off for a fixed period of time, which can range from 60 minutes to 2½ hours. If after this period of time the Stage 3 emergency still exists, power is restored to this grid but then the next grid in the sequence is blacked out, and so on, until the situation is stabilized — the blackout thus "rolls" from one grid to the next.

In California, each customer's electric bill includes the number of the power grid (from 1 to 14) that customer belongs to; this gives customers at least some advance notice of when their electricity might be turned off in the event of a Stage 3 emergency. The grids are set up in such a manner as to ensure that a large percentage of customers in the same neighborhood would not be blacked out concurrently, which could invite looting and other related problems. Normal electricity customers can fall within the areas reserved for emergency use (if they are near a hospital or other critical infrastructure), in which case their electricity bill will indicate a power grid of 99 and they will not be affected by rolling blackouts.

Elsewhere

Not all states are on this system; in many East Coast states (such as New York State and New Jersey), "brownouts" rather than rolling blackouts are implemented during power emergencies: In this scenario, instead of the power being cut off altogether to a certain percentage of customers, the voltage is reduced by a certain percentage to all customers — the resulting dimming of electric lights being the origin of the term "brownout." Brownouts can cause significant damage to unprotected electronic equipment, but usually have no effect (other than reduced performance) on incandescent lights or some types of motors.

Republic of Ireland

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On several occasions in the 1980s and 1970s trade union strikes in Irelands power utility ESBled to rolling blackouts. However, this has not occurred since 1991. For such eventualties the ESB have a "zone rota" system in place. The country is divided into "regions" which in turn are subdivided into "zones" (Known as A, B, C, X, Y, and Z) And advertisements are placed in the national newspapers informing customers which region and zone they are in. And what times of the day they have a High, Moderate or Low risk of supply interruption. (Customers fortunate enough to live close to a hospital may find they are on a "priority line" and don't lose power at all). The authorities appeal to the public to conserve electricity (especially during hours of peak demand) however if and when electricity demand exceeds available supply in some or all of the "high risk" zones. If there is still a shortfall once all the high risk zones are out then the "moderate risk" zones start experiencing power cuts. The level of risk in each zone changes every three hours moving from "Low" to "Moderate" to "High" and back to "Low".

Blackouts