Newbie question regarding Series Vs Parallel and the need of microinverters

[LilMT]

So I am planning a small system for a cabin.
I have 6 panels 415W, VOC 49.6V, ISC 10.66A
I used the string sizing tool and plan to purchase a classic 250 (more than I need but I might expand later)
Batteries are going to be a 48V array of the Renogy hybrid Gel, which apparently have a max charge rate of 60A.
Planned panel array is 2 parallels of 3 in series.  rough output should be around ~150V at 20Amp (I think)
That should give me approximately the 60A charging for my battery array correct?
Also, do I just use a combiner box and take the output from the array straight to the classic or should I use micro inverters to combine the array and then take to a rectifier and then to the Classic?

Sorry if these are stupid questions but I just needed someplace to start.

Thanks,
LilMT

[Vic]

Hi LiMIT,  Welcome to the Forum,  NO questions are stupid !

Please post the Classic String Sizer output,  or,  give the manufacturer and model number of the PVs that you are thinking of/ going to use.  Need to know the PV Vmp  ...

What is the purpose of this system,  ie  off-grid,  grid backup,  etc?

Thanks,   Vic

[boB]

6 X 415 watts  into a 48V battery (roughly) would be about 52 amps.

Perfect !    That is, if you were to get 100% out of the panels which is hardly ever the case.

I would expect to get somewhere in the upper 40s in amperage though.  Nothing wrong with that !

boB

[mike90045]

No microinverters, no rectifiers

Just the PV, combiner box, controller

[Highflyer]

boB,

Would the Hawk's bay charge controller be a better fit when it is available?  Would the efficiency be better?

[LilMT]

Thank you for the help.

I have attached the PV data sheet and highlighted the one I am looking at.

I have also attached a snip of the sizing tool as well as the output PDF.  (I think I got the bits and pieces into the right areas).

This system is going to be off grid.  The Solar is to help offset a generator.

Someday, hopefully I will be able to increase size of solar and rely even less on generator but the winters in Montana get a little dark.

Thanks,
LilMT

[Vic]

Hi LiMIT,

Thanks for all of the added info.

Have been wondering about you using three strings of two of the 405 Watt PVs into a Classic 150,  on your system.

Three PV strings would necessitate adding a Combiner,   but if your system did need added PVs later,   a Combiner would be needed anyway.

Strings of two 405W PVs would have a sufficiently high voltage input to a Classic 150,  to all it to work well.  Since Gel batteries do not need an EQ,  the string Vmp of about 83V should be fine.

Gel batteries are not common in off-grid systems.  They often do have a fairly low maximum charge current.  Although,  a 60 A max for the Gels that you are considering,   is fairly high.

The Classic 150 is less expensive,   than is a Cl 250.

Attached,   is the MN Sizer output for the above configuration.

FWIW,  Vic

[LilMT]

Vic,
Thank you for the info, I had thought about that and perhaps I am looking at it incorrectly.
If I use the Classic 150, I believe it is rated at Max output of 86Amps?
I have not spoken directly with Renogy yet and I do plan to before I gait everything together but, I have read that they will not honor warranty on batteries if charger is rated higher than 60 Amps.  Even if limited by software and other factors.
That is one of the reasons I was looking at the Classic 250, the other reason are and again perhaps I have this way wrong but....
By doing an array of 3 in series by 2 paralleled I think I increase my voltage and lower my amperage and should be able to go with smaller supply wire.  Admittedly I am only going about 100' so not a big factor.
The other thought is that for the reminder of the system I am looking at one of the prewired kits that Midnight puts together.  Specifically the "MNEMS4448PAECL250" which MSRP is slight less than the one with the Classic 250.

After I speak with Renogy I may revamp the plans though.

Thanks again for all the help and please feel free to tell me I am off base on my thinking. 

As I am going down this journey I am finding that the more I discover the less I know. 

