One of my concerns would be the potential maintenance costs in the future - the inverter (which turns the solar energy into electricity) needs replacing after about 10 years. They cost over £1,000 alone. If the panels have been on the roof for a number of years I'd figure in a potential bill for replacement in a few years time and knock that off the purchase price (in the same way you would knock off money if the house had a boiler which would need replacing shortly). For this reason, I can't see that a house with solar panels would be worth more than one without, but people look for different things when purchasing a property and, for some, it may be a positive thing.