In a dusty northwest India desert dotted with cows and the occasional camel, a solar-power plant is producing some of the world’s cheapest energy. Built in 2018 by India’s Acme Solar Holdings Ltd., it can generate 200 megawatts of electricity, enough to power all the homes in a middle-size U.S. town. Acme sells the electricity to distributors for 2.44 rupees (3.4 cents) a kilowatt-hour, a record low for solar power in India, a country that data trackers say has the world’s cheapest solar energy. …