Thread: Any experiences with ebay flexible panels

Originally Posted by DiscoMick

Useful article - thanks for posting it.
I'm a novice at this electrickery, but as I understand it, put very simply, the output varies so regulators limit it, often to 10 amps, which batteries can easily handle.

The output of a regulator depends mainly on two things, the amount of input current/voltage available (from the panel/s in the sun) and the size of the electrical load. The load may be a discharged battery, a nearly fully charged battery, or a battery system with a load, e.g.a fridge. It has no way of reading the label on a battery that might recommend limiting input current, as placed on some AGM batteries. If you attempt to put more power into a solar regulator than it is designed to handle, it will either 1. blow a fuse, 2. emit smoke or 3. intelligently limit currents to a pre programmed level, if it is expensive enough. As Drivesafe frequently points out, an automotive battery can usually handle shed loads more current than the 10 amps a small panel set puts out, like from an alternator. It's voltage that requires the most control, not amps.

Originally Posted by Dorian

...It appears to me that the most important number for a solar cell is Vmp (Voltage, max power) and if your charging batteries, it needs to be around 14-15 Volts.

I think you might be miss understand what the article says a bit.

Vmp is the panel voltage at which your panel puts out it's maximum power. For the most efficient operation of your panel you need to keep your panel voltage as close as possible to Vmp regardless of what the Vmp of the panel actually is.

Of course Vmp must be a least 14- 15 volts if your going to charge a battery but it's not a problem if it is higher than that for battery charging purposes.

If Vmp of your panel is actually 20V then fine, your panel will be producing power at it's maximum possible potential for the current sunlight conditions if it is being allowed to operated at 20V. Note, it's maximum potential is not the same as it's rated power output.

Now you can't charge a battery at 20V so you need something to drop the voltage supplied to battery to ~14V. This is the job of the regulator, either a PWM or a MPPT regulator.

The PWM regulator drops the voltage to ~14V by lowering the panel voltage to ~14V. Since the panel is no longer operating at Vmp some of it's potential is being wasted.

The MPPT regulator drops the voltage to ~14V by converting excess voltage from the panel (over and above the ~14V required to charge the battery) into current. The panel voltage is held at Vmp. Since the panel voltage is held at Vmp the full potential of the panel is always available.

So a Vmp of 14 - 15 V is not necessarily the most important thing when charging batteries. It just needs to be a least 14 - 15 volts. If Vmp is very much higher than 14 - 15 volts then all the better - provided you use an MPPT regulator. If Vmp is very close to 14 - 15 volts then great - just use a cheap PWM regulator and you won't be any worse off.

Originally Posted by DiscoMick

...I'm a novice at this electrickery, but as I understand it, put very simply, the output varies so regulators limit it, often to 10 amps, which batteries can easily handle.

No regulators don't regulate current, they regulate voltage.

Originally Posted by Ferret

I think you might be miss understand what the article says a bit.


The MPPT regulator drops the voltage to ~14V by converting excess voltage from the panel (over and above the ~14V required to charge the battery) into current. The panel voltage is held at Vmp. Since the panel voltage is held at Vmp the full potential of the panel is always available.

So a Vmp of 14 - 15 V is not necessarily the most important thing when charging batteries. It just needs to be a least 14 - 15 volts. If Vmp very much higher than 14 - 15 volts then all the better - provided you use an MPPT regulator. If Vmp is very close to 14 - 15 volts then great - just use a cheap PWM regulator and you won't be any worse off.


No regulators don't regulate current, they regulate voltage.

IV-ISC.gif


I understand what you are saying, however if you are charging a 100Ah house battery that's dropped down to say 11.2V then the battery will quite happily draw 20 + amps, which is 200 + watts. And this is probably when you need every bit of amps you can get, if the regulator is happy to output 12 amps say, and the panel is only capable of 6 amps at Vmp, it's going to let the solar panel drop down to battery voltage which will reduce it amps output (blue line).

I was surprised with this revelation as I always thought that as the load voltage dropped the amperage would increase to keep the wattage constant as every other electrical thing on the planet does.

