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

[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

[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

[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.

[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.

[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???

[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]

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???