Due to a miscalculation in Wednesday's report 'Dirty reality behind solar power' on page A1, the amount of coal needed to produce a one-square-metre solar panel was misstated as 40kg; the correct amount is 260kg. Other calculations should have been made clearer. A solar panel in Guiyang can be charged at peak rates for only an average of 2.8 hours a day; in addition, much of the energy generated will be lost during the process of conversion and storage. Hence two one-square-metre panels, with a combined capacity of 260 watts and requiring 520kg of coal to manufacture, would be needed to power a 22-watt LED street lamp for 12 hours a day in Guiyang. The coal-electricity conversion rate of a mid-sized power plant in China is 374g/kwh in 2005, according to the Chinese Academy of Social Sciences. So 520kg of coal would be able to generate enough power to run a 22-watt LED street lamp for 12 hours a day for 14 years, not 30 years as stated in the article. The article also incorrectly stated that a solar panel with a capacity of one kilowatt would generate enough energy to keep a fridge cool for a day; it should be able to run the fridge continuously in a city like Guiyang.