Adding 2 more panel, 400 watts total, 100 amp hr battery

SolarShed

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Hi, I have this system, 12v

100 amp hr Renogy Smart Li batt with self heating
Renogy 40 amp MPPT Li charge controller
Renogy 1000w Pure sign wave inverter
2 x 100 watts NOMA solar panels

The 2 panels are connected in parallel (want more amps, with voltage the same)

I can get 2 more of the exact same NOMA solar panels, to make 400 watts total and would like to add them in via parallelization on my fuse block.

My charge controller can handle 540 watts in on the PV, so I'm not over that.

Would having a 100 amp hr battery be a problem here? Or do I have to get another battery also?

From what I've read, in terms of sizing, my solar panels are slightly bigger than my battery, by about 25%, for example, 300 watt is more suitable for 100 amp hr battery, I realize the disadvantages of going too small of a PV system, but is there any harm of them going a little bigger?

Thanks
 
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MisterSandals

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The 2 panels are connected in parallel (want more amps, with voltage the same 12v)
Why do you want more amps? It does not change the watts that go to the SCC.

In lower light conditions, your parallel panels may not produce enough voltage (battery voltage + ~5V) to start charging. This may be early morning, late afternoon or a cloudy day.

Your panels are likely 22Voc (and about 18Vmp). Does your SCC indicate an MPPT range (optimized range) for solar input?
The converse of this is that you should never exceed the SCC's max input voltage (plus temp adjustment).

What is the max input voltage of your Renogy SCC? That is the key to being able to answer your questions. Same for panel Voc's if not ~22Voc.
 

Short_Shot

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You don't need your panels to be 12v. It's a bit more ideal for them to be placed in series depending on the maximum voltage of your controller since you have mppt.

Just don't exceed the solar controller voltage under any circumstances, in fact you may want to make sure your series open circuit voltage is under 80% or so of that rating because cold days increase voltage.

You may find it beneficial to put them in 2 groups of 2 panels in series then parallel those to the controller.

As for how much solar vs battery, that's almost irrelevant as long as the charge rate isn't exceeding the capability of the battery.
 

SolarShed

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thank you all for your replies.

I'm glad that at least my original question is not an issue (that you can have too much solar panel for a battery system).

Now to help answer some of your other questions, here's a couple of photos for the specs of my SCC and PVs

Renogy Rover 40 Li mppt (RVR-40)

DSC_0724.jpg

The solar panels (4 of them)
DSC_0723.jpg

If I'm understanding correctly, its the Voc that is important here, so 21.84 x 4 = 87.4 V so that puts me at roughly 87% of the SCC solar input, however, related to the next question, why is this an issue if my panels are in parallel and the voltage should be well below 22 V?

As for why parallel vs series, I really don't know why I went parallel, however, these self-heating lithium batteries need at least 4 amps of power for the self heating to work. Living in a relatively northern climate, winters are long and cold. What is the advantage of series in this case?

For the 2 extra panels, I plan on just connecting it to my existing fuse block here (each panel has its own 10 A fuse) as shown below

DSC_0659.jpg

Please let me know if I'm doing something wrong here, last thing I want to do is burn down my shed.

thanks so much for your input!
 

Short_Shot

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Current from the panels is irrelevant to your battery heating issue as long as the wattage is there.

To illustrate: 1 amp at 87v is the same power as 7.25 amps at 12v. Both are 87 watts.

The controller does the translation between the two sides for you.
 

SolarShed

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Current from the panels is irrelevant to your battery heating issue as long as the wattage is there.

To illustrate: 1 amp at 87v is the same power as 7.25 amps at 12v. Both are 87 watts.

The controller does the translation between the two sides for you.
That's good to hear. It's going to be interesting how this is going to work in the winter with the self-heating, and the interplay between the Sun and the temperature. Adding an extra two panels should help boost the power.

So if the recommendation is to keep the input voltage at 80% or less than what the SCC can handle, than I think I will keep my panels parallel for now. 🤔
 

MisterSandals

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however, these self-heating lithium batteries need at least 4 amps of power for the self heating to work.
They need 4 amps at the battery voltage (12.8V) which is 4A x 12.8V = 51.2W

Your 2 panels provide 200W
If in parallel, that will be 18Vmp x (5.5A x2) which is 198W
If in series, that will be (18Vmp x 2) x 5.5A) which is 198W

So its the output of your array that we can match to better meet what you solar charge controller is optimized for. That optimized point for the MPPT algorithm is probably around 50% of your max input voltage, which is 100V. This 100V must never be exceeded lest you let out the magic smoke.

I am looking for the MPPT voltage range online, this voltage is where the hardware and software in your Rover are optimized to run the most efficiently.

If you are going to 4 panels, you could combine all 4 in series but at 88V, its too close to the max and any increase in temperature will raise the voltage even higher.

So arranging your 4 panels in series pairs first and then those pairs in parallel (2S2P) this will result in an array that is
(2 x 18V) and (2 x 5.5A) = 396W

And most importantly for this discussion, the array voltage will make your MPPT Rover happy.
 