Thanks,
LilMT

[Vic]

Hi LiMIT,

Personally,   would AVOID using Gel batteries.   There is little to recommend them,  verses using AGM batteries  --  both of these types are Sealed.

If you really need a sealed battery,  generally for off-grid applications,   AGMs would probably serve you better.

It is possible that given your MT location,   that you are planning on putting the batteries in the living quarters,   where sealed batteries are sometimes better.

Flooded Lead Acid batteries are generally more forgiving,  than sealed batteries,   cost less for given Ah Capacity,  would probably last about twice as long as a sealed battery,   BUT do require maintenance,   as you probably know.

Your 100 foot distance twix the PVs and the power system,   is a bit far for running a string Vmp of about 83 V   ...   but a Classic 150 will run more efficiently than the 200 or 250,   even at the identical input (PV) voltage,   and,  with a higher input voltage on a 200 or 250  there will be a bit of additional efficiency loss.   You could beef-up the cable run from the PVs,  for a reasonable cost,   and this would help a bit if you were to add more PV,  later.

Many trade-offs.   But,   please do some more research on using Gel batteries for daily charge cycling.   Gels are not at all common for off-gridders.

The string Vmp of two PVs per string would still have sufficiently high enough voltage to be able to charge and EQ Flooded Lead Acid (FLA) batteries,   IMO.

Sizing batteries to meet the loads on the system is usually the best place to start a system design,  from there,  the amount of PV (and other power sources) needed to generally recharge the batteries on a typical day,   follows,   for a balanced system.   This PV power system may be a bit experimental,   but if added battery capacity is needed,  later,   adding new batteries to older ones usually does not work too well,  and so on.

All,   IMO.   Vic

[LilMT]

Vic,

Excellent info.  You hit it on the head about having the batteries indoors, in the living space.  I have a concern about having a battery shed as even last week we hit -41F ambient.

I will continue a review of the battery technology, and perhaps I can figure a safe way to keep a battery shed warm.

Thanks again,
LilMT

[Vic]

-41 F   !!! !    Wow,

Please DO look into AGMs.   They are fairly common for off-gridders.

You might check out the Northern Arizona Wind & Sun Forum,  for more discussion on batteries,  and much more:
https://forum.solar-electric.com/

Please do let us know how you are doing with the system.

Keep warm,   Vic

[LilMT]

I will check into AGM, and as I make headway I will keep you all posted.

Thanks much,
LilMT

[ClassicCrazy]

I  hear there are some new types of lithium batteries that have heater in them - so they will use the PV to heat themselves first to bring above freezing before they start charging. I don't know much about them and they probably are pricey.
The other option for sealed batteries are called Lead Crystal - sort of like a gel or agm but they claim the electrolyte is such that they will never sulfate. They have good specs at cold temperatures - which is pretty much why I ended up buying some of the Soneil brand.  I got them for their cold weather performance since they had to be in an unheated shed here in Wisconsin winters. And my battery supplier had them in stock and said they were well regarded. So far I haven't had any problems with them. They do tend to start acting a bit goofy if they get down lower than -20 F since they just don't seem to like to take an absorb charge and will go to Float pretty quickly. But then I think they charge gradually at Float .
If I was smart I would have designed some kind of insulated box for them since then I could have kept them warmer or put a small heater in there on the very coldest sunny days which would have helped. But of course you don't want the insulated box on them the rest of the year when you want to keep them cool and not getting hot. So best would be a box with removable top and sides.
I think Soneil is pretty bad because when I have had tech questions and emailed them I never heard back. So I just had to go with published info and what my battery supplier recommended.
I try not to take more than 20% out of them for greater longevity just like you would do with flooded lead acid .
Maybe Vic would know answer to this question - The Classic uses temperature to de-rate capacity so the 20% capacity figure is less when cold than when warm.  But which figure would you use for long life - the warm battery figure or the de-rated  cold  battery capacity ?
Maybe it doesn't matter that much anyway .
here is the link to the batteries and of course always be skeptical of some of the ad hype claims !
When I got them the price was comparable to flooded lead acid .
It is nice not have to mess with adding water and taking specific gravity readings. I just hope they last as long as they claim.
I have the 2v 540 amp cells to make up 24v
https://soneil.com/products/battery/

