Does someone understand this picture? (Solar heating)

[Kolika28]

Homework Statement

I'm working with solar heating systems, and my teacher added this picture to his PowerPoint. But I don't understand the picture. Could someone help me?

Relevant Equations

The only thing I understand is that $I_0$ is the energy from the sun. But the other arrows confuse me, and there is now explanation for what the stand for in the presentation

Homework Statement:: I'm working with solar heating systems, and my teacher added this picture to his PowerPoint. But I don't understand the picture. Could someone help me?
Homework Equations:: The only thing I understand is that $I_0$ is the energy from the sun. But the other arrows confuse me, and there is now explanation for what they stand for in the presentation

 

[berkeman]

It looks like Io is the overall insolation, right? The blue first layer is the glass cover, and the black layer is the thermal absorber? Then Ib would be the reflected intensity (thermal/light energy), and the other arrows represent what escapes and what gets re-refleted back toward the absorber?

I can probably find a better explanation via Google Images...

 

[berkeman]

I can probably find a better explanation via Google Images...

Right at the top of the page of images when doing a Google Images search for reflection losses in a thermal solar heating system

http://www.renewableenergyfocus.com/view/17067/solar-thermal-technology-update/

 

[Kolika28]

Thank you so much! So I0 is the solar radiation, the yellow arrow is reflection? But Ig still confuse me a bit, mostly because it points both up and down. And what does this equation mean

 

[haruspex]

Ig still confuse me a bit, mostly because it points both up and down.

I_g is the thermal radiation from the hot glass. Necessarily it radiates equally up and down.
The total power reaching the base is I₀+I_g, and the thermal radiation from the base is related to its temperature by Stefan's law. In equilibrium, these two must be equal.
I do not understand the I₀=I_g equation. I would guess that applies in some special circumstance, but I cannot think what.

 

[Kolika28]

I_g is the thermal radiation from the hot glass. Necessarily it radiates equally up and down.
The total power reaching the base is I₀+I_g, and the thermal radiation from the base is related to its temperature by Stefan's law. In equilibrium, these two must be equal.
I do not understand the I₀=I_g equation. I would guess that applies in some special circumstance, but I cannot think what.

Thank you so much for this great explanation! Really appreciate it!

 

[haruspex]

Thank you so much for this great explanation! Really appreciate it!

There is something incomplete in the picture, though. The radiation that comes through the atmosphere from the sun includes an IR component, some of which is absorbed and reradiated by the glass.