IMM wrote:

"Franz Heymann" wrote in message
...

"The Natural Philosopher" wrote in message
...

Franz Heymann wrote:



So with a large area of Thermolux you might get to 200% more easily

than

with other panels?
Please, please understand that there is no such concept as "efficiency

per

square foot" in either engineering or in physics. Efficiency is

usually

simply the ratio between the output power and the input power of a

system.


Actually that is not totally so. Efficency is a term that can be applied
to more things than power.

For example, one could define the efficiency of a roof in terms of the
amount of water that runs off versus the total amount that falls on it.


One can define an efficient business as one that has the highest sales
value, or margin value, per employee.

Efficiency is a measure of the efficacy against a theoretically perfect
system,

That is the beginning of a circular argument.


of something doing the job it is designed to do. As normally
measured by how much it produces of the desired output versus how much
input it needs.

If we for example take solar energy, it is not menaingful to say that
e.g. civering every roof in lonbdon with a .3% efficient solar panel is
inefficient, if the cost of so doing would actually be less than
building and running an equivalent power station over the same .
timescales.

One could argue that in terms of various resources one or the other is
more efficient.

The power station takes up less space, but uses more fossil fuel. The
electric panel is inefficient in overall thermodynamic terms, but maybe
more efficient in the actual use of sunlight, since we don't have to
wait a couple of million years for the trees to turn back into oil...The


power station has far less labour content involved, but perhaps uses
more materials.

uppose fo an instant that we cracked fusion power. Who cares about
efficiency, since the actual waste products - helium and heat - are
totally insignificant in a global context. At that point electcity would
become the cheapest form of energy, subject to no taxes at all probably,
and we would all be driving electric cars, and heating our houses
electrically, immediately :-)

Thanks for the homily.

I agree that in general usage, "efficiecy" is bandied around with gay
abandon. However, the discussion about solar panels was a
scientific/engineering one. To talk about "efficiency per unit area" in
such a context is pure nonsense.


What balls!

I reserve a part of a roof of 20ft x 10ft, 200 squ foot. I put in flat
plate collectors, I get n volume of solar heated hot water on a certain
isolation at a certain time of year. I put in the same 200 squ foot
Thermomax solar collectors. I get n x 2 volume of hot water on the same
isolation and certain time of year. For each squ foot of roof the Themomax
is 100% more efficient. Is that clear?

I could use 400 squ foot of flat plate collector on the roof, twice the
area, and produce the same volume of solar hot water as the Thermomax solar
collectors which takes up half as much square footage.

The area is "very" important in this instant. Is that clear?




Yes, but efficiency is independent of that IMM.


Thats tantamount to saying a 5oKw boiler is twice as efficient as a 25Jw
one.

Because it takes up the same floor space.



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