Internet keeps dropping

wifi keeps dropping for about 10-15 seconds at a time, every few minutes for the past 6 weeks. Started after a storm caused electricity to go out for a few hours, after the electricity came back on the wifi started experiencing problems and has been persistent since.   When the wifi is functioning the speeds are fast. Xfinity techs have been here at least five times and have had us change modem and routers twice and they have changed both inside and outside cables and none of this has made any difference.  We need to see what else xfinity can do at this point as streaming live tv or listening to music over wifi is impossible. Thanks