Crazy thing is, the cost of these systems has gone down even further since then. You can get a 800w plug-in solar set with panels and an inverter for around 200€. Shipping might be 70€ or you can pick it up locally at the dealer. Add another 50-100€ for attachment material and you are good.

So for 250 to 400€ you can get a system that will break even latest after four years, likely earlier.