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10-22-2020, 09:08 AM
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#1
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Senior Member
Join Date: Feb 2020
Location: East of Austin, Texas
Trailer: 2021 Escape 5.0 / 2022 F150 SuperCab
Posts: 2,900
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MPPT question ....
Well, it's said that no question is dumb if you don't know the answer, and in spite of tons of reading I'm not ashamed to admit I'm still unsure about this one ...
Hypothetical Scenario- Three identical monocrystalline PV panels with integral diodes, wired in parallel to the controller
- Assume all wiring is properly sized and presents no 'bottleneck' throughout
- Panel "A" - flat on roof, half-shaded at the moment in question
- Panel "B" - flat on roof in 'full sun' but far from ideal 'sun angle' at the moment in question
- Panel "C" - portable in full sun and tilted / oriented for 'optimal sun angle' at the moment in question
- MPPT controller with voltage and current ratings to handle the maximum potential output of the entire 3-panel array
Q1: In that scenario is there any benefit in disconnecting / isolating any of those panels from the controller in order to gain maximum net charging voltage and current to the battery?
Q2: In that scenario, even if there is no 'benefit per se' in disconnecting / isolating any of those panels from the controller, are any of the panels effectively 'ignored' by the controller / not contributing to the realized controller output?
I think the answer to both Q1 and Q2 is "No", that through some 'magic' the MPPT controller will manage to harvest the best yield possible from each and all of the panels without any of them 'dragging down' the system output and with each making some contribution, but would like reassurance about that from some of the 'solar pros' here.
Thanks In Advance!
(the learning always continues )
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10-22-2020, 10:17 AM
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#2
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Member
Join Date: May 2020
Location: Galveston, Texas
Trailer: NA
Posts: 53
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You are correct in that the answers to both questions is no.
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10-22-2020, 10:40 AM
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#3
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Senior Member
Join Date: Feb 2015
Location: Lanesboro, MN, between Whalan and Fountain, Minnesota
Trailer: 2016 Bigfoot 25RQ - (2018 Escape 5.0 sold)
Posts: 2,174
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Quote:
Originally Posted by Centex
I think the answer to both Q1 and Q2 is "No", that through some 'magic' the MPPT controller will manage to harvest the best yield possible from each and all of the panels without any of them 'dragging down' the system output and with each making some contribution, but would like reassurance about that from some of the 'solar pros' here.
(the learning always continues )
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Started my "solar education" four years ago when we drained the battery on our 24' Cougar a number of times out west, twice with the slide extended. We then purchased our 25RQ Bigfoot with an 80 watt panel and realized what just 80 watts could provide.
I don't buy into the MPPT advantage. Sure it exists, but the difference is so small does it really matter?
For us what matters is: do we have sun, is it shady, what direction is our angled panel on our 5.0 sitting, etc., not a slightly larger harvest at temps below 35 F.
Question: Why did we purchase a Victron 100/20 for our 100 watt portable at $150 vs another Go Power at $50?
Answer: Since the Victron had bluetooth to read the various inputs/displays, we could bury the Victron underneath the rear bench, and we had the discretionary money.
Enjoy,
Perry
__________________
Those who know everything use pens. Intelligent people use pencils.
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10-22-2020, 12:58 PM
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#4
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Senior Member
Join Date: Feb 2020
Location: East of Austin, Texas
Trailer: 2021 Escape 5.0 / 2022 F150 SuperCab
Posts: 2,900
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Quote:
Originally Posted by TX_Clint
You are correct in that the answers to both questions is no.
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Thank you, Clint!
Quote:
Originally Posted by Perryb67
I don't buy into the MPPT advantage. Sure it exists, but the difference is so small does it really matter?
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Fair enuf - that's the sort of thing I'm trying to figure out myself.
Quote:
Originally Posted by Perryb67
For us what matters is: do we have sun, is it shady, what direction is our angled panel on our 5.0 sitting, etc., not a slightly larger harvest at temps below 35 F.
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More fair enuf and mostly understood though I'm not following on the temperature factor? I'll do very little, if any, camping at daytime temps below 35F.
Quote:
Originally Posted by Perryb67
Question: Why did we purchase a Victron 100/20 for our 100 watt portable at $150 vs another Go Power at $50?
Answer: since the Victron had bluetooth we could bury the Victron underneath the rear bench, and we had the discretionary money.
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I can understand that - in your case not a matter of MPPT per se but a matter of other desirable convenience features.
I also now understand from your other thread that you have a mix of PMV and MPPT, essentially running one controller per panel? And that came about as a matter of 'growth over time', which I can certainly understand.
