The last thing consumers want to hear is an increase in power costs this summer following the news last week of rising threats of rolling blackouts across half of the US. Tight supplies of natural gas, crude, and coal have pushed up residential electricity rates this year. A nationwide weather outlook for this summer forecasts extreme heat — all of this will force households to crank up their air conditions, resulting in oversized power demand that could stress national grids. Bloomberg cites new data from Barclays Plc that says monthly power bills could be 40% more than last year’s. The...