Hi Antonio,

could you explain the meaning of the acronym 'CPC'? It could not be clear to everyone (e.g., to me...)

Daniele

3D-CPC is a three-dimensional compound parabolic concentrator.

See http://www.edmundoptics.com/optics/optical-lenses/specialty-lenses/compound-parabolic-concentrators-cpcs/3213

Section 9.2 of this article on Solar Concentrators reviews the design of compound parabolic concentrators. If the light entering is within the acceptance angle, it goes through the concentrator exit; if it is outside the acceptance angle, it is reflected back out the entrance.

Thus you want to keep your light within the acceptance angle parameters of your CPC.

CPC means Compound Parabolic Concentrator, that is a reflecting concentrator realized by rotating by 2pi around the optical axis the profile of a parabola inclined (tilted) of the acceptance angle.

Hi Peter, I agree that to use the CPC as solar concentrator I need to send light within the acceptance angle, but I am interested in studying the CPC at uncommon conditions, just to find new optical properties, not necessarily those of a solar concentrator.

Antonio - the optical analysis is the same; I see the link is missing:

http://www.powerfromthesun.net/Book/chapter09/chapter09.html

Hi Antonio,

Not sure if I understand the question correctly, but if we translate the radiance of the Y axis on the attached graph in absolute optical efficiency or transmission, the FWHM will correspond to the 50% and if this is constant, the spread of angles from the acceptance angle will be constant, i.e. roughly +-2 degrees. This has been analysed by R. Winston for a 3D CPC (see e.g. Nonimaging optics, pp.57-64) and is constant because the number of reflections for incidence angles above the acceptance angle is constant and equal to 2 or 3 reflections. Hope this helps.

Georgios

Hi Peter,

thanks for the link to chapter 9 on Concentrating Collectors. May you send me the reference of the book?

Hi Georgios,

Thanks for your answer. I know the book of Winston. I think to have not been clear in the short question, so I reply to you and Peter sending a part of a manuscript I am preparing for publication. In this part you will find exactly what I am looking for when I study the reflected flux from a CPC. The remaining part of the manuscript cannot be shown, but I can give you all the information necessary to understand the chapter on the reflected flux.

Hi Georges,

as you can see in the file attached previously, the number of reflections of the reflected beam is higher than four; this is why I explored incidence angles far higher than the acceptance angle (5° in my simulations).

@Antonio - the book is online: http://www.powerfromthesun.net/book.html

"Power From The Sun" by William B. Stine and Michael Geyer

Hi Antonio!

I read your "analysis of reflected rays" and i didn't understand how is possible that backscattered flux remains constant for thetain > acceptance angle. The flux is proportional to the subtended area by the curve of reflected radiance, it can't remain constant with the decrease of radiance peak but with the same FWHM. It is possible note this behavior for thetain < acceptance angle, where the reflected flux increases with the increase of the incidence angle. Can you me better explain your simulation of the optical system?

To have a constant reflected flux, we need to have a constant integrand in the integral of eq. (37) of my note. The integrand is the product: sin(teta)*cos(teta)*L(teta). As the term sin(teta)*cos(teta) increases with teta for teta

Hi Antonio, I had a look into the attached chapter and the in-depth analysis you did for the back reflected rays and the number of reflections, and it indeed seems that the FWHM is directly related to the number of reflections in the concentrator. To confirm that, would it be useful to examine if the FWHM is still constant for incidence angles below the acceptance angle, as according to figures 28 and 30 of your paper this is where there is a deviation from the linearity and Liouville's theorem?

Hi Georgios, as you can see in Fig. 30, the number of reflections of reflected rays is not constant, but is increasing linearly starting from 5.