Part of what I'm trying to understand is whether there's advantage in going with MPPT from the start of one wants to anticipate expansion involving different panels with different outputs due to shading, orientation, etc. Would, for example, the answers to Q1 and Q2 be different if the single controller for that 3-panel array be different were a PMV type?
Just as with things like Bluetooth (which I think can now be had on some PMV controllers) there's an attraction to the convenience of a single-controller setup in my mind, IF that offers competitive performance (watts to the battery).
Though there is some price-premium just for MPPT, it seems that the $ difference is not a meaningful one by my measure when capacities and 'features' are comparable to a PMV controller. Not that 'money is no object' - just that relatively small money isn't a hurdle
Thanks for your input, Perry!
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10-22-2020, 02:21 PM
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#5
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Senior Member
Join Date: May 2013
Location: ..., New Mexico
Trailer: 2013 Esc19/'14 Silvrado
Posts: 4,193
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Now I am upset. I switched out my Morningstar Sunsaver PMV solar controller for the more expensive MPPT version. My understanding was this is necessary to solar charge the new lithium battery I bought. Are you saying it wasn't necessary?
__________________
Myron
"A billion here, a billion there...add it all up and before you know it you're talking real money." Everett Dirkson
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10-22-2020, 02:49 PM
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#6
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Senior Member
Join Date: Dec 2012
Location: Edmonton, Alberta
Trailer: 1979 Boler B1700
Posts: 14,935
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The scenario which is not discussed here is the same set of panels, but wired to separate MPPT controllers. That would allow each controller to optimize the output of each panel (allowing a panel which is harmless but not contributing much to be more useful), and is a case which would more effectively take advantage of the MPPT behaviour.
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10-22-2020, 03:34 PM
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#7
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Senior Member
Join Date: Feb 2020
Location: East of Austin, Texas
Trailer: 2021 Escape 5.0 / 2022 F150 SuperCab
Posts: 2,900
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Edit to delete - gone to do more independent research first
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10-22-2020, 04:47 PM
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#8
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Senior Member
Join Date: May 2013
Location: ..., New Mexico
Trailer: 2013 Esc19/'14 Silvrado
Posts: 4,193
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I don't understand why multiple solar controllers are needed - unless one is stuck with low rent cheapo types that can come pre attached to a solar panel.
Page 9 of my SunSaverDuo PMV charging solar controller owners manual indicates what is important is not how many solar panels you got but how many batteries are connected. (Of course they must only be lead-acid.)
And I quote:"Ground the solar module(s) to the vehicle chassis with black wire. Multiple 12V nominal solar modules may be wired together in parallel and grounded with one wire. ..."
__________________
Myron
"A billion here, a billion there...add it all up and before you know it you're talking real money." Everett Dirkson
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10-22-2020, 05:10 PM
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#9
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Senior Member
Join Date: Sep 2018
Location: Ridgway, Colorado
Trailer: 2018,5.0 TA
Posts: 325
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Here's an article that explains it pretty well I think. https://www.solar-electric.com/learn...trollers.html/
They claim it will increase output 10% to 15% in the summer and 20% to 45% in winter. This would have been amazing for my off grid system that I used to have many years ago. Another 20 to 45% gain in the winter would have made a big difference.
Since we aren't big on winter camping I don't think I would change our controller out but if I was putting in a new system I would for sure use one. I saw a 40A MPPT controller for $170 so not that pricey.
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10-22-2020, 07:46 PM
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#10
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Senior Member
Join Date: Feb 2015
Location: Lanesboro, MN, between Whalan and Fountain, Minnesota
Trailer: 2016 Bigfoot 25RQ - (2018 Escape 5.0 sold)
Posts: 2,174
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Quote:
Originally Posted by MyronL
I don't understand why multiple solar controllers are needed - unless one is stuck with low rent cheapo types that can come pre attached to a solar panel.
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In our case multiple solar controllers were not needed. I wanted the Victron because I already had a Victron BMV-712 battery monitor and liked the bluetooth feature. The Victron 100/20 controller was only about $150 and we had the discretionary money.
One cool thing with Victron's bluetooth, we can read the 712 on our phones to see the state of charge driving down the road.
Enjoy,
Perry
__________________
Those who know everything use pens. Intelligent people use pencils.
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10-22-2020, 08:05 PM
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#11
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Senior Member
Join Date: Jul 2010
Location: Rockwell, North Carolina
Trailer: 2015 Escape 5TA
Posts: 170
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When using MPPT technology panel voltage is key. The higher voltage you can provide to the MPPT controller the more amps the controller can provide to the battery bank. Caution the controller needs to be rated for the voltage the panels provide.