SolarShed

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They need 4 amps at the battery voltage (12.8V) which is 4A x 12.8V = 51.2W

Your 2 panels provide 200W
If in parallel, that will be 18Vmp x (5.5A x2) which is 198W
If in series, that will be (18Vmp x 2) x 5.5A) which is 198W

So its the output of your array that we can match to better meet what you solar charge controller is optimized for. That optimized point for the MPPT algorithm is probably around 50% of your max input voltage, which is 100V. This 100V must never be exceeded lest you let out the magic smoke.

I am looking for the MPPT voltage range online, this voltage is where the hardware and software in your Rover are optimized to run the most efficiently.

If you are going to 4 panels, you could combine all 4 in series but at 88V, its too close to the max and any increase in temperature will raise the voltage even higher.

So arranging your 4 panels in series pairs first and then those pairs in parallel (2S2P) this will result in an array that is
(2 x 18V) and (2 x 5.5A) = 396W

And most importantly for this discussion, the array voltage will make your MPPT Rover happy.
Oh this is a brilliant suggestion!

I should do some homework on this... do I need more hardware to do this?
 

MisterSandals

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I should do some homework on this... do I need more hardware to do this?
You only need the parallel connectors and you may already have a set of them for your 2 panels.

So to make a 2S2P array:
1) take 2 panels, connect the + of one panel to the - of the other.
2) take the other 2 panels, connect the + of one panel to the - of the other.

This give you 2 strings of 2 panels in series. The wiring for the string is just like 1 bigger panel (1 +, 1- wire).

Now connect them in parallel, exactly like your current 2 panels, presumably with a Y connector.
3) Take both + wires from your strings and connect them to the corresponding Y connector.
4) Take both - wires from your strings and connect them to the corresponding Y connector.

The Y connectors (you are using some now right?) connect to your SCC exactly like you are doing currently.

Its frightfully simple.
 

SolarShed

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This is dead simple, I'll need a couple of Y connectors, which is no big deal, as right now I just have the two panels connected to the fuse block (shown in the above picture). Your instructions are very clear. Thank you!

I wanted to follow up on the whole keeping the mppt happy part.

Here's some efficiency curves for the Rover.
_20210819_220530.JPG


voltage (Vmp) is defined as the
arrays maximum power point
voltage, presumably, when the sun is dead on under perfect conditions, but I'm a reading this right that the efficiency is actually better for a 20 Vmp array when dealing with 12v systems?
 

MisterSandals

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but I'm a reading this right that the efficiency is actually better for a 20 Vmp array when dealing with 12v systems?
That's what it looks like to me. There were other conversations where others pointed out that the smaller the conversion from array voltage to battery voltage, the more efficient the MPPT algorithm.

If you want to put 4 panels in parallel, you'll have to wire and fuse (for each panel wen 3 or more in parallel) to handle any back current. My guess is even with a little less efficiency, it'll be far easier as 2S2P for your array.
I'd be interested to hear opposing arguments or opinions.

One last bit from looking at your setup. This circuit breaker (pic below) is an audio circuit breaker - not very good, can get hot, will likely not handle rated amps and is prone to failure (i ran out of bad things to say, i wanted to continue).

Screen Shot 2021-08-19 at 9.27.36 PM.png
 

SolarShed

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this is very interesting. I'm on the fence now, and I wonder if taking a small hit on the efficiency would be ok. I guess I could try both but it would be hard to compare the two unless the conditions are exactly the same.

If I go parallel first, I'll just get another 2, 10 amp fuses for my fuse block shown below and wire up the 2 extra panels as the other 2 are shown in picture. The two wires coming out of the fuse block to the SCC are 10 gauge.

DSC_0659.jpg

With regards to the fuse for my battery, really? WTH? A supposedly knowledgeable solar store sold that to me. Anyways, do you have a suggestion for replacement? something like this, anl fuse type


Or another type? Would be awesome to know
 

chrisski

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this is very interesting. I'm on the fence now, and I wonder if taking a small hit on the efficiency would be ok. I guess I could try both but it would be hard to compare the two unless the conditions are exactly the same.
When I look at the charts, it’s only a 2% - 4% efficiency difference. That may be one to three minutes extra for every hour charging. So instead of five hours to recharge the battery, it will take five hours and fifteen minutes. To me, getting an extra solar panel would be a better solution. The higher voltage may actually be not as high of a loss because voltage loss is reduced in the wires, but that’s a lot of math.
With regards to the fuse for my battery, really? WTH? A supposedly knowledgeable solar store sold that to me. Anyways, do you have a suggestion for replacement? something like this, anl fuse type
For a lithium battery, an ANL fuse may not have the AIC rating, which means it could blow and then arc across the open circuit. A class T fuse would work but those are pricey. Also, a lot of the less expensive ANL fuses for audio systems do not meet the main battery requirement for the ABYCC, but the more expensI’ve ones do.
 

