Automotive Solar Panels

[carnage1]

We are mounting solar panels on the electric car we are building. I would like to know what parameters are important and how to look for them. My biggest concern would be a rock hitting one of them or some other damage.
I apologies for not having better questions on this subject but I don't know where to start.
The panels will be set up to charge the on board batteries as we require a higher peak power than the panels alone would provide.

Luck is a difficult thing to verify and therefore should be tested often. - Me

 

[IRstuff]

Not much that you can do. Some sort of wire mesh, like chickenwire? Not too dense, as that will reduce transparency.

Anything solid will require extreme transparency, which would be quite expensive for AR coatings.

Bear in mind that you'll only net about 600 kWh/m^2 on a perfect MIL-HDBK-310 day, so probably significantly less on any given day


TTFN

FAQ731-376

 

[GregLocock]

...give or take a factor of a thousand.

We did encapsulate one array with some glass fibre mat over the front of the cells to solve a thermal problem.

Experiments were done to demonstrate that this did not markedly reduce the output of the cells, I wasn't convinced.

Actually I wouldn't get too worked up about it. Try cracking a cell and see what I mean - the output scarcely changes.

Are you using diodes to isolate poor or shadowed cells?


Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[patprimmer]

I would consider a covering in clear acrylic sheet. It will give fairly good rock protection anv very good light transmission If you want mre rock protetion at the cost of less light transmission try polycarbonate sheet. If you want it light weight with even less transmission, try twin wall PC sheet.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[MikeHalloran]

Or just mount and connect the cells so replacement is simple.

Stay off gravel roads, and don't draft dump trucks.



Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

Does increasing the temperature affect the output of a solar cell?

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[IRstuff]

Temperature increase results in increased junction leakage, resulting in a lower output power.

TTFN

FAQ731-376

 

[carnage1]

I didn't even think to ask about temps, that is good to know.
Would it be beneficial to design the mounting of the solar panels to promote cooling as much as possible or will the cells simply being uncovered keep them cool enough that temperature is not an issue?

So I should be able to use pretty much any cells then and just add a very thin acrylic sheet over it, or it sounds like I may not need the cover if I orient them in a manner that they are unlikely to take a strike.
SO is 600 w/m^2 about average for a really sunny day? Or does it vary significantly by brand?

Lastly I am not sure about the best way to isolate the cells, I think we are going to use either a 24 or 48 volt system so I know we would need a lot of cells in each series to get our voltage that high. Or we could run a very parallel system with all the cells isolated and run them into a dc to dc converter but I think that would be less efficient than the losses from the series arrangement of cells. The minimum is that each series of cells will have a protection diode that prevents it from robbing the rest of the system.

Luck is a difficult thing to verify and therefore should be tested often. - Me

 

[IRstuff]

The energy value was a basic swag.
MIL-HDBK-310's 1% solar day is about 9000 kW*hr

Cell efficiency - 15%
Converter efficiency - 80%
some view factor loss ~ 80%
some latitude loss ~ 80%


TTFN

FAQ731-376

 

[GregLocock]

That sneaky old k got in there again.

Yes, typically in good sun the output of a panel drops by about 30% when stationary compared with 80 kph. Panel cooling is a very good idea. Leave a cell out in the sun and then spray water on it - you'll see a dramatic spike in output.

You should aim for as high a string voltage as you can get away with - even the best maximiser/ dc-dc converters will have a 0.6V overhead. On the other hand putting all your cells in one long series string means that if one goes bad- whether due to dirt, major physical damage, shadowing, or a dry solder joint then the whole string will die.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[patprimmer]

he acrylic cover will increase temperature if ou are not very careful about the ventilation. Acrylic actually makes a very good cover for solar wate heaters because it lets in light and keeps in heat.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[floattuber]

We used adhesive plastic, kinda like giant scotch tape, to help protect the cells and keep then intact. Using a solid cover will definitely increase temperatures and adversely affect your output.

There are flexible cells on the market, but they don't produce as much power as the fragile ones.

 

[saltwatersolar]

Have a look at "solara" solar modules, made in Germany. They are slightly flexible (about 3 %) but are monocrystalline, ie, more efficient for their area than traditional flexible solar modules, which are amorphous and take up about twice as much room.
I think Solara use a stainless steel backing, but I'm not sure what flexible transparent cover they use on the front of the cells. They are often used on yacht decks and can be walked on, so they would be resistant to rocks too, id say.

 

[dgallup]

Dear Solara Energy Customers,

We apologize, but as of 6:00am PST Thursday, October 4th, Solara Energy, Inc.
has ceased operations. We appreciate the 7 years of loyalty and support from
our customers. We sincerely regret any adverse effects this may or has caused.

Sincerely,

Solara Energy, Inc.

 

[maxaccel]

how about this
http://www.nanosolar.com/blog3/

 

[RossABQ]

We apologize, but as of 6:00am PST Thursday, October 4th, Solara Energy, Inc. has ceased operations.

Solar incentives must have expired...