when I lived in a house with a solar hot water system it was always the case that when you wanted hot water (cold winter days) you'd have to turn on the electric booster, and when you didn't want much hot water at all (40 degree summer days) it would be boiling over
We have instant gas hot water now and find it brilliant. Costs us about $160/year to run for a house with two people. Neat temp control and other features too.