Solar Panels at Factor e Farm

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(Also see 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 (6.14 inch)

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

Mechanical

  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. Clear plastic pony beads 1/4" Craft store 8 per panel, 120 Total
  10. 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
  11. 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

Electrical

  1. Heat Shrink – Shrink tube for wire exits @ junction boxes, 1/4”x1” x 45 (about 15 panels, 3 per panel - 3" per panel - about 50" needed - Grainger $11 for aver 12 feet [7], enough for 16 panels
  2. Flux Pen - $1.25 at Grainger 2 and $4.50 at - HMC Electronics - 3 per panel, need about 45 pens. Get 56 to be sure.
  3. Tabbing Ribbon – 2 mm wide to match the front contact
    1. Exact length requirement: 6.14" for the cell length, 0.25" for crimp allowance (crimp itself is .125"), 0.25 for intercell spacing, and 6.14 for the tab
    2. Total: 12.78 per cell, times 2 for 2 contacts per cell, times 490 cells, is 1044 feet
    3. This is an underestimate - the first and last cell in a column (70 columns total) requires a small extra distance under 1/2" to the bus bar. This requires an extra 70 inches, or about 6 feet. Total: 1040 feet.
    4. Bus Ribbon - 6 mm or 1/4" wide for a Total of 80' - which is the total length of the 5 sheets of 4x8 that were used for framing - times 2 for both top and bottom.
    5. I got: these 3 products: Total of 1170 feet of 0.0059"x0.0757" tab ribbon, items [8] and [9]. Total of 100 feet of 0.008"x0.197" bus ribbon - [10]
  4. GE RTV 615 optically clear silicone Circuit Specialists RTV615-1P 1 pint (for 4 panels of his, our panels are 1.6 times bigger) - need 6 pints - $1620 for 6 pints at [11], $1290 at [12]
    1. Pint to ml conversion table - [13]
  5. Xylene (xylol) solvent Hardware store 1 pint (for 4 panels) - 1 gal Not at L
  6. Silver solder - recommended for silver contacts on solar cells - Grainger, $10/lb
  7. 4-wire terminal - to accommodate blocking and bypass diodes as well; 300 VAC/VDC terminal block
    1. Need 9 of these (7 plus 2 for partial panel) - every other panel needs a blocking diode (2 panels in series give 24V in our system)m part 7527K84 at McMaster Carr - $2.61 each, $23.49 total
  8. 3-wire terminal - to accommodate bypass diode, and no blocking diode
    1. Need 7 of these, part 7527K83 at McMaster - 2.15 each, $ 15.05 total
  9. wire for panel connection - assuming 1.5' per panel, 22.5'... what kind? Not sure what kind
  10. junction box - 15x Plastic case, 4.7” x 2.6” x 1.5” - $2.29 at Radio Shack
  11. 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
  12. 14 bypass Schottky diodes (shottky are a bit more, but 0.3 V drop instead of 0.7 V is important) - DO-201AD package -
  13. 7 blocking diodes -
  14. Rubber grommets for junction boxes (3 per panel) to fit 9/32” hole exactly (Rubber grommets, 8" ID, 11/ 32 OD, groove diameter 4", groove width 1/16", 3/16" thick suggested). $4 at Harbor Freight
  15. Template Sheet for soldering cells and transferring them to panel structure

Tools

For Mechanical

  1. Plexiglas "plastic sheet" cutters - L/M prob. Not at L
  2. Metal Rulers, Tsquare (Tsquare not absolutely necessary, I have a nice 1.5' metal ruler) Choices available at Lowes

For Electrical

  1. Controllable temp soldering iron - got 3 from Harbor Freight for $36 - [14]
    1. 3 soldering irons on loan from EE dept @ Mizzou - 2 variable temp and 1 regular
  2. needle nose pliers - $2 at Harborfreight L = selection and price list.
  3. Reamer bit - ? Not at L
  4. 7/32 drill bit (might want an extra or two?) L/M. L=4.69 for cobalt, 4.97 for titanium
  5. Two brushes for encapsulant, addl. brushes for silicone. is foam okay for these applications?
  6. Multimeter - $5 at Harbor Freight

Outstanding Items - 7.15.08

  • Xylene - available at Menards
  • Tiny brushes for encapsulant - Menards
  • Junction boxes - Radio Shack
  • Schottky diodes - Grainger or HMC or All Electronics
  • Wire terminal -
  • Rubber grommets - box from Harbor Freight, see above
  • Needle nose pliers - Harbor Freight, see above
  • Wire requirements for 8 amp current - [15]
    • Wire runs from solar cells will be either 150 feet or 50 feet, depending on location of battery bank.

