12 volt system questions

[Newfiejeff]

I have a new 12 volt system:
Xantrex XC2000 inverter/charger
Victron Energy 150/85 charge controller
Two 6 volt 400AH lead carbon batteries
Two Longi 355 watt solar panels and One Longi 350 watt solar panel all connected in series

Question:
1) I have starting in the fall as the sun gets lower in the sky partion shading from some branches no on all of them at once but one at a time as the sun moves across. I am going to move them next year but wondering in series is that ok or should I connect in parralel?
2) It seems that I yield about 1500 to 2000 watts a dead to float the batteries. Based on my system how many more batteries should I get?
3) I had a small bar fridge running all summer and no issues but was yielding about 3000 watts, but since less sun I disconnected it.
4) What should I change/add,etc to my existing system to make it that much better?

I welcome all feedback

 

[sunshine_eggo]

1) partial shading can be devastating. Parallel may be a benefit, but maybe not. WHAT ARE YOUR PANEL Voc and Imp VALUES?
2) 1500 to 2000Wh/day? I don't understand why you're asking the question. What is the max charge current of your batteries?
3) Okay.
4) Impossible to answer. "Better" is a system that meets your needs with a little in reserve, but doesn't result in excessive cost. How is your system not meeting your needs?

 

[Newfiejeff]

see attached for panels specs, it’s number 2 and number 3

2) I am yielding about 2000 watts per day from float of the previous day to the next float of the current day. I assume I am using about that much each day. Not 100% but I think the max charge is 65%.
4) my system currently meeting my needs but I am a little cautious or not generous in what I use. If I have a sunny day then all is great if I have a rainy day my one day use is all I get then I have to turn on the generator to charge the batteries if the next day is rainy, basically no reserve.

So if I have no reserve and I used installed extra batteries like two more than am I going to need another 3 panels?

 

[DThames]

Based on the comment about using all reserve on a rainy day, if you double your battery size, you might get closer to a two day reserve, but with a power drain at night, maybe less than two days. Anyway, you might double your battery and double your panels, if that is an option. I like the idea of a LOT of panels. After your rainy day, you will still want to power loads AND charge the battery at the same time. Or if you get only 2 or 3 hours of sun the next day, you want to get as much into the battery as possible. So being able to run loads and charge or charge fast is attractive to me.

 

[12VoltInstalls]

like the idea of a LOT of panels

That offers hope. Hope is an important component of a dependable system.

So if I have no reserve and I used installed extra batteries like two more than am I going to need another 3 panels?

So what latitude are you? Locale?
A wildhat guess says you need two more batteries. I would add four, however, if you can spend for that. That’s reserve.

Adding panels should be done based on what you need to recharge 100% in one day all else being equal. So if 3 panels recharge a pair adequately, then yes, a second string of 3 sounds appropriate. If, however, you are northerly latitude then for winter a total of 6 panels 3S2P may not be adequate; you may want 3S3P to factor for low sun hours and/or overcast periods.

It’s not a “rule” per se, but here in northern Vermont USA the winters want me to have 4 to 5 times the panel wattage required in July, and with our typical extended cloudy days for weeks on end in December that isn’t always enough. But following the 400% more panels than needed you’ll be ridiculously overpaneled more than half the year in my locale.

I’m hoping that thought process is useful as you think through your situation.

 

[DThames]

That offers hope. Hope is an important component of a dependable system.

So what latitude are you? Locale?
A wildhat guess says you need two more batteries. I would add four, however, if you can spend for that. That’s reserve.

Adding panels should be done based on what you need to recharge 100% in one day all else being equal. So if 3 panels recharge a pair adequately, then yes, a second string of 3 sounds appropriate. If, however, you are northerly latitude then for winter a total of 6 panels 3S2P may not be adequate; you may want 3S3P to factor for low sun hours and/or overcast periods.

It’s not a “rule” per se, but here in northern Vermont USA the winters want me to have 4 to 5 times the panel wattage required in July, and with our typical extended cloudy days for weeks on end in December that isn’t always enough. But following the 400% more panels than needed you’ll be ridiculously overpaneled more than half the year in my locale.

I’m hoping that thought process is useful as you think through your situation.

