Businesses and households expect reliable electricity to be available at the flick of a switch. But the frequency of large-scale blackouts in the United States has not fallen in the last 30 years, and big blackouts remain a common occurrence throughout emerging markets.
The risk of massive failures affecting the supply to millions of customers and darkening whole regions or countries may even be increasing as demand rises, especially for air conditioners, and electricity networks are integrated over increasingly wide areas.
India's power failure earlier this year has heightened concern about the reliability of power networks integrated over wide areas, and raised questions about the wisdom of China's plan for an ultra-high voltage super-grid.
On July 31, power cuts rolled across 22 states in the north of India, which are home to 620 million people (and about 320 million electric customers), about 9 percent of the global population. It was easily the biggest power outage in history.
Other mass blackouts recently have included the Java-Bali blackout in Indonesia in 2005 (100 million people); the 2009 Brazil-Paraguay blackout (which left the whole of Paraguay and parts of Brazil without electricity); and the 1999 South Brazil blackout (75 million people).
But the advanced industrial countries are not immune -- though widespread failures are much rarer. In August 2003, a blackout cut power to 50 million people across the Northeast United States and neighbouring parts of Canada, in some cases for up to four days.
Just a month later, in September 2003, a blackout cut power to 4 million people across southern Sweden and eastern Denmark. Five days after that, the whole of Italy was plunged into darkness by a cascading power failure across the country's grid.
Blackouts are expensive. The August 2003 blackout in the United States resulted in $3 billion of insurance claims, according to one estimate.
But many insurance policies exclude power failure, and in any event only cover the direct economic costs, not the inconvenience and widespread disruption to daily life and business activity. The total cost of the August 2003 blackout was almost certainly many times the published insurance claims.
Restarting a network after a big blackout is no simple task. Most power plants rely on power from the grid in their start up procedure to work fuel and pumping systems and other control equipment. Only a small proportion of power plants are equipped with black start capability to begin generating power again in the event