Why 17 volt PV panel for 12V systems?

 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

  PV panels maximum power point changes with the temperature of the panel.
When the panel is hot , the mpp point is lower , cold higher.

Since panels are used in all types of climates , the manufactures choose a
mpp voltage the works worst case to still charge batteries , which need
about 14.5 volts to charge

This is why mppt charge controllers are used , they converter the ever
varying maximum power point on the solar panels to the fixed voltage needed
for the battery. Even this isn't quite true as batteries have there own
chemistry issues with temperature vs. charge voltage needed. Most higher end
charge controllers have a temperature probe option to optimally charge the
battery based on measured battery temperature and adjusts the charging
voltage accordingly

www.solar-guppy.com/forum , a free, non-commercial , no spam, solar products
discussion board

 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......

wrote:

 On Sat, 16 Oct 2004 10:50:25 +0200, Bill Darden


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