PV modules under shades...

System · August 2006

Hi there and to all of you, I need your technical advice, is that OK?

I am trying to make a solar light and gonna put it in an urban city garden, but the issue is...there are trees, buildings, etc...surrounding the designated installation spot, and so quite..most of the time shaded by some tree leaf-branches and buildings (shadows), at that spot that we are thinking to install it there.

So, will a Mono- or Poly-Crystalline PV module not produce charges at all to charge the battery when one part of the module is shaded by the tree leaf-branches and/or buildings at and during certain time of the day? I mean will the Mono- or Poly-Crystalline PV module power drop to zero when shaded, such as of just one part of the module, by those shadows of them?

My solar light needs 10-15Wp module to maintain its battery provided totally no block or shade. So I am thinking to use 20Wp. Thinking since it is shaded, so put in more Wp, thinking it should help to compensate that...but then there above, the questions above come to my mind..and so I am hesitating now.

Next question is will it be better or rather is it a must we use Amorphous PV module then in such case? If it is so, and can anyone advise where can i get Amorphous panel? Mono- or Poly-Crystalline PV modules are readily available in the market that I can just go and buy like 10pcs or less, but then seems not Amorphous panel to me.. Anyway I am tryng to make less than 10 sets of the light, so will need find stock or off the shelf panels of that..
And anyone have the Amorphous PV module (framed) dimensions and electrical data for like 10Wp..15Wp...20Wp?

Hoping for some advice to clear the doubts soon..thanks.

Cheers!
SolarFish

BB. · August 2006

Re: PV modules under shades...

You pretty much need sun on the panel to charge... My 3.5 kW array can put out a 100-200+ watts just pointing at blue sky/no sun (I have evening shade)... So, if you assume 5% power in open sky shade, you would need approximately 20x the nominal panel rating... Of course, any direct sun will help (especially if the panel is significantly oversized)... If there is no open sky, but filtered light through overhead trees--you are probably out of luck with solar.

If you are going to do more than one of these lights--it would probably be best for your make a mock-up and meter it with a logging current meter (to dummy load like 14 volts of zener diodes (heatsink with small panel) or a big old storage battery that is not fully charged) to see how much energy you get per peak panel watt...

You did not say what the light/load was... Assuming 15 watt peak at 5 hours of sun would support, roughly, a 4 watt light source for 12 hours during summer... During winter, much less. Are you assuming battery for 1 day of storage, or 3+ days of energy storage? Does the light have to work--or is it more for mood lighting and not much use during dark days of winter, etc.?

-Bill

System2 · August 2006

Re: PV modules under shades...

Would your location, and the design of your light fixture, permit mounting the panel in a different location, away from the actual fixture, where it will see the sun for most of the day? Of course that would require running a wire from panel to fixture.
Wayne

System2 · August 2006

Re: PV modules under shades...

First of all, the reason I am hesitating is because a solar garden light manufacturer told me quite some time ago that why they used mainly Amorphous and not Mono- or Poly-Crystalline PV for their solar garden light products because in case of some shadows or shades or dirts/bird drops...covering just one part (like 2 or 3 solar cells of eg. a total 2x8 solar cells) of a Mono- or Poly-Crystalline PV panel, then the solar power generation could drop to almost zero (if not totally zero), whereas this would not happen to Amorphous PV which would just reduce a small bit of power generation in proportion to the (small) area of shades/shadows on the panel. So, is this true?

If this is true, using a Mono- or Poly-Crystalline PV panel will post a bigger problem to the solar light that I am thinking to make for the garden I mentioned. I am not too worried about the buildings' shades/shadows because they only shade my panel during morning and evening time, and so I should still have about 1.5-2 hours of direct sun in the noon period, but then eg. the tree leaf-branches (there are other obstructions as well, like street lamp posts nearby, etc..) are quite close to the spot there where i want to install the solar light (thinking total 5-6 sets I am gonna to make and install for 5-6 locations/spots within the garden). Presently I am thinking 1.5-2 hours of direct sun should be good enough for me, but then if in this 1.5-2 hours time, one portion of the panel is shaded and then the solar power/charges drop to almost zero...meaning that I will get almost zero solar power the whole day and everyday too!...it is then the solar side of the light is not be working at all. Will this happen to my light if I use Mono- or Poly-Crystalline PV panel?

Should I switch it to using Amorphous panel in this case? Or does Amorphous better for such case anyway? As is it true that this would not happen to Amorphous PV which would reduce just a small bit of power generation in proportion to the (small) area of shades/shadows on the panel??? Hm...tough...

Thanks Bill for the information on your experience of getting just 5% power in open sky shade, so I shouldn't expect panel to be used in this manner then as I can't afford to put 20x bigger size panel. Rather I wish to count on the 1.5-2 hours noon direct sun period for my particular solar light case above, especially in this case my light is just a small power item and also just to run 4-8 hours every night. It is a 2-2.5W light bulb, for mood lighting, summer mainly. Energy storage of 3 days for the battery is fine with me.

Wayne, no sir...can't seperate that at this stage..

SolarFish

BB. · August 2006

Re: PV modules under shades...

I have a few observations... May help, or not...

Amorphous panels tend to be much cheaper (per watt) than the Crystalline--but less efficient. If size is not an issue and you can use a physically larger panel, Amorphous should be fine. In times past, the Amorphous tended to degrade under sunlight much faster than the crystalline--but my knowledge is not current, you will need to check that your self. Don't know about if they are more bird dropping proof or not--but it is possible.

At this point, you are probably best to just find the best price per watt and get those (assuming that the panel life / quality is satisfactory).

Other suggestions... Get several panels and string them together in a "high voltage" configuration and use a MPPT type solar controller to drop the voltage back down to battery bus voltage (if you can find a small enough MPPT controller--otherwise the controller losses would be too great). You could also use a regular controller with two panels in series (assuming you are under the controller's maximum voltage rating) and have better bird dropping/shade performace--However, you would be paying twice as much for panels (two in parallel would give you more power, two in series would give the current of one panel, but not die with a bit of shading).

An off-the wall suggestion... use a tightly focused LED bulb / solar array mounted in a sunny area (if there is one) of the property and use a scattering reflector to bounce the light down to where it is needed. Probably not practical though...

Also, if you use LED's (or other small bulb), you don't need 12 volts DC, but could run 3-5 volts DC with a directly connected 12 volt panel--this will also give you better shadow performance with one panel. And, if LED, you don't need a conversion circuit to support the lower voltage of the LED.

Something else you did not mention--the type of battery you will want to use. Solar heat, cycling, poor charging, etc. is a tough environment. If you can, cheap NiCad's might be the way to go (replace them every year or three). And make sure that the individual cells don't get reversed voltage'd... That will kill the cells quicker than almost anything else.

Do you have a design life for this project? Maintenance requirements?

-Bill

PV modules under shades...

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