24V panels on a 12V system

BFL13 wrote:
I haven't tried it, but AFAIK, the 12/24 PWM can be put on 12v batts and have a 24v array. It just won't do more than that array's Isc, which is about half what a 12v panel's Isc/watt would be. Wrong??

Yes, you can connect it, but this would be a wrong thing to do :)...
It will provide 12V output, yes, but because the current of 24V array is twice lower than of 12V array, you will lose half the power.

red31 wrote:
I thought ya could connect a 24v panel directly to a 12v battery, disconnect when battery voltage is desirable.

I guess that would be a true "manual charge controller" :)

Phil

I thought ya could connect a 24v panel directly to a 12v battery, disconnect when battery voltage is desirable.

Almot wrote:

KD4UPL wrote:

Johnny G1 wrote:
C40 Xantrex controller 12- 48 volts and a good controller.

This model of controller, while excellent in it's own right and nearly indestructible, is not an MPPT model and won't work for matching higher voltage panels to a 12v system.

Yep. PWM controllers can be 12/24/48V, but this merely means that they will automatically recognize the battery input, i.e. can be used on 12, or 24, or 48V battery bank on the condition that the array output is the same as the battery bank. Ex, for 48V bank it would require 48V nominal array, i.e. 2*24V panels in series. It won't convert 24V panel output (or 100V of a few panels in series) into 13V charging voltage for 12V bank.

I haven't tried it, but AFAIK, the 12/24 PWM can be put on 12v batts and have a 24v array. It just won't do more than that array's Isc, which is about half what a 12v panel's Isc/watt would be. Wrong??

I've been using a $100 Eco-Worthy 20a MPPT controller on a single 24v 230w panel for over a year now. I liked it so much that I picked up a second one to run a 220w panel.

Lots of step down DC voltage converters (transformers) out there. Or better yet, MPPT controllers.

KD4UPL wrote:

Johnny G1 wrote:
C40 Xantrex controller 12- 48 volts and a good controller.

This model of controller, while excellent in it's own right and nearly indestructible, is not an MPPT model and won't work for matching higher voltage panels to a 12v system.

Yep. PWM controllers can be 12/24/48V, but this merely means that they will automatically recognize the battery input, i.e. can be used on 12, or 24, or 48V battery bank on the condition that the array output is the same as the battery bank. Ex, for 48V bank it would require 48V nominal array, i.e. 2*24V panels in series. It won't convert 24V panel output (or 100V of a few panels in series) into 13V charging voltage for 12V bank.

Johnny G1 wrote:
C40 Xantrex controller 12- 48 volts and a good controller.

This model of controller, while excellent in it's own right and nearly indestructible, is not an MPPT model and won't work for matching higher voltage panels to a 12v system.

Thanks for the prompt replies, I have searched google for this info with no luck. In regards to the free panels, No they are not free but very low priced.

Thanks for all of the great info.

Larry

Access to free panels sounds like "used panels". Make sure that they are of the same or close wattage and voltage, because MPPT works the best when panels are closely matched. It will still work with mismatched array, but not as efficient.

Also, panels are aging at the rate ~1% a year, so 10 years old array of nominal 500W will work as 450W. So plan accordingly. Panels with glass too scratched will have lower yet efficiency, so pick only those that look good.

Panels brand - I prefer known brands in both panels and controllers, but with free panels it doesn't matter much.

MPPT controller type and brand:

Make sure controller has enough input voltage, this is particularly important when running a series array of panels. In parallel array only amps are added on the input, while input volts are the same as of a single panel.

Nominal controller output in amps is less important than input voltage limit, but still important. MPPT won't fry if total output amps exceed its rating - it will just clip it off, so you will lose some power at the peak sun. To give you an idea, for 500W array you need 30A controller in most places, and 35A for high elevations. I would suggest Rogue 3048 for array up to 490-500W. For 750W it would be 45A controller (or 60A for high elevations), and in this case I would choose Morningstar 45 or 60 respectively.

I would avoid no-name MPPT controllers from Ebay. Their efficiency is unknown, reliability is questionable, they are often lacking essential features like adjustable setpoints and remote voltage and temperature sensing, and the very MPPT feature can be a fake, i.e. they simply cut down the volts from 24 to 12 without proportional increase in amps. Also, the may have a low limit of input voltage.

Again on the input voltage limit:

It is important if you connect panels in series, and not important when in parallel. If there is any shading - from one panel to another, or from superstructures on the roof, or from trees - you'll be better off with a parallel array. Even on a good panel with many diodes, total solar production of a multipanel array may drop as much as 50% when only one of several panels in series is shaded. Parallel array is more difficult to wire, though.