||This article needs additional citations for verification. (July 2009)|
A rolling blackout, also referred to as load shedding, is an intentionally engineered electrical power shutdown where electricity delivery is stopped for non-overlapping periods of time over different parts of the distribution region. Rolling blackouts are a last-resort measure used by an electric utility company to avoid a total blackout of the power system. They are a type of demand response for a situation where the demand for electricity exceeds the power supply capability of the network. Rolling blackouts may be localised to a specific part of the electricity network or may be more widespread and affect entire countries and continents. Rolling blackouts generally result from two causes: insufficient generation capacity or inadequate transmission infrastructure to deliver sufficient power to the area where it is needed.
Rolling blackouts are a common or even a normal daily event in many developing countries where electricity generation capacity is underfunded or infrastructure is poorly managed. Rolling blackouts in developed countries are rare because demand is accurately forecasted, adequate infrastructure investment is scheduled and networks are well managed; such events are considered an unacceptable failure of planning and can cause significant political damage to responsible governments. In well managed under-capacity systems blackouts are scheduled in advance and advertised to allow people to work around them but in most cases they happen without warning, typically whenever the transmission frequency falls below the 'safe' limit.
On 9 July 2012, the Alberta Electric System Operator ordered power companies in the province of Alberta to institute rolling blackouts during a heat wave as six generating plants failed during peak demand in the heat of the afternoon.
In 2004–05, electricity demand outstripped supply by 7–11%. Due to a chronic shortage of electricity, power-cuts are common throughout India, adversely affecting the country's potential for economic growth. Even in the nation's capital of New Delhi, rolling blackouts are common, especially during the hot summer season when demand far outstrips supply. Rural areas are the most severely affected; it is common for the 44% of rural households having access to electricity to lose power for more than 12 hours each day. The states periodically and chronically affected by load-shedding are Delhi, Uttar Pradesh, Tamil Nadu, Bihar, West Bengal, Odisha, Assam, Maharashtra, Madhya Pradesh, Rajasthan and Andhra Pradesh. The states of Punjab, Goa, Gujarat and Kerala are largely free of any load-shedding due to surplus power. Karnataka still occasionally experiences power cuts. Mumbai, India's financial capital, however continues to enjoy uninterrupted power supply throughout the year.
|This article's factual accuracy may be compromised due to out-of-date information. (April 2012)|
Japan instituted rolling blackouts starting on 14 March 2011 due to power shortages caused by the 2011 Tōhoku earthquake and tsunami. The Tokyo Electric Power Company, which normally provides approximately 40,000 MW of electricity, announced that it could only provide about 30,000 MW, a shortfall of 25 percent. This is because about 40 percent of the electricity used in the greater Tokyo area is supplied by nuclear power plants in the Niigata and Fukushima prefectures. Two of those plants, the Fukushima Dai-ichi and Fukushima Dai-ni, were automatically taken offline when the first earthquake occurred and have sustained major damage related to the earthquake and subsequent tsunami. Rolling blackouts of three hours were expected to last until the end of April 2011 and will affect the Tokyo, Kanagawa, Shizuoka, Yamanashi, Chiba, Ibaraki, Saitama, Tochigi, and Gunma prefectures.
Rolling blackouts began nation-wide in Pakistan in early 2008 and continue presently in 2013. It intensifies in the long summers, with many places around the country having no electricity for 20 hours per day. According to Pakistan Electric Power Company (PEPCO), Pakistan's electricity shortfall is normally 2,500 Megawatts (MW) but reaches around 6,000 MW or more during the summer season. The country's electricity problems were so severe that violent riots some times takes place in some regions, including Punjab, the country's most populous province.
Blackouts were practiced in Poland during economic crises of 1979-1982.