SolarShed

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When I look at the charts, it’s only a 2% - 4% efficiency difference. That may be one to three minutes extra for every hour charging. So instead of five hours to recharge the battery, it will take five hours and fifteen minutes. To me, getting an extra solar panel would be a better solution. The higher voltage may actually be not as high of a loss because voltage loss is reduced in the wires, but that’s a lot

For a lithium battery, an ANL fuse may not have the AIC rating, which means it could blow and then arc across the open circuit. A class T fuse would work but those are pricey. Also, a lot of the less expensive ANL fuses for audio systems do not meet the main battery requirement for the ABYCC, but the more expensI’ve ones do.
Great information!

I might just leave it at its most efficient setting (all parallel) just because in the winter there's very little sun and it gets cold so perhaps that few percent might help. But again I'm willing to experiment this.

I'm having a hard time finding a 40 amp class T-Type fuse. They seem to be for much larger amp. rates systems, like 200 and above. I guess it's not that common for small systems?

I'm all for safety so if you can recommend a vendor that would have this fuse along with the fuse holder I'd be happy to purchase it. Preferably a fuse holder that would allow me just to crush the wire into the block rather than having a clip.
 

Hedges

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If you are going to 4 panels, you could combine all 4 in series but at 88V, its too close to the max and any increase in temperature will raise the voltage even higher.

May or may not be too high. You have 14% headroom before it reaches 100V.
To consider all 4 in series, need "Temperature Coefficient of Voc" from PV panel data sheet, also record cold temperature for your location, or locations you might visit.
You can probably show it will always be below 100V, but need to do the math. I use 16% headroom for a practically always safe figure.

So arranging your 4 panels in series pairs first and then those pairs in parallel (2S2P) this will result in an array that is

Safe voltage, and sufficient for charging a 12V battery.
Only 2p, so no fuses needed.
6.03A Isc, so 12A for two in parallel. So long as wires are at least 12 awg will be fine. Only if panels mounted far away would there be any issue.
 

pitmaster2002

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I will put my .02 cents in as I am running the same Rover charge controller and 4 100w panels that you have. I have ran this for over a year and found that running at 2s2p is far better than running at 1s4p on the panels to this charge controller especially for the winter months.

What I have noticed is that during morning and late afternoon or low light on cloudy days the voltage on the solar panels would drop to 12v or lower and that prevented the controller from charging my 2 12v 100ah AGM batteries that are in parallel. Since I changed it to a 2s2p on the panels the charge controller is happy with an input voltage ranging from 24v to 30v even with low light conditions and winter conditions. Now I charge the batteries in half the time and the system is working correctly with no issues at all. At max light the controller is getting 10.5amps from the 2s2p setup and pushing out 20.5 to 22amps to the batteries with any load I might have connected to the inverter.

So as MisterSandals said go with a 2s2p setup you will be much happier.
 

circus

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If you want to put 4 panels in parallel, you'll have to wire and fuse (for each panel wen 3 or more in parallel) to handle any back current. My guess is even with a little less efficiency, it'll be far easier as 2S2P for your array.
I'd be interested to hear opposing arguments or opinions.
Parallel...if there's partial shading....it depends.
self-heating lithium batteries need at least 4 amps of power for the self heating to work. Living in a relatively northern climate, winters are long and cold.
That sound terrible. I'd like lithium in my van but we go weeks below 0°F and very little sun. Explain.
 

Hedges

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That sound terrible. I'd like lithium in my van but we go weeks below 0°F and very little sun. Explain.


Lithium batteries are quite efficient, so charging and drawing current doesn't cause much self heating.
The exhaust air from an inverter probably carries more heat - those tend to have 5% to 15% losses. So possibly ducted air would give free heating.

0 degrees F is quite cold. Just at 0 degrees C or below, max charge current for (most) lithium chemistries drops to zero.
You would likely need active heating of the battery if it is kept in a cold location.

My suggestion for setting up a lithium battery system is determine maximum charge rate that your PV or other sources can deliver (e.g. 0.5C, 0.2C or whatever), then set a low temperature charge cutout in BMS appropriate for that current. If 0.1C, maybe +7 degrees C. If 0.5C, maybe +15 degrees C. That should ensure battery doesn't get damaged. Then try to keep battery that warm (at least during charging hours) so you don't waste PV production.

 

SolarShed

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Thank all for all your help and information here.

I hear you all, I have to go with 2P2S or cautiously, 4S. I'm not sure I understand what 1S4P is...if that is what all parallel means, than ok I get it.

For the wiring of the solar panels, right now it is rated for the specs above, 6 amps etc. (I believe its 16 or 18 AWG or whatever the minimum requirement would be out of the box). if I go partial series, 2P2S, would any of the wiring exceed their ratings? If so, it might require me some effort for me to replace the wires in panels, which is not easy, but not impossible.

With regards to the self-heating battery, its a bit of a weird name for it, I admit, because indeed batteries can self-heat. But in this case, it actually has heaters built-in to the battery. When the temperature drops below 5 oC, the BMS diverts incoming power to the heaters rather, than the battery cells, and when the internal temperature reaches 10oC, the heaters turn off and sends the power to cells to charge. But, in order for the the heaters to work, the power in needs to be at least 4 amps.
 
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