Cheers Glen

Originally Posted by Dorian

IV-ISC.gif


I understand what you are saying, however if you are charging a 100Ah house battery that's dropped down to say 11.2V then the battery will quite happily draw 20 + amps, which is 200 + watts. And this is probably when you need every bit of amps you can get, if the regulator is happy to output 12 amps say, and the panel is only capable of 6 amps at Vmp, it's going to let the solar panel drop down to battery voltage which will reduce it amps output (blue line).

I was surprised with this revelation as I always thought that as the load voltage dropped the amperage would increase to keep the wattage constant as every other electrical thing on the planet does.

Cheers Glen

Regardless of what your battery 'wants", a MPPT solar regulator will deliver no more volts x amps than your panel V mp x A mp, less around 5% to 10% lost power. So an available 6A at 17V mp from the panel (~100W) will deliver no more than 8A at 12V (~95W) or thereabouts to the battery.

Originally Posted by Dorian

IV-ISC.gif


I understand what you are saying, however if you are charging a 100Ah house battery that's dropped down to say 11.2V then the battery will quite happily draw 20 + amps, which is 200 + watts. And this is probably when you need every bit of amps you can get, if the regulator is happy to output 12 amps say, and the panel is only capable of 6 amps at Vmp, it's going to let the solar panel drop down to battery voltage which will reduce it amps output (blue line).

I was surprised with this revelation as I always thought that as the load voltage dropped the amperage would increase to keep the wattage constant as every other electrical thing on the planet does.

Cheers Glen

Maybe I don't understand exactly what you're trying to say but I think you should watch this video.

YouTube

In particular when they start explaining things about high / low charged batteries and current around 4:30 mins into the video

Originally Posted by Ferret

I think you might be miss understand what the article says a bit.

Vmp is the panel voltage at which your panel puts out it's maximum power. For the most efficient operation of your panel you need to keep your panel voltage as close as possible to Vmp regardless of what the Vmp of the panel actually is.

Of course Vmp must be a least 14- 15 volts if your going to charge a battery but it's not a problem if it is higher than that for battery charging purposes.

If Vmp of your panel is actually 20V then fine, your panel will be producing power at it's maximum possible potential for the current sunlight conditions if it is being allowed to operated at 20V. Note, it's maximum potential is not the same as it's rated power output.

Now you can't charge a battery at 20V so you need something to drop the voltage supplied to battery to ~14V. This is the job of the regulator, either a PWM or a MPPT regulator.

The PWM regulator drops the voltage to ~14V by lowering the panel voltage to ~14V. Since the panel is no longer operating at Vmp some of it's potential is being wasted.

The MPPT regulator drops the voltage to ~14V by converting excess voltage from the panel (over and above the ~14V required to charge the battery) into current. The panel voltage is held at Vmp. Since the panel voltage is held at Vmp the full potential of the panel is always available.

So a Vmp of 14 - 15 V is not necessarily the most important thing when charging batteries. It just needs to be a least 14 - 15 volts. If Vmp very much higher than 14 - 15 volts then all the better - provided you use an MPPT regulator. If Vmp is very close to 14 - 15 volts then great - just use a cheap PWM regulator and you won't be any worse off.





No regulators don't regulate current, they regulate voltage.

I'm sure you're right. All mine say 10A.

It just needs to be a least 14 - 15 volts. If Vmp very much higher than 14 - 15 volts then all the better - provided you use an MPPT regulator. If Vmp is very close to 14 - 15 volts then great - just use a cheap PWM regulator and you won't be any worse off.

Yes GSL state that to work efficiently , their MPPT regulators need at least 4-4.5 volts above max regulated ie about 18.5 volts Vmp. The regulators like a higher Vmp and gain a little efficiency so I am pleased the Vmp of the panel I bought is supposed to be 22 volts. There is no sticker on the back.
Regards Philip A

Originally Posted by DiscoMick

...All mine say 10A.

Which means if your battery wants to draw more than 10 amps and your panel can supply more than 10 amps then you will probably be seeing smoke, hopefully only from the fuse.

Another way of looking at it is - a regulator rated at 10 amps is not a good choice for panels over ~150 watts in rated capacity. Though since you will never get rated capacity you might be able to push it a bit.