On several occasions in the 1970s and 1980s, trade union strikes in Ireland's power utility, the Electricity Supply Board (ESB), led to rolling blackouts. However, rolling blackouts have not occurred for this reason since 1991. For such eventualities, the ESB have a zone rota system in place. The country is divided into regions which in turn are subdivided into zones, referred to by the letter codes A, B, C, X, Y, and Z. During periods when blackouts may occur, advertisements are placed in the national newspapers informing customers which region and zone they are in, and at 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 do not 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, supply is cut in some or all of the "high risk" zones. If there is still a shortfall once all the high risk zones have had power cut, 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".
South Africa 
There is a long history of rolling blackouts in South Africa, with multiple causes. In South Africa the major producer and distributor of electricity is Eskom, which provides over 95% of the country's energy usage. During the 1980s Eskom mothballed three of their coal-fired power stations, as there was an excess of generation capacity at the time. With the demise of Apartheid in the 1990s came massive investment and economic growth. At the same time the government tried to deregulate the electricity supply industry by inviting the private sector to build new power stations to meet the rapidly growing demand for electricity. Eskom was at the time prevented from building new power stations (including de-mothballing the three existing power stations) or from strengthening the transmission network. The transmission network is especially important in delivering power from Mpumalanga, where the majority of the power stations are located, to other parts of the country such as KwaZulu-Natal and the Western Cape. With no bidders coming forward to construct new power stations, there was effectively no investment into new generation plants during the early 1990s, which eventually led to the shortage of capacity that was experienced in the 2000s.
In 1998, the Department of Minerals and Energy released a detailed energy review in which it explicitly warned that unless "timely steps were taken to ensure that demand does not exceed available supply capacity", generating capacity would reach its limit by 2007.
Blackouts in Western and Northern Cape 2005–2006 
The energy consumed by the Western and Northern Cape are only partially supplied by Koeberg nuclear power station, with the balance of the energy supplied by the coal-fired power stations in Mpumalanga via the transmission network. In December 2005, a bolt left in Koeberg Unit 1 reactor after maintenance caused extensive damage to the rotor, resulting in it tripping out. Consequently, there was insufficient power to supply the Cape, with the transmission network only partially able to supply the electricity demand. As a result, rolling blackouts were implemented across the two provinces.
The blackouts and the accompanying brouhaha in the media resulted in Eskom and the government announcing a number of plans for new power stations, and Eskom started returning mothballed power stations to service as well as expediting plans to build new gas-fired power stations to support the Western Cape supply.
Country-wide blackouts 2007–2008 
With the freeze on any new developments being placed on Eskom during the early 1990s, South Africa was faced with a situation where for the next few years the electricity demand kept rising, without any new power stations being built to keep up the necessary supply. By October 2007 the situation had deteriorated to such an extent that Eskom implemented rolling blackouts throughout the country. Blackouts occurred in most suburbs throughout the country for a period of two hours at a time.
The situation came to a head on 24 January 2008 when the national grid was brought to near collapse. Multiple trips at a number of different power stations rapidly reduced the available supply, resulting in Eskom declaring force majeure and instructing its largest industrial customers (mainly gold and platinum mining companies) to shut down their operations and reduce consumption to "minimal levels", just sufficient to evacuate workers that were still in the mines.
In January 2008, with no short- or medium-term relief available to ease the power shortages, Eskom warned the public that the country's electricity demand would exceed the supply until 2013 (when the first new power stations would be brought online).
In January 2008 Tajikistan faced its coldest winter in 50 years, and the country's energy grid began to fail. By February 2008 Tajikstan's energy grid was near collapse and there were blackouts in most of the country. Hospitals throughout the country were on limited electricity use, and nurses and doctors were forced to keep newborn babies warm with hot water bottles. There were reports of newborns freezing to death. The UN reported that with so much energy required to keep warm there was a danger of people starving to death.
United Kingdom 
The Three-Day Week of January to March 1974, introduced to limit electricity consumption, and thus conserve coal supplies which were severely reduced due to industrial action, meant that non-essential commercial users were only allowed to consume electricity for three days each week. Home electricity supplies were also limited in some areas.
