Sizing an array for MPP Solar LV2424

[erik.calco]

Can someone give me tips on sizing an array for 1 unit? I'll have up to 13' x 13' of surface available for the panels. The distance between the SCC and panels will be 40-80' depending on how close I put it to the main breaker panel. I have plenty of 10 AWG solar cable, but will buy other gauge if needed, though would like to leverage existing hole through cinder block that can't fit much more.

As I understand it, it's about 5.5 amps per 100w panel. It's the voltage limitations that I'm not sure about. I'm in cold climate, so would need at least a 25% buffer. The manual has this:

So, let's say to be safe I want to stay under 100Vdc. Would I add up the 21.3 Voc in series and ignore parallel, so that 4Sx3P would be 4x22V or 88V?

With the dimensions of 13'x13', I can theoretically fit up to 24 100w panels. So, I did some breakdowns:

100W mono: Dimensions: 35.6x25.9x1.18 in. 600W, 3x2 of that would be 72x78, or 6’x6.5’. 2400W would be 12’x13’.

Nominal V: 24x100w.. 1S=132Ax12V, 2S=66Ax24V, 3S=44Ax36V, 4S=33Ax48V, 6S=22Ax72V, 8S=16.5Ax96V.

Voc: 24x100w.. 1S=132Ax22V, 2S=66Ax44V, 3S=44Ax66V, 4S=33Ax88V, 6S=22Ax132V, 8S=16.5Ax176V.

Voc: 8x100w… 1S=44Ax22V, 2S=22Ax44V, 4S=11Ax88V

I haven't purchased the LV2424, yet, but am using it to baseline an initial configuration. How big of an array can it handle w/o losing efficiency?

For batteries, I will be starting with 4x90A Lion UT 1200s, so with the LV2424 I'd do 2S2P for 180A at 24V. Just ordered them today.

Can anyone share items they used with a similar setup for circuit breakers, bus bars, etc,... ideally links to products or even ebay.

I do plan to have a breaker box for inverter output that will contain 20A circuits replacing the circuits in my home main box as I expand. The ultimate goal is to eventually replace 4 of the 20A circuits that have what I consider to be "critical load".

LV2424 Manual

 

[Will Prowse]

Would I add up the 21.3 Voc in series and ignore parallel, so that 4Sx3P would be 4x22V or 88V?
Yes. And you would have a good deal of headroom for cold morning spikes. As long as the VOC of the series string is lower than 145v, you are set.

But what is the total power output of your array in watts? This MPP unit can handle 2kw array, so be sure not to exceed that limit. It can max out at 83 amps, but its rated for 80 amps. I would keep it below 80.

Considering the size of array that you are building, you may consider using larger panels. 100w panels are pretty small for this application. Also, with larger panels, you can put them all in series and skip the branch connectors. Boost the voltage up to 80-120v VOC and keep the amps nice and low for that long wire run.

 

[Mac6792]

Would I add up the 21.3 Voc in series and ignore parallel, so that 4Sx3P would be 4x22V or 88V?
Yes. And you would have a good deal of headroom for cold morning spikes. As long as the VOC of the series string is lower than 145v, you are set.

But what is the total power output of your array in watts? This MPP unit can handle 2kw array, so be sure not to exceed that limit. It can max out at 83 amps, but its rated for 80 amps. I would keep it below 80.

Considering the size of array that you are building, you may consider using larger panels. 100w panels are pretty small for this application. Also, with larger panels, you can put them all in series and skip the branch connectors. Boost the voltage up to 80-120v VOC and keep the amps nice and low for that long wire run.

I seem to recall Ian stating that while vdc max is 145 you need your voltage not to exceed 115 for the mppt controller. Perhaps someone could clarify

 

[erik.calco]

@Mac6792

https://www.altestore.com/howto/solar-panels-pv-and-voltages-a98/

I believe 115 refers to Vmp. From usa-mpp-solar.com description of LV2424:
3) 2000 W MPPT charge controller (30 to 115V PV Vmp DC Voltage - max 80A)

Here you see a 250W panel reference sample from the manual:

 

[Mac6792]

Right. I had nearly the exact same question in the thread I started. This is how Ian answered it.

Paneling for a 2400KW PIP

I've been going around in circles trying to determine the best way to panel this 24 volt MPP 2400kw All in one. It's a max 2000Watts solar input, Max 145VDC input., Max 80Amps in. My goal is to get the max wattage I can given the space and input limitations. I'm less concerned about...

www.diysolarforum.com

 

[erik.calco]

Right. I had nearly the exact same question in the thread I started. This is how Ian answered it.

