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Discussion Starter #1 (Edited)
Hey everyone! So I finally found a way to mount my solar, but before I commit I really need some help with power levels.

I’ve got 2 - 305w Sunpower Mono Panels trying to wire in parallel and planning on using an MPPT and 300ah lithium. I got about 60v Open Circuit from each when I tested with multimeter, so should I trust they’re good to go?

Additionally, they seem to have a high vmp at 55. Would this mean that they’re less efficient for their big size than say 6 - 100w panels at 100w/12v? Should I even sweat the difference in lost amps? Thanks in advance!

70401
 

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Hi,
The higher Vmp definitely does not mean less efficient.
Larger panels have a higher Vmp because they have more silicon cells hooked in series -- generally the highest efficiency panels are the larger ones. The manufacturers web site may list their maximum efficiency.

The Voc is the voltage with an open circuit, and your controller should be able to handle this with some margin. The margin is needed because in cold weather the Voc will go up a bit over the spec.

If your controller sees a higher voltage than it can handle, it will shut down and it may even be damaged.

Also watch the max current. On the PV panel size if you hook them in parallel, then you are going to want a rating of at least twice the short circuit current Isc -- so, about 12 amps for your two panels.

There is also a maximum current that the controller can handle on the charging lines to the battery. You have 610 watts, so for a 12 volt house battery, your max current will be about 610/12 = 51 amps.

Gary
 

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Discussion Starter #3
Hi,
The higher Vmp definitely does not mean less efficient.
Larger panels have a higher Vmp because they have more silicon cells hooked in series -- generally the highest efficiency panels are the larger ones. The manufacturers web site may list their maximum efficiency.

The Voc is the voltage with an open circuit, and your controller should be able to handle this with some margin. The margin is needed because in cold weather the Voc will go up a bit over the spec.

If your controller sees a higher voltage than it can handle, it will shut down and it may even be damaged.

Also watch the max current. On the PV panel size if you hook them in parallel, then you are going to want a rating of at least twice the short circuit current Isc -- so, about 12 amps for your two panels.

There is also a maximum current that the controller can handle on the charging lines to the battery. You have 610 watts, so for a 12 volt house battery, your max current will be about 610/12 = 51 amps.

Gary
Thanks so much Gary. Do you have any mppt’s that you’d recommended?
 

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Hi,
This is one that would likely work

Its a Victron, which is a good brand -- there are lots of other ones out there, so have a look around for other possibilities.

The link is to Northern Arizona Wind and sun -- they are a good outfit to deal with with good support. I'm guessing you could call them and give them your setup, and they could confirm this is a good controller choice and probably give you some hints on how to set it up. You want to be sure its set up for your Li batteries and that the feature that prevents trying to charger the battery at temperatures less than freezing is turned on. They have a Youtube video on how to set one up.

Gary
 

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I have a Morningstar PS-MPPT-40M with 600W of solar. Allows upto 120 open circuit voltage- so you should be able to
run your panels in series. It has custom programming capability. Victron is easier to program via bluetooth. The morningstar requires addition accessory for usb and pc/laptop with msview software. There is no lifepo4 setting, but they
have a way to make it work. Info is on their website.
 

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Discussion Starter #6
If my max current is at 51amps, it's alright to use the 50amp mppt? I've heard about allowing a cushion of around at least 25amps for those cold weather situations, but I've also heard I'd be lucky to get anywhere near max amps. I appreciate the help!
 

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Hi,
This is one that would likely work

Its a Victron, which is a good brand -- there are lots of other ones out there, so have a look around for other possibilities.

The link is to Northern Arizona Wind and sun -- they are a good outfit to deal with with good support. I'm guessing you could call them and give them your setup, and they could confirm this is a good controller choice and probably give you some hints on how to set it up. You want to be sure its set up for your Li batteries and that the feature that prevents trying to charger the battery at temperatures less than freezing is turned on. They have a Youtube video on how to set one up.

Gary
That is what I have & when the snow clears @ my cabin I am going to try it out & replace my PWM. I’m experimenting with solar & so far I have been able to run my cabin on 12v (led lights, ARB Fridge, Clone Diesel Parking Heater (the biggest power consumer @ night), device charge station). FLA 130Ahr solar charged & usually fully charged to 100% SOC mid to late morning with 2 - 100W in parallel.

When I install my Victron I will place the 2-100W panels in series to start.

Location; Approximately “Summerland BC”.