United States 
In April 2006, parts of Texas experienced rolling blackouts due to excessive air conditioner use because of unexpectedly high temperatures. The longest power outage lasted for a period of five hours, affecting areas in the Middle to the South of Texas.
In February 2011, North and Central Texas experienced rolling blackouts due to 50 power plants tripping offline. Temperatures ranged between 8 °F and 19 °F, the coldest in 15 years. The time of the power outages ranged from 20 minutes to over eight hours. Areas affected included Bell, Bexar, Brazos, Collin, Comal, Dallas, Delta, Denton, El Paso, Fort Bend, Guadalupe, Harris, Hays, Hill, Hidalgo, Hunt, McLennan, Montgomery, Navarro, Palacios, Smith, Tarrant, Travis, Webb and Williamson counties, as well as some counties in New Mexico, Including Doña Ana, Otero, and Eddy Counties.
The 2006 and 2011 blackouts were the only two to occur in two decades.
Though the term did not enter popular use in the U.S. until the California electricity crisis of the early 2000s, outages had indeed occurred previously. The outages were almost always triggered by unusually hot temperatures during the summer, which causes a surge in demand due to heavy use of air conditioning. However, in 2004, taped conversations of Enron traders became public, showing that traders were purposely manipulating the supply of electricity to raise energy prices.
On 13 December 2003, shortly before leaving office, Governor Gray Davis officially brought the energy crisis to an end by issuing a proclamation ending the state of emergency he declared on 17 January 2001. The state of emergency allowed the state to buy electricity for the financially strapped utility companies. The emergency authority allowed Davis to order the California Energy Commission to streamline the application process for new power plants. During that time, California issued licenses to 38 new power plants, amounting to the addition of 14,365 megawatts of electricity production when completed.
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 some of California cities, 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 electric bill will indicate a power grid of 99 and they will not be affected by rolling blackouts.
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.
- Gerein, Keith (9 July 2012). "Rolling electricity blackouts strike Edmonton and across the province". The Vancouver Sun.
- "Information on Indian Infrastructure & Core Sectors". India Core.
- "Electricity and power shortage holding India back". Free-press-release.com.
- Range, Jackie (28 October 2008). "India Faulted for Failure to Improve Power Supply". The Wall Street Journal.
- [dead link]
- "Serving Mangaloreans Around The World!". Mangalorean.Com.
-  – Tokyo Electric Power Company
-  – nikkansports.com
- "India offers Pakistan electricity to curb load-shedding". The Express Tribune.
- "Electricity load shedding in Pakistan intensifies in summer 2011". Infopakistan.pk. 26 April 2011.[unreliable source?]
- "Unscheduled loadshedding irks people in Punjab". The Nation. 2 October 2011.
- "Another day of outrage at outages across Punjab". Dawn (Karachi, Pakistan). 18 June 2012. Archived from the original on 18 June 2012. Retrieved 18 June 2012.
- "Mail and Guardian – Govt chose guns over power stations". Mg.co.za.
- "Eskom declares force majeure". Moneyweb. 25 January 2008. Retrieved 12 February 2009.[dead link]
- McGreal, Chris (26 January 2008). "Gold mines shut as South Africa forced to ration power supply". The Guardian (London). Retrieved 12 February 2009.
- Old Eskom power stations revived, Fin 24, 2 February 2011
- Farangis Najibullah (13 January 2008). "Tajikistan: Energy shortages, extreme cold create crisis situation". EurasiaNet. Retrieved 2008-02-08.
- Situation Report No. 4 – Tajikistan – Cold Wave/Compound crisis (25 February 2008) United Nations Office for the Coordination of Humanitarian Affairs
- "ERCOT may initiate more blackouts Wednesday night, Thursday morning". The Dallas Morning News. 2 February 2011.
- Heinz, Frank. "Outages Suspended, But Conservation Critical". NBC 5 Dallas-Fort Worth.
- "Texas weathers rolling blackouts as mercury drops". Reuters. 2 February 2011.
- Lauren Johnston (2 June 2004). "Enron tapes anger lawmakers". CBS Evening News.