Furstrated- Unable to get rated solar Amperage

[bhvm]

Hello Folks,
I come to you with great hope. I have invested huge amout in solar Equipment and yet unable to get even half of rated output.

My Solar setup consists of -

Solar Panels- 250 wp, ( I brought 4 panels)
VOC 37.6v
Short circuit current- 8.5A
Rated voltage 31.4V
Rated amperage- 7.94V

Batteries- 12v Lead acid 150 AH in series for 24 system

24V 1400VA inverter

DC LED lights and other load via inverter.

Solar Charge controller-

http://www.vitronicscontrols.com/solar-IPS-charger.html

24v, 20A, PWM type. The best controller i could find in india.
---------------------------------------------------
Now,
DO as I might, I am unable to get the rated Amps out of the system.
Currently I have connected TWO pannels in parallel, That should make them ABOUT 30V, 16A... Thats good enough for 24v System to charge at worst case 15A charging, No?
I get only 6 Amps!

Now I connected 4 panels in parallel, That should be 30v, 32A. lets Take it down to 20A worst case, But NO!
What I got max ever was 10A!
As a result, what happens is 24V Battery bank runs down to 22V and The inverter Trips. I don't know why the charge controller can't provide full 16A+ and bring battery bank upto atleast 25v with Sun brightly shining?

How is this happening? I have already returned the Panels thrice and Changed controllers 4 times (with different models). Are companies lying? Why can't i never seem to get rated outputs?
IMG_20140605_171102_HDR.jpg2014-06-05_17-12-57_HDR.jpg

[Sunking]

Assuming you have no shade, orientation and tilt angle issue there nothing wrong with the equipment, it is operator error. You need a minimum 36 volts for a 24 volt battery system with a PWM controller. You only have 30 volts. Get a
MPPT controller and connect your panels in a 2 x 2 configuration of 2 panels in series in parallel with two more panels in series.

[bhvm]

Assuming you have no shade, orientation and tilt angle issue there nothing wrong with the equipment, it is operator error. You need a minimum 36 volts for a 24 volt battery system with a PWM controller. You only have 30 volts. Get a
MPPT controller and connect your panels in a 2 x 2 configuration of 2 panels in series in parallel with two more panels in series.

thanks for the quick reply. the open voltage of panel is about 36v. however when connected to the controller, the Voltage is brought down to what Battery voltage is, even on multi meter attached externally.

[Sunking]

thanks for the quick reply. the open voltage of panel is about 36v. however when connected to the controller, the Voltage is brought down to what Battery voltage is, even on multi meter attached externally.

That is how a PWM controller works. You need 36 Vmp panels, not Voc. You are going to have to use a MPPT controller and connect the panels in 2 x 2.

[inetdog]

thanks for the quick reply. the open voltage of panel is about 36v. however when connected to the controller, the Voltage is brought down to what Battery voltage is, even on multi meter attached externally.

Let's put some numbers in:

1. If the open circuit voltage Voc is exactly 36 volts, then the maximum power voltage, almost independent of light level, will be about 29 volts. That means that for whatever amount of light hits the panels, and regardless of how well they are aimed, the maximum power out will come at ~29 volts, but if you pull the voltage even lower you will get more current, all the way down to the short circuit current, Isc.

In your case you have the actual numbers from the labels on the panels:

Voc 37.6V
Vmp 31.4V
Isc 8.5A
Imp 7.94A


Now if you use an ammeter connected directly across the panel (put a blanket over it before connecting...) you should read 8.5A under absolutely perfect conditions.
And four panels in parallel should be able to give you 34A. Yes.

However, that will not happen if the angle of the panels is not close to perpendicular to the sun, with no clouds, near noon on a cool day.

If the current into the batteries is independent of the number of panels you have in parallel, then your biggest problem is that your PWM controller is not doing the job because it does not have enough voltage room to work with.
You should allow a volt or two drop in the controller, although really good ones will work with less. That means that you could get full panel current as long as the battery voltage under charge stayed below 29.4 volts.

One other reason for the PV output voltage to drop so low (~25 volts?) at a current of only 10A is that your wires between the panels and the CC are simply too small or there is a bad connection somewhere. Can you measure the voltage at the panel end of the wires?

