How to wire solar panelsL Series or Parallel?

[Paul Elliott]

Originally Posted by CSY Man

No, shading ain't a problem as the panels are behind "everything".

I will gladly take your word for it, but on my boat, no matter where I look I see occasional shading from the mast and shrouds. This may not occur often enough to be a significant factor, though.

I may be more sensitive to the "shading thing" than others, because I deliberately put my three 100W panels on top of the dodger -- one of the worst possible locations. I get shading from the mast, rigging, boom, mainsail, genoa, etc. Still, the panels make a huge difference in my power budget. I may eventually break down and install a bimini-mount, or transom-arch, but for purely esthetic reasons I haven't been able bring myself to do so. My next step will be an MPPT regulator.

[CSY Man]

The panels are wired in parallel with #8 wire,

Hmm, so if ya wired them in series instead, you would get even more...?

As for the max output I ever got, the 10.3 in the Exumas, that was with the old Flex Charge controller, and before the 2000E.
Looks like you got 15 % more with the 2000E?
Excellent.

I have seen on average 10% more, but the batteries are usually fully charged as I have been sitting at the dock since I installed the MPPT.
I understand that the real gains are in cloudy weather or with low batteries? (30% or more.)

My wire run with the 10 gauge from panels to solar regulator is about 18 feet or so..36 feet round-trip.
From the MPPT to the panel switch is about 5 feet, also using 10 gauge.
From the panel switch to the house bank is another 15 feet run, but super thick cable...2 Oth or whatever it is called. As thick as my finger, no loss there.

So, uh, yes I could probably get a few amp-hours from changing my set-up to series....?

[Tropic Cat]

I'm having some trouble understanding Paul's math. Not Ohm's Law, which makes sense for the losses explained but the fact that you cut the current to the batteries in half when you series the panels which does reduce losses, but it's explained in Paul's post as being better.

So, I guess I'm old school, Fancy controller or not, I'm having difficulty understanding that putting the panels in series puts more power into the batteries. By my way of thinking you do have 1/2 the losses when in series because you have 1/2 the current to the batteries compared with parallel panels. I've always been taught that it's the current that charges batteries, and more is probably better. The only reason voltage is increased in a charging circuit to begin with is to increase the charging current. That's what a voltage regulator is for.

[rleslie]

CSY

E-mail the MPPT manufcaturer and ask them which way will deliver the most effective charge. The MPPT is built for specific manner of usage and may not operate properly is wired in a manner other than to their specs.

Rick - I'm with you.......in series makes no sense to me.

Roger

[Thermal]

CSY Man - No, If I wired them in series I could get 42.4V open circuit volts from the panels according to the specs, and since the 2000E specs say max PV open circuit voltage is 30V, the thing would probably fry - and then I'd get 0 amps . Heavier wire would give you a smidge more, but hardly worth it at the price of copper today ( I got mine when I could still get #8 at 90c/ft out here.)
Rick - It's the current (and loss) in the wires between the panels and the controller that CSY wants to reduce by wiring in series. The "fancy controller" is then somehow supposed to drop the voltage to a charging voltage around 13 or 14 and increase the current correspondingly - so from the controller to the battery would be much higher than between the controller and the panels.

[Paul Elliott]

Originally Posted by rickm505

I'm having some trouble understanding Paul's math. Not Ohm's Law, which makes sense for the losses explained but the fact that you cut the current to the batteries in half when you series the panels which does reduce losses, but it's explained in Paul's post as being better.

So, I guess I'm old school, Fancy controller or not, I'm having difficulty understanding that putting the panels in series puts more power into the batteries. By my way of thinking you do have 1/2 the losses when in series because you have 1/2 the current to the batteries compared with parallel panels. I've always been taught that it's the current that charges batteries, and more is probably better. The only reason voltage is increased in a charging circuit to begin with is to increase the charging current. That's what a voltage regulator is for.

Rick, the MPPT controller is similar to a switching power supply regulator, while a "standard" regulator is like a linear regulator. When the standard regulator is trying to apply full charge to the batteries, the best it can do is to essentially connect the panel directly to the battery.

A switching regulator is like a DC transformer: it will convert one voltage to another with little loss. 16V at 5A ideally becomes 12V at 6.667A -- the same power out as in. A linear regulator is like a variable resistor: the best it can do is convert 16V @ 5A to 12V @ 5A -- the power is lost in the regulator.

It may help to consider the solar panel as a voltage source (battery) with a series resistance, or output impedance (actually, it is more like a current source with a shunt diode, but in the ideal case, they are equivalent, and it is easier to think about the voltage-source model). As you may know, maximum power is transferred when the load resistance matches the source resistance. For example, you will get more current when the load is a short-circuit, but there will be no power delivered to the short-circuit -- it is all dissipated in the source output resistance.

A solar panel typically delivers it's maximum power at an output voltage of 16V or so. If you connect the panel directly to a low battery (say 12V), you effectively have a load resistance that is too small, and you are wasting power in the panel's output resistance. The MPPT controller "learns" the optimum load for the panel (and this depends on temperature, sunlight levels, and panel variations). The MPPT controller then uses it's switching-regulator to convert the optimally-loaded panel output to the voltage that the battery needs for maximum charging.

If you have two panels in series, then the optimum load voltage will be 32V or so. The current from the series-connected panels will be half that of the parallel-connected panels, so the wiring losses will be halved. The MPPT controller switches the voltage down (32V to 12V, for example) and the current up (5A to 13.333A) with little power-loss.

Note that once the batteries become charged enough that the controller begins to reduce the current, either type of controller (MPPT or linear) will give the same results. Also, the "duty-cycle" or "pulse-with-modulated" (PWM) regulators behave the same as linear regulators. They just don't get as hot.

[Paul Elliott]

Originally Posted by Paul Elliott

(A long-winded explanation)

In case you were looking for the short version:

The MPPT controller will, with very little loss, convert a high-voltage, low-current source of power (the series-connected solar panels), to a low-voltage, high-current output, suitable for charging a battery. The lower current from the panels will give lower resistive losses in the connecting wires. In most cases, this isn't that big a deal.

More importantly, the MPPT controller will load the solar panels to the point where they are delivering their maximum power (Maximum Power Point Transfer). The controller will then convert this power as appropriate to charge the battery.

A MPPT controller will perform the optimal panel loading and voltage conversion with single panels, paralleled panels, or panels in series, up to the maximum input voltage and current rating of the controller. There is really no downside to the MPPT technology, other than cost. It is definitely not voodoo.

[Tropic Cat]

I think I understand it now...LOL

[Therapy]

Originally Posted by rickm505

I think I understand it now...LOL

I don't have solar panels.

Heck, I don't have a boat.

But I want one with solar panels.

And I wish to thank you all for your posts in my ongoing dream of having a nice working boat whose workings I understand.

My knowledge base grows each day.

Thank you all again.