Useable in the loosest possible sense of the word since charging it would then take a few hours. By which point lack of daylight or a change in the weather would probably mean no more flying for the day. And even if that could somehow be made to work (perhaps with swappable batteries), it ignores the fact that anyone trained in flying an electric aircraft would be poorly equipped to fly a conventional light aircraft with issues like carburettor icing, shock cooling, leaning with altitude etc.