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Posted by John Beardmore on August 4, 2005, 10:15 am
 


No.  About 14% of the incident energy is converted into electricity
rather than heat at the black surface of the panels.



If there is a 4" gab between roof and panels, may there not be some loss
by  convection ?  A 'chimney effect' between the panels and the roof ?


Cheers, J/.
--
John Beardmore

Posted by Ed Earl Ross on August 4, 2005, 9:19 pm
 
John Beardmore wrote:

I was not clear enough. I meant PV generated electricity is
typically used a short distance from the PV panels. The point of
use may be in and around a building, which has the PV system. The
electricity ultimately becomes heat. If used locally to the
building the net amount of heat is determined by reflection and
absorption of sunlight.

For example, a PV system generates electricity used by a 100W bulb.
The bulb emits heat and light. The light from the bulb is absorbed
by its surroundings and becomes heat. All the electricity becomes heat.

If PV electricity is used remotely, energy is removed from the
local environment. The effect is similar to reflecting sunlight,
for the local environment.

Basically, PV electricity does not change the energy equation for a
building with its own PV system, except as listed below.
1. Absorption heats the building
2. Reflection of sunlight prevents heating.
3. PV making electricity for use in and around the building is the
same as absorption. If the electricity is used at a remote
location, the effect is similar to reflection, because that energy
does not heat the building.
4. Cooling effect by convection and conduction--previously forgotten.


Perhaps, convection and conduction will remove heat from a
building. It depends on relative temperature differences. In your
example, if air temperature is hotter than shaded roof, airflow
will add heat to the building.
--
Humbly--Ed

"If the man doesn't believe as we do,
we say he is a crank, and that settles it.
I mean, it does nowadays, because now we
can't burn him."  (Mark Twain)

Posted by John Beardmore on August 5, 2005, 4:36 pm
 
Guess I'm nitpicking that energy may be moved into the house, but it
gets there electrically.  Yes, much of it will degrade to heat in the
end.



But without the panels the roof would have been unshaded.

Has the roof been hitherto shaded, nobody would have put panels on it.
--
John Beardmore

Posted by Ed Earl Ross on August 5, 2005, 10:09 pm
 John Beardmore wrote:

The roof under the panel should be cooler with solar panel shading,
and the shading will help cool the house.

There are many variables, and each installation is different. IMO,
it is impossible to make a blanket statement about heat gain or
loss due to a PV installation.
--
Humbly--Ed

"If the man doesn't believe as we do,
we say he is a crank, and that settles it.
I mean, it does nowadays, because now we
can't burn him."  (Mark Twain)

Posted by John Beardmore on August 7, 2005, 10:14 am
 
OK, so far so good.



OK, but can you think of any scenario that would make the house
warmer in summer ?


Cheers, J/.
--
John Beardmore

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