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

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).

Rainy day mental exercise...

Calculate the mass of a thermal.

Calculate the heat capacity of a thermal.

Calculate the energy input required to heat the thermal some small amount for buoyancy, say 2 deg C.

Compare to the heat output of terrestrial sources. A Nuc powerplant is typically a few GW (thermal). Most other anthropogenic sources are smaller.

Sit back in awe and ponder the wonders of nature.

I'm a big fan of gravitationally confined fusion power.

-Evan Ludeman / T8

To follow up on what Evan (T8) said: I gather the latent heat energy released via condensation in a sizable thunderstorm is similar to a small atom bomb. And that's only a side-effect of the solar input. A hydrogen bomb big enough to take billions of years to burn out gets my respect! :-)

OK - back to the subject at hand (solar farms as thermal generators). I'm not an engineer or physicist but I suspect that part of the consideration is the mass of the structure and it's ability to hold enough heat to effectively transfer it to the air around it. So plowed fields, rock faces on mountains, and heavy metal silos do well to form thermals. But the light weight frames that hold the solar panels don't hold the heat well - and they shade the ground below them. And despite what people think they "should' do - they really don't generate thermals very well.
ROY

On Tuesday, June 27, 2017 at 8:07:35 AM UTC-4, Roy B. wrote:
OK - back to the subject at hand (solar farms as thermal generators). I'm not an engineer or physicist but I suspect that part of the consideration is the mass of the structure and it's ability to hold enough heat to effectively transfer it to the air around it. So plowed fields, rock faces on mountains, and heavy metal silos do well to form thermals. But the light weight frames that hold the solar panels don't hold the heat well - and they shade the ground below them. ...

Roy: "holding" the heat is not the issue. To generate a thermal it needs to pass it on to the air, not hold on to it. The sunlight coming in at 1 kilowatt per square meter offers that much enery no matter the structure. Except that some of the light is reflected rather than absorbed. Put dark solar panels (or black plastic bags) over a light-colored surface and you'll get more heat absorbed and therefore transferred to the air (minus 15% or so that gets turned into electricity in the PV panels). Put them over a surface that's already dark and there would be no effect. Also, leafy plants use some of the heat to evaporate water (drawn up by the roots), that part of the energy is "lost" to thermal generation (until condensation occurs). Remove those leafy plants and replace with solar panels (or a parking lot) and you'll avoid the evaporation and get stronger thermals. So it all "depends".

Question: How much energy does it take to produce a solar array (Aluminum mining, refining, manufacture, Silicon panel manufacture, etc.)? How does it compare to the energy output of the array over its life?

Question: Does the previous question add anything to the discussion on solar farms creating thermals? There has to be a forum out there that is better suited for environmental debates. Let's focus on soaring.

I routinely fly high over the Florida Power & Light solar farm near the northeast side of Lake Okeechobee. Occasionally, there are pronounced markers indicating a thermal is cooking off the panels. It's a smaller solar farm, so I'm really eager to see what the mega-solar farm does for us.

Paul A.

On Tuesday, June 27, 2017 at 11:50:59 AM UTC-7, Paul Agnew wrote:
Question: Does the previous question add anything to the discussion on solar farms creating thermals? There has to be a forum out there that is better suited for environmental debates. Let's focus on soaring.

I routinely fly high over the Florida Power & Light solar farm near the northeast side of Lake Okeechobee. Occasionally, there are pronounced markers indicating a thermal is cooking off the panels. It's a smaller solar farm, so I'm really eager to see what the mega-solar farm does for us.

Paul A.

I've flown over the (boiler on a stick) solar plants near Primm, NV and haven't found they produce much lift. Haven't seen a cloud over them either.
But have thermaled over the cooling tower of the Pottstown, PA nuclear power plant. First watched a dirigible fly over the towers... The deck angle went to 45 degrees up, leveled out, 45 down, leveled out. And there was a cloud. All good indicators.
But these days the latter type have security people who think "shoot first, ask questions later" (there was an article about it in Soaring) so they aren't as useful for low saves as they used to be.
I live and fly near many Gigawatts of PV panels. Believe one site is a good thermal source, but it wasn't bad before the plant went in.
You'd think PV panels should be like an asphalt parking lot (car park), but the panels are not mounted on the ground. I know the roof of my house is cooler under the panels than the unprotected roof. Wonder if the cooler air underneath panels being brought into the thermal weakens it?
Perhaps they're better lift sources in the evening?
Jim