Using very thin lexan sheet 1.2 mm

[Lenny]

I'm considering using a very thin lexan sheet (1.2mm) for my front glass. The set-up would be lexan-eva-solar cells-eva-tedlar This would not be a roof mount module rather it would be used as a solar generator. The loss of efficiency (88% light transmittance) would more than be made up by the reduced weight (stuff weighs 1.2 kg a square meter!!) Does anyone know why this might be a bad idea ?

[rollandelliott]

because it will flex and crack your cells! minimum I"d use is 1/8" thick lexan which is about $100 for a 4x8 sheet, not too cheap!

[dvhenry]

Also I would not suggest anything other than glass if using eva, for a number of reasons (check the thermal and mechanical properties on the data sheet of the grade of lexan you would like to use to discover why) . Use sylguard or similar for lexan.

[Lenny]

thanks for the info here are the specs quoted to me

Technical Data

Thermal Expansion mm/m 0,065


Do you think using a polycarbonate of 3.2mm would be better Its still half the weight of tempered glass and I can get 92% light transference BTW 3.2 mm would cost me $16.00 USD a square meter

[Lenny]

Slyguard to expensive for me I can get EVA for 4.50 sq meter. I was thinking of using regular plate glass to keep cost down. I figured the EVA will act as a laminate and I wont be using generator in bad weather ie hail storm. Any comments appreciated

[dvhenry]

Keeping the expansion rates with each (your glass or pollycarbonate, encapsulation material and PV cells) as close as possible is critical for your panels to last, sylguard is much more flexable than eva, giving some room to play.

EVA requires heat and vacuum, What does pollycarbonate do at the required temps? when cooled to normal temps what happens? I have not tried, but I doubt the Resaults would be good.

EDIT: I should note that my comments are in relation to the mechanical and thermal properties as I understand them, I have NOT built any panels (although I intend to).

[dvhenry]

I can get EVA for 4.50 sq meter. I was thinking of using regular plate glass to keep cost down.

This sounds good to me, have a look at http://fieldlines.com/board/index.ph...topic=145005.0
Yes, its a link from one of the 'sticky threads' on this forum (It's not a bad idea to read all 'stickies' on these forums).

[Cochran Solar]

Using Lexan Versus Glass Plate Versus Tempered Glass, Using Sylgard Versus EVA

Here are my suggestions for the diy solar panel builder. I have done a lot of research and demonstration projects on this subject. I have found that most solar panel prices now are around a $1.25/watt. This is where you want to start. Most panels are 220-240 watts. So the first thing I would do is figure the total price of the panel factory made versus home made.
Example 230 watts x $1.25 = $287.5 for factory built panels.
Then I would figure the cost of materials for the given scenarios and go from there.
If using Lexan nothing less than a 5mm will do, due to flexing and breaking of cells. Lexan flexes and the cells that are plastered to it will not. They snap.
Lexan is not cheap either. Locally at big box stores it is around 300 USD for a 4'X8'X.25" sheet.
Plate glass is very fragile, but can be easily cut to different sizes. It also will flex. The cost locally at the glass store here in town is about $40USD for a 3'X3'X.25" panel precut.
Last is tempered glass. It is impact resistant and flexes a lot less than lexan and plate glass. It is only about $5USD more per sheet than plate glass. It has to be ordered and can not be cut or drilled after tempering. Also it has about the same properties as the solar cells.

Next are my theories, thoughts and experiences on using eva versus sylgard.

Sylgard is the most expensive of the two, but takes the least amount of time to encapsulate panels. Mix and pour it on. There is a wait time for it to set. So you need a space to allow your panels to lay perfectly flat for at least a week. it is around $50USD dollars for the kit to do one 3X3 panel. It is a silicone elastimer similar to silicone caulk, which will allow for expansion and contraction of the material it is adhered to. This allows for the glass and cells to expand and contract at different rates and not crack. In other words you do not want the cells solidly fixed to the glass surface.

Eva is the least expensive, about $200USD for a roll 5'X30', but is the most labor/time consuming of the two, and if not done perfectly with due diligence you will be left with air bubbles. The best home method I have tried is to use a heat gun and gallon zip lock bag filled 3/4 of the way with water. You alternate heating the film and cooling with the bag as you move around in small areas.

Example costs for a 3'X3' 36 cell panel 172 watts
Tempered Glass $45, Sylgard $50, 40 6"X6" Cells $80USD, Aluminum Frame $40, solder tape, flux and other materials about $20USD. Total=$235 or about $1.35 per watt.
Labor about 2 hours and about 2 weeks lead time to get materials and assemble panel.

In conclusion, unless you need a custom panel for a specific need I would buy the regular panels that come with a warranty and have regulatory approvals, especially if you are thinking of a grid tie system.

Secondly, I would always suggest a grid tie whether or not you have battery backup, because there is the potential to sell excess power back to the power company if they offer it. If not the meter will still spin backwards and cut down on your power bill and also provide an outlet for excess. So there will be no need for a diversion load.

The most economical and simplest systems to install in the market now are those with micro inverters. These have individual inverters that mount to the panel and provide 120/240 volts at about 1 amp and tie together in strings. They offer the convenience of modular design so that if there is a failure, you can replace one $160 inverter instead of a $2000-$3000 large inverter. Also if one fails the whole system is not shutdown. The other panels and inverters will still be producing electricity. They also make it easy to start on a budget. One panel and inverter is all you need to get started and you can add panels and inverters as you have time and money. Just plan on how many watts total you would like and start there for sizing the racking and space requirements.

For example 4000 watt system.
20 panels and inverters total.
Once you have your racking installed, you can add one panel and inverter per month for about $500USD.
200 watts per panel and inverter combo for 20 months would equal 4000 watts. This is about the max that one can put on one 20 amp breaker.
No fancy wiring or planning just simple plug and play.

Thanks for your time and I hope I was not to long winded to be of help.
Remember the goal is to reduce power costs not to save money by cutting corners on equipment installation. The manufactured panels are the best route and are getting cheaper as you read this. Most of then have 25 year warranties on output and are storm rated. Some are even rated to survive substantial impact from hail stones. Do more research on panels and micro inverters and see for yourself.

Thanks
Charles Cochran
Cochran Solar

Slyguard to expensive for me I can get EVA for 4.50 sq meter. I was thinking of using regular plate glass to keep cost down. I figured the EVA will act as a laminate and I wont be using generator in bad weather ie hail storm. Any comments appreciated

[Naptown]

Charles
Nice post with good information there
A couple of corrections however.
Maximum # of Enphase inverters on one breaker is 15 for the M190 and 17 for the M215.
If you are going this route a better value are higher watt modules. (you will get more watts per inverter $ by using a 250W module with an M215 than a 200W module with an m190.)