How to wire solar panelsL Series or Parallel?

[CSY Man]

Well, I have my 2 Siemens 75 panels wired so I get 17 volts at the regulator.

Another guy have his panels wired so he is getting twice the voltage, but half the amps. Hes theory is that the voltage loss is less and he does not require quit as thick wire as I do. (I run 10 gauge)

Sounds like a reasonable argument if the regulator can handle 34 volts.

How does others wire their panels..?

[jemsea]

CSY Man We have 3 75 watt Siemens panels wired in parallel using 16/2 wire to the controller.

John

[CSY Man]

16 gauge wire....?

How long is your wire run?

(I am still confused and keep mixing them together: Are you trippling the voltage, or not? 51 volts? What kind of controller do ya have?)

[FreeSail]

Where do you have your panels mounted ?

[CSY Man]

Above the bimini top, behind the back stay.

[jemsea]

The controller is a Flexcharge USA or so it says on it.

We have 2 panels mounted beside the cockpit in the lifelines and one on deck forward of the dodger. We can tilt all three to keep up with the sun side to side but not fore and aft.

Our system runs all 3 wires to the controller, then the 3 are connected together so the panels are in parallel, and that connection is the input to the controller.

At present our system will keep up with the reefer and all our daily electrical needs except the laptop. It is a Dell and seems to need more power than the reefer.

We will probably need to either get another panel or a wind generator at some point ---or maybe just reduce our electrical usage.

[donradcliffe]

The new MPPT charge controllers can use higher input voltages, and can convert the higher voltages to up to 25% more amps, changing the philosophy for solar panel wiring. Series wiring two panels will cut the power losses in the wiring by a factor of 4 with the same size wire.

Roughly speaking, if your voltage drop from the panels to the controller is 1 volt and you are getting 10 amps, the power losses are 10 watts, which can be converted to an additional 0.5 amp into the batteries by the MPPT if you go from parallel to series wiring.

[CSY Man]

Okay thanks.

That answered my question as I recently installed one of them MPPT controllers, a 2000E.

[Paul Elliott]

Sorry to complicate things, but series-wiring may cause difficulties if your panels are occasionally shaded. Even when partially shaded, a panel may show a high impedance and will effectively block the current from the other series-connected panels. This depends on the nature of the shading, the configuration of the panel's cells, and whether or not there are "bypass diodes" (these are different than "isolation diodes") on each panel. Even with the bypass diodes, you will see some power-loss from the non-shaded series-connected panel.

If the panels are parallel-connected, a shaded panel will still reduce it's output, but at least it won't negatively affect other non-shaded panels.

I would love to be able to buy panels with per-cell bypass diodes, because these would work extremely well in a series array. Unfortunately, I haven't been able to find any. Solar panels are optimized for land-based operation (this is where the volume is). There, partial shading isn't a big concern.

[rleslie]

Originally Posted by CSY Man

Well, I have my 2 Siemens 75 panels wired so I get 17 volts at the regulator.

Another guy have his panels wired so he is getting twice the voltage, but half the amps. Hes theory is that the voltage loss is less and he does not require quit as thick wire as I do. (I run 10 gauge)

Sounds like a reasonable argument if the regulator can handle 34 volts.

How does others wire their panels..?

I ran your friend's theory by an friend who is an electrical engineer, sailor and solar panel user. He said your friend's theory is bunk.

Your #10 wire should be more than sufficient with the length of a run with your solar panel location.

We have a similar set-up (two 120W panels) and a MPPT controller. We ran the panels to a positive bus bar w/#12 (approx. 12 feet) and then into the MPPT with #8 (about 4 feet). The MPPT/Panels gives us power sunrise to sunset.

Contact the MPPT manufacturer and get there advise on the wiring.

Roger

[CSY Man]

Thanks all of you for the input.

Shading is not a problem on my boat..Except from clouds.

Some says I get more from going series and some says I don't?

Hmm, I will contact the maker. (The one who makes my charge controller)

Thanks again ya'll

Dag

[Paul Elliott]

Regarding wire size and power loss, here is the math:

#10 wire has a resistance of about 1 Ohm / 1000ft. Assume that the distance from the panels to the regulator is 25ft, or 50ft of wire. This gives a resistance of 0.05 Ohms.

Your 75W panels each put out about 4.7A at full power (running at 16V using an MPPT controller). If they are connected in parallel, the current will be 9.4A

The power lost in the #10 wire will be (current squared) * resistance, or 4.4 Watts, with a parallel configuration.

The power lost in a series configuration will be (4.7 squared) * 0.05, or 1.1 Watts.

This 3.3W difference might work out to about 1AH per day of lost charging current. Not all that significant, but if you can get it for free by using a series configuration, why not? As I mentioned previously, if partial shading of a single panel is a possibility, you are probably better staying with the parallel connection.

[CSY Man]

Thanks Paul.

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

I will look under them and see how much work is involved in changing the wireing, and also look in the owners manual to see what they recommend.

On a side note:

The normal output I have seen on good summer days in Florida with the sun overhead and not a cloud in sight have been right around the max the panels are rated for: 8.8 amps.

I the Exumas last year in June with the sun overhead and no air pollution, I saw a peak of 10.3 amps! Quite a bit more than the rating.

Is the panels rated for a New York latitude or what...?

If so, how much more could one get around Equator?

[Paul Elliott]

Originally Posted by Paul Elliott

Assume that the distance from the panels to the regulator is 25ft, or 50ft of wire.

Note that if the controller is close to the panels (say 5 ft of wire instead of 50ft), then the loss with #10 wire will truly be insignificant. You will still need to figure out the loss from the controller to the batteries, and series-connected panels will make no difference in the controller-to-battery run.

[Thermal]

CSY Man - I have almost the same setup as you do, and get about the same output. The two panels are 80w Kyocera, and I just got a 2000E controller. The output I was getting with the old controller was 8.9A, and after putting in the new 2000E I got 10.4A. This was just a few days ago around noon, so a couple of months after summer solstice, but then Honolulu is a few degrees south of the Exumas. The panels are wired in parallel with #8 wire, a run of about 25' from panel to battery. You supposed to get more than the rated amp output of the panels when using an MPPT controller since that rating is at the rated output voltage and the controller is supposed to "recover" some of the energy lost when it drops the voltage to the 13 or 14v for charging the batteries.