Solar concentrator for my 4.5W PV

[Marco]

I have 3 PV panels each rated 1.5W connected to some 12v lead acid cell.

The panels are mounted facing up at around 30deg to the sky (the inside of my greenhouse.

Could build a concentrator from curved wood (say 4mm ply) lined with tin foil and point the panels facing the tin foil? (And place the panels at half focal distance of curve.)              

Marco.

[veewee77]

Well, you could, but then heat will become a factor and the panels get less efficient the hotter they are, so it might be counter-productive to do that.

If you point the panels at the foil reflector instead of directly at the sun, you'll lose a lot of efficiency to start with because foil is a poor reflector.

It would be better to leave the panels ointed directly at the sun but just put flat reflectors on the sides to add extra light to what is already there without adding a lot of extra heat.

like this:

  \

   \ <---  Reflector

    \

     \

  --> |

  --> | <--- Solar panel

  --> |

  --> |

     

    /

    <--- Reflector

  /

Set the angle of the reflectors to get the most radiation on the panels.

This method will likely add a bit of output without too much added heating of the panels.

1.5w isn't much to start with, though.

Doug

[Bruce S]

Marco;

   You might want to move the panels to the outside of the greenhouse. Inside there is light defraction and will lessen the panels full output.

Even with single pane clear glass I have noticed a difference which is where I had my motorcycle sized battery charger at until I moved it to outside the glass.

Even at 1/2 the focal point the ehat will quickly become a factor and could get hot enough to melt any plastic that may be on the panel.

And as Doug said, you could add reflectors to the sides of the panels to get a longer charging time.

Hope this helps

Bruce S

[GaryGary]

Hi,

There is some material on soft and ridge concentrators here that might be helpful:

http://www.builditsolar.com/Projects/PV/pv.htm#Tracking

I agree with Bruce that you should move the cells outside if you can.  If the greenhouse glazing is glass, it will absorbe 10% to 20% or even more of the solar energy, depending on the type of glass.  

Gary

[craig110]

If your goal is to experiment with reflectors, then by all means do so, of course.  If your primary goal is to get a bit more power, however, it might be easier to just add another small panel to your setup.  I just took a peek on eBay, and there is a 10 watt panel available for $35, including shipping to anywhere in the US.  (No, I'm not the seller...)