Solar panel production

wellbuilt · July 2019

hi all , quick question
I’m sitting here looking at my mate on my out back system .
I’m in mpg bulk charge now , it’s 730 1015 in the am , my battery’s are at 89%
I’m bringing in 2500 watts ? on my out back fm 80 .
This number seems low to me .

wellbuilt · July 2019

I have 4425 watt array @ 36 o pointed south .
And it’s a clear day and heavy thunder storms washed off the panels last night .
I would think I would see 3000 watts plus on a day like today .
I would see 700 watts on one string of 3 295 watts panels .
But that was a little later in the year last week of August

BB. · July 2019

"Knowing" your battery bank is at 89% state of charge (the question is how do you know--Various ways to estimate state of charge and all have their issues)--But assuming 89% state of charge on a lead acid battery bank with a 10%+ rate of charge from the solar array, I would assume that your battery bank voltage is at the charging voltage setpoint (like 14.8 or 29.6 or 59.2 volts) and the battery bank is naturally limiting the input charging current (as the FM 80 is in voltage controlled charging mode).

And your battery bank is pretty much full at this point... A good rule of thumb is to charge your battery bank to >90% state of charge but not to 100% SoC every day... Charging to 100% is hard on a FLA battery bank (it is close to a "short" EQ equalizing charge which involves gassing and such--Not great to do every day).

What is the voltage at the battery bank, and what is your charging voltage set point for the FM 80?

The only time you get 100% of the available array current is when the controller is in "Bulk" charging mode... The battery bank is below the charging setpoint, the controller is in Bulk mode (not float), and the battery bank is closer to 80% or less state of charge.

When the charge controller is in Absorb mode, it is in voltage regulation mode and the battery bank is naturally limiting the input charging current--And therefore, you are harvesting less than 100% of your array's available power.

-Bill

BB. · July 2019

I should add, I am sure you know all of what I posted above--So I may be missing something??? Like you have a good size load on your DC battery bus and the battery bus is below Absorb setpoint???

-Bill

PS if you have a combiner box and several parallel strings of panels, you can always turn off one string at a time and make sure they are all producing the same amount of current, or use a DC Current Clamp DMM to measure the current flow in each string...

littleharbor2 · July 2019

My array in Baja is aimed true solar south @ latitude 30 degrees. A few weeks ago I was there and with the sun being just below its peak ,(summer solstice) in the sky my panels wouldn't even see the sun till 9 30-10 00 in the morning. The sun is rising so far to the north-east that it would make sense to have two arrays oriented south east and south west to be able to capture the long hours of sun of summer. Luckily, in my case I have sized my array to produce plenty of power at any time of the year although it's close in late june. gotta keep an eye on SOC for the month around June 21st.

Dave Angelini · July 2019

Some kind of tracking is needed if you run heat-pumps for cooling or have all day pumping loads. The whole cooling strategy of tracking is for power early and late in the day during summer. The other way is too cycle batteries in summer. Not a fan of that one....Saving batteries for winter deep cycling is the key to long battery life offgrid.

A bit toasty today down on the baja

littleharbor2 · July 2019

It's not so much the heat as it is the humidity that is so brutal. I prefer the pedestal fan over the AC unit down there. AC requires the house to be sealed up tight. My place is built out of stone and retains heat all night. Hopefully there's a sea breeze coming in, especially at night. I leave all the windows and doors open to help cool with the sea breeze. Not sure if any of this makes sense but it definitely works for me especially after I acclimate to the heat. I would probably go into shock walking out of an air conditioned space and into the furnace that is Baja in the summer.

Dave Angelini · July 2019

During our 10 years on the sailboat there was no where as hot as baja (or places like the mid east)
When we got down into the tropics it was far more pleasant.
Even with high humidity in the tropics, the clouds would come in and hide the sun. The trade winds stopped the need for a fan.
I remember those nights in Baja. The fans kept the bugs off also. Excellent fishing. Either too much wind or not enough for sailing.

A few clients live there and you just set the temp for about 78F and it works pretty well. Cooling will spoil you for desert life

