cheap solar cells on ebay

[Harold in CR]

Not sure if it would reduce output or not. I'm favoring Aussie Jester's mentality. "Why split hairs". "If it loses a tad of output, just add another panel". After all, you are saving money building your own panels. 8) 8) :lol:

 

[John in CR]

The silicone wouldn't reduce the cell output if it got in front of the cell?

The cells have to be totally encapsulated with something. Everything placed between the cell and the sun will reduce output, so the clearer the better, and I understand there is some silicone that cures as clear as glass.

Also, each surface between the cell and the sun will be a point of refraction (I believe is the correct term) resulting in additional reflection before sun gets to the cell. For glass I believe that number is 3% at each surface, plus there is additional blockage by the glass itself (or other materials, eg silicone) based on its thickness. That's why I questioned Harold's plan for a replaceable glass over some kind of plastic. It will add 2 surface/air interfaces costing an extra 6% loss of sun right off the top, plus whatever gets absorbed by that extra layer. As the angle of incidence with the sun gets away from 90%, that total % loss to reflections increases tremendously, so at 8 or 9am that 3% reflection of one surface may be more like 20-30% (look at a window pane from a shallow angle if you doubt it). Multiply by 3 surfaces instead of one, and very little light gets to your panel. Actually a fish tank with water is a more accurate portrayal of 1 surface. A pane of glass has two. It's that extra reflection that really kills output early am and late pm when the sun is at low angles to a fixed panel. That's why you can't multiple that effect by 3 with a secondary separate layer. That's another reason you can't have any air space in addition to the likelihood of condensation.

Between your cells and the sun you only want 1 surface exposed to air, so it reflects the minimum possible. You want the materials between the cells and that surface to be as thin and transparent as possible, so they absorb as little of the sun's energy as possible. Then you want those materials to remain waterproof and transparent for decades.

 

[Harold in CR]

That's why I will build a tracker, to try to keep the panels looking directly at the Sun. IF I can find glass thick enough, cheap enough, I will skip the plastic layer under the glass. Real answer ------------------ It depends

 

[John in CR]

That's why I will build a tracker, to try to keep the panels looking directly at the Sun. IF I can find glass thick enough, cheap enough, I will skip the plastic layer under the glass. Real answer ------------------ It depends

Come up with something good and it should be readily marketable, since my guess is that tracking would at least double output. Do the utility PV installations typically track the sun? Tracking would be especially beneficial here in Costa Rica, because the mornings are typically so nice, and 9-10am sun seems to be as strong here as noon sun in the states. Where I am clouds are typical after 2 or 3pm, and with our strong morning sun for the house I'd be tempted to run dual panels with half directed to take advantage of morning sun.

If we can keep materials cost down, these cells now at $.37/watt including shipping and soldering supplies and diodes, have the potential for incredibly cheap panels. Since we don't have or need A/C or heat, a smallish battery bank would make it relatively easy to reduce our tie to the electric company to being just a bad weather backup system.

 

[yopappamon]

Does the encapsulation need to be flexible? Or could you use something like this self leveling acrylic?

http://www.goldenpaints.com/technicaldata/selfgel.php

It's only $25 for 32 oz. and is clear. My concern with the GE silicone is it's not clear but a little milky. You can get water clear silicone, but it is a lot more expensive.

 

[Harold in CR]

Rather than experiment with unknown products, I am going with the GE II Silicone. It was recommended by the Guy in one of those info statements I posted earlier in this thread.

I found a source for 2500 W Sine wave Inverters for under $300.00. Very low idle amp draw. Very high efficiency. There is a guy using them for a year or so, and put 2 together to run a well pump on 240V. I'm pretty sure he used the same type. I will check the thread.

If we could just get batteries cheap enough ??? Guess no one is going to do the comparison of Lipo's to Golf Car batteries, I asked for, EH ??? I could carry several lipo's on the Plane. Golf car Batteries are tough to put in carry-on Luggage. Figuring the Peukerts Effect, I'm thinking buying packs of Lipo, will be a good investment, being as they can be bought as money comes available, and can be bought in different voltages.

 

[yopappamon]

I found a source for 2500 W Sine wave Inverters for under $300.00. Very low idle amp draw. Very high efficiency. There is a guy using them for a year or so, and put 2 together to run a well pump on 240V. I'm pretty sure he used the same type. I will check the thread.