Paneling for a 2400KW PIP

I've been going around in circles trying to determine the best way to panel this 24 volt MPP 2400kw All in one. It's a max 2000Watts solar input, Max 145VDC input., Max 80Amps in. My goal is to get the max wattage I can given the space and input limitations. I'm less concerned about...

www.diysolarforum.com

How long will your cables be from panel to SCC? This article on Choosing the Right Wire Size demonstrates efficiency you might gain with series unless your cable lengths are short that you'd have to weigh against the cons of shading. I plan to max series within voltage limit and cut down a very big tree.

 

[Mac6792]

How long will your cables be from panel to SCC? This article on Choosing the Right Wire Size demonstrates efficiency you might gain with series unless your cable lengths are short that you'd have to weigh against the cons of shading. I plan to max series within voltage limit and cut down a very big tree.

One other thing Ian said was "60 to 115V is the operating Solar Panel voltage range 145V is the max before damage occurs. 115V to 145V - No Charging occurs - dead zone "
To answer you question - probably 30-40 Feet. I may pick up 4 LG 360 watt panels(1440 watts) off craigs list and run them as 2 Series strings connected Parallel putting my voltage around 85 voc/18 amps. (105voc with a 25% buffer as I'm in the northeast)

 

[erik.calco]

@Mac6792 That's about what I'm going for, 100 or so voc. Also in NE.

Considering moving Inverter a good distance from main AC circuit breaker panel to get it closer to solar panels. Not sure how much AC line loss differs from DC.

 

[SCClockDr]

@Mac6792 That's about what I'm going for, 100 or so voc. Also in NE.

Considering moving Inverter a good distance from main AC circuit breaker panel to get it closer to solar panels. Not sure how much AC line loss differs from DC.

The primary difference is voltage. 12 volts vs 120 volts means 100 amps vs 10 amps a secondary difference is the AC power is somewhat inductive which results in an additional 30% reduction in true current.

 

[erik.calco]

The primary difference is voltage.

The DC side will be over 100V Vmp @ 10 AWG. On the AC side on standard 20A household wire, the distance would be double because it would include AC incoming AND AC outgoing. So basic choices are 80' DC and within 5' of AC incoming and outgoing, or 40' DC and 40' AC incoming and 40' AC outgoing.

Of course, Vmp and Voc are not normal. I suppose average V is what you'd want for calculating efficiency. But who knows what that is.

Because of the complication of the additional AC legs, I'd prefer the 80' DC if the loss difference is not significant.

 

[SCClockDr]

How much $ is 160' of between 8awg & 2awg copper?

 

[DENWA]

But what is the total power output of your array in watts? This MPP unit can handle 2kw array, so be sure not to exceed that limit.

Where do get this from? I keep hearing your videos not to exceed the rated input but where did you read this?

Its my understanding of MPPT solar input stages will self regulate on Input current not allowing them to exceed a safe value.

When I asked MPP solar, Ian says you can't over power the soalr input if you stay inside the volateg ranges.

Do setting persist after Power loss? and Rated Solar Questions

Recently bought this: https://www.ebay.com/itm/PIP-812LV-800W-12V-120Vac-Solar-Inverter-40A-MPPT-charger-Gen-Util-20A-RV/254345565459?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649 I was wondering after reading manual and watching the Videos: 1. If ALL power is dropped ( no grid...

www.diysolarforum.com

Just trying to understand your rationale and avoid hearsay.

 

[Ascssmith]

What Will is asking you is “total power output of your array in watts”. = How much wattage in solar panels do you have coming in...

So from your initial question you said this: With the dimensions of 13'x13', I can theoretically fit up to 24 100w panel
So that would equal 2400 watts (24*100), which is over the 2kw = 2000 watts.

 

[erik.calco]

What Will is asking you is “total power output of your array in watts”. = How much wattage in solar panels do you have coming in...

So from your initial question you said this: With the dimensions of 13'x13', I can theoretically fit up to 24 100w panel
So that would equal 2400 watts (24*100), which is over the 2kw = 2000 watts.

Wow. This was only 6 days ago? Seems like weeks have gone buy.

This was primarily a question of how many I could string in series than anything else. There are many constraints, with voltage being the primary one (115 Vamp and 145 Voc on this SCC). I quickly learned how to calculate that including temperature coefficient (typically around 17V with -30C coldest historical temp). This SCC has an 80 amp limit, but your biggest problem there if running a long line is efficiency. So, you try to max voltage within parameters to minimize current.

I just started out with my physical constraints of 13'x13' to be sure I utilize the full capacity of the 2424lv I was considering. It is not a requirement to use all 169 sq ft. It is a goal to utilize 90% of the capacity of the SCC, so we're looking at a 1.8+kw nominal array size.

 

[KBWaldron]

Would I add up the 21.3 Voc in series and ignore parallel, so that 4Sx3P would be 4x22V or 88V?
Yes. And you would have a good deal of headroom for cold morning spikes. As long as the VOC of the series string is lower than 145v, you are set.

