Solar: What is realistic?

jkjenn

Sometimes it helps when people share real world data.

I have not turned my batteries off since I had lithium batteries  installed in early April, because I wanted some real life observations. I have camped about every other week with electric hookups. I sometimes deploy the portable panel, but not frequently.

Last weekend, my T@b was parked at my brother's with rooftop solar, only. I left the batteries and fridge on, but the solar was all but useless due to cloudy and rainy weather. Driving home, the battery bank was partially charged, but it was under 50% Monday night. This has been a mostly cloudy week in W PA (pretty typical) and so I knew I was going to be completely draining my batteries for the first time.

The Lion Energy batteries, like most good lithium batteries, come with a BMS built into shut them down and protect them when they reach a certain point. That point varies by manufacturer. 

When I checked my batteries this AM, I learned that the BMS had shut them down overnight. The Victron app showed me that the voltage had reached 10.0v volts (That is the stated low voltage disconnect for the 10ah Lion battery.). Even the small amount from morning rooftop solar, with the sun in the east and the trailer pointing south/southwest, had provided enough power to charge the batteries sufficiently to turn the batteries on, again.

The current state of charge on the Vicfron, however, was now reading 100% with a current voltage reading of 13.29 (full sun.) I know full well that the state of charge is not at 100%, so I will be interested to see what kind of voltage reading I get when the sun goes down.

This time of year is as good as it gets for solar, and it is a mostly sunny day, today. Here are the readings I am getting. 

Portable 100w Renigy Eclipse with Vuctron Smart Solar 75/10, aligned with sun



T@b Factory Rooftop Solar (Sunflare 105w) mostly, but not directly in line with sun



Victron BMV

Denny16

The Victron voltage reading is the battery voltage plus the solar charging voltage.  You are correct Jenn, it is not the actual battery voltage.  Switch off the solar controller, and you should get an accurate battery voltage check, best done with the battery disconnect switched odd also, for the most accurate reading on the BMV display.
cheers

Horigan

On your last image your 100% state of charge voltage seems low.  I don't know what the setting should be for lithium, but when I added solar to my T@b with AGM batteries I had to revise my 100% state of charge voltage from 13.6V to 14.4V.  I would research what the full state of charge voltage should be for lithium and update our Victron app accordingly.  Then fully recharge your batteries with shore power, then re-sync your Victron to indicate when you're at 100%.

I'm sure others will chime in with more experience than me.

jkjenn

Denny16 said:

The Victron voltage reading is the battery voltage plus the solar charging voltage.  You are correct Jenn, it is not the actual battery voltage.  Switch off the solar controller, and you should get an accurate battery voltage check, best done with the battery disconnect switched odd also, for the most accurate reading on the BMV display.
cheers

Thanks, I am aware of this. I posted to show others what to expect, not because it was a problem. As an FYI, to my knowledge, I was the first T@b owner to install a Victron BMV and have used it extensively for long-term off grid camping.

Horigan said:

On your last image your 100% state of charge voltage seems low.  I don't know what the setting should be for lithium, but when I added solar to my T@b with AGM batteries I had to revise my 100% state of charge voltage from 13.6V to 14.4V.  I would research what the full state of charge voltage should be for lithium and update our Victron app accordingly.  Then fully recharge your batteries with shore power, then re-sync your Victron to indicate when you're at 100%.

I'm sure others will chime in with more experience than me.

I will wait until I am confident I have 100% SoC and then do a manual calibration. I will be camping with shore power this week.

Maybe I wasn't  clear, but I purposely let the batteries drain so I could know what to expect. Thankfully, everyone went according to expectations.

I shared the data so people would have a ballpark realistic expectations of how a mostly sunny day will yield with solar. It appears to have recharged to around 17% today with 205w of solar.

Verna

Great job, as usual, @jkjenn!  Thanks for the info. 

Denny16

    OK Jenn.
cheers

Tabnero

heading out next week for 9 days will chime in at that time.