A rolling blackout, also referred to as rota or rotational load shedding, rota disconnection, feeder rotation, or a rotating outage is an intentionally engineered electrical power shutdown in which 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.
Rolling blackouts are a measure of demand response if 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 they 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 power to 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. 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.
These have wide-ranging impacts, and can effect the expectations of communities – i.e. in Ghana dumsor describes the widespread expectations for intermittent unexpected power outages due to rolling blackouts.
Rolling blackouts in developed countries sometimes occur due to economic forces at the expense of system reliability (such as in the 2000–01 California energy crisis), or during natural disasters such as heat waves. The 2021 Texas power crisis involved rolling blackouts caused by the February 13-17, 2021 North American winter storm and lack of winterization.
After the 2011 Tōhoku earthquake and tsunami, Tokyo Electric Power Company implemented rolling blackouts. Its service area were divided to five blocks and blackouts were implemented from 6:20 to 22:00. The schedule from 15 to 18 March 2011 was as follows:
|Time||15 March||16 March||17 March||18 March|
|6:20–10:00||Block 3||Block 4||Block 5||Block 1|
|9:20–13:00||Block 4||Block 5||Block 1||Block 2|
|12:20–16:00||Block 5||Block 1||Block 2||Block 3|
|15:20–19:00||Block 1||Block 2||Block 3||Block 4|
|18:20–22:00||Block 2||Block 3||Block 4||Block 5|
Intermittent access to electricity causes major economic problems for businesses, which incur costs in the form of lost resources, reduced patronage, or curtailed production if electrical equipment—for example refrigeration, lighting, or machinery—abruptly stops working. Businesses in areas that are subject to regular blackouts may invest in backup power generation to avoid these costs, but power backup is itself a cost because generators must be purchased and maintained and fuel must be regularly replenished.