New House Thermal

On Thu, 29 Jun 2017 17:02:56 -0700, JS wrote:

Just got off the roof, where I measured my installation with an IR
thermometer. Believe that's what Bob meant by heat gun.

Exposed roof: 135 to 140F, 57 to 60C Shaded roof: 100F, 38C.
PV panels: 120F, 49C

Do you know what the electrical output from your panels was at that time?
Watts/m^2 would be v.interesting.

Just curious. I thought about fitting solar electric and/or water heating
panels to my roof a while back, but its a non-starter because the town
council owns a row of very large oaks just over my southern fence (10m
from the house), and I haven't a cats chance in hell of getting them
trimmed.



--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

On Friday, June 30, 2017 at 4:16:52 AM UTC-7, Martin Gregorie wrote:
On Thu, 29 Jun 2017 17:02:56 -0700, JS wrote:

Just got off the roof, where I measured my installation with an IR
thermometer. Believe that's what Bob meant by heat gun.

Exposed roof: 135 to 140F, 57 to 60C Shaded roof: 100F, 38C.
PV panels: 120F, 49C

Do you know what the electrical output from your panels was at that time?
Watts/m^2 would be v.interesting.

Just curious. I thought about fitting solar electric and/or water heating
panels to my roof a while back, but its a non-starter because the town
council owns a row of very large oaks just over my southern fence (10m
from the house), and I haven't a cats chance in hell of getting them
trimmed.



--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

Didn't look, Martin.
The system has been in so long that as a rule I don't think about it any more. This was a test for the temperatures, for anyone who'd like to calculate if thermals would be better or worse.
Jim

On Fri, 30 Jun 2017 08:07:42 -0700, JS wrote:

On Friday, June 30, 2017 at 4:16:52 AM UTC-7, Martin Gregorie wrote:
On Thu, 29 Jun 2017 17:02:56 -0700, JS wrote:

Just got off the roof, where I measured my installation with an IR
thermometer. Believe that's what Bob meant by heat gun.

Exposed roof: 135 to 140F, 57 to 60C Shaded roof: 100F, 38C.
PV panels: 120F, 49C

Do you know what the electrical output from your panels was at that
time?
Watts/m^2 would be v.interesting.

Just curious. I thought about fitting solar electric and/or water
heating panels to my roof a while back, but its a non-starter because
the town council owns a row of very large oaks just over my southern
fence (10m from the house), and I haven't a cats chance in hell of
getting them trimmed.



--
martin@ | Martin Gregorie gregorie. | Essex, UK org |

Didn't look, Martin.
The system has been in so long that as a rule I don't think about it any
more. This was a test for the temperatures, for anyone who'd like to
calculate if thermals would be better or worse.

Yes, understood, Jim. I was just curious to see if it was possible to see
how much of the roofanel temp difference was due to generated power
and how much was down to albedo difference.

Just wish I was in a better position both w.r.t latitude (51.779N) and
oak trees to consider adding some solar stuff to my roof.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

The panels presumably are isolated from the roof with an air gap, thus their lower temperature. They passed some of the heat on to the air. The thermal-generating effect would depend on the flow of heat to the air, not the temperature of the sun-illuminated object. In a steady state equilibrium, that flow equals the solar input, minus the reflected light, and minus any power siphoned off in other forms (whether electricity from the PV panels, or evaporation of water from green plants).