Solar thermal vs Solar electric

 Ever wondered what is the difference between these two and which one
is more efficient. Solar thermal is an old technology but has an
efficiency of 70% where as pv or solar electric has an efficiency in
the range of 14-18%. Solar thermal (lets say for hot water needs) is
the best way to own a system and appreciate the benefits of a solar
energy system because its cheaper then a pv system. Once you have this
system, you can go for a pv which can provide electricity for your
entire home.

  varavooru@gmail.com wrote:

Solar thermal efficiency varies depending on the design of the collector
and the differences in temperatures inside/outside the collector. I've
been told that air heaters typically run about 80% efficient since they
work at relatively low temperature differences. A typical flat plate
water heater is around 50% efficient. Both are orders of magnitude less
costly than solar PV but they won't run anything electric.

Anthony

 In terms of actual conversion of available sunlight, using modelling
programs like Fchart, it is possible to get values of actual heating
produced given available sunlight.   For thermal solar collectors, it
is possible to convert as much as 60-65% of available light on average
throughout the year (ie. light actually hitting the collector) into
usable heat.  That takes into consideration heat loss on the
circulation lines, and performance of a coil heat exchanger, so is
fairly realistic.

So in real life situations, solar thermal can provide about 4+ times
the energy output of PV for a given surface area.

Evacuated tubes used by Apricus have a round absorber and have the
advantage of being able to passively track the sun throughout the day,
which means more heat output morning and afternoon.  Flat plates will
provide heat output mainly during the middle of the day, as they are
flat and don't passively track the sun.   Evacuated tubes with a round
absorber (like Apricus) do not have quite as high peak solar
conversion values as evacuated tubes with flat absorbers (Sunda,
Thermomax etc), but more than make up for that with the passive
tracking.    Passive tracking is also useful if you don't have the
collector facing the equator.  If you face further east, morning
output will be good, but drop off in the afternoon, and vice versa,
but the total day performance drop will be much less than a flat
absorber evacuated tube, or indeed a flat plate collector.

Hope that provides some more clarity to the issue.