Help Me Sort Out These Off-grid Concepts

ETS1001 · September 2021

Hi There,

The more I research, I more I find out what I don't know and end up with more questions. I feel like I need to start from the beginning Just some background, I have an off-grid house with existing solar panels, battery bank, charge controller and inverters.

Concept 1: The main purpose of a solar array is just to charge the battery bank via the charge controller. True? False? It depends?

Concept 2: If battery bank is at 100%SOC, excess power from the solar array during the day is not used to power appliances via the inverters?

Concept 3: Too much solar can overcharge your battery bank? (this is what I've been told by a vendor recently)

I guess what I'm getting at is that I want to expand the system to run a freezer or additional fridge, run AC, charge my car, etc.

Without getting into a ton of detail, this is what I have:

1,980 Watts total solar power
(2) 5500W inverters - 48v
(1) Outback charge controller 60A
300Ah Lithium battery bank (12) 100Ah batteries. each battery has its own built-in BMS.

Currently, depending on which on-line calculator I use and my in-line power meter, I come up with 10-12KWh usage per 24 hours.

Is there an 'Off-grid for Dummies 101' book out there?

Thanks,
ETS

Dave Angelini · September 2021

1 The array is there to charge the batteries and power loads during the day. The day is when you can try and charge the car. You might be light on solar for that. Always charge the battery first for the night, then power large loads.

2 Wrong see 1.

3 Definitely yes and the battery maker should have given you set-points for the FM60 to prevent overcharge. Also need set-points for the inverter/chargers. They are Outback?

Good Luck !

Photowhit · September 2021

ETS1001 said:

Concept 1: The main purpose of a solar array is just to charge the battery bank via the charge controller. True? False? It depends?

True + lol.

The array is a source of power to charge your battery bank, + run loads during the day. (See charge controller 'float' mode below)

ETS1001 said:
Concept 2: If battery bank is at 100%SOC, excess power from the solar array during the day is not used to power appliances via the inverters?

False, in fact we even have a couple terms for running large loads when the batteries have fully charged. 'Load shifting' and 'opportunity loads' once you've lived with solar for a while, you will realize it's nice to run those heavy loads from the the array, with the batteries really only adding a momentary boost to start large loads.

So many will like to run things like washing machines, vacuums, shop tools, while the sun is out and the batteries fully charged. In addition, you might find running such things as a water heater or preheater, during this times works out well. Again see battery charging 'float' mode below.

ETS1001 said:
Concept 3: Too much solar can overcharge your battery bank? (this is what I've been told by a vendor recently)

Yes and No... A vendor that just said that without an explanation, I wouldn't do business with again.
If you had an array hooked directly to your battery bank, certainly! Over charging will kill any battery bank pretty quickly.

A properly designed system with a god charge controller, set properly, should handle considerable 'over paneling'. The FM60 may be showing it's age at this point, but lithium batteries can usually handle a very high charging rate. It's one of their advantages.

ETS1001 said:

1,980 Watts total solar power
(2) 5500W inverters - 48v
(1) Outback charge controller 60A
300Ah Lithium battery bank (12) 100Ah batteries. each battery has its own built-in BMS.

Currently, depending on which on-line calculator I use and my in-line power meter, I come up with 10-12KWh usage per 24 hours.

In most areas of the country, you will want a larger array to handle a daily load of 10-12 kWhs.
Perhaps you are in the sunny southwest or have miss calculated your daily loads. In general I wouldn't count on a properly angled fixed array of 1980 watts to produce more than about 1550 watts ever sunny hour 2-3 hours either side of 'solar noon', most areas of the country have an average of 5-6 hours of direct sun in the summer and taper off towards winter. In the Southwest perhaps 7-8. That would leave yu in a charging deficit in winter assuming the same usage, and perhaps even now...

So I was going to leave you with my 'canned' reply for lead acid battery charging, but you are using lithium, so let me just post the float mode info;

FLOAT;

Once the Controller has determined the battery is fully charged it reduces the voltage to a point where very little current is flowing to the battery. This will prevent the battery from over charging and heating up.

While in 'Float' the charge controller watch for voltage drop, which would indicate a load. If the voltage begins to drop the charge controller will allow as much current to flow from the panels/array to compensate and maintain the voltage. If the voltage can be maintained, the load will in essence be running directly off the array/solar. If the voltage drops below the preset float voltage, the controller may start a whole new cycle if it stays there for a period of time.

ETS1001 · September 2021

Dave & Photowhit,

Thank you for the replies. Your info is inline with my research during the past 6 months. I'm not sure what the heck this on-line vendor was talking about. I guess they don't want to sell me new panels and gear. Maybe I can work with another 'Designer' there.

BTW, I worked with the battery vendor to adjust my absorption and float values in my outback MX60. The inverters are old Xantrex 5500's. I'm looking to expand my system so I can run an additional refrigerator, maybe air conditioning, charge my car longer, etc.
Also, I live is San Diego County where there is no shortage of sunshine.

littleharbor2 · September 2021

With a pair of SW5548's you shouldn't have any trouble running an additional refer., provided the balance of your system is well matched.

