Why a 130W solar module does not produce 130 W when connected to battery?

[Subhayan]

Suppose, a solar module of 130 W is connected to a 12 Volt battery.
Vnominal = 18 V
Cnominal = 7.22 Amps

The current received is around 7 amps on peak hours oriented in a perfect direction and angle. (I am not talking about a specific company, its in general)

V of battery= 12.3 Volts
I from module= 7 Amps

So, the wattage we are receiving is around 86 W.

So, where is this 44 Watts going? This 44W is not wasted but it is not produced because of the poor match between the Module and the charge controller

This is the case when the sun's radiation is at peak. And for the other times the situation is more gloomy.
So, the customer has paid for 130 W but he is not receiving 130 Watts at any point of day , at any time of year.

Any Solution???

[Sunking]

Yes get a MPPT Charge Controller. Same thing will happen with a PWM charge controller. Power is not going anywhere. By using a PWM controller or connecting the panel directly to the battery you are pulling down the panel voltage below Vmp to meet the battery voltage. Panels are current sources not voltage sources. Us an MPPT controller and you should get an output current from the controller up around 10 to 11 amps.

[Subhayan]

Yes get a MPPT Charge Controller. Same thing will happen with a PWM charge controller. Power is not going anywhere. By using a PWM controller or connecting the panel directly to the battery you are pulling down the panel voltage below Vmp to meet the battery voltage. Panels are current sources not voltage sources. Us an MPPT controller and you should get an output current from the controller up around 10 to 11 amps.

Thanks for replaying.
But I think there is some glitch on your solution. the module I mentioned has a
Vmpp= 21.2 V, Impp = 7.6 AMp

Vnominal = 18 V, I nom = 7.22(As told earlier)
See, 18 * 7.22 = 129.96 Watts
So How can any charge controller draw a current of 10 -11 Amps from this module?
If it draw s 11 Amps , then the voltage would be (130/11)= 11.81V.
So, hows this voltage is supposed to charge the battery.
My question was simple, if the module is not producing the lebelled wattage(in this case 130), at any point of day and any time of year, why it is called 130 W module??.
And, is there any technology available to overcome this???

[axis11]

Factory label is based on tests conducted on lab conditions.

So How can any charge controller draw a current of 10 -11 Amps from this module?

Thats the power of MPPT.

If it draw s 11 Amps , then the voltage would be (130/11)= 11.81V.
So, hows this voltage is supposed to charge the battery.

Those conditions will exist on cold weather and when batteries SOC is low.
More often you will get less than 11 but still at a higher current compared to the output of a PWM controller.

[Sunking]

Thanks for replaying.
But I think there is some glitch on your solution. the module I mentioned has a
Vmpp= 21.2 V, Impp = 7.6 AMp

Vnominal = 18 V, I nom = 7.22(As told earlier)
See, 18 * 7.22 = 129.96 Watts
So How can any charge controller draw a current of 10 -11 Amps from this module?
If it draw s 11 Amps , then the voltage would be (130/11)= 11.81V.
So, hows this voltage is supposed to charge the battery.
My question was simple, if the module is not producing the lebelled wattage(in this case 130), at any point of day and any time of year, why it is called 130 W module??.
And, is there any technology available to overcome this???

No glitch in my summary, you just do not understand how PWM and MPPT charge controllers work, and that solar panels are current sources, not voltage.

A PWM CC i sa series device where Input Current = Output Current.

A MPPT controller is a true Dc-to-DC power converter where Input Power = Output Power - Efficiency. So if you input 130 watts, and the controller has 95% efficiency comes out at 123 watts. Go in 18 volts @ 7.22 amps, you come out at 13 volts @ 9.46 amps.

[crotalus]

Subhayan,

A little background first. And then we will make this simple.

The panel rating is based on a standard for testing and certification. The numbers that are used are lab conditions called Standard Test Conditions. These are measured under lab conditions of 1000W per sq meter of “sunlight” with a standard spectrum of 5,500K. STC is a calibrated light with the panel facing directly into the test light, and at 25 degrees Celsius and an Air Mass of 1.5G. This information was obtained from the National Renewable Energy Laboratory (NREL) at Golden Colorado. In real life you would probably never see this.

Next let us look at a Watt is a Watt is a Watt.

Watts = amps * volts
Amps = watts / volts
Volts = watts / amps

I have Trojan battery that has a charge voltage of 14.8 volts, absorption voltage of 13.6, float voltage of 13.2 volts, and an equalizer voltage of 15.5 volts as per the manufacturer. So using your specs we can take;

Watts = 18 * 7.22 = 129.96 watts. The most possible under ideal conditions which from this point on we will assume and forget any losses due to inefficiencies.

Charge - Watts = 7.22 * 14.8 = 106.86 Watts
Absorb - Watts = 7.22 * 13.6 = 098.19 Watts
Float - Watts = 7.22 * 13.2 = 095.30 Watts
Equliz - Watts = 7.22 * 15.5 = 111.91 Watts

Using a MPPT controller what we would see at the very most is:

Charge - Amps = 129.96 / 14.8 = 8.78 amps
Absorb - Amps = 129.96 / 13.6 = 9.55 amps
Float - Amps = 129.96 / 13.2 = 9.85 amps
Eguliz - Amps = 129.96 / 15.5 = 8.38 amps

As you can see the result of using a MPPT controller is a slight boost in the amount of amps available for charging that would give you the entire 129.96 watts your panel is capable of. There will be some people that will say you are wasting you money on a MPPT controller with a small system. You will have to be the judge of that.

There was one mention on temperature in a previous post. As the ambient temperature goes up the efficiency of the solar cells drops. As the ambient temperature goes down the efficiency of the solar cells goes up. Remember the STC of 25C.

I have a MPPT controller on my small travel trailer. There was one time I observed an output that exceeded the rated Imp of my panels. The condition was at an altitude of about 9,300 feet on a very clear day with no clouds and no visible pollutants in the air. There was still a lot of snow in the mountains very near by and the outdoor temperature was 15F (-26C). The extra cost of a MPPT controller was worth the money for me.

I hope this is a simple explanation.

Keith

[Subhayan]

Subhayan,

A little background first. And then we will make this simple.

The panel rating is based on a standard for testing and certification. The numbers that are used are lab conditions called Standard Test Conditions. These are measured under lab conditions of 1000W per sq meter of “sunlight” with a standard spectrum of 5,500K. STC is a calibrated light with the panel facing directly into the test light, and at 25 degrees Celsius and an Air Mass of 1.5G. This information was obtained from the National Renewable Energy Laboratory (NREL) at Golden Colorado. In real life you would probably never see this.

Next let us look at a Watt is a Watt is a Watt.

Watts = amps * volts
Amps = watts / volts
Volts = watts / amps

I have Trojan battery that has a charge voltage of 14.8 volts, absorption voltage of 13.6, float voltage of 13.2 volts, and an equalizer voltage of 15.5 volts as per the manufacturer. So using your specs we can take;

Watts = 18 * 7.22 = 129.96 watts. The most possible under ideal conditions which from this point on we will assume and forget any losses due to inefficiencies.

Charge - Watts = 7.22 * 14.8 = 106.86 Watts
Absorb - Watts = 7.22 * 13.6 = 098.19 Watts
Float - Watts = 7.22 * 13.2 = 095.30 Watts
Equliz - Watts = 7.22 * 15.5 = 111.91 Watts

Using a MPPT controller what we would see at the very most is:

Charge - Amps = 129.96 / 14.8 = 8.78 amps
Absorb - Amps = 129.96 / 13.6 = 9.55 amps
Float - Amps = 129.96 / 13.2 = 9.85 amps
Eguliz - Amps = 129.96 / 15.5 = 8.38 amps

As you can see the result of using a MPPT controller is a slight boost in the amount of amps available for charging that would give you the entire 129.96 watts your panel is capable of. There will be some people that will say you are wasting you money on a MPPT controller with a small system. You will have to be the judge of that.

There was one mention on temperature in a previous post. As the ambient temperature goes up the efficiency of the solar cells drops. As the ambient temperature goes down the efficiency of the solar cells goes up. Remember the STC of 25C.

I have a MPPT controller on my small travel trailer. There was one time I observed an output that exceeded the rated Imp of my panels. The condition was at an altitude of about 9,300 feet on a very clear day with no clouds and no visible pollutants in the air. There was still a lot of snow in the mountains very near by and the outdoor temperature was 15F (-26C). The extra cost of a MPPT controller was worth the money for me.

I hope this is a simple explanation.

Keith

Thanks for the replay . It was very helpful.

Im my module
Voc 21.5 V
Isc 8.05 Amps

So what are you saying is that if proper MPPT charge controller is connected, the incoming current to the battery will exceed the short circuit current (Isc)???? How is that feasible? Please explain

[ckhorne]

So what are you saying is that if proper MPPT charge controller is connected, the incoming current to the battery will exceed the short circuit current (Isc)???? How is that feasible? Please explain

Read up on MPPT charge controllers. From xxx: Mod note - don't include links to the competition of our sponsor - bad form.

"The power point tracker (and all DC to DC converters) operates by taking the DC input current, changing it to AC, running through a transformer (usually a toroid, a doughnut looking transformer), and then rectifying it back to DC, followed by the output regulator."


What the MPPT does is vary the current so that voltage is within the range needed for charge. If your panel was generating 100w under normal conditions, your current charge current at 12v would be 100w/12v = 8.3amps. However, if your panel was in ideal conditions (such as crotalus's example), then it may produce 130 watts; the mppt controller would maintain the same 12v, buy yield 10.8 amps. (These are all assuming no inefficiencies in the charge controller).

In other words, with an mppt, incoming current has little bearing on output current. That's the whole point...

[RageFury]

Read up on MPPT charge controllers. From

"The power point tracker (and all DC to DC converters) operates by taking the DC input current, changing it to AC, running through a transformer (usually a toroid, a doughnut looking transformer), and then rectifying it back to DC, followed by the output regulator."


What the MPPT does is vary the current so that voltage is within the range needed for charge. If your panel was generating 100w under normal conditions, your current charge current at 12v would be 100w/12v = 8.3amps. However, if your panel was in ideal conditions (such as crotalus's example), then it may produce 130 watts; the mppt controller would maintain the same 12v, buy yield 10.8 amps. (These are all assuming no inefficiencies in the charge controller).

In other words, with an mppt, incoming current has little bearing on output current. That's the whole point...

So as I understand it the MPPT Controller changes the voltage and the Amps as the situation requires. Though it only has the Voltage and amps the Panel(s) provide. No more and no less. Thus if the MPPT Controller steps the voltage down you get higher Amps as a consequence and when it steps the voltage up you get lower Amps as a consequence. In both situations the watts should remain the same no?

[ckhorne]

So as I understand it the MPPT Controller changes the voltage and the Amps as the situation requires. Though it only has the Voltage and amps the Panel(s) provide. No more and no less.

Incorrect. It can use the total power (watts) that the panels provide. It can reconfigure the volts and amps up or down as needed, within the power (volt*amps) sent to it. 2volts @ 12 amps is the same as 12v @ 2 amps in terms of power (both are 24 watts).

Contrast this to a PWM controller that is limited to the amount of input current (amps) given to it. It can not reconfigure the total current to deliver more current than the panel provides.

Thus if the MPPT Controller steps the voltage down you get higher Amps as a consequence and when it steps the voltage up you get lower Amps as a consequence. In both situations the watts should remain the same no?

Correct.

[russ]

Volts x amps = watts

No magic watts appearing or disappearing though with PWM there can be watts lost.

As someone pointed out - a 130 watt panel would only put out 130 watts for a few minutes at solar noon on possibly a great summer day or possibly a sunny cold winter day.

[Sunking]

So as I understand it the MPPT Controller changes the voltage and the Amps as the situation requires. Though it only has the Voltage and amps the Panel(s) provide. No more and no less. Thus if the MPPT Controller steps the voltage down you get higher Amps as a consequence and when it steps the voltage up you get lower Amps as a consequence. In both situations the watts should remain the same no?

You almost have it correct. There is some power loss. Again, Power In = Power Out - Efficiency Loss

As an example lets use 100 watt input with 95 % efficiency in the MPPT controller or 95 watts output

Input = 100
Output = 95 watts.

Input = 5.55 amps @ 18 volts = 100 watts
Output 7.9 amps @ 12 volts = 95 watts

Nothing magical happened. We just use a True DC to DC converter instead of a voltage regulator to drop the voltage down. Very simple math of conversions minus losses.

Works much like a Transformer Power transfer. Current and voltage are inversely proportional. Electrical Power or Watts is a product of Voltage x Current. So at 100 watts all the following statements are TRUE:

100 watts = 1 volt x 100 amps
100 watts = 10 volts x 10 amps
100 watts = 100 volts x 1 amp
100 watts = 1000 volts x .1 amps
100 watts = 1,000,000 volts x .0001 amps

Now here is the Eye Opener lets use the same panel and battery, except this time we use a PWM Controller where Input Current = Output Current.

Input = 18 volts @ 5.55 amps = 100 watts
Output = 12 volts @ 5.55 amps = 67 watts.

[inetdog]

So as I understand it the MPPT Controller changes the voltage and the Amps as the situation requires. Though it only has the Voltage and amps the Panel(s) provide. No more and no less. Thus if the MPPT Controller steps the voltage down you get higher Amps as a consequence and when it steps the voltage up you get lower Amps as a consequence. In both situations the watts should remain the same no?

Exactly right! Very similar to what a transformer does for AC, just harder to implement.

Now if the output voltage of the panels were exactly right at any given moment during charging, a PWM CC could be slightly more efficient than an MPPT controller simply because there is less electronics between the panels and the batteries. But in practice that never happens.

So the tradeoff is really just between the added cost of the MPPT controller versus the potential savings in panel cost from their greater efficiency and the lower cost per watt panel selections.


There have been statements that all other things being equal a PWM controller can be expected to last longer than an MPPT controller just because it has fewer active electronic components. But I have no statistical results to either verify or refute that. You can infer a relationship from the manufacturer's warranty period.

[RageFury]

Incorrect. It can use the total power (watts) that the panels provide. It can reconfigure the volts and amps up or down as needed, within the power (volt*amps) sent to it. 2volts @ 12 amps is the same as 12v @ 2 amps in terms of power (both are 24 watts).

Contrast this to a PWM controller that is limited to the amount of input current (amps) given to it. It can not reconfigure the total current to deliver more current than the panel provides.

Thanks for the clarification, but I thought that is what I said. Did I articulate it incorrectly? Would not surprise me if I did lol...

[RageFury]

Thank you all for your responses. Still learning.