The World Bank now ranks off-grid solar as the cheapest way to bring electricity to at least 398 million people who still live without it. A joint report released this week by the World Bank’s Energy Sector Management Assistance Program (ESMAP) and the off-grid solar industry association GOGLA treats the technology as permanent infrastructure. Systems once sold as a stopgap until the grid arrived now power households, businesses and factories, and 95% of surveyed customers still had working solar home systems four or more years after buying…