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.

Work Flow for 9.11.08 and 9.18.08

Mike, Richard,

We are getting ready for building the solar panels. Here's an update.

We have so far picked up:

1. 1/8" polycarbonate - total of 5 8x4 sheets, cut to size

2. Insect screen - 2 rolls, 4x5 feet each

3. 3 hack saws for cutting side bar

4. Scissors and exacto knives for cutting screen

5. 24 cans of white spray paint

6. sand paper

7. Pony beads - 720, 6mm tall

8. Side bar - 200 feet coming in today

9. Metal backing - 5 8x4 sheets coming in today - will get it cut to size today with plasma cutter

10. GE Silicone II sealant, 12 tubes

11. 1 caulk gun

12. 16 one inch C-clamps

13. Stainless steel screws, washers, and nuts, 1" long

14. Silicone rubber - we're ordering it today from McMaster Carr

Does the above list cove all that we need? Let me know if we missed something.The work flow that I propose is as follows, please comment:

Step 1: Prepare materials

1. spray paint front and back of metal backing

2. Cut screen to size

3. Cut side bar to size

4. Attach screen to backing

5. Attach pony beads to screen

6. Caulk the side bars to the backing

Step 2: Drill holes, assemble panels

1. Mark hole locations

2. Sandwich and clamp backing-sidebar-glazing together, using 2 c-clamps on each side

3. Drill holes in the clamped sandwich

4. Use 2 screws on each side to hold finished product together, stack and wait until the solar cells will be soldered the week after

These two steps give us panels - ready to be filled with solar cells. Note that we are not caulking the glazing yet - we'll do that after the panels are in. Step 1 could accommodate up to 10 people working side by side. Step 2 can accommodate 4 people to mark holes, 2 people to do the sandwiching, and 1 person on drill press to actually drill. 1 person could screw the finished product together and stack it up. The workflow could go directly from Step 1 to step 2, as soon as materials are prepared. Because paint drying is the limiting step, we could consider painting the working side first, and painting the back at the end - so that we minimize the paint drying time in order to move on to the next step. 30 minutes should be more than enough for the spray paint to dry, with 5 minutes between coats. We need 2-3 light coats of spraypaint.

Several prep steps for you guys:

1. Richard, can you pass on Richard Hurley's book onto the others so they can read through it prior to coming? The more the people are prepared, the more solar panels we will complete. We estimate that it will take 3 hours per panel for a skilled person, and 6 hours for novices. Taking that we are all basically novices, it may take a total of 6 hours per panel. In two days, we expect to produce 12 panels with 6 people working diligently for 6 hours per day. We may be able to finish all 15 if we work 8 hours each day. I would hope that we can achieve this goal - with 6 people as a good working limit for the number of people and workstations that can fit in the silo.

2. Mike, can you set up a Google group for Factor e Farm Work Days? Sign us all up. DONE

3. Mike, let me know ASAP how many professional quality soldering irons you can come up with from the University.

4. Mike, remember to see if you can grab a 5 gallon bucket of flyash from Dr. Liu for CEB testing.

5. Mike, let me know if your father has spare 16" tires for LifeTrac. We need 4 more for dually configuration.

6. Can you guys bring any folding tables? We need a significant amount of good working surface. We can use the drums and plywood that we have here for work tables.

7. Richard, remember to snag some paint for us if you have it.

8. On the way up to our place, you guys should lead a discussion in your van on how you will see the workflow happen, given the above discussion on work flow and the number of people that will be working. On our side, Britany, myself, and Jessica (WOOFer), and Brittany's mom and brethren if needed. Getting a good work flow will take the largest amount of time - so streamlining this will be key to getting everything done on Saturday and Sunday. The first order of business is to set up the workspaces and get people working effectively. The greatest amount of time will be needed for spray painting and marking holes/drilling. I think we should have no problem getting everything done this weekend - and if we don't finished, the Factor e Team will be there - including Jessica and Brittany's bro, who is coming Tuesday. We should be all set for the following weekend - where it appears that we'll be more pressured for time for the actual soldering - as that is a relatively slow process.

Talk to you soon. Things are picking up. Today I will order the electrical components for soldering and connections.

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