Better than you suggest
Northern latitude wouldn't be as much of a problem as you think. One of the reasons for poor performance on the ground is the angle of incidence plus much greater distance the light has to travel though UV absorbing air. At high altitude there will not be as much UV absorption as the air is thinner, there is less depth, and the sun will have to go further round before it's obscured.
If the idea is to eventually have a network of these planes, then I foresee a ring of (say 8) them with the ones is strong sunlight transmitting their 'excess' as lasers to the ones in darkness.
Remember folks you read it here first - dang, should have got a patent in!