The Unit can take #6 AWG wires;

70420
 

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I think its OK

That 610/12 = 51 amps calc is on the conservative side in that it does not account for the controller inefficiency and the actual charging voltage is going to be above 12 volts, so current will be less. It will be a very rare day - maybe high altitude and cold and clear - that you will get the full 610 watts.
I believe that the Victron will just limit the current to 50 amps or shutdown if you exceed the 50 amps, but it would not hurt to check with them or Nothern AZ Wind and Sun to make sure.

Gary
 

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If my max current is at 51amps, it's alright to use the 50amp mppt? I've heard about allowing a cushion of around at least 25amps for those cold weather situations, but I've also heard I'd be lucky to get anywhere near max amps. I appreciate the help!
Best to check the Manufacturer Specs;

Here is page 12 on my Victron manual;

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Discussion Starter #10
I'll definitely call to check first. Also, if they're in parallel, would the 64.2v open circuit on each panel be ok if it's a 100 | 50 unit? I wasn't sure they remain at 64.2v and just double amps to 51, or if the unit needs to account for both at 128.4v and 51amps
 

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I'll definitely call to check first. Also, if they're in parallel, would the 64.2v open circuit on each panel be ok if it's a 100 | 50 unit? I wasn't sure they remain at 64.2v and just double amps to 51, or if the unit needs to account for both at 128.4v and 51amps
Hi,

I think the Voc of 64 volts should be fine with the Victron - lots of margin to handle cold days. Well below the Victrons 100 volt limit on input voltage.

If you hook the two PV panels in parallel, the highest voltage the controller will see on the input side is the 64 volts, or maybe a bit more on a really cold day. The max current the controller will see on the input side is twice the 5.96 short circuit amps, or 12 amps.
If the two PV panels are putting out their full 610 watts (a very very good day), the controller on the input side will see the Vmp voltage = 54.7 volts, and a current twice the Imp of 5.58 amps, or 11.2 amps.
All this should be easily within the Victrons specs.

I would not hook the PV panels in series, as that will get the max voltage up to 128 volts or so, which exceeds the Victrons max input voltage by quite a bit.

On the output side of the controller on a really good solar day where the panels might actually put out 610 watts. The controller is 98% efficient at best, so the 610 becomes 598 watts, and if you assume a charging voltage to the battery of 12.5 volts, then the max charge current is 598/12.5 = 48 amps -- so, below the 50 amp rating. I think it should be fine, but worth checking with them to be absolutely sure.


Gary
 

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This thread got me re-interested in my solar charger I purchased last spring for my cabin. I have not yet installed it as I am slowwwwly building the electrical system & have temporary solar that is run by a PWM 30amp non-configurable solar charger.

So the other day I hooked my Victron MPPT to a battery so I could connect “bluetooth” & check out the configurable system (output side to the battery). Sometimes I buy stuff & do not understand how it works until I am using it. With this Victron “Gadget” it is pretty much as I thought, but thumbing thru the settings & screens I learned a bit more.

One thing that I did not know was a setting called “Streetlight”🤔. It is an “on/off” setting & as I have not read about it yet I filed that to learn later. Would it not be cool if a solar panel could provide some charge to a battery if under a streetlight @ night or in a high lighting area “parking lot boondocking”.

I love the battery monitor I have in my van (no solar). I was going to buy one for my cabin. I then wondered if I purchased this Victron 100 | 50 if it would have enough “monitoring” of the battery for me (also being a 3 phase programable charger profile). My conclusion for my cabin is with this Victron solar charger I will not need a battery monitor at all. Where a battery monitor would give me more information, I can get enough out of the monitoring that the Victron solar charger provides me.

My recommendation for budget conscientious DIY van builders; If you are doing solar on your van & you install this Victron bluetooth solar charger (or something similar) you will not need a “Battery Monitor”.



Some iPhone App screen shots (no solar panels hooked up yet);


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I have actually gotten a charge from a light. it was in my parking garage and the van was parked right under a fairly bright light. I would guess in the old days we would call it a 150-200watt or more light. The distance from the light to the solar panels was about 1 foot. The van showed charging of 3-4 watts if I am remembering correctly.

That streetlight mode isn't going to get much but I suppose it is better than nothing. I was actually surprised because I got in the van and saw the Victron Color control showing the MPPT was active. I had 2 100 w panels in series at the time. I would guess 50+% of the light from the fixture was hitting the panels due to the close distance, which convert 10-15% of the light energy to electricity, which would imply about 30-50 watts of light energy hitting the panels, so the light was putting out maybe 60-100 watts of light energy, probably using twice that in electricity. All very speculative but interesting for an engineer/math nerd.
 
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