Awesome, can you provide a link?

Are they just inverters or are they the kind you can back feed your house?

 

[Harold in CR]

They are straight Inverters. 12VDC to 120VAC. They are sold in a Box Store, in the North of USA. No stores south of Iowa and NOT available online. Have to check the thread for the store. Back later.

 

[Jeremy Harris]

Harold,

They may not be readily available in Central America, but over here we can get ex-data centre backup batteries pretty cheaply. A lot of the big data centres (banks, insurance companies etc) replace their UPS batteries long before their warranty runs out (they typically have a 5 to 8 year warranty).

These batteries are high capacity, sealed lead acid (usually AGM) and will last for years if looked after. They sell here for little more than scrap value, so are often snapped up by people wanting big standby supplies for solar or wind power systems. To give you an idea of what I'm on about, here's a link to a local (to me, unfortunately) supplier: http://cgi.ebay.co.uk/Rechargeable-ind-Battery-Pack-YUASA-12-volt-100-amp-/220660199734?pt=UK_ConsumerElectronics_Batteries_SM

It may be worth looking around somewhere local to you to see if you can find a source for these batteries, as they are probably the best value going for a high capacity solar system.

Jeremy

 

[Harold in CR]

Thanks Jeremy. I'm familiar with standby Batteries. We used to sell them, from Phone Co. Remote locations and such. I'm going to put the word out, and see what comes up. Down here, they use EVERYTHING to DEATH, and then, recycle whats left for other projects. My Spanish is not good enough to have a big conversation with the right people, so, I have to enlist someone that might help me.

SHHhhhhhhhhhhh, don't let John hear about those type batteries. :lol:

 

[Harold in CR]

Farm & Fleet. Sale right now for under $200.00 NOT UL approved. Not much of a Warranty, but, this guy I know swears by them. Offered by Don Schumacher of Drag Racing Fame. Made in Mexico.

I'm a little short right now, or I would have at least 1 waiting for me, in Fl. The guy offered to get one and ship it to me. Some of these Forum guys are real gems. Includes this place as well. 8) 8) 8)

 

[Evoforce]

Well, I have been using a 2000 / 4000 peak watt inverter from harbor freight for years. It works excellent and is alot cheaper than you will find most places. I also have a 800 watt inverter that I also have run with success. The only periodic mantainence I have had to do is replace cooling fans.

I also have the same model that I use on my boat. I ran solar on my boat for many years too.

 

[Harold in CR]

Looks good. No Harbor Freight down here. Got a ballpark price ??

 

[Evoforce]

Looks like I paid $149.99 for it. As long as you are going to keep your system 12 volt you can save yourself money using the automotive/RV side of things.

 

[Harold in CR]

As long as you are going to keep your system 12 volt you can save yourself money using the automotive/RV side of things.

Exactly what I was thinking. Lighting, fans, small appliances all designed to run on 12V. Inverter for larger things. Plenty of 12V DC motors available, also.

Now to figure Batteries. 2 Golf Car Batteries, here, cost $420.00. Yeah, import and duty fees.

If they are 175 ahrs, would that be 3500 mah ?? Couldn't sleep, so, I'm doing design work ??????????

I see my figures on the ahrs is WAAYYYYY off. 17,500 mah is correct ??

 

[fizzit]

If they are 175 ahrs, would that be 3500 mah ???

What? 175 amp hours = 3500 milliamp hours? 1 ah = 1000mah.

 

[Harold in CR]

Yeah, I don't convert numbers too well, anymore. So, I guess it's 175,000 Mah ??

 

[Evoforce]

Harbor Freight has website.

 

[veloman]

I tested my cells a few minutes ago. .48 volts in the shade, .55 in the 6pm sun.

I'm watching a few youtube videos on how to wire them together.

I want to make this first panel with as little complicated as possible. It only needs to work when it's dry, I won't be leaving it outside when I'm not charging my batteries. Any advice on materials, keeping costs low, and with stuff I can get at home depot?

I need a surface area of 32" x 24" for these 40 cells.

Any links to a proper inverter for this 20 volt setup? I am looking to charge at 21volts max.

Thanks for any help.