wellbuilt · July 2019

Hi bill , I check my soc about once a month . I look at 8 battery’s or so .
And I get a good SG reading 1.275 1.285 and I stop checking .
Then I reset my outback battery Monitor .
Every 2 months I check all the battery’s.
The battery’s are new about a year old , and don’t use much water .
I’ve only added 3 16 oz bottles of water to 16 battery’s this year .
‘I use about 10 to 15% of my capacity every day .
I think my absorb is set to 58.56 and end amps are 8 amps .
Float is 54
eq 60.7
My battery is 16 gc 215 sams club battery’s 430 ah
I switch in to float at about 450 watts going in .
This morning I was down at 85% by 1000am I was @89% then I maxed out at 2400 I was in mppt bulk .
I was using 300 plus watts running 30 or so recessed lights the flat screen TV 2 68” fans a radio small frig Mikita battery charger ?
im trying to burn power .
I’m at 100% buy 1230 or 100 pm should I turn off the array ?
I could turn off 2 of my 5 strings of panel for less charging ?
I’m at the cabin 3 days a week and leave with the battery’s at 100% .( I turn off the system )
I could leave some out side lights on to burn more power over night ?
Of course 4/5 months of the year my panel are covered with snow for weeks at a time so I go 2or 3 days and charge with a generator to 100% and turn off the system for 2/3 weeks . I get down to 0 o in side my battery box if it’s cold out side .
If I run the system 3 out of 7 days a week . Dose it matter if when I’m at the house I charge to 100% ?
I’m not thinking there is a problem with the system .
I know I’ve seen 3600 watts before , but just not today .
How should I run my system . I’m still new to all this but I’m starting to under stand some of it .

mike95490 · July 2019

you don't need to leave lights on to drain batteries. The more you use them, the faster they die.

My guess from your light water usage, you may be undercharging a bit

wellbuilt · July 2019

Hi mike , I’m using about 10 to 15% of my battery capacity now , should I cycle the battery a little deeper ?
Bill said not to reach 100% every day , so how should I go about that ?
If I should not use more power , then should I turn off some solar strings ?
It is cool here , and even if it get, warm 80 90o the house stays 67 70 o all the time .
I’m at the house on weekends so my system is off 4 out of 7 day a week or more .
Last time I checked the battery cells I was a little low but not enough to water them ,
next week the cells should take about a oz of water each .
Next week I will drop the battery to 80 % and turn the solar on at 1100 and see how much solar power I get .
My fm80 is set to 40 amp solar input but I have never seen more then 25 amps in , I think this is because I’m all most charged by 12noon .
I am getting a better understanding of all this stuff thanks to you bill LH Dave rick and the rest of the guys . I can’t thank you enough .
John

Estragon · July 2019

My first year (active use was ~5 months) was similar in water use for 12xL16s. They use more (~2 gallons/yr) now 5 yrs on.

The only time I see anything like full pv output is if the bank is quite low and the sun comes out near noon. Normally bulk is done well before then, so as Bill explained, charging current tapers off naturally. I never "burn off" power as I figure there's a certain amount of wear and tear on controllers and inverters doing so. I do run loads like water pumping with the extra daytime solar though.

mcgivor · July 2019

There are various ways to limit the charging, shutting down everything is probably the safest, 4 days of self discharge wouldn’t amount to much and dramatically reduce cycles. Another world be to raise the end amps or lower the voltage but juggling settings can become confusing. If it's possible to fully charge before leaving for the 4 day absence I would be inclined to shut everything down with the batteries isolated, not much could go wrong that way.

wellbuilt · July 2019

Hi estragon , I will drop a string or 2 of panels and see how that works for now .
Using 3 string of 3 295 watt panels should still give me 2100 watts +- I’ll see how it go’s .
Just when I think I’ve got something figured out , I realize I don’t know anything thing .🤣
I will break out the chicken blood and feathers and continue chanting John

mike95490 · July 2019

Battery life is a fine balance between under charge (sulfation) and over charge (+ plate corrosion) Getting it just right is tricky, Some say to not get to a complete charge daily, but I'd modify that "For summer only". Winter is often demanding enough to require all the charge you can get, or even resort to running the generator. The only thing to be sure of , is that batteries will eventually die.

wellbuilt · July 2019

Hi McGivor , my end amps turn to float at 8 amps , I was told by another source that if my battery’s where down to excepting 600 watts I could figure they where fully charged .
At 8 amps my battery are only excepting 450 watts with a 200 watt draw from the system .
At 600 watts going to the battery’s my amps are around 11 amp if I remember correctly .
When I turn my system on after I’ve been away for a week my resting voltage is at 51.7 so 5 points above full charge ?
I was thinking the system was not calibrated correctly .
Should I turn up my end amps ?

wellbuilt · July 2019

Hi mike , at what point do battery’s start to sulfate 80% 90% 99% is it ok to let the battery sit at 90/95% for 5 days .
Or is it better to get to 100% ? .
I do check it with a Hydrometer but it’s hard to get a good consistent reading .
I bought a hydra volt Hydrometer which gives me a consistent readings and is temperature compensated but also seams funny that it gives good consistent reading all the time . I think it may be a false security . But I’m running with it .
I’ve been killing the same type of batteries in a different system for four years .
The system just floats year round and I pump water with it every couple weeks The batteries use very little water even after four years and I run a small pump 300 watts for an hour or so and the voltage pops back up to 100% .
I was snowed out of the place one year and left with the battery low we escaped in a blizzard and didn’t go back until spring .
I eq the battery’s and they have been chugging along for 2 years now .
My POC charges 40 bucks a month just to be hooked to the grid so if I get 3 years out of this set of battery’s I’m good with that ?
My neighbor has been running on 12 go battery’s for 10 years and just replaced them , he told me that they where down to 60% capacity ?
It seams pretty good . I’m still chanting and call in a witch doctor .

