Solar Panels at Factor e Farm

(linked from Solar Cells)

Basic Design

1. Cell specifications

• Ersol Manufacture [1]
• E 6+ BluePower, 300 pieces of 3.65Wp and 200 pieces of 3.50Wp [2]
• 156 mm square cells

2. Panel plans

• 4x9 cell panels, total of 36 cells per panel
• Estimated 17-21 Volts per panel will account for voltage drops due to heat and travel through wires; A voltage regulator is recommended in this case. See Hurley pg 17-18)
• dimensions – 29”x56” for each panel
• 112 designer watts
• we have enough solar cells for 15 panels

look @ pg. 43 of hurley for an example layout of the panels. The example is 4x8 as well, though the cells are larger than in the example, about 6.14 in^2. These sound fairly large, about 2.5'x4.5'. If we are working on two at a time with a small team of people, we will need significant table space.

Parts

1. 1/4” Plexiglas – Lowes/Menards (L/M) – Not at L? according to website

What to use? Acrylic, polycarbonate... What are the differences btwn all those brand names? Although not all questions are answered, this website [3] gives the best discussion on yellowing and durability of different types of plastics and brands that I have seen to date.

[4] Regal Plastic, KC MO: XL-10 (UV stabilized Polycarbonate) 4'x8'x3/32" $112; 4x8x3/16 $189; UF-5 (Acrylic with some UV protection) 4x8x1/8 $158 Lexan (non-stabilized Polylcarbonate) 4x8x1/16 $53.50; 4x8x3/16 $158

McM - 1/4" plexiglas substantially more expensive than 1/4" polycarbonate for less impact resistance. Using UV resistant type, we can reduce cost. However, the sizes it comes in will be difficult to work with, as 48" x 96", the largest size, might be wasteful given that the panels will be 2.5' x 4.6', roughly. 3x10' sheets would be wonderful yet are not available. sigh.

We have been debating whether to get Acrylic (Plexiglas) or UV stabilized Polycarbonate for the panel cover. Both are have nearly the same transparency: (92%- Acrylic and 89% Polycarbonate). Comparatively, Acrylic handles UV rays much better than non-stabilized polycarbonate. However, UV-stabilized Polycarbonate reduces the yellowing-effect of the sun. I did not find comparative data on how UV=stabilized Polycarbonate compares to Acrylic. But, let's assume, until proven otherwise, that they are comparable. So, the main differences left are price and strength. Polycarbonate is generally more expensive. For example, at McMaster-Carr, a 4'x8'x .236" thick sheet of UV-stabilized Polycarbonate is $213. A similar sheet of Acrylic would cost $139.

However, the price factor is negated when strength is compared. Polycarbonate is considerably stronger than Acrylic. I found the following figures: Izod impact of 1/8" Polycarbonate is 13-16 lb-ft/in while that of Acrylic is .4-.9 lb-ft/in. These figures can be found in many places, including here: [5] Furthermore, acrylic looses 50% of its strength when temperatures are lowered from 60 degrees F to 9 degrees F. Polycarbonate on the other hand only looses 15% of its strength.

So, without exact data, I think it would be safe to use .118" thick polycarbonate. A 4x8 sheet of said thickness is $106. Cheaper than Acrylic. That seems to be the way to go.

The remaining question is, however, does thickness matter? And if so, how much does it matter? As far as we can estimate, hail is the biggest possible culprit. What is the impact power of hail? Is it a concern in our area? [6] According to the above link, a 1" diameter piece of hail creates an impact of less than one ft-lb. A 1 1/4" diameter hail has an impact of 4 ft-lbs. The Izod impact strength test says the acrylic would break and polycarbonate would not.

Are we at risk for such hail near Kansas City? [www.riskmeter.com/RiskMeter/White%20Papers/Hail_white_page.pdf] The map from this pdf document shows that we are indeed a highly hit zone. Areas such as the northeast and west of the rocky mountains are low-risk areas and one might consider an acrylic covered panel without fear of premature destruction.

Next question: Can we find a cheaper/local source of Polycarbonate? Can we get it in the size we need?