[bhvm]

thanks for replies everyone.
1) I have brought 4 seperate cables for the panels (1 each for each panel till the controller ) to minimize voltage loss. cables are copper.
2) I didn't know controllers are so inefficient! 36v for 24v system is as good as 10v loss at whatever current is going. too bad.
3) I connect the panels in series today. that gives me about 60v at 8a per set.
however the amperage actually went down. which mean voltage was not the issue and something else. I'm running the setup in series today. let's see.

[Mike90250]

thanks for replies everyone.
1) I have brought 4 seperate cables for the panels (1 each for each panel till the controller ) to minimize voltage loss. cables are copper.

2) I didn't know controllers are so inefficient! 36v for 24v system is as good as 10v loss at whatever current is going. too bad.

No, it's not the controller, a 24V battery needs over 33V for proper charging and equalizing. And everything has loss. MPPT controllers have least loss, only 5%. PWM (like the kind you have) will have 30% under good conditions, because you end up with power mis-matches that the MPPT solves.

3) I connect the panels in series today. that gives me about 60v at 8a per set.
however the amperage actually went down. which mean voltage was not the issue and something else. I'm running the setup in series today. let's see.

Stop doing that. you can fry your controller.

In series, you ADD voltage, the amps stay the same. 8 amps would be correct for panels in series. Panels are fine, controller is working.
In parallel, you ADD amps, so 2, 8A panels would expect 16 amps, if the voltage was correct for the batteries.

[mapmaker]

2) I didn't know controllers are so inefficient! 36v for 24v system is as good as 10v loss at whatever current is going. too bad.
3) I connect the panels in series today. that gives me about 60v at 8a per set.
however the amperage actually went down. which mean voltage was not the issue and something else. I'm running the setup in series today. let's see.

Let me try to explain: Power (watts) = Volts X amps

A solar panel has its highest voltage (Voc) when there is nothing connected to it. that means the amps are zero and the power (volts X amps) is zero.

A solar panel has its highest current (Isc) when it is connected to a short circuit. In that case its voltage is zero and the power (volts X amps) is zero.

To get any power out of a panel, the current must be somewhere between 0 and Isc, and the voltage must be somewhere between 0 and Voc. For your panels, in parallel, that maximum power voltage (Vmp) is too low to charge a 24 volt battery. Don't forget that a panel's Vmp is also temperature dependent. That means when your panels are in the hot sun, their Vmp drops even lower.

When you put your panels in series the Vmp is about 62.8 volts. That's fine if you have an MPPT controller which can lower the voltage while increasing the current. An MPPT controller finds that point (volts X amps) where maximum power occurs.

Your controller pulls the voltage down while NOT increasing the current. Since it has to pull the voltage down from about 60 to 30 volts, without increasing the amps, you lose half your power.

--mapmaker

[bhvm]

Dear all, Thank you for detailed replies. let me reply one by one.

No, it's not the controller, a 24V battery needs over 33V for proper charging and equalizing. And everything has loss. MPPT controllers have least loss, only 5%. PWM (like the kind you have) will have 30% under good conditions, because you end up with power mis-matches that the MPPT solves.




Stop doing that. you can fry your controller.

In series, you ADD voltage, the amps stay the same. 8 amps would be correct for panels in series. Panels are fine, controller is working.
In parallel, you ADD amps, so 2, 8A panels would expect 16 amps, if the voltage was correct for the batteries.

1) I thought charging a 24v System shall use MAX 27v. Because I have never seen a battery bank charged to more than 26.5v in practical. Is there a difference in solar charging and mains charging protocol? In college projects, we used to happily charge a 12v battery bank with 15v transformer. I eXtrapolated the same and thought 31v panels would be good enough and minimize losses. hence i brought such panels. I think I made a mistake here.

2) The Controller I Brought is a very expensive (By indian Standards) and Is supposed to support maximum 500W worth of panels. I am running it happily since morning. I Have put 2 panels in series and the controller shows a maximum of 150w solar being extracted (6A in my Ammeter). Thinking 50% bucking loss, I was atleast expecting 250W (30 volts by 8A something)

3) When going from series to parallel, or so on, I did not gain or loose any Amps I feel. The Controller shows about 150W in series mode, and 140W in parallel mode. This is the confusion.

Let me try to explain: Power (watts) = Volts X amps

A solar panel has its highest voltage (Voc) when there is nothing connected to it. that means the amps are zero and the power (volts X amps) is zero.