mcgivor · July 2019

As soon as a lead acid battery becomes less than 100% fully charged sulfation begins, soft crystals form but this is normal, it's the amount of time those crystals, which are easily broken down by changing, are allowed to acclimate and harden, if left for 4-5 days there would be minor " nomal " accumulation which would be easily broken down with a 100% charge, left too long however, 3 months + an equalization may be required as the crystals begin to harden and need an overcharge to break them down.

Estragon · July 2019

I have end amps set to ~1% of capacity on my banks, which still seems to be working well. Supposedly as they age, they may not get to that low and I'll need to raise it a bit, but not so far. For 430ah, that would be 4-5a.

I have skip days set, and the lightly discharged 12v bank goes straight to float most days. The more heavily used 48v bank normally gets down to rebulk voltage so rarely skips while I'm here.

BB. · July 2019

The theory is below 75% state of charge and not charging or discharging, that is when the hard black crystals start seriously forming.

However, if the battery back is actively cycling daily, even 50% to 80%, they will not sulfate.

And you can charge over 90% SoC once a week (and one major vendor said once a month... I guess doing an EQ cycle at that time).

In general, once the soft fluffy gray lead sulfate forms into black crystals, those crystals are dead material and shed during an EQ cycle.

Bill

wellbuilt · July 2019

A lot to think about here , I guess in going to figure out a routine so my batteries don’t charge so much

wellbuilt · July 2019

Thanks guys

wellbuilt · July 2019

Hi fellas , I used 12% of my battery last night by 530 am .
I left just 1 string of 295 watt panels on this morning . At 200 pm I’m @ 92% and I’m bringing in 700 to 750 on this string.
Is it better to turn off all my solar production for the day and not start a charge cycle?
That would leave me with 70 % charge +- tomorrow morning .
Or just charge the battery with some solar . Please advise thank john

Estragon · July 2019

IMHO it would be better to charge than not. 70% isn't bad, but with my luck the weather would turn on me.

wellbuilt · July 2019

Thanks for the reply Estragon
It looks like the weather is going to turn after lunch my battery is down at 76 % so I will have to charge up this morning .
Charging to 90% is going to be tricky on weekend trips , it’s more doable for 3 or4 day stays .
I’ll have to figure out a system of doing this.

Dave Angelini · July 2019

I do not do anything but tell my clients to go to full as often as possible. They have large solar banks that go thru absorb quickly and don't spend allot of time getting to setpoints. They get as long of a battery life as anyone else, in my opinion.
This is over 200 offgrid power systems now, over decades.

There is too much else to do in life, in my opinion than to play with battery strategies. Who knows maybe there is something to skipping days and a possible month of battery life is gained.

Use them or lose them and fill them up.

wellbuilt · July 2019

Thanks for the reply Dave , I won’t sweat it to much , I’ll just cut back a little when it’s convenient .

Dave Angelini · July 2019

Just follow the battery specs and set-points. Do the maintenance and probably 10 years or so from now you will notice a loss in capacity and it will be time to replace. I have rarely heard of any of my folks who do the basics having a battery failure. You just can't skip it, ever!

wellbuilt · July 2019

Thanks Dave, I chyecked battery’s this morning I was at 95% on the mate I checke 8 out of 16 battery’s SG was 1.275 to 1.280 on all but on battery . I had one cell on one battery 1.265 or a bit more .
I charged with the generator this morning got up to 100% and left for home .
I still have good water over the plats so I left it for another month .

Dave Angelini · July 2019

Last point from me, be careful on waiting a month. There will be a time when you start using more water. Best to check and top the battery every month. I know they are new but with 2 strings you need the extra effort. Do an EQ and the next day top them off, or something similar. Where are you that you have to run a genset this time of year please?

wellbuilt · July 2019

I have been turning off my system when I’m not there, I had to work today.
So I wanted to get my bank full before I left , so I charged with the generator a left for work at 800 am battery’s where at 88% at 530 am .
Should I leave the solar charging when I’m not there?
I don’t think I will be back up for 2 weeks .
and haven’t really decided how to run the system yet
I did not read your # 26 post until I all ready was deep into a charge this morning .
So should I just leave my system in float for the week if I leave early in the am ?

Solar panel production

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