# Two 70W panels, average expected output



## stampee (Jan 31, 2013)

Hi all: I now have two 70W mfg rated panels I have constructed. I built a tracking platform and have them mounted on that. The cells were factory B-rated cells that I used, claimed to be good for 70W from the seller.
I am showing 6 amp output at 13.8V into my batteries at this time. In bright winter sun. I do not have vertical tracking, so have an average angle set for this time of the year that I got from solar tracking charts. I also am manually adjusting the horizontal east west angle because I haven't finished the automatic tracking system at this time.
I am wondering what I can expect for maximum output? 6 amps seems a little low to me. I was hoping for more like 8 amps output from the 2 panels.
I understand that the mfg claim of 70W is laboratory conditions.
These are self made panels I built for what that is worth. I am curious what kind of amperage's other people get either with self made panels or store bought ones.
Thank you
-Stampee


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## wy_white_wolf (Oct 14, 2004)

How are you reading the current?

What was the state of charge of the battery at the time you took the reading?

WWW


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## stampee (Jan 31, 2013)

wy_white_wolf: That is a good point you brought up. I have an analog ammeter inline with the batteries. Both were pretty low maybe 50% charge left in them. How does one actually measure what they are getting for output then since the batteries may change the reading?
Thank you
-Stampee


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## 12vman (Feb 17, 2004)

They should be around 8 amps connected in parallel..

Position them into full sun the best that you can. Take a Volt/Ohm meter that reads current. (Most meters will handle 10 amps.) Short the panels out with the amp meter and read it. Test each one seperatly and add the numbers. That is "actual" current..


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## stampee (Jan 31, 2013)

12Vman. Thank you. I shall do so if I get sun tomorrow. Now they are saying snow and rain for the next 5 days here. Never fails!
Thanks to everyone.
-Stampee


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## ace admirer (Oct 5, 2005)

12vman, is short circuit amps close to working voltage amperage? i would have expected shorted currect to be higher than working.

in NC about 5 Hours of useful sunlight out of 24.


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## wy_white_wolf (Oct 14, 2004)

ace admirer said:


> 12vman, is short circuit amps close to working voltage amperage? i would have expected shorted currect to be higher than working.
> 
> in NC about 5 Hours of useful sunlight out of 24.


ISC (amps short circuit) would be higher than IMP (amps maximum power). My guess without seeing the details on the cells he should be about 4.4A ISC and 4.0A IMP for each panel.

He does need to test each panel individually.

WWW


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## stampee (Jan 31, 2013)

I just tested the cells pointed as directly as I could manually. I read 19.8V 4.45A on one panel and 20.0V 3.75A on the 2nd panel. The 2nd may have had some tree branch shade on it. Those numbers are about what you have told me I should have. 
Combined output I read only 4.05 short circuit output. I do not understand this either. Measurement is being taken right at the panel leads as close to the cells as possible.

Connected to the 2 batteries I only show 1/2 amp going into the battery bank. The batteries are old, and I ran them down to the low voltage alarm on the inverter last night.( I forgot to turn it off before going to bed). I do not understand where the latent extra power is going to, if there really is any excess power?
I was showing 6 amps yesterday into the batteries and peaked at 7 amps a few times.
Any further assistance would be appreciated.
What really confuses me, is if a person has a potential of say 10 amp output in full sun, and their batteries are only taking say 5 amps of charge. Then they are wasting the other 5 amps doing nothing? It seems to me many times batteries do not take full amperage, yet I cannot believe everyone with solar is just throwing that excess of power away.
Thank you
-Stampee


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## stampee (Jan 31, 2013)

These are the cells I am using.
specification: Average Power (Watts): 1.8 Wp 
Average Current (Amps): 3.6 Imax 
Average Voltage (Volts): 0.5 Vmax 
Effeciency: 17.6%
-Stampee


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## wy_white_wolf (Oct 14, 2004)

stampee said:


> These are the cells I am using.
> specification: Average Power (Watts): 1.8 Wp
> Average Current (Amps): 3.6 Imax
> Average Voltage (Volts): 0.5 Vmax
> ...


That would give you a working amperage of 7.2A instead of 8. Remember amerage will be that of the weakest cell so the numbers from your tests look ok. I'd guess you have a bad connection somewhere.

What charge controller are you using? Just for a test hook them 1 at a time and together to the batteries without the charge controller and measure the amps and volts.

The one panel reading low should show you what happens when even slght shade is on the panel. 

WWW


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## justin_time (Dec 2, 2012)

stampee said:


> IWhat really confuses me, is if a person has a potential of say 10 amp output in full sun, and their batteries are only taking say 5 amps of charge. Then they are wasting the other 5 amps doing nothing? It seems to me many times batteries do not take full amperage, yet I cannot believe everyone with solar is just throwing that excess of power away.
> Thank you
> -Stampee


Amps arnt being wasted doing nothing rather not being generated in the first place.
I will assume max power for your panels is somewhere at 17.5 volts and 4 amps or there about. 17.5x 4 = 70 watts so you have a 70 watt panel, but that is only if you are using them up at 17 volts you are not...your using them at 12 so, 12 x 4 amps = 48 watts, you really only have roughly a 50 watt panel depending on state of charge of you batts. so together both panels as your using them "may" net you, 96 watts total, at best, not your expected 140 watts. 
And as a battery charges up the amps it takes slows down. lots of variables.


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## stampee (Jan 31, 2013)

Thank you. It looks to be a bad day for any further testing, overcast and dark outside now. I do not have the charge controller connected at this time. I was hooked directly to the batteries. I will try one at a time each panel when I next get some sun and see what happens.
-Stampee


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## ace admirer (Oct 5, 2005)

shadeing could cause great losses in panels depending on where bypass diodes are located in the panel


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## 12vman (Feb 17, 2004)

ace admirer said:


> 12vman, is short circuit amps close to working voltage amperage? i would have expected shorted currect to be higher than working.
> 
> in NC about 5 Hours of useful sunlight out of 24.


The working voltage current level will be slightly lower if you include the internal resistance of the battery. A battery won't be a dead short unless there are shorted cells in it..


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## ace admirer (Oct 5, 2005)

Thank You


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## 12vman (Feb 17, 2004)

Quote..
*"What really confuses me, is if a person has a potential of say 10 amp output in full sun, and their batteries are only taking say 5 amps of charge. Then they are wasting the other 5 amps doing nothing? It seems to me many times batteries do not take full amperage, yet I cannot believe everyone with solar is just throwing that excess of power away.
Thank you
-Stampee"*

This is where a diversion type charge controller comes in handy. Most charge controllers control voltage by shorting the input from the panels to control the charge voltage. Most controllers have heat fins on them and just disperse the unnecessary energy as heat into a heat sink. (The Fins) A diversion type charger will divert the unused energy to an external load (Water Heater Element) to act as a load to control the charge voltage to the battery. By doing this, the unused energy is now heating water..


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## stampee (Jan 31, 2013)

Thanks all for the help. I cannot do much more until the sun comes out again for testing.
They say it may be another 3 days now.
-Stampee


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