A solar panel has its highest current (Isc) when it is connected to a short circuit. In that case its voltage is zero and the power (volts X amps) is zero.

To get any power out of a panel, the current must be somewhere between 0 and Isc, and the voltage must be somewhere between 0 and Voc. For your panels, in parallel, that maximum power voltage (Vmp) is too low to charge a 24 volt battery. Don't forget that a panel's Vmp is also temperature dependent. That means when your panels are in the hot sun, their Vmp drops even lower.

When you put your panels in series the Vmp is about 62.8 volts. That's fine if you have an MPPT controller which can lower the voltage while increasing the current. An MPPT controller finds that point (volts X amps) where maximum power occurs.

Your controller pulls the voltage down while NOT increasing the current. Since it has to pull the voltage down from about 60 to 30 volts, without increasing the amps, you lose half your power.

--mapmaker

May I know how much drop in Volts I get due to heat? damm! Indian summers are hot! Its already 42.C Ambient in noon (That 110F+). On No Load voltage, I got 31v on My meter. Do you think its going down to something 24v on load? As a result no charge??
When panels are connected to controller, The panel voltage is whatever the Battery voltage is. This is also confusing. Or Is the controller bringing the panel to its knees and all it gets is Float battery voltage with poor Current output? I dont think a 60V panel could be brought to knees without significant Amps. Atleast 8 Amps as the spec says.

[Mike90250]

here's a voltage chart of typical requirements.

http://www.trojanbattery.com/BatteryMaintenance/Charging.aspx

Daily bulk is nearly 30V, and Equalization is 31 volts. To perform EQ, you need to start with fully charged batteries.
You will need to provide about 3 volts more, because of inherent losses internal to any charge controller. So you really need panels that can supply their full amps at 35 or 36 volts.

I'd suggest you plan to wire your panels, 2 in series, to get 60 or 70V, AND obtain via mail order, a proper MPPT charge controller. At this point, from not having been charged properly, your batteries are likely pretty well trashed.

About the only thing you can do at this point is look at
http://www.vitronicscontrols.com/sol...t-charger.html from the same vendor you got the PWM charger from. Maybe they can exchange it.
Or look at another brand of MPPT controller that can handle 80Vdc from the PV array.

[bhvm]

here's a voltage chart of typical requirements.

http://www.trojanbattery.com/BatteryMaintenance/Charging.aspx

Daily bulk is nearly 30V, and Equalization is 31 volts. To perform EQ, you need to start with fully charged batteries.
You will need to provide about 3 volts more, because of inherent losses internal to any charge controller. So you really need panels that can supply their full amps at 35 or 36 volts.

I'd suggest you plan to wire your panels, 2 in series, to get 60 or 70V, AND obtain via mail order, a proper MPPT charge controller. At this point, from not having been charged properly, your batteries are likely pretty well trashed.

About the only thing you can do at this point is look at
http://www.vitronicscontrols.com/sol...t-charger.html from the same vendor you got the PWM charger from. Maybe they can exchange it.
Or look at another brand of MPPT controller that can handle 80Vdc from the PV array.

Thanks for deep insight. The Current controller seems happy at 60v.
I am going to ask them about MPPT ones. They're also sending in a technician tomorrow. He'll check stuff and let us know. I am also doubtful about wires. I feel that the wires are slightly warmer. The ones in Series panels are warmer than other wires. What does that say?

[inetdog]

The ones in Series panels are warmer than other wires. What does that say?

Mostly that says that if they are the same size as the others they must be carrying more current.
That is also consistent with the individual panel voltage being too low to delver the needed current to the batteries.

[bhvm]

yes they're the same size. I'll replace them and report back. let's see if it improves amperage.

[inetdog]

yes they're the same size. I'll replace them and report back. let's see if it improves amperage.

Not a sure improvement, but worth looking into. I would measure the voltage at the panel and at the CC end of the wires before I went to too much trouble replacing the wires. Unless I knew for sure that they were smaller than #14 AWG (if shorter than 25 feet) that is.

[bhvm]

They look like 1 Sqmm to the eye. Today I will see if I can make series connection at panel itself and Combine 2 cables to bring power downstairs. Will that help? If wires are hot means they're wasting half the power, aint it?