Hi,
I've had the panels since august this year. They work and generate hot water.
Do they save you money? well that really depends on your hot water usage. The driver for me to install them was from an eco view point rather than a straight economical viewpoint. I think if I was doing a new build they would be a no-brainer as you have the plumber on-site and have to put in some form of DHW system, so the additional costs taking into account the grant would be relativly small.
see my post here for the performance:
http://www.askaboutmoney.com/showpost.php?p=531500&postcount=10
My overriding observation would be that knowing how much water the panels are producing has led me to really think about my energy usage, and I belive that in order to get the best from a system like this you need to have very inteligent control systems. On my own system I have not finalised how the control should work, but my current thinking is the following:
1 - Immersion: Set Immersion thermostat low (say 50 DegC) and have it come on for a shor period of time in the morning to ensure there is HW for showers. This only works if you cylinder has an imersion at the top of the cylinder, some I have seen the immersion is low down which I don't understand.
2 - Secondary HW coil (I.e. from the central heating): put a motorised valve on this which is controlled by time/temperature/Boiler i.e, in the evening, if the water is not hot enought andthe boiler is on, then open the valve and heat the water.
This I belive would give the most econmical heating routine. However there is a building requirement that some provision is made to heat the cylinder to over 60 deg. c at least once a day - up to you have you deal with that, I have never seen a system which "enforces" this.
Let us know what you decide