1 February 2018. Across the world, power downtime keeps going up. Power outages increased in frequency and were more widespread in 2016, affecting 33% more people. Among the top 15 US utilities, the most recently reported average downtime was more than two hours, with some outages averaging more than seven hours.
CLEAN TECHNICA
https://cleantechnica.com/2018/01/27/why-we-need-a-solar-storage-solution
At industryabout.com:
