Payback Time for a 30 Tube Kit
Our 30 tube kit, if fully installed professionally, will cost around £1,800 (about £1,400
if you install it yourself). The amount of time it takes to recoup
this amount of outlay will depend on the price of the fuel which normally heats the water. The more
expensive that fuel is the more cost-effective these kits are.
The following sequence of graphs gives the estimated payback time for a number of fuels all based on
November 2013 figures. Allowance has been made for fuel price inflation.
Vacuum Tube Technology
for year-round performance.
Our solar collector panels utilize vacuum
tube technology and are designed especially
for colder climates such as the
UK. However please note that a
back-up heat source is always required in the
UK. The system will work very well on
bright sunny days in the winter, however on
dull overcast days there will be very little
heat contribution (hence the back-up source
will have to make up the deficit on these
Below is a graph of a typical
day's panel performance.
This was plotted from a day in May
2010. The system in question comprised
a 30 tube collector panel with a 250 litre
unvented twin coil cylinder.
The overnight temperatures of the cylinder
from the previous day's solar input
at the top and 50°C at the
Showers were taken and washing done between
0700 & 0800hrs, this reduced the bottom
of the tank temperature to 25°C as cold water is
introduced at the bottom.
The panel temperature reaches
33°C soon after 0800,
the pump starts and the bottom of the
cylinder starts to be heated.
The cylinder heats steadily throughout the
day (sunny with broken cloud conditions
throughout the day). Small amounts of
water are drawn from the cylinder
throughout the day. Up to 1400 the
top of the tank temp falls slightly, this
is due to the convection currents occurring
as the bottom is heated, which mix the
water and hence the top temperature
falls. The average temperature
throughout the whole cylinder is however
increasing during this period.
By 1400 the entire cylinder has reached
By 1900 the cylinder temp is 75°C
interesting example of the cold weather
performance of evacuated tube collectors is
demonstrated by this series of
photos. These were taken on 29th
September 2008 when there was a light
covering of snow at an installation in
Reading UK. Even though the panel is
covered with snow, it was a bright day and
the light could penetrate to the
tubes. The panel temperature rose
quickly, but even with the panel
temperature at 58°C (at 10:00am) the
snow stays un-melted on the tubes. This is
testament to the efficiency of the highly
insulated vacuum tubes. Note also
that the snow remains on the collector
panel after the snow has melted on the
start of the day the tank temperatures
were: Top 48°C, Bottom
At 17:00 they were: Top
46°C (210 litre
the panel temperature had reached 72°C.
the panel temperature had reached 32°C.
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