fred wrote:
How effective are these ? Are they much of an improvement over the old types ?

I would imagine you can get a bit more energy transfer but a much more
complex system.
Once the panel has got frost on it then that acts as an insulator and
the efficiency will drop off until the frost has melted.
I have solar thermal tubes and these do very well for 7 months of the
year giving me most of the hot water I need. The remaining 5 months the
gas boiler runs for about 15 mins twice a day for DHW. I suspect the
improvement offered by thermodynamic panels would have a much higher
capital cost and only save a bit of gas and you still need the power to
run the heat pump. All my system needs is a central heating type pump
and temperature difference controller consuming a watt or so.