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Old 16-01-2020, 16:40   #1
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What is the ramifications if MPPT is over rated

Sorry, couldn't find exactly the answer I needed when I searched the forum. Apologies if one does exist. A link to it would be highly appreciated.

So here goes

I want to purchase two MPPTs that will handle a future solar array as well as the initial array that I will be setting up.

My initial array will be 4 x 50W panel, series of two and parallel of two. I plan that each parallel will have its own MPPT (sail boat with shadows on one group or the other).

Each panel is 50 W, 20.8 Voc, 17.8 Vmp, 3.07 ISC, 2.84 IMP, temp range will be 60F -100F.

4 house batteries at 105 Ah each. I don't currently need to fully charge, but in the future with 200W+ panels, I might want to fully charge (usual usage is about 125 A/day).

I do not want to purchase additionally or different controllers in the future PV plan.

Can I use two controllers that are sufficent to handle the 4 x 200W with the 50W panels today?

If not, why?

And if so, what size rating?
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Old 16-01-2020, 16:49   #2
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Re: What is the ramifications if MPPT is over rated

There are two very minor problems with purchasing an MPPT significantly larger than you need.
  1. $$$ - They just cost more
  2. minor loss of efficiency
If you really plan to use them in the future then you save $$$ in the long run, but if you never use them then you've spent more than you needed to.

You may get a bit less efficiency out of the lightly-loaded MPPT conversion, most of the efficiency values are built around full output. There is always some self-consumption and you may lose a bit with way less than nameplate solar attached. How much? Maybe a couple of percent, so probably not a reason not to do it.

The one thing to watch for is maximum input voltage. You could get away with something today that will handle 40 or 50V Voc, but you may want a higher rating for future expansions.

As to what size, something like the Victron 100/30 would allow future higher voltage arrays and gets maxed out at about 400W, your proposed future size.
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Old 16-01-2020, 17:20   #3
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Re: What is the ramifications if MPPT is over rated

FYI but (2 of) 75/15 won't cost more and will handle 250-280W just fine even 300W if you get a super deal on that size panel.

And you can buy one now maybe $130 delivered, and watch out for future deals on the second.

For either, est to get "24V" (actually 40+Voc rated) or higher to give the MPPt some headroom.
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Old 16-01-2020, 19:07   #4
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Re: What is the ramifications if MPPT is over rated

Ok, thank you both for your input. From my read I'm still not sure if I should get 2 100/30 or 2 75/15. Or was the suggestion 1 100/30 and 2 75/15?

Thanks again for your help.
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Old 16-01-2020, 19:08   #5
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Re: What is the ramifications if MPPT is over rated

The latter
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Old 16-01-2020, 19:29   #6
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Re: What is the ramifications if MPPT is over rated

You currently need/want two controllers for shading reasons.

Your final configuration of 4x200W would require 2x100/30 or 4x75/15. So kind of up to you to weigh total costs and when you want to spend the money. You could just buy two bigger units now, or buy two smaller units now and buy another two when you build the bigger array.
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Old 16-01-2020, 19:39   #7
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Re: What is the ramifications if MPPT is over rated

Awesome, thanks. My thoughts would be to simplify future implementation and space to mount the controllers. Thinking of taking out the loan for the big guns.

Thanks again
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Old 17-01-2020, 10:01   #8
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Re: What is the ramifications if MPPT is over rated

IMHO I would always go a bit bigger. I just bought a boat which had two cheap French controllers. Both caught on fire within a month of each other. Get a name brand and slightly larger larger than you need and you will be fine.
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Old 17-01-2020, 12:41   #9
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Re: What is the ramifications if MPPT is over rated

4x75/15 would give max efficiency, and still leave room to double the panel wattage serviced in future.
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Old 17-01-2020, 14:04   #10
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Re: What is the ramifications if MPPT is over rated

I used streetlight regulators for solar powered LED street lighting--which uses two panels to charge a battery which switches on the street lamp at dusk one it senses no or low output. I wired that to the masthead LED light and one low powered LED lamp over the wheelhouse access so I could find my key and stuff.

I uses one for each twin panel--same as they do on the street lamps--and one just hooks them all together in parallel along with any other gear--because they have blocking diodes to prevent damage to the panels and regulators. They were adjustable too--and in five years I never had any issue with them. They came with the panels--each panel pair was 100 watts twelve volts regulated output.

OR you could contact Fronius and see what they have on offer--
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Old 17-01-2020, 14:39   #11
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Re: What is the ramifications if MPPT is over rated

Hi, why bother, just buy 1 solar 180-200W flexible panel and 1 MPPT 30A that accept up to 50V, these day are so cheap, here is an address where I order 17 of them 5 years ago for members and I in our marina and all of them still working fine today, and they run 24/7 days all year round (yes run in winter here too).
https://www.aliexpress.com/item/4000...chweb201603_53
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Old 17-01-2020, 20:00   #12
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Re: What is the ramifications if MPPT is over rated

Quote:
Originally Posted by Seas The Moment View Post
Sorry, couldn't find exactly the answer I needed when I searched the forum. Apologies if one does exist. A link to it would be highly appreciated.

So here goes

I want to purchase two MPPTs that will handle a future solar array as well as the initial array that I will be setting up.

My initial array will be 4 x 50W panel, series of two and parallel of two. I plan that each parallel will have its own MPPT (sail boat with shadows on one group or the other).

Each panel is 50 W, 20.8 Voc, 17.8 Vmp, 3.07 ISC, 2.84 IMP, temp range will be 60F -100F.

4 house batteries at 105 Ah each. I don't currently need to fully charge, but in the future with 200W+ panels, I might want to fully charge (usual usage is about 125 A/day).

I do not want to purchase additionally or different controllers in the future PV plan.

Can I use two controllers that are sufficent to handle the 4 x 200W with the 50W panels today?

If not, why?

And if so, what size rating?
Depends on the shading and panels.

If the panels have no bypass provision, then anY shading of a single cell will prevent output from that series string. If the series string in parallel is unshaded, it will provide full output.

This could all be fed into one controller, no problem.

If the panels have no bypass diodes and a cell in both series strings will be shaded, you’re gettin’ nuthin’ for solar.

For 2S2P at 200 W, a single EPEVER TRACER 20A would be plenty, give you a nice display and an optional WIFI or BT adapter if desired.

If you add more panels later, buy a controller to suit that array, either same or different if there is better tech by then.
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Old 18-01-2020, 07:39   #13
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Re: What is the ramifications if MPPT is over rated

Yes with 200 W panel it will give max 12-15 amps, but for couple extra dollars you could buy 30-40 or 50 amps unit it doesn't matter today, has nothing to do with the worry about might be over the requirement of a MPPT.
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