Larry

[LilMT]

Larry,
Thanks for the info.  I have been looking at the Lithiums and when I get to the point of a long term solution I will most likely go that way.  I spent the night looking at the lead crystal batteries and found a few suppliers and a little information.  Based on what I found that they are very similar in spec to the Hybrid Gel that I have been looking at.  Very similar input and output characteristics. 
One thing I failed to mention is that the place I am working on is eventually going to be my primary living, but while I am working on it(3-5 years) it will only be weekend and short vacations.  Hence the wanted protection of interior batteries.
I have even looked into the iron edison batteries but just cannot justify the cost and complexity at this point.

I will continue researching and let you all know what I end up doing along with challenges and successes



Thanks all,
LilMT

[Vic]

I  hear there are some new types of lithium batteries that have heater in them - so they will use the PV to heat themselves first to bring above freezing before they start charging. I don't know much about them and they probably are pricey.
The other option for sealed batteries are called Lead Crystal - sort of like a gel or agm but they claim the electrolyte is such that they will never sulfate. They have good specs at cold temperatures - which is pretty much why I ended up buying some of the Soneil brand.  I got them for their cold weather performance since they had to be in an unheated shed here in Wisconsin winters. And my battery supplier had them in stock and said they were well regarded. So far I haven't had any problems with them. They do tend to start acting a bit goofy if they get down lower than -20 F since they just don't seem to like to take an absorb charge and will go to Float pretty quickly. But then I think they charge gradually at Float .
If I was smart I would have designed some kind of insulated box for them since then I could have kept them warmer or put a small heater in there on the very coldest sunny days which would have helped. But of course you don't want the insulated box on them the rest of the year when you want to keep them cool and not getting hot. So best would be a box with removable top and sides.
I think Soneil is pretty bad because when I have had tech questions and emailed them I never heard back. So I just had to go with published info and what my battery supplier recommended.
I try not to take more than 20% out of them for greater longevity just like you would do with flooded lead acid .
Maybe Vic would know answer to this question - The Classic uses temperature to de-rate capacity so the 20% capacity figure is less when cold than when warm.  But which figure would you use for long life - the warm battery figure or the de-rated  cold  battery capacity ?
Maybe it doesn't matter that much anyway .
here is the link to the batteries and of course always be skeptical of some of the ad hype claims !
When I got them the price was comparable to flooded lead acid .
It is nice not have to mess with adding water and taking specific gravity readings. I just hope they last as long as they claim.
I have the 2v 540 amp cells to make up 24v
https://soneil.com/products/battery/
Larry

Hi Larry,

Thanks for mentioning your Lead Crystal batteries.   Have never known enough about them to be able to  have any opinion on them.   But,  IIRC,  you have had them in service,  for a number of years.,  which is good.

The heated Li batteries sound like they should solve that one negative for Li  --  low temp charging. Assume that there must be the ability to heat them from a genset,  or other AC power source,   a good tip.

Our climate is generally quite mild,  so,  we essentially ignore the low temperature effects on battery Capacity.   BUT,  it would seem these effects are not due to depletion of acid in the electrolyte,   but just from the effect of low temps on chemical activity/mobility,   which is reversible when the batteries do warm.   So,   to me,  it would seem that it OK to ignore this Capacity reduction.

Perhaps,  if fully-charged batteries got extremely cold,   there might be some possibility of damage due to stratification (FLA),  or some SG gradient in batteries  --  not just between the lower and upper parts of the batteries,  causing localized freezing,  etc.

Am not a battery engineer,  or expert.  Seems like there are always  many things remaining to learn about them.

Just opinions.

And,  Larry,  how cold has it been in your area this Winter?   73 Thanks,  Good comments and question.   GL,  Vic