That's because the sky's bright enough to provide enough heat for our daily hot water requirements (save for the occasional exception).
Our consumption should now fall to practically nothing until late September (if last year's anything to go by, rainy though it was).
With oil being around 50p/l at present - even with BoilerJuice's discount - our panels should save us about £300 this year.
At that rate, the investment'll be paid off in 9 years.
edited: my maths was wonky!