Is there any mechanism that would get series panels to operate at their optimum voltage?For example, if one panel has a Vmppt of 17 volts and one at 18 volts and they are connected in series, is there and natural mechanism that would make them tend to operate at Vmpp if the controller selects a voltage of 35 volts for the string? Obviously the controller cn pick the maximum output voltage for the system, but is there anything really pushing individual panels in a string toward their individual maximum output?Jim

What I can tell you is that with my series panels the voltage is all over the place. It depends on the SOC, the sun angle, clouds and maybe other factors. My 6 series panels can range from 78v to around 120vWhether you can force them to operate at any given voltage ( or would want to) I have no idea.

Ideally you would want to pick the voltage for each panel independently to get max output. In parallel if panels have very close Vmpp under the same conditions, you get very close to max output. In series I'm not sure if small variations among the PVs lead to significant differences in the voltage from one panel to the next or not. I need a jumper cable with MC3 connections on it, or maybe a piece of foil to be able to measure the voltage between PVs.Jim

HiTech wrote:series I'm not sure if small variations among the PVs lead to significant differences in the voltage from one panel to the nextI don't know either. The analogy I go by is a series of water pumps, where differences in voltage (pressure) do not matter, but capacity (amps) yes. So it's important to match amperage ratings carefully, as the max amperage of the string is the lowest of all the panels."Picking" the voltage would require a device which would likely consume power itself.

Exactly, a small MPPT controller. Some of the newer grid tie solar systems seem to be moving to one controller and inverter for each panel. Jim

2oldman wrote:What I can tell you is that with my series panels the voltage is all over the place. It depends on the SOC, the sun angle, clouds and maybe other factors. My 6 series panels can range from 78v to around 102v. Whether you can force them to operate at any given voltage ( or would want to) I have no idea.That's interesting thinking more about it. 78v is an average max power point voltage of 13 v per panel. Any idea what conditions drive the voltage that low?Jim

MPPT and series solar panels | Good Sam Community

16 Replies

MEXICOWANDERER
Explorer
Jun 08, 2013
Why not use a voltmeter in series, panel output versus controller output? This differential should help you to evaluate characteristics of potentials with regard to battery SOC.
HiTech
Explorer
Jun 08, 2013
2oldman wrote:
What I can tell you is that with my series panels the voltage is all over the place. It depends on the SOC, the sun angle, clouds and maybe other factors. My 6 series panels can range from 78v to around 102v.

Whether you can force them to operate at any given voltage ( or would want to) I have no idea.

That's interesting thinking more about it. 78v is an average max power point voltage of 13 v per panel. Any idea what conditions drive the voltage that low?

Jim
HiTech
Explorer
Jun 08, 2013
Exactly, a small MPPT controller. Some of the newer grid tie solar systems seem to be moving to one controller and inverter for each panel.

Jim
2oldman
Explorer II
Jun 08, 2013
HiTech wrote:
series I'm not sure if small variations among the PVs lead to significant differences in the voltage from one panel to the next
I don't know either. The analogy I go by is a series of water pumps, where differences in voltage (pressure) do not matter, but capacity (amps) yes. So it's important to match amperage ratings carefully, as the max amperage of the string is the lowest of all the panels.

"Picking" the voltage would require a device which would likely consume power itself.
HiTech
Explorer
Jun 08, 2013
Ideally you would want to pick the voltage for each panel independently to get max output. In parallel if panels have very close Vmpp under the same conditions, you get very close to max output. In series I'm not sure if small variations among the PVs lead to significant differences in the voltage from one panel to the next or not. I need a jumper cable with MC3 connections on it, or maybe a piece of foil to be able to measure the voltage between PVs.

Jim
2oldman
Explorer II
Jun 08, 2013
What I can tell you is that with my series panels the voltage is all over the place. It depends on the SOC, the sun angle, clouds and maybe other factors. My 6 series panels can range from 78v to around 120v

Whether you can force them to operate at any given voltage ( or would want to) I have no idea.

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MPPT and series solar panels

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