new on solar energy

BB. · May 2014

Re: new on solar energy

I don't have any experience doing solar cell soldering--This video is as good as any to start:

https://www.youtube.com/watch?v=NJYaI3NGfXk

My 2 cents worth of comment--If he kept the iron "tinned" with solder, I don't think he would have the copper oxidation problem.

It is also possible that his iron is very hot for the job (or too hot), and this will oxidize the solder pretty quickly (I use a wet towel or even wet paper towel to keep tips clean--re-flux/tin tip when needed).

He is also using rosin flux... There are various "no clean" fluxes that may work well too (you need some sort of solvent to clean the rosin flux off the finished cell).

Of course, production solar cells are soldered with hot air/IR or other methods in production.

He was also soldering on a glass table (nice flat surface). Using some sort of heat resistant material with less thermal mass may make soldering the cells easier too (in the old days, it was asbestos blocks/plates). Perhaps transformer winding paper or other thin/flat stock would help.

-Bill

voyager · May 2014

Re: new on solar energy

Hi Bill. I am waiting all the things to arrive, to manufacture the panels. Surely I will have everything in one week.

Meanwhile, I'm starting to do some stress testing with the polycarbonate. En a week, I'm going to build a small cell with polycarbonate and encapsulation and I will continue with the stress tests.

keep in communication,

Regards,

Juan

mike95490 · May 2014

Re: new on solar energy

voyager wrote: »

Thank you Bill. Can you recommend any suitable soldering iron to solder solar cells?

It depends on the solder you chose (listed low to hi melting points)
Low temp
old school tin/lead
or lead free solder. Each requires a different temperature iron. The shape of the tip of the iron, must match closely, the footprint of the parts being soldered, to insure the most efficient heat transfer (fastest soldering to avoid dissolving the metalization off the cell)

Much better to practice with scrap wires till you get the knack of soldering.

BB. · May 2014

Re: new on solar energy

Tin/lead eutectic solar (around 60/40) should be the best...

High tin content is just to meet "low lead" government edicts. In general, from what little I know, tin/lead traditional solder is the "technically" better choice overall.

-Bill

voyager · May 2014

Re: new on solar energy

I am thinking in doing the solder of the cells with hot air. I found it in amazon:

http://www.amazon.com/WEP-858D-Soldering-Station-Suitable/dp/B0055B6NGE/ref=sr_1_3?ie=UTF8&qid=1400945233&sr=8-3&keywords=soldering+hot+air+station

Anyone has experience with this kind of soldering?

Thank you

voyager · May 2014

Re: new on solar energy

A photograph of the project progress. The three panels are as shown in the picture. Next Sunday I will receive all the components and I'll start welding cells. Finally, I'm going to do the soldering with a soldering iron in the traditional manner.

I installed the 12 AWG 4 wire cable (Red/Black/White/Green-Ground) for the GT inverter installation, that will arrive next Sunday.

Bill, I know you commented me, that is not necessary to use diodes. It is assumed that the investor. will avoid any possible return of energy to the panels. However, to be quieter, is there any disadvantage if I install the diodes to each panel? If so, could you guide me how to calculate the size of the diodes? and how to connect them?

Attachment not found.

Regards

Juan

ILFE · May 2014

Re: new on solar energy

Juan,

Whenever I received junction boxes, they came with the necessary diodes either in them, or ready to be installed in them.

(I had a friend ship me some solar panel kits over, which included the junction boxes. I chose to go with commercial panels, though, rather than to build my own. Had the price difference been huge, I may have opted to go with building them. But, the built and installed cost (turnkey) on each panel, was nil, in comparison to using manufactured panels. I live in Cambodia, by the way. Our farm is off-grid, so building my own array wasn't out of the question. It was just a smarter choice to go with commercially manufactured panels.)

With modern controllers, they (diodes) really aren't necessary, though.

voyager · May 2014

Re: new on solar energy

Thank you ILFE.

voyager · June 2014

Re: new on solar energy

Hi guys, I finally received yesterday all the components to build my first 3x300W panels.

Last week, I did a first test with only a small section of polycarbonate without solar cells, without the chemical encapsulates. The strength and structure of the polycarbonate is perfect after being exposed to: the hot environment, freezing environment, and rain. I mean exposed it to more than 50 ° C (122 ° F) on a hot day (on a metal base, thinking the plastic may melt) and for more than 3 hours and then throw it in the freezer. I repeated this for a week. Today the polycarbonate is perfect.

I am ready to begin the construction of my second test with a small section of the polycarbonate only with two solar cells soldered in series, and the chemical encapsulating the cells. I am going to take measures of voltage, temperature and reviewing the structural resistance to conditions of: Hot environment, freeze environment, and rain. I will share pictures in a week.

I have a couple of questions.

1) Is this the place where I am going to solder the "tabbing wires" ends (+ and -), to the junction box?

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2) which is the distance that must exist between the cells soldered in series in a column? and which is the distance between a column of cells and the other column of cells in a panel?

Thank you,

Juan

inetdog · June 2014

Re: new on solar energy

ILFE wrote: »

With modern controllers, they (diodes) really aren't necessary, though.

You may be confusing blocking diodes (generally not used anymore, but also generally not mounted in the junction boxes of the panels themselves) with bypass diodes (two or three per panel to allow current to flow even if one or more cells in the panel are shaded.

Bypass diodes are particularly necessary if you put two or more panels in series. If you do not have the bypass diodes installed the other cells and panel can try to force full current through a shaded cell that will not produce that much current. The result is damage to the cell, and possibly even fire.

voyager · June 2014

Re: new on solar energy

Hi Fizzycist, in my case I am going to connect the panels in parallel. In the future I am going to install more or less 10 panels.

When I Bought the junction box, it came with the diodes installed (This is what you name as "Blocking diodes"?). I want to know if in my case I need to eliminate this diodes that came installed with the junction box?

I understand that in my case I don't need bypass diodes?

Thank you

BB. · June 2014

Re: new on solar energy

You don't need blocking diodes.

You should have bypass diodes for safety.

The diodes in the j-box are usually bypass diodes. And they may have 1-3 bypass diodes, depending on the box design and panel Vmp they were designed for.

-Bill

inetdog · June 2014

Re: new on solar energy

voyager wrote: »

Hi Fizzycist, in my case I am going to connect the panels in parallel. In the future I am going to install more or less 10 panels.

When I Bought the junction box, it came with the diodes installed (This is what you name as "Blocking diodes"?). I want to know if in my case I need to eliminate this diodes that came installed with the junction box?

I understand that in my case I don't need bypass diodes?

Thank you

Whether you need the bypass diodes or not (and even in the case of one bad cell or minimal shading they do provide a protective effect), there is no loss of efficiency to leave them in place. They do not drop the voltage or consume power during normal use the way blocking diodes (which are always in series with the panel output) would.

voyager · June 2014

Re: new on solar energy

Thank you BB and Fizzycist:

I will be waiting to have the following electric characteristics in each panel (72 cells - 6"x6" - Mono - 4.2 Watts per cell):
- Maximum Power a t S T C ( P m a x ): 300 Watts
- Optimum Operating Voltage (Vmp): 37.46 Volts
- Optimum Operating Current (Imp): 8.01 A
- Open-Circuit Voltage (Voc): 46.12 Volts
- Short-Circuit Current (Isc): 8.56A

The panels are going to be connected in parallel.

The diode inside each junction box says "10A10 MIC", I dont know what it means. I supose it is 10 Amperes.

I will appreciate if you can help me to know if it is the correct diode according to my panel Vmp?

Moreover, I want to comment, I did the test panel (without chemical compound encapsulating the cells). I did the solder in the way that BB explained to me using a glass. The first time, use a 30 Watts soldering iron and I saw that it really was hard to melt the tin. Change to another 50Watts soldering iron, and I had a better experience. I've been testing the voltage measuring and calculating the watts of the test panel and they are fine. Now I'm waiting to get a new soldering station that allows adjusting the temperature and also will allow me to use hot air to make the welds. This is the new soldering station:

http://www.ebay.com/itm/181139781537?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

I want to try to solder the cells with hot air and build a second panel test (with the chemical compound encapsulating the cells). Lets see how is the experience.

Regards,

Juan

Cariboocoot · June 2014

Re: new on solar energy

Just so you have something to compare your ambitious project with: http://www.solar-electric.com/kyocera-kd320gx-lfb-320-watt-polycrystalline-solar-panel.html/

BB. · June 2014

Re: new on solar energy

It is probably this diode (family):

http://www.wontop.com/pdf/10A05.pdf

It should do the job fine. (I am always worried about diodes stuffed in solar panel j-boxes--8 amps * 1 volt drop = 8 watts of heat--That is not an insignificant heat source--But it does seem to be the "industry standard" for how to do a bypass diode).

-Bill

Cariboocoot · June 2014

Re: new on solar energy

BB. wrote: »

It is probably this diode (family):

http://www.wontop.com/pdf/10A05.pdf

It should do the job fine. (I am always worried about diodes stuffed in solar panel j-boxes--8 amps * 1 volt drop = 8 watts of heat--That is not an insignificant heat source--But it does seem to be the "industry standard" for how to do a bypass diode).

-Bill

Possibly because most of the time they do nothing. Any time a panel is placed where one section is shaded for a significant amount of time this 'near max rating' will cause trouble.

BB. · June 2014

Re: new on solar energy

And us engineers are always designing for "worse case" situations... Drives everyone crazy.

-Bill

inetdog · June 2014

Re: new on solar energy

Cariboocoot wrote: »

Possibly because most of the time they do nothing. Any time a panel is placed where one section is shaded for a significant amount of time this 'near max rating' will cause trouble.

And even worse, two or three bypass diodes stuffed into the same box (and maybe potted together) will really have a hard time of it when more than one section of the panel is shaded and it is in a series string.
How about a design in which one bypass diode is added to bypass both of the other two or three? Cuts the power loss in those cases by a factor of two or three. Wonder why that is not done more often?

Cariboocoot · June 2014

Re: new on solar energy

inetdog wrote: »

And even worse, two or three bypass diodes stuffed into the same box (and maybe potted together) will really have a hard time of it when more than one section of the panel is shaded and it is in a series string.
How about a design in which one bypass diode is added to bypass both of the other two or three? Cuts the power loss in those cases by a factor of two or three. Wonder why that is not done more often?

Possibly because the makers figure, and rightly so, that panels should not be located so that such a situation occurs. Their idea is that you may get a passing shadow over one part of the panel and the single bypass diode for that section will not generate much heat for that brief time period.

voyager · June 2014

Re: new on solar energy

BB. wrote: »

Actually, you do not really need any blocking diodes. If you are connecting GT AC inverters, they don't feed back to panels.

And if you are using them for battery chargers, you do not need blocking diodes if you are using a solar charge controller (controller will block reverse flow).

What you need are bypass diodes. These are reversed biased diodes about every 10-24 cells or so. These diodes prevent shaded cells (pipe, trees, etc.) from being over voltaged ("dark cells" go high resistance and will be damaged if there is more than ~12 volts or so across the dark cells).

If you have 30 cells in series, then the diodes should bypass every ~10-15 cells (two-three sets total).

http://www.digikey.com/en-US/articles/techzone/2012/dec/active-bypass-diodes-improve-solar-panel-efficiency-and-performance

-Bill

Hi Bill, Based in your comment, and in the following diagram:

Attachment not found.

If I am going to build panels with 72 cells each one, Can I have a 10 Amps bypass diode every 24 cells? Is it correct?

Thank you in advanced.

BB. · June 2014

Re: new on solar energy

As I understand--You are correct.

-Bill

voyager · July 2014

Re: new on solar energy

BB. wrote: »

As I understand--You are correct.

-Bill

Hi Bill, I am back again with a good advance in my project. I am ready to finish this weekend 2 panels:

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In my tests, I detected temperatures in the solar cells of about 80 degrees Celsius (176 degrees Fahrenheit). I also saw that above this temperature the cells appear to decrease the voltage production. So, I decided to install an additional system, through which water can pass through the polycarbonate ruffles. What I'm expecting as a result, is the cells cool down the temperature and I am going to take advantage of the hot water leaving the system to inject it into my house to reduce the consumption of gas in the water gas heater (like a real solar water solar heater system). I already made a simple prototype and it worked. I had done several tests like freezing water inside the polycarbonate and see if it affects the material or break the cells and there was no problem. Anyway, it's a very interesting experiment, because in the end, if it works, I would have solar cells that generate electricity and hot water at the same time like a water solar heater.

I will have complete two panels and ready for next weekend.

However, I have doubts about the connection of the diodes. In the next picture, I wrote some IDs to identify the diodes (D1, D2 and D3) and also for connections (A1, X1, X2 and A2):

Attachment not found.

If I replace the symbol with a image of a diode, it looks as follows:

Attachment not found.

(Disclaimer: I use diodes 10A and 15A, because they were the ones I had available - I hope there is no problem with the difference)

You can see that D1, goes from "-" to "+". D2 goes from "+" to "-". D3 goes from "-" to "+".

I understand that the diode works when it goes from "+" to "-" like D2. Maybe I need to install inverted the diode D2, like the following diagram?:

Attachment not found.

I really appreciate your help because I think that is very important to connect the diodes with the correct polarization and avoid a damage in the panel.