Additional chargers might be required as the battery bank grows or as the need to more quickly charge is addressed. I have two all in one units with something close to normal panel sizing and a third charger that I can switch on if I want to speed things up or if the solar conditions are poor.

 

[Leeds]

Have you verified that the panels have bypass diodes installed? If you pop open the back panel on them you should several diodes that are strung between the two wires that exit the box.
If your panels are missing them then any shading on any panel will be the same as that shading on all three panels simultaneously.
(This is likely not an issue but it's simple to check and correct)

 

[sunshine_eggo]

see attached for panels specs, it’s number 2 and number 3

Consider that when they are in series, they all operate at the lowest current panel, so the 355W panels are going to run at the 350W panel current. Not a big deal in this case, but worth noting as you upgrade things.

2) I am yielding about 2000 watts per day from float of the previous day to the next float of the current day. I assume I am using about that much each day. Not 100% but I think the max charge is 65%.

2000Wh - it's good practice to keep your units straight.

I asked about the charge rate because lead-acid batteries need a range of charge currents to stay healthy. Brands vary. It's important that your actual charge current falls in a typical range of 0.06 - 0.15C or 6-15% of capacity. In your case, 24 - 60A. Your particular battery model may indicate different criteria. Charge at too low a rate, and it encourages sulfation. Charge at too high a rate, and you stress the materials and shorten their life.

so if you add batteries, you may be forced to add panels.
If you add panels, you may be forced to add batteries OR decrease your maximum charge current (Victrons can do this).

You add panels to increase your DAILY energy availability.
You add batteries to increase the time available between charges.

In most locations, it can be very difficult to keep a system's scale appropriate and never need to run the generator.

This tool can offer a prediction of how often your battery will fail to be fully charged:

JRC Photovoltaic Geographical Information System (PVGIS) - European Commission

Photovoltaic Geographical Information System (PVGIS)

re.jrc.ec.europa.eu

Entering my system:



Shows that 2.07% of days will result in my battery dipping below the prescribed 40% level (I'm using 60% of my NMC battery capacity).

It's not exact, but it factors in historical weather and available solar for your location. You can define a custom usage profile for how many Wh you use for each hour of the day. It will NOT factor in shading of any kind.

 

[Newfiejeff]

Newfoundland Canada is the location, see attached battery specs.
They are lead carbon in a gel not lead acid.

 

[sunshine_eggo]

Newfoundland Canada is the location, see attached battery specs.
They are lead carbon in a gel not lead acid.

You're going to need some hefty tilt to harvest in the winter.

No spec attached.

Lead-carbon batteries are lead-acid batteries with a carbon additive.

 

[12VoltInstalls]

You're going to need some hefty tilt to harvest in the winter.

Yup. I would just add a ton of panels and mount them vertically: no snow accumulation

 

[Newfiejeff]

See attached, they are a gel compound, no maintenance and nothing to open.

 

[Newfiejeff]

So trying to understand. If my current panels on a sunny day is putting out great power and to see on my SCC that the power going to the battery is like 45 amps then by doubling my panels would put it to 90 amps which is over the battery recommended charge rate. Then I would have to reduce the charge rate on the controller to match the batteries. So then on those days the extra panels are not really doing anything .
correct understanding?

 

[12VoltInstalls]

Then I would have to reduce the charge rate on the controller to match the batteries. So then on those days the extra panels are not really doing anything .

Sortof. The overpaneling is provision for getting some charge on overcast days and getting the fullest capacity charge in the least amount of time.

Newfoundland Canada is the location

And you will probably not see the same output with the short days.

So the panels will be ready and willing for good sun days, and give you some charge on certain overcast days, and basically not be inputting anything late spring, summer, early fall because overall production will be higher than your demand.
That’s how I operate- overpaneled half the year, and on sunny days in winter.

The extra panels are headroom. Like in your car, say it has a 175hp motor. So you use 30 to 80- sometimes 100- or so horsepower much of the time- the other horsepower headroom isn’t used but it’s there when you need it to climb hills, pull out in traffic.

 

[sunshine_eggo]

See attached, they are a gel compound, no maintenance and nothing to open.

Still lead acid. Just GEL type.

You'll need a smart battery sense, smartshunt+temp sensor or BMV-712+temp sensor to interface with your MPPT and apply temperature compensation.