In some parts of the world, solar energy is now the cheapest source of electricity in history, thanks to policies that encourage the development of renewable energy, according to the International Energy Agency's (IEA) annual World Energy Outlook, released recently. While sunlight is free, the technology required to convert it into usable electricity can be expensive. To encourage more people and companies to use solar energy, the report says, countries are putting policies in place to make it cheaper to buy solar equipment. Today, more than 130 countries have policies to reduce the cost of building new solar installations. The IEA took such policies into account for the first time this year when it calculated solar costs in its annual World Energy Outlook, so it compared the estimates of solar energy costs in each region with last year's, and the results showed that the cost has dropped by 20% to 50%. As a result, the report concludes, solar will become the "new king of electricity supply" as prices continue to fall. The report points out that in most countries around the world, the cost of building solar power plants is consistently lower than that of building new coal - or gas-fired plants. For utility-scale solar projects built in the United States, Europe, China and India this year, the average cost of power generation over a plant's life cycle is estimated at between US$35 and US$55 MWh. The global average cost of solar power was US$100 MWh four years ago and $300 MWh a decade ago, according to the World Economic Forum. By contrast, the cost of coal now ranges from US$55 to US$150 MWh, according to the IEA's latest report, roughly where it has been for more than a decade. The IEA therefore predicts that even if the economy recovers next year, global coal use may not return to pre-pandemic levels.