How to best use solar panels

[Tenor]

I have 5, 50W solar panels that are rated for 3.15A and 15.9V.  I am hoping to acquire at least one more for balanced numbers.  My house system is 24V, with a Vanner for the 12V needs.  So, here is the question, would I be better off with a solar controller that will keep these panels to 12V at about 18A (assuming I get another panel) or get a controller to keep these to 24V at 9A (again assuming 6 panels)?  Thanks!

Glenn

[Sean]

If you had six identical panels, you'd be better off running series pairs and getting the 24-volt controller.  I recommend the Blue Sky 3024.

The reason is that there will be less loss in the connection on the PV side at the higher voltage (and/or you can use smaller gauge wire).

-Sean
http://ourodyssey.blogspot.com

[H3Jim]

I agree with Sean.  go 24 volt, get the 3024 controller.  The controller can also be daisy chained with another 3024 controller if you ever buy more panels with a different output.

[ol713]

Hi;
    I too have a MC-7 with a system like you described.   I went with
    solar panels in series for 24vdc.  The house batterys and inverter
    are all 24vdc.  I used a heilitrope controller which has a switch
    that will charge two different battery banks. I use one for house
    batterys and one for start batterys.  It comes in handy when the
    start batterys are low and need a little charge to get started.
                                        Good luck.   Merle

[Tony LEE]

I wonder whether those panels are the lower voltage type meant for maintenance charging without the use of a regulator to prevent overcharging rather than normal panels where the voltage is more like 18V.

If so, they may not give the performance  you expect once a controller is wired in.

[Sean]

I wonder whether those panels are the lower voltage type meant for maintenance charging without the use of a regulator to prevent overcharging rather than normal panels where the voltage is more like 18V.

If so, they may not give the performance  you expect once a controller is wired in.

A PV panel is a PV panel.  There's nothing magic about the rated output voltage.  If you string enough panels together, you'll have plenty of oomph to charge.

A controller will make the most of the output even when the voltage is lower than the nominal voltage of the batteries you are charging.

Remember that no panel puts out its rated voltage across all conditions -- that figure is based on "ideal" conditions (perpendicular angle of incidence, full sun, no atmospheric attenuation conditions, 35° latitude).  Which is why a charge controller is recommended in almost every application.

Where higher nominal voltage becomes a benefit, and here I am not talking about 10% higher but 100% and up, is in lowering the transmission loss between the PV panels and the controller.

-Sean
http://ourodyssey.blogspot.com

[Tony LEE]

"A PV panel is a PV panel.  There's nothing magic about the rated output voltage.  If you string enough panels together, you'll have plenty of oomph to charge.
A controller will make the most of the output even when the voltage is lower than the nominal voltage of the batteries you are charging."
-----------------------------------

Bit like saying "A controller is a controller" so there is nothing magic about them.

Neither statement is true and can be taken the wrong way by those not familiar with the ins and outs of solar systems.
For instance, a simple shunt controller can't charge a battery unless the PV output voltage is more than the battery charging voltage plus any voltage drops in the system. Simlarly for any pulse width modulation systems.

It is true that some modern controllers - so-called Maximum Power Point Trackers (maximisers) - work by converting a low output voltage into one high enough to charge the battery, but most simple ones will not.

Oils ain't oils either.

[Sean]

Bit like saying "A controller is a controller" so there is nothing magic about them.

However, that's not what I said.  I was talking about the PV panels themselves, and truly there is no magic.  Rated output voltage is a function of the number of PV wafers wired in series.

... For instance, a simple shunt controller can't charge a battery unless the PV output voltage is more than the battery charging voltage plus any voltage drops in the system. Simlarly for any pulse width modulation systems.

It is true that some modern controllers - so-called Maximum Power Point Trackers (maximisers) - work by converting a low output voltage into one high enough to charge the battery, but most simple ones will not.

Yes, you are right, and I should have been more clear.  I was explicitly talking about the 3024 controller that I previously recommended for the application, which is an MPPT controller.

-Sean
http://ourodyssey.blogspot.com