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Old 05-22-2020, 02:46 PM   #1
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Misc. solar panel & controller questions (Mismatches? Amperage?

As I plan to start off small and grow my solar system, to what degree can I mismatch solar panels going forward? With a proper MPPT controller, can I run panels with different output voltages/ranges? Different amperages? Different chemistry (mono vs poly)?

With an MPPT controller rated at "100 amps", is that the amperage of the input? Output? Both? If just input, it seems I could run more panels in series to boost volts while keeping amps low, but if it also applies to the charging side, that 100 amp controller would be limited to 1300-ish watts regardless of panel wiring configuration.

Through the course of the day, panel output goes fluctuates, but is that mostly a change in volts or amps?

Thanks,
Fat Boy
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Old 05-22-2020, 03:32 PM   #2
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Quote:
Originally Posted by FatBoySTL View Post
As I plan to start off small and grow my solar system, to what degree can I mismatch solar panels going forward? With a proper MPPT controller, can I run panels with different output voltages/ranges? Different amperages? Different chemistry (mono vs poly)?
Not sure about the specifics, of this question. Its a best practice to use matched panels, but I think you can use different panels in some circumstances. Intuitively it seems like you would want all the voltages to be the same if wiring in parallel and the current to be the same if wiring in series, but that's just a guess.


Here are some videos to get you started:
What's Worse? Mismatched Solar Panels with Different Amps in Series or Parallel?
How to wire mismatched solar cells

Quote:
With an MPPT controller rated at "100 amps", is that the amperage of the input? Output? Both? If just input, it seems I could run more panels in series to boost volts while keeping amps low, but if it also applies to the charging side, that 100 amp controller would be limited to 1300-ish watts regardless of panel wiring configuration.

The 'nominal current' (amps mentioned in the title) refer to output current. So regardless of what you do on the Charge Controller Input/PV Array side, the max it will be able to output is 100A.

There will usually be a separate max input current rating, and more importantly max input voltage rating. Because panels are rarely operating at 100%, it often makes sense to oversize your PV array a little bit as long as you stay within the input specs.

Quote:
Through the course of the day, panel output goes fluctuates, but is that mostly a change in volts or amps?

This is something I'm still trying to wrap my head around. What I've gathered so far:
- Cell/panel temperature will affect volts
- Solar Irradiance (i.e. light intensity) will affect amps
- Angle will affect amps
- Partial Shade will mostly effect amps
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Old 05-22-2020, 05:20 PM   #3
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For partial shade tolerance, wire one SC per panel.

Then no mismatch problems.

All the panels going into one SC should match, most especially if you want MPPT efficiency benefits.

If just using PWM, then matching VOC spec is better than nothing.

Forget amps, except at the output to the battery.

Be careful not to exceed Volts input rating, in fact stay 80-85% under for safety so you don't damage the SC.

Then follow the maximum input Watts limit for a given desired output voltage, usually have some wiggle room there, NP overpanelling a bit since you will so rarely see even 60-70% rated output, get more value per SC that way.

Victron SmartSolar give a lot of flexibility, their pricing makes it cheap to have a bunch of their smaller ones rather than one big expensive one

e.g. 75/15 unit at $120 or so is a bargain, well matched with a 40+VOC panel to get good MPPT - max 60-65V,

up to 220-280 Watts per, hence the "15A" for a 12V system.
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Old 05-22-2020, 05:40 PM   #4
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Quote:
Originally Posted by FatBoySTL View Post
but if it also applies to the charging side, that 100 amp controller would be limited to 1300-ish watts regardless of panel wiring configuration.
If your battery bank is 12V, yeah.

One of the main reasons I changed my battery bank from a 24V configuration to a 48V configuration was that the 100A charge controller was current-limited to 2400W when I was putting 3050W up on the roof.

Some people here say 12V is the simplest, perhaps there's some truth in that. However once you want to go higher than around 1200W _continuous_ (PV input or discharge rates), I'd say its probably time to start looking at a higher voltage system, at least as an option.
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Old 05-22-2020, 05:56 PM   #5
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If your battery bank is 12V, yeah.

One of the main reasons I changed my battery bank from a 24V configuration to a 48V configuration was that the 100A charge controller was current-limited to 2400W when I was putting 3050W up on the roof.

Some people here say 12V is the simplest, perhaps there's some truth in that. However once you want to go higher than around 1200W (PV input or discharge rates), I'd say its probably time to start looking at a higher voltage system, at least as an option.

I agree with Kazetsukai here, I think you are at the system size that 24V is at least worth considering if you haven't already bought 12v components. High amperage charge controllers are pretty pricey, and wiring losses are quartered when you halve the current.


You would almost certainly need to buy a 24v to 12v converter for some loads, but really that doesn't add too much extra complexity or cost in the big picture.
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