Wednesday, 27 November 2013

Optical Properties of Solar Panels


All you ever wanted to know about Incidence Angle Modifiers…

When light strikes a transparent material, some of the light is reflected, some is absorbed on the way through and the rest is transmitted.  For low iron glass of the type used in solar panels with the light arriving ‘straight on’ (perpendicular to the surface) the figures are typically 8% reflected, 1.5% absorbed and 90.5% transmitted.

Light incident on a the clear cover for a solar panel is mostly transmitted, but some is absorbed or reflected
 Most of the light incident on a solar panel does not arrive perpendicular to the surface, but at some other angle as the sun moves across the sky over the course of the day and year.  The incidence angle is defined as the number of degrees between a ray of light and the line perpendicular to the surface.  As the angle of incidence increases so does the proportion of light reflected at a glass surface.  Since the light is not travelling straight through but at an angle with a longer path through the glass the proportion of light absorbed by the glass also increases.

As the light arrives at shallower angles, the proportion reflected increases

 The effect  light angle has on solar panel performance is quantified by a property called the Incidence Angle Modifier (IAM).  The IAM is measured and reported as part of the standard test procedure for solar panels and is defined as the efficiency of the solar panel at a given incidence angle divided by the efficiency when the light arrives perpendicular.  It takes into account not only the changes in transmission at the glass, but also any changes in reflection at the absorber.
For a flat plate solar collector, the IAM starts at a value of 1.0 when incidence angle is 0 and decreases as shown in the diagram as the incidence angle increases.

The incidence angle modifier captures the loss of efficiency as the angle of light changes from straight on

Evacuated tube type solar collectors have a different geometrical relationship with the light from the sun.  Only the light arriving on the centreline of the tube will arrive at the glass with an incidence angle of zero, as you move away from the centreline, the incidence angle increases and the so the proportion of light reflected and absorbed also increases.  This is partly explains why evacuated tube collectors often have a ‘zero loss efficiency’ (or optical efficiency) lower than that for flat plate solar collectors (the other factor being the gaps between the glass outer and the light absorbing surface inside).
Since a tube has circular symmetry, the proportion of light transmitted is unaffected by the direction the light is coming from.  The light passing through the outer glass wall for a single tube would be unaffected by the angle the light arrives from in the transverse direction (around the tube).

The geometry of a tubular solar collector gives higher reflection losses for light arriving straight on
but has circular symmetry, so the reflection doesn't change as the light angle changes
An evacuated tube solar collector is made up from a number of tubes installed side by side.  A gap is left between the tubes so they don’t touch one another and there is a gap between the outer glass and the inner light absorbing surface.  Consequently, a proportion of the light is not collected and passes between the tubes.

Tube collectors have gaps between each tube which cannot collect light

Some evacuated tube collectors have a tubular shaped absorber (so called Sydney Tubes or tube-in-tube collectors).  A feature of the geometry of these is that as the angle of incidence increases in the transverse direction (around the tubes), the absorber area increases compared to the effective area of a planar absorber – less light passes through the gaps. 

Tube collectors with tubular shaped light absorbing surfaces 'close the gap' as the light arrives at shallower angle

The transverse IAM for these products rises higher than 1.0 before falling to zero as the angle approaches 90 degrees. 

The IAM for a Sydney tube collector rises above 1.0 as the light arrives at shallower angles

All this is just another reason why you can't compare solar thermal panels by their simple gross efficiency.



  1. Positive site, where did u come up with the information on this posting? I'm pleased I discovered it though, ill be checking back soon to find out what additional posts you include. Zonnepanelen

  2. Thank you because you have been willing to share information with us. we will always appreciate all you have done here because I know you are very concerned with our. Zonnepanelen kopen

  3. Very efficiently written information. It will be beneficial to anybody who utilizes it, including me. Keep up the good work. For sure i will check out more posts. This site seems to get a good amount of visitors. Installateur zonnepanelen

  4. I am impressed. I don't think Ive met anyone who knows as much about this subject as you do. You are truly well informed and very intelligent. You wrote something that people could understand and made the subject intriguing for everyone. Really, great blog you have got here. Zonnepanelen kopen

  5. Nice Informative Blog having nice sharing.. Zonnepanelen

  6. This is a great inspiring article.I am pretty much pleased with your good work.You put really very helpful information. Keep it up. Keep blogging. Looking to reading your next post. Zonnepanelen

  7. This particular is usually apparently essential and moreover outstanding truth along with for sure fair-minded and moreover admittedly useful My business is looking to find in advance designed for this specific useful stuffs… Erotische massage

  8. This particular is usually apparently essential and moreover outstanding truth along with for sure fair-minded and moreover admittedly useful My business is looking to find in advance designed for this specific useful stuffs… Warmtepomp

  9. Hello, this weekend is good for me, since this time i am reading this enormous informative article here at my home. Zonnepanelen

  10. I am looking for and I love to post a comment that "The content of your post is awesome" Great work! Zonnepanelen

  11. Pretty good post. I just stumbled upon your blog and wanted to say that I have really enjoyed reading your blog posts. Any way I’ll be subscribing to your feed and I hope you post again soon. Zonnepanelen kopen

  12. If you don"t mind proceed with this extraordinary work and I anticipate a greater amount of your magnificent blog entries Installateur zonnepanelen

  13. I just couldn't leave your website before telling you that I truly enjoyed the top quality info you present to your visitors? Will be back again frequently to check up on new posts. Zonnepanelen kopen

  14. The website is looking bit flashy and it catches the visitors eyes. Design is pretty simple and a good user friendly interface. Affinity at Serangoon

  15. I came onto your blog while focusing just slightly submits. Nice strategy for next, I will be bookmarking at once seize your complete rises... חשמל כשר

  16. Saint Seiya Mobile ialah gim aksi dengan sentuhan alur kisah bergaya RPG. Kali ini, kita menjelma menjadi. ENP GAMES Co., Ltd. 4.0. 5. Download Saint Super Seiya Omega Cosmos apk 2 for Android. Seri mengekor seorang. best game for Saint Seiya Omega Ultimate Cosmos. Home REVIEW DAN DOWNLOAD GAME ANDROID Saint Seiya Omega. Saint Seiya Omega Ultimate Cosmo, Game Fighting Dari Serial Saint. Saya hendak sekali karena jarang rilis game offline dengan genre jenis ini. Omega sendiri adalahsekuel dari Saint Seiya sehabis peperangan di Holy Wars. Download; Extrak file "zip" nya dengan winrar/zip (kalo tidak punya pc, Saran game android Hd, keren, offline. download game saint seiya omega offline. dengan alamat link: