Description of my system. Experiencing problems with voltage drop.

[Ilnarello]

Hello everyone.
I "built" my first solar panel that consists of 30 3x6" cells 0.5V 3.6A each.
Cells soldered in series and put on plexiglass with aluminum frame and encapsulated with epoxy resin (some bubbles left). In theory I had to receive 15V 3.6A and 54 watt as a result. In reality I receive 17.5V 2.7A on the full sun and about 15V 0.5A around 5pm with little clouds (if I measured current properly) with no load.
For my battery bank I have one small 12V 7Ah battery BP7-12

Today I have received cheap chinese charge controller. Description says it protects panel from reverse discharging, so I didn't put diode on my panel.


SITUATION 1
I have connected them all together and put the panel on the sun. There is plenty of space beneath the panel. It gave me nice 14V. After about 30 minutes there was voltage drop, I started receiving only 5-6V out of my panel. When sun went down and it became shady it returned back to 14V.
QUESTION 1: Is it because the panel overheat, therefore increased resistance and as a result voltage drop?

SITUATION 2
Back to the time when I was receiving 14V out of my panel.
For the load terminal I have connected 12V car socket

Checking voltage with multimeter and receiving nice solid 12V. Pluging a plasma ball lamp

and it's working. Plugging car GPS and it looked like it is charging. So I unplugged loads and left the system alone to charge.
In evening, after panel cool down and started producing 12V I plugged GPS to the socket. GPS wasn't charging, controller started blinking. A checked the voltage with multimeter on the socket while gps was plugged, it was 5V, despite battery had 12V. Unplugged gps and voltage went back to 12V.
QUESTION 2: Battery is not fully charged or controller is glitching? I charged the battery several days before I plugged it to my system.

SITUATION 3
I decided to unplug the panel and check the terminal with multimeter. There was 2.5V
QUESTION 3: Is my controller deffective (faulty)? As I understand, since it protects from backflow there must be 0V. Right?

Hope to hear productive answers

Best regards
Ilnar

[bcroe]

Long ago I attached cells to a sheet of Lexo*n. When put in really strong sun it worked,
but then I started hearing these "cracking" noises. The current capability nosedived in
a few minutes, though open circuit voltage was still there. Looking at the back, I
could see light where the sun had cracked the cells, which had a different co-efficient
of expansion than the support material. Now I only use glass.

This could have happened to you. Bruce Roe

[Ilnarello]

Today I fried my panel.
I left it on the sun for whole day, and after I returned from work found out it's done. It looks like cells are cracked and it doesn't produce any voltage.

However, question 3 is still disturbing me. I have 2.5 flowing back to terminal 1, which is solar panel terminal. Is it normal?

[PNjunction]

I hate to say it, but I'd dump the diy panel, and also return the controller.

Instead, with that battery, invest in a commercial "nominal 12v panel" rated anywhere up to 60 watts and no larger. That battery will handle about 3a continuous without creating hotspots internally.

Invest in a controller like the Morningstar Sunsaver 12v / 6a model.

What makes it hard to support is that you are using "loose cells" to construct your panel, in addition to us not knowing how well you constructed it. Loose cells that you can obtain as an individual have not passed the manufacturer's test procedures, and are really scrap. When cells don't pass the test, they don't proceed to put the ARC or anti-reflective coating on them either. Most diy builds also suffer from moisture ingress. Even if your cells were sold a "Grade A or Grade B", these cells are KEPT by the manufacturer for use by themselves or to other oem's, not us. A seller of loose cells can say *anything they want to* about them.

Also on the very low end is that charge controller. It may work for some, or may fault out immediately. Some vendors will be happy to send you replacements over and over again, when instead they should have improved the quality to reduce the rate-of-return in the first place.

Here is the total irony of doing a DIY solar panel system as an introductory to solar - it should only be done as a learning experience AFTER you have a commercial solar setup as a reference for what *should* happen under normal circumstances.

Otherwise, you don't know where you have gone wrong - is it my diy panel? Is it my controller? Have I made the right power budget calculations? You can't tell when you diy and go cheap.

Grab yourself up to 60w of panel, a quality CC like the Morningstar (or Steca or Samlex etc etc) of about 6A capacity or more and NOW you can actually learn something.

One thing we also don't know is if that battery is used, new, or has become toast.

Try again with just a little bit better quality, and I think you'll be far happier in the long run.

[Ilnarello]

Try again with just a little bit better quality, and I think you'll be far happier in the long run.

Thank you very much for your answer.

Why should I not to go over 60W?