But what is the total power output of your array in watts? This MPP unit can handle 2kw array, so be sure not to exceed that limit. It can max out at 83 amps, but its rated for 80 amps. I would keep it below 80.

Considering the size of array that you are building, you may consider using larger panels. 100w panels are pretty small for this application. Also, with larger panels, you can put them all in series and skip the branch connectors. Boost the voltage up to 80-120v VOC and keep the amps nice and low for that long wire run.

@Will Prowse Are we better going with a higher input voltage so as to reduce the amps in the line between array and MPPT, or does it make no difference? I would think the first since the higher the amps the more loss in the lines.

 

[SCClockDr]

@Will Prowse Are we better going with a higher input voltage so as to reduce the amps in the line between array and MPPT, or does it make no difference? I would think the first since the higher the amps the more loss in the lines.

Your logic is correct.

 

[mrdavvv]

Where do get this from? I keep hearing your videos not to exceed the rated input but where did you read this?

Its my understanding of MPPT solar input stages will self regulate on Input current not allowing them to exceed a safe value.

When I asked MPP solar, Ian says you can't over power the soalr input if you stay inside the volateg ranges.

Do setting persist after Power loss? and Rated Solar Questions

Recently bought this: https://www.ebay.com/itm/PIP-812LV-800W-12V-120Vac-Solar-Inverter-40A-MPPT-charger-Gen-Util-20A-RV/254345565459?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649 I was wondering after reading manual and watching the Videos: 1. If ALL power is dropped ( no grid...

www.diysolarforum.com

Just trying to understand your rationale and avoid hearsay.

Yes i have the same question. Im currently in the same situation, paneling for a LV2424, however Ian mentions than you can safely exceed the available PV capacity as the hybrid inverter only "Takes" the requiered power up to 2000W, and the rest i guess is wasted: post

However some people mention that you cannot exceed the 2000W in panels, so what should i look for?.

Im currently planning on using 4x400W (1600W), but it would be better to use 6x385 (2310W) and have all the capacity available.

 

[erik.calco]

The most important thing, as Ian said, is to never exceed the voltage limit. Amps are not much of a concern. Though you'll still need to include appropriate breakers/fuses, wiring and connectors for the amps.

I chose to go with 2 panels per string instead of 3. If I did 3, then I'd be within voltage limits "most of the time". But, that one time I'm over could toast the MPPT. With 2 panels, it will take lightening to go over. I can tell you that two panels so far have peaked at 80V for me so far. That would of been 120V if I had 3, which would of been fine. But on that really cold sunny day, you can get a spike. They can also spike at odd times. Someone said in morning before sun is all the way up, because inverter hasn't begun to pull on it, yet. I haven't witnessed that with mine. But, it's yet another reason to be well below voltage limits. Don't forget temp coefficient in calculations.

That said, I'll never be anywhere near the amp rating of my MPPT when I have all 6 panels online. A 40 amp breaker is unlikely to pop under normal use, so I'll be far from the 60 amp limit. And 6 panels totals 2000W. My 15 amp breaker has yet to pop with a one string.

The obvious downside is you need lower gauge wire between the combiner and the inverter. I haven't cost out my expansion yet to determine where the combiner will be located. Because one side of the combiner will have 8-10 gauge, while the other side will have 2-4 gauge. I need to figure out which side is cheaper per foot. I'd also like to experiment with performance impact of different gauges/lengths before I commit. I can do that with a single string before I add strings, or swap strings once I have 2 online. In short, you can plan experiments as you scale instead of having all the answers up front. But, obviously, you'll need to learn enough to understand your general parameters and options.

 

[mrdavvv]

Hello @erik.calco

For the MPPT charge controller we have the hard limit of 80A, and i think thats where the PV Max Power number comes from. According to this guys, going over the MPPT amp limit its generally not an issue (Unless you go crazy and put x2 values): Link

Howemever Im undecided if i should trust the chinese electronics to hold the charging of 80A or just underated the PV input so they never go full capacity, around 1600W of panels (66A).

I came to the same conclusion of using x2 strings with as many parallels as you need, so you never go over the voltage limit under any condition.

 

[erik.calco]

Hello @erik.calco

For the MPPT charge controller we have the hard limit of 80A, and i think thats where the PV Max Power number comes from. According to this guys, going over the MPPT amp limit its generally not an issue (Unless you go crazy and put x2 values): Link

Howemever Im undecided if i should trust the chinese electronics to hold the charging of 80A or just underated the PV input so they never go full capacity, around 1600W of panels (66A).

I came to the same conclusion of using x2 strings with as many parallels as you need, so you never go over the voltage limit under any condition.