Regards,

Juan

BB. · July 2014

Re: new on solar energy

I am a little confused with your last drawing... It look like the "cathode" marking band is switch "end for end" with the middle diode.

You want all the diodes to be facing the "same direction". Or, the middle one, will short out that string of cells.

Think of the diodes as if they are "water check valves". When the panel is in full sun, the check valves are all closed and there is no bypass flow.

However, if one of the strings is shaded, the flow needs to bypass that string of cells... So the diode on the left instead of seeing normal - to + voltage of ~9-14 volts from a good string... It will see the voltage across its leads inverter (now + to -) and the diode will turn on and let the current bypass those blocked cells. If you did not have the diode there, there would be no current flow and too much voltage across the shaded cell (aka solar diode) and the over voltage would damage that shaded cell.

By the way, your count of strings/cells is wrong somewhere--If 72 cells total:

72 cells / 3 strings = 24 cells per string or ~12 volts Vmp per series group of cells (not 18 cells per string).

-Bill

voyager · July 2014

Re: new on solar energy

Thank you Bill. Some pictures of the 2 panels with the cells encapsulated with the chemical compound:

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Regards

BB. · July 2014

Re: new on solar energy

Looking very nice!

-Bill

voyager · July 2014

Re: new on solar energy

Hi Bill, again me, with another advance of my project. I am including some pictures.

They are my two initial panels:

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A picture at the back of the panel where you can see the diodes box and JUNCTION BOX with MC4 cables and connectors:

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A picture of the water system (like a real solar water heater system), it will supply hot water to my house. The water is going to pass from panel 1 to panel 2 and then to panel 3 and then to my house. That is the way I am going to give the water the temperature that it needs:

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A picture with the installation of the inverter (in the future I will be changing it with a better inverter). It is going to be install in a room with a very good temperature:

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Tomorrow in the morning I am going to connect all the system. Next week I will be finishing the third panel.

Finally, this is a diagram. I will appreciate if you can make a review and tell me if it is correct. The diagram has a mistake because I am using 20A fuses in the positive of each panel (not 15A fuses):

Attachment not found.

Thank you for all your help. I appreciate all the effort to guide me and teach me. I am very happy to be part of this forum. Tomorrow I will be posting results.

Regards,

Juan

BB. · July 2014

Re: new on solar energy

Juan,

You do very nice looking work there!

One question about the AC inverter... Is that an Inverter/Charger or an inverter with an AC input and transfer switch to AC output?

Or is that, what we call, a "suicide cord". A male plug that will have 120 VAC on it when the inverter it powered up--So you can plug it into a standard wall receptical to power the home when the AC power has failed (and you flip open a Branch or Main breaker to isolate you from the utility grid)?

If it is a suicide cord and some from of "manual" isolation--Think twice about that--It is very easy to make a mistake and run the risk of fire or electrocution.

If you need a manual transfer switch--I have one similar to this one in my house (I used it with a small Honda eu2000i generator). It is very easy to wire up--Connect your Inverter to the "Generator input plug" and you are ready to go. You can also switch circuits individually if your total home loads would exceed the AC inverter's ability.

There are also automatic transfer switches too--From simple to very complex (start/stop/run/exercise genset, etc.).

-Bill

voyager · July 2014

Re: new on solar energy

Hi Bill, thank you.

BB. wrote: »

One question about the AC inverter... Is that an Inverter/Charger or an inverter with an AC input and transfer switch to AC output?
-Bill

This is a grid tie power inverter 2500 Watts (110 Volts output). The input is DC (from the panels) and the output is AC. It works with an input of 28V-48V. Each panel is generating 35 Volts Vmp.

Bill, and the following diagram, is it correct?:

Attachment not found.

- Juan

BB. · July 2014

Re: new on solar energy

OK--GT inverter--Then that is fine.

The wire size from the array to the GT inverter is capable of supporting 50 amps (according to your code)?

Also--You should have a dedicated branch circuit from your main AC panel to the GT inverter. The dedicated circuit should be:

2,500 Watts * 1/110 VAC * 1.25 NEC derating = 28.4 ~30 amp minimum 110 VAC branch circuit

Or based on your 900 Watt array:

900 Watts * 1/100 VAC minimum * 1.25 Wiring derating * 1.25 Solar derating = 14 amp ~15 amp minimum branch circuit rating with 900 Watt solar array

If you do not plan on adding more panels to the 900 Watt array, then a 15 amp circuit is "enough"... If you plan on installing more panels--Then you may want to install a 30 amp branch circuit (check the inverter's rating/installation manual--I am taking some guesses here).

-Bill

new on solar energy

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