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10-22-2020, 09:47 PM
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#12
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Senior Member
Join Date: Dec 2012
Location: Edmonton, Alberta
Trailer: 1979 Boler B1700
Posts: 14,935
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Quote:
Originally Posted by MyronL
I don't understand why multiple solar controllers are needed - unless one is stuck with low rent cheapo types that can come pre attached to a solar panel.
Page 9 of my SunSaverDuo PMV charging solar controller owners manual indicates what is important is not how many solar panels you got but how many batteries are connected. (Of course they must only be lead-acid.)
And I quote:
"Ground the solar module(s) to the vehicle chassis with black wire. Multiple 12V nominal solar modules may be wired together in parallel and grounded with one wire. ..."
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Yes, you can connect as many as you want in parallel. The point of multiple MPPT controllers is not to handle multiple panels in identical conditions, but to individually optimize panels in different conditions (differing primarily in amount of shade and angle to the sun).
Quote:
Originally Posted by DanandDaphne
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Unfortunately they put this nonsense in the first paragraph:
Quote:
To put it simply, they convert a higher voltage DC output from solar panels (and a few wind generators) down to the lower voltage needed to charge batteries.
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No, that's not the point. And the text which follows is nonsense, too, until they finally get on track with this:
Quote:
Maximum Power Point Tracking is electronic tracking - usually digital. The charge controller looks at the output of the panels and compares it to the battery voltage. It then figures out what is the best power that the panel can put out to charge the battery. It takes this and converts it to best voltage to get maximum AMPS into the battery.
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... which is still not quite right, but closer.
An MPPT controller keeps the panel at the voltage at which it produces maximum power in the conditions of the moment, regardless of the battery voltage.
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10-23-2020, 10:01 AM
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#13
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Senior Member
Join Date: Mar 2017
Location: Northern Nevada, Nevada
Trailer: 2014 Escape 15A
Posts: 330
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Another point to keep in mind: Some solar controllers (my Victron's anyway...) need a minimum of 5v differential between the panel and battery voltage to flow current. This plays into the parallel &/or series layout...
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10-24-2020, 11:37 AM
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#14
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Senior Member
Join Date: Feb 2020
Location: East of Austin, Texas
Trailer: 2021 Escape 5.0 / 2022 F150 SuperCab
Posts: 2,900
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Thanks very much to all for the replies.
The net-effect of all was to send me 'back-to-school' on the interweb, better equipped to know what to look for, how to better sort wheat from chaff, and better consider pros and cons in the context of my real-world overall 'solar-system' goals.
To cut to the chase I've come to the conclusion that for my interests, building / specifying a system 'from scratch' with likely a limited PV array to start but with growth in mind if I learn that's beneficial over time: - The extra cost of MPPT controller(s) are worth it both for the potential harvest gains and the 'extra features' more readily available with MPPT controllers
- The slight extra gain that might well be realized if using separate controllers for each PV panel (or some subsets of panels) isn't worth the added complication, cost, and multiple-monitoring interfaces that would impose. For me there's significant value in having a single (Bluetooth) interface for controller configuration and monitoring.
YMMV, and my own 'conclusions' are subject to change as the learning always continues, but for now I'm moving my 'system scheming' focus to other details
Thanks again for all the help, it's a challenging + stimulating (= Fun) learning curve for sure!
(PS to Perry - yes, I now understand how/why temperature that you mentioned plays a role in MPPT optimization, so thanks for that 'hint', one of many in the replies that guided my continued 'schooling' )
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10-24-2020, 01:28 PM
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#15
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Senior Member
Join Date: Aug 2016
Location: Santa Rosa, California
Trailer: 2014 Escape 15B sold, 2019 Escape 19
Posts: 367
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Quote:
Originally Posted by dstreight
Another point to keep in mind: Some solar controllers (my Victron's anyway...) need a minimum of 5v differential between the panel and battery voltage to flow current. This plays into the parallel &/or series layout...
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The 5v is only needed for the controller to start charging, it will continue until the panel (or in a serial configuration the sum voltage) is less than 1v above the battery. In a serial configuration charging will start earlier in the day and continue later as the sun goes down. My four 80w panels are configured in parallel, with an open voltage of 24.3v and optimum operation 20.9v, I don't see any issues starting the charge in very low light situations.
In a serial configuration, shading on one panel will bring down the output significantly more than in a parallel setup where the non shaded panels output is not affected by the the shaded one.
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