 

[John in CR]

I'd go with smaller groups of cells and then connect the smaller panels together in series afterward. No telling how many you would break trying to move 40 cells around once they are soldered together. For a non mobile panel, so weight isn't a concern, I'd listen to the guy from Harold's earlier post that's been making panels for decades, so the materials you need are thin glass. Since you live in civilization and can get it cheap, get tempered glass, as thin as is available. The other materials is the proper clear silicone (no acetic acid released during cure) and something to thin it.

Here's what I suggested to Harold in a PM this morning:
...assuming the silicone will cure between 2 layers of glass, you can do it all at once. Pour silicone on the back of the front glass with just masking tape to contain it at the edges, lay the cells face down, look underneath for air pockets to get rid of, get your wiring out of the edge, pour the back silicone, place the back glass, remove the masking tape, use some vertical wood strips to keep the edges of the glass aligned, put a piece of plywood, and some weight, and wait a week or whatever for curing, trim the excess silicone from the edges, and put your frame.

 

[veloman]

Hmmm, what's the need for the back piece of glass? Could you just use a painted piece of plywood as the only backing?

Is silicone toxic or anything to handle? I watched a video on youtube of this guy using epoxy in the manner you described.

I'm thinking of doing two panels of 20 cells each, 4x5.

If I were to build a portable panel, what else is a good option instead of the glass?

It's funny, when I was living in TX last month, I found a large sheet of thin glass by the dumpster, ended up giving it away on craigslist. There's no way I would of brought that thing home with me when I moved!

I may just buy this plexiglass, should work just as well, right? $20 for two of my panels. I know we have some sort of plywood/partical board in the garage here. Then I just need silicone.

http://www.homedepot.com/Building-Materials-Plexiglass/h_d1/N-5yc1vZ1xh6Zbrdg/R-202038047/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053

 

[Jeremy Harris]

Single component silicones cure by absorbing moisture from the air, either creating acetic acid as a by product (these are the ones you don't want to use) or creating alcohol. If you thin these and then sandwich the stuff between two layers of glass then it will take months or years to cure, as the only access to the atmosphere will be at the edges.

Two component silicones cure just fine when sealed up like this, but they are expensive (Sylgard 184 is the most commonly used one on panels, but they are all pretty expensive.

One way to use thinned single component silicone might be to replace the rear glass layer with a layer or two of woven fibreglass cloth. This would probably add some strength and hold the cells in place, yet would allow the silicone to cure, as it's porous.

I'm intrigued by the idea of thinning silicone sealant and would be very interested to know how well it works. Sylgard 184 is ridiculously expensive here in Europe and I've not yet found an alternative at a reasonable price.

I have experimented with epoxy, but it goes yellow pretty quickly in sunlight. Someone has suggested using epoxy but with a UV coated polycarbonate front sheet, on the basis that it's the UV that yellows the epoxy and the polycarbonate would block it well enough to give the epoxy a fairly long life. The idea was to make the panel as I described above, with fibreglass cloth as the backing for the cells. Once impregnated with epoxy resin the back panel should add a fair bit of strength. I might try it on a small panel and see how it stands up.

Jeremy

 

[Harold in CR]

Jeremy, did you read the 2 posts I made on page 3 of this thread ?? One was a link to fieldlines, where I got the idea to thin Silicone. The guy shows photos of his experimenting.

The other was an excerpt of a guy from the Solar Industry, talking about Silicone Gels .

I'm thinking, any time a simple compound can be packaged as a "Specialty" item (Sylgard) for example, it always winds up being an expensive item. Where 's all the Chemists when we need one ???

I found the GE I Silicone, here. They have no idea about GE II Silicone . Looks like another trip to Florida, OR, Shipping another Plywood Crate down here.

 

[veloman]

Well I found a perfectly sized sheet of thin plexiglass in our garage . I just read that you should use a 45watt soldering iron instead of a 30watt, to properly solder. My 30watt that I've used on wiring seemed to have trouble getting hot enough at times.

Are there any cheap alternatives to Slygard 184? I need some sort of clear medium between the cells and the plexiglass, particularly for shock absorption and holding them down - never mind moisture since I don't plan on leaving this first panel outside when I'm not using it.

It almost seems that to do it right, you aren't saving a heck of a lot of money over buying manufactured panels, not even counting your labor.

 

[Jay64]

Veloman, you should really get those parts at Lowe's instead of the orange box. :lol: :lol: