Why 17 volt PV panel for 12V systems?

[JB]

When I search for high power PV modules (120W or 180W) I found the output
voltage for maximum power is about 17 Volt. Vendors advise these type of
panels for 12 volt systems.

It seems to me there's an efficiency loss here! Would it be more efficient
to use a 14 volt for output voltage in maximum power PV panels? If so, why
manufacturers produce such high output voltage panels?

I also verify that for 24 Volts systems it is used 36 volt output voltage
for maximum power PV panels! Again, isn't this a loss in efficiency?

I'm prety sure I'm missing something here, but I can't figure out what!

José Barriga

 

[Bill Darden]

Some standard wet (Sb/Sb), wet "Maintenance Free" (Ca/Ca) and AGM
batteries require an absorption voltage of 14.8 VDC at 77 degrees F.
At o degrees F, the same battery requires 16.38 VDC. If you want to
equalize wet and some AGM batteries, you will require between 15 and
16.4 VDC. Some charge controllers need some "headroom" in order to
properly regulate the charging voltages.

For more information on charging, please see Section 9 in the Car and
Deep Cycle Battery FAQ on www.batteryfaq.org.

Kindest regards,

BiLL......

 

[[email protected]]

Some standard wet (Sb/Sb), wet "Maintenance Free" (Ca/Ca) and AGM
batteries require an absorption voltage of 14.8 VDC at 77 degrees F.
At o degrees F, the same battery requires 16.38 VDC. If you want to
equalize wet and some AGM batteries, you will require between 15 and
16.4 VDC. Some charge controllers need some "headroom" in order to
properly regulate the charging voltages.

For more information on charging, please see Section 9 in the Car and
Deep Cycle Battery FAQ on www.batteryfaq.org.

Kindest regards,

BiLL......

Also keep in mind that the junctions used to control the charge
current will drop .6 or more volts, and that the 17 volts is likely
open connection voltage.

 

[JB]

Also keep in mind that the junctions used to control the charge

current will drop .6 or more volts, and that the 17 volts is likely
open connection voltage.

No, I'm referring to Maximum Power Voltage. For these kind of panels Open
Connection Voltage is over 22 Volts.

José Barriga

 

[JB]

Some standard wet (Sb/Sb), wet "Maintenance Free" (Ca/Ca) and AGM
batteries require an absorption voltage of 14.8 VDC at 77 degrees F.
At o degrees F, the same battery requires 16.38 VDC. If you want to
equalize wet and some AGM batteries, you will require between 15 and
16.4 VDC. Some charge controllers need some "headroom" in order to
properly regulate the charging voltages.

For more information on charging, please see Section 9 in the Car and
Deep Cycle Battery FAQ on www.batteryfaq.org.

Kindest regards,

BiLL......

I'm a bit surprised here. I'm far from being an expert on batteries (just
some general culture), but what I know for Lead-Acid bateries the maximum
recommend voltage (during charge) is 13,8 Volt for room temperature. Higher
temperatures the maximum recommend voltage (during charge) is lower than
13,8 V and lower temperature the maximum recommend voltage (during charge)
is higher than 13,8 V. This is the reason that some charger have a
temperature sensor, because sensing the temperature it is possible to fully
charge the battery without degrading its performance over time.

Am I wrong?

José Barriga

 

[[email protected]]

No, I'm referring to Maximum Power Voltage. For these kind of panels Open
Connection Voltage is over 22 Volts.

José Barriga

Perhaps then, the mfg, realizing that over time the cell's voltage
drops off a bit, has deemed it necessary to start out high, extending
the useful life of the array. I have noticed that most arrays for
12volt charging that I have seen start out between 16+ volts to over
20 open circuit. While it does seem to be a bit of overkill, perhaps
BP or some other mfg could offer an answer.

 

[Gymmy Bob]

No. You are correct.
Your car battery will charge up to 15.4 VDC on a really cold day.
Lead acid battery capacity will also drop to about 40% in extreme cold.

 

[Bill Kaszeta / Photovoltaic Resources]

Perhaps then, the mfg, realizing that over time the cell's voltage
drops off a bit, has deemed it necessary to start out high, extending
the useful life of the array. I have noticed that most arrays for
12volt charging that I have seen start out between 16+ volts to over
20 open circuit. While it does seem to be a bit of overkill, perhaps
BP or some other mfg could offer an answer.

Most PV module characteristics are given at 25C/78F mostly because
that temperature is practical for routine factory testing and sorting.

The professionals in the business understand how to translate these
characteristics to the real world and calculate the expected output
for all the conditions.

Based on testing and monitoring it was determined 20 years ago
that a maximum power voltage of 16.5 to 17.5 was optimum for silicon
solar modules for charging 12-volt batteries. These days with a lower
proportion of the applications being used for battery systems, many
larger PV modules have much higher voltage ratings.
Bill Kaszeta
Photovoltaic Resources Int'l
Tempe Arizona USA
[email protected]