How are you coming up with 66A for 2 strings totaling 1600W? I can tell you my 320W panels are around 10.x amps, so 3 strings is around 31A for 2000W. Now my 100W panel is 5.5A, but that's a 12V panel. You'd be able to put quite a few of those in series with the LV2424. I don't remember the specs, but I think we're talking 20V, so I'd be comfortable with 4-5 of those 100W panels in series. So, that's 1500W on 3 strings for 20A.

Obviously, I'm roughing it with the numbers cuz these are just estimates. If we used Renogy 100W (RNG-100D), with Voc of 22.5V, can do 4 in series. So 4 strings at 1600W. Isc is 5.75A or 23A. Not adjusting for temp coefficient, but these params are well within LV2424 limits. If you did 2 strings, you'd double that to 46A.

 

[mrdavvv]

I was thinking that maybe the 2000W PV input limit its based on the 80A maximum power that the MPPT can supply to the batteries. So in that case and according to the guys or the link that i posted, we can safely go little bit higher:

MPPT controllers, in general, can handle over sized arrays. They have the capability to throttle back the amps to stay within their heat and rated amp limit. I would not go much more than 150% over the controller rating. If your controller handles 4000w at 48V, it could most likely handle 6000w and still be able to self limit. A lot depends on the array voltage and how the controller "de-tunes" the PV array to stay within limits.
In all cases, follow the mfgs suggestions.

Not considering the PV lines amperage in my past message., more about the MPPT charger output in relation to the maximum input of the PV system, if we have 1600W on solar, it should relate to 66A @24V for the MPPT battery charger at maximum. (Aproximately).

 

[erik.calco]

I was thinking that maybe the 2000W PV input limit its based on the 80A maximum power that the MPPT can supply to the batteries. So in that case and according to the guys or the link that i posted, we can safely go little bit higher:



Not considering the PV lines amperage in my past message., more about the MPPT charger output in relation to the maximum input of the PV system, if we have 1600W on solar, it should relate to 66A @24V for the MPPT battery charger at maximum. (Aproximately).

That makes sense. I never thought of the the limit based on the battery bank.

Taking a moment of production I had with 2 panels online in series (image below), 9A for 245W would be 73.5A for 2000W. My setup is not optimized, but I'll be happy if I can produce 60A from 6 panels when I'm done in perfect sun.

Note that in the configuration, you can set max AC charging current at 60A and max total charging current to 140A in the configuration (image below). The difference is 80A max for solar, or 1920W. 140A would be 3360W. Personally, I try to minimize AC charging (cloudy days at night only), in part because of the inefficiency of the inverter, so leave charger source priority to Solar only, and will change if I need a boost from utility.

Also note that you'll realistically be feeding a load with PV in addition to charging the battery. While there is a lot of configuration, it's hard to really get a handle on where all your load is powered from. It would be more clear if you turned off AC in, as a complete off-grid setup would be. I just never know when it is passing AC from in to out. Every day I get more of a handle on it as I observe this output and change the load on it in various conditions:

 

[svetz]

You might also like: Figuring out how many panels in series and parallel based on your MPPT

 

[erik.calco]

@mrdavvv one other thing to consider, if you can point your panels in different directions, some people do this to smooth production over more hours in the day. I'm doing 2 panels per mount, so with 6 panels, can point in 3 different directions. If doing tracking or on a roof, this doesn't matter, though even with the same direction for all panels, you can also factor in shading traveling across them. These options provide a way to lower total power at any given moment while optimizing production for an entire day.

 

[tictag]

Because SCCs are generally very efficient devices e.g. 95-98%, it is always the output FETs that determines the maximum PV input power. FETs always have a voltage drop across them to operate (as all semi-conductors do) so when current flows through them, power loss is inevitable. This power loss is expressed as heat, hence the large heat-sinks on high-power SCCs. There is only a finite amount of heat that can be dissipated, so SCCs have a limit to the current they can supply.

Exceeding the input PV power specification could potentially lead to excessive current flow into the battery, which in turn will heat the FETs beyond tolerance and potentially cause a cascade FET failure (many FETs are usually wired in parallel, so if one FET fails, the others take on the load, which in turn puts them at higher risk of failure - there is always a 'weakest link' when it comes to parallel FETs). It is very unlikely that input current would be anywhere near output current, due to the relatively higher voltage of PV arrays.

I don't know the impact of excessive voltage but I'm guessing this will be due to component tolerances, such as the dialectic breakdown specification of capacitors etc.

I know that it may sound 'conformist', but I would just advise not exceeding either the maximum PV power or maximum PV voltage specifications!

I'll also bet my own money that a manufacturer 'know' that there products have been used outside of specification when it comes to warranty claims - they're not stupid.

Definitely agree with the comments about having as higher voltage on PV input as possible, within specification, obviously!