1. Cutter for plexiglas -
2. case backing, aluminum – McMaster Carr or local sheet metal shop
3. 1” by 1/4” aluminum bar< 72.5'W+140'L-5'for corners= 207.5' good thing you don't have to worry about saltwater spray. imagine ordering this much stainless steel! This might be a bit much for local stores, we shall see Not at L
4. u-channel for edges (will we do clips or do full bars and drill? One will require more drilling, the other more cutting?? the difference will necessitate only about 5' additional. pg 96)Not at L
5. stainless steel screws - assuming 18 per panel, at least 270, on pg 132, SS pan head slotted machine screw 10-24 1.5"L (or up to 2") L only has 1/4" decking screws, only 1/3 threaded. Inappropriate for the application
6. stainless steel machine screw nuts - at least270 Stainless Steel Machine Screw nut 10-24 screw size, 3/8" width, 1/8" height. Not at L
7. stainless steel 18-8 large OD flat washer 10 screw size 13/64" ID, 1/2" OD, .033" -.047" thick.Not at L
8. GE Silicone II sealant, clear (needed for junction boxes) L selection
9. shrink tube – Shrink tube for wire exits @ junction boxes, 1/4”x7/8” x 30 (2 per panel)Not at L
10. window screen – L/M - suggests fiberglass insect screening medium. Must evaluate pros and cons of using metal or fiberglass. Cannot use metal, the purpose of this screen is to prevent conduction with aluminum backing, which would cause massive loss of voltage, thus a very fine screen made of nonconductive material would work best. Lowes Selection
11. tabbing ribbon – need 12.5” per cell – total of about 520 feet! <rd pg 79-82. we might need more per cell, more like 15". it must run between the cells as well as along them. so, maybe as much as 620'
12. bus ribbon - estimating about 82'. We will need to do a scaled schematic/structural drawing to calculate this
13. GE RTV 615 optically clear silicone Circuit Specialists RTV615-1P 1 pint (for 4 panels) - 1 quart (4 pints per quart correct?) Not at L
14. Xylene (xylol) solvent Hardware store 1 pint (for 4 panels) - 1 gal Not at L
15. 60/40 solder - or PB free silver based? For the health of the assemblers? Add'l cost for heavy metal health and safety protection equipment...- though 60/40 available locally @ L/M L has lead free, though it seems more geared for plumbing than anything else
16. 2-wire terminal - 300 VAC/VDC terminal block , 2 circuits, .69" center-to-center, 65 amps (adjust ampage to cell output) Not at L
17. wire for panel connection - assuming 1.5' per panel, 22.5'... what kind? Not sure what kind
18. junction box - 15x Plastic case, 4.7” x 2.6” x 1.5” Not at L
19. epoxy for junction box - needed to withstand at least 400*F temps (suggested J-B Weld Epoxy, Max temp. 500°F or similar, 2 oz. tube Not at L
20. Clear plastic pony beads 1/4" Craft store 8 per panel, 120 Total
21. Silicone rubber strip 3/32" thick, 2" width 36" long - wont the bar be 1" wide? what is the need for 2" unless you intend to cut it? Possibly at L
22. 15 Schottky diodes (shottky are a bit more, but .3 V drop instead of .7 V is important) Not at L
23. Rubber grommets for junction boxes (2 per panel, 30 total) to fit 9/32” hole exactly (no moisture!) (Rubber grommets, 8" ID, 11/ 32 OD, groove diameter 4", groove width 1/16", 3/16" thick suggested) Not at L

Tools

1. variable temp soldering iron x2 – may have to order online, will call -St. Jo L does'nt have
2. needle nose pliers - L/M prob. Must decide on what kind, what features needed esp. for crimping.L = selection and price list.
3. Plexiglas "plastic sheet" cutters - L/M prob. Not at L
4. Flux Pen 186FP Mildly activated rosin, type RMA HMC electronics - says 2 pens or as needed for 4 panels, so 6 pens? Not at L
5. Reamer bit? Not at L
6. 7/32 drill bit (might want an extra or two?) L/M. L=4.69 for cobalt, 4.97 for titanium
7. two brushes for encapsulant, addl. brushes for silicone. is foam okay for these applications?
8. Metal Rulers, Tsquare (Tsquare not absolutely necessary, I have a nice 1.5' metal ruler) Choices available at Lowes

Work Plan

Hope to have 4 people total. Lots of cutting, soldering, silicone and epoxy brushing to do. Split into two teams, rotating duties,

Duty 1: Soldering and wiring, Duty 2: Panel assemblage.

Since panels can be prepared before the cells are soldered together, these two tasks can be done simultaneously, saving time. Cutting will be taxing, so this will require lots of rotation, and will also require proper safety equipment. Cutting of U channel, aluminum bar, plexiglas, possible precutting of Tab and Bus? Having to cut as you go might slow down the process.

Will necessitate refreshments, possible gas reimbursement (its expensive these days!). Might have to have a beer or two at the end of the day...

possible schedule (who am I to set a schedule?) saturday: 8:00 wake up, work at 9:00, break at noon or one for lunch, continue til 7:00? 8hrs x 4ppl= 32 human hours Sunday: 8:00 wake up, work at 9:00, break at noon or one for lunch, continue til whenever we need to leave.

During the process, we need to be documenting it all with video and picture. Might want to borrow an extra camera.

I have Hurley's book printed and in a binder, so it will serve us well in shop. Might want another? We will see. Might be able to seperate cells and panel work sections.

Participants:

Still have to figure out who all is going. Vince says maybe, he is wigged out on working two jobs and can barely think right now. He will finish up MSA on saturday and probably spend two days sleeping. Sri, a friend from here in columbia, very scientifically minded med student and sustainability enthusiast says she really wants to go. Everyone wants the weekend of the 11th because the weekend I have been proposing contains independence day. What about grid independence day! We will see what happens. There are several more interested parties, including mike. We could end up with as many as 6 participants. I might try to come down the weekend before that as well, as sitting around watching fireworks doesn't seem to be an appropriate celebration of independence for me. A friend of mine from natural resources (spec. soil science) has also spoken of coming out the weekend of the 11th, pending his new job schedule.