Must admit I nearly got caught out by the long flashing eye lashes of those sexy looking excavated tubes - with the super duper efficiency and capability of operating in almost all conditions. So I needed a big slap in the chops by my Austrian friends, who offered to sell me both systems, one costing almost three times the other... but surely I was going to get a lot more hot water....No!....a lot more reliability... definitely not!
One thing is for sure they will cost you almost twice as much as a flat plate system, without any significant increase in performance (well 8% maximum) and yes they are always less reliable. Don’t believe me... then read the Cranfield Institute of Technology independent report. (see below).
You certainly wouldn't try and replicate what we have done at Moonstone, quite honestly its a bit mad - but the point was to try and achieve all our hot water demands and heating through large solar water storage and large oversized panels - and we got pretty close - 92% of our hot water & heating came just from Solar thermal energy.
Draw your own conclusions, there are plenty of heated debates going on various forums which will convince you either way: You can see live date at www.barillasolar.co.uk/livefeed.aspx showing the difference between the two systems, in addition the Centre of Alternative Technology CAT - has both systems alongside one another - at the end of September 2010 when I last looked at 11.30am on a slightly cloudy day - there was only 2 degrees difference between the two tank temperatures.