The reason isn't hard to understand. Solar and wind provide power about 10 to 20 percent of the time, which means that when the sun's not shining, the wind's not blowing, you still need power for your hospitals, your homes, your cities, your factories.
Причину понять легко. Энергию Солнца и ветра можно получать только 10 — 20% времени, но и в те моменты, когда Солнце не светит и ветер не дует, больницам, домам, городам и заводам всё равно нужна энергия.