Vic · September 2021

The only drive-by comment that comes to mind, is, that even with Li batteries, this system does not seem very balanced -- 11 Kw of inverter, 1980 W STC solar, and even with Li batts, "only" 300 Ah ...

MO Solar, please, FWIW, IMO, VIc

ETS1001 · September 2021

Hi Vic,

The system was designed and put in over 10 years ago. Ive been here 6 months. I'm trying to upgrade and improve as I can. The 12 Li batteries replaced 8 Trojan L16 FLA batteries that were 7 years old. There is also a new Kohler 12kW propane generator connected to a ATS.

One of the features I wish I had is battery and usage monitoring. The only thing I have is the battery voltage reading from the inverters. Maybe at least a Victron Smart shunt? That would be easy to install.

wellbuilt · September 2021

say dose any one know how smart the victron smart shunt really is ?

I use a out back Battery Monitor and it doesn’t seem to be very accurate I reset it every few weeks but is a hassle

Dave Angelini · September 2021

San Diego? My brother Phil (USNR) told me about a guy like you in SD? You the same guy? Ex Navy? Same last name as me?

Anyway since you are new and if you are going to do this and want expansion capability with excellent monitoring, a networked power system is the way to go. Either Outback or Schneider has really nice cloud monitoring with smart phone and Web graphics that make offgrid easy. The screen below can be for many clients or just private. Each can have settings changed and lot's of graphics.

Image: https://us.v-cdn.net/6024911/uploads/editor/g0/3d8tt6e2q51q.png

Dave Angelini · September 2021

wellbuilt said:

say dose any one know how smart the victron smart shunt really is ?
I use a out back Battery Monitor and it doesn’t seem to be very accurate I reset it every few weeks but is a hassle

Are settings that you programmed staying the same or changing? Maybe it is just bad? Accuracy can be a moving target with older flooded batteries as the programming is going to need to be updated. Resetting does what?

wellbuilt · September 2021

Hi Dave
the setting seam to stay put . But over time the voltage and the100% full dosent seam to line up .

It my understanding that the out back fmdc monitor resets every time the controler runs thru absorb .

If my sg reads a little low at full 100% charge and gos to float , I reset at dark (end of float ) for the day @ 54 volts
and the following days or weeks my 100% matches the voltage and my sg stays 1.275 or above on all cells .
Then drifts off slowly .

I bring in about 3500watts or so with my 90% lite blinking on the fmdc monitor after a 2 hour absorb
then I go into float at the end of the day I have brought in 5500 watts ? I’m not using the power ? Sooo it seams funny
I un plug the fmdc from the mate at full charge and the reading seam to line up ?

ETS1001 · September 2021

Hi Dave, I could be that guy, you got the Navy bit right. Wife had guests from work over a couple of months ago. I never caught his last name though. First name was Andy. I'm going to be looking into Schneider, that is what a local contractor is recommending. I'll have to do more research. Thanks.

Photowhit · September 2021

wellbuilt said:

say dose any one know how smart the victron smart shunt really is ?
I use a out back Battery Monitor and it doesn’t seem to be very accurate I reset it every few weeks but is a hassle

I'm not familiar with Victron's shunt based monitor, but have some experience with Trimetric. I even own ne somewhere...

Usually the problem is with the settings. Battery type, Battery bank capacity (which will change over time), With the Trimetric, you can also set some widgets to correct a perceived loss, even after checking all the settings. Sorry for being so vague, I haven't used mine in my current setup and it's been 7 years since I helped a friend with his, he hand his 4GC batteries as a 880ah battery bank, while configured are a 24 volt bank.

Photowhit · September 2021

Vic said:

The only drive-by comment that comes to mind, is, that even with Li batteries, this system does not seem very balanced -- 11 Kw of inverter, 1980 W STC solar, and even with Li batts, "only" 300 Ah ...

With a 48 volt system, it's a 14.4 kWh battery bank, so not tiny, In a very sunny location, and Lithium's great efficency. He might be okay, but yeah <2000 watts of array with a daily use of 10-12 kWhs, that's just a very cloudy day and 2 nights to 0.

wellbuilt · September 2021

My GC battery’s are 3 seasons old and don’t show any signs of loosing power . Hemmm

Dave Angelini · September 2021

ETS1001 said:

Hi Dave, I could be that guy, you got the Navy bit right. Wife had guests from work over a couple of months ago. I never caught his last name though. First name was Andy. I'm going to be looking into Schneider, that is what a local contractor is recommending. I'll have to do more research. Thanks.

Drop me an email (below) and I will ask him. He is out on one of the carriers doing trials this week. I remember he said out in the rural part of SD county.

Help Me Sort Out These Off-grid Concepts

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