Basic Solar question

[YGoHom]

I recently installed 400w with a Victron controller. It seems to supply all the power we need for our residential fridge, water pump, heater, lights, phone and pc charging, so that’s huge for us not needing to use the generator.
I’m just hoping that someone can give me a good idea of how the solar and battery sections relate? I know about bulk, absorption and float. I’m terrible with watts, volts and amps

[DavidM]

Looking at the left hand screen, it is showing 31.72V and 8.2A of solar input to the controller. That gives you a total of 31.72*8.2= 260 watts of solar input which is about what the display is showing. It is less than the rated 400 watts due to sun angle, clouds or shading.

MPPT controllers which this one is, take input solar voltage and convert it down to what the battery needs. The lower part of the left hand screen shows the voltage and current that is being sent to the battery which is 13.85V*18.4A= 255W. The difference in input wattage vs output wattage is efficiency losses. 5W is very good. It is in bulk mode which means that the controller is putting out all it can into the battery.

The right hand screen shows absorption mode which slowly raises the current to about 14.5 volts where it then switches to float to maintain the charge on the batteries. It is getting close to that point at 14.34 volts. The solar input is less than the left panel at 251 watts, maybe because the sun angle is lower. The solar output is 14.34*17.1= 245 watts, about the same efficiency loss as the left hand screen.

What kind of batteries is it charging. The screens indicate you are getting good performance out of your panels.

David

[YGoHom]

Thanks, David. Yes, it’s a Victron MPPT 100/30 controller , with 4 panels wired in series parallel, I believe the term is. 2 and 2. I have 2 6v 230ah batteries in series.
I’m in southern CA with full sun and no obstruction right now.
Great to know it’s working well. Thanks!

-Robb

[imnprsd]

Having a Victron bluetooth display on your cell phone is nice.

I recommend you forget about measuring watts and start thinking in terms of AMPS!

Your residential AC cycles on and off and probably uses 1.5 amps of AC power when it's running an 3-4 amps when it starts. So if you are concerned about battery power when traveling and boondocking, I recommend you set your frig thermostat to 45-46F and try to not open the door that often and try not to keep the door open that long when you want something inside.

Your 420AH FLA battery bank is good for 50% so you really only get 200-210AH.

Here's the rub. It takes about 10x more DC amps to run your AC appliance. For example a 2A AC appliance will roughly take 20A of DC power storage when using your inverter. And if you use this for 2 hours then you have used 40AH out of your battery bank.

At full charge, you have 200AH to work with, but that's only on your first day. Then for reasons I will not go into here, your next charge cycle will only leave you 180AH; and then after the next rapid generator charge cycle you may only get 160AH of useful battery storage.

...And last but not least, don't bother assum your EMS battery voltage meter inside your coach is accurate after you have been charging your battery and have not powered anything to it with a substantial load for at least 1 hour... but you can keep an eye on it. Basically, the best time to take a volt reading is at 5-6AM in the early morning, when the sun is not out (since you have solar panels); and at night when you go to bed... and you think you have a good voltage reading to estimate your available AH for over night use.

Here's the methodology I'm starting to use:

I will assume a 90% State Of Charge (SOC) when I go to bed; and a 50% SOC when I need to start recharging my house batteries (4-GC2-6V-Golf Carts) which gives me 40% of available battery AH.

So if I figure 420AH x 40% then I have 168AH to use, and again that's with a strong battery.

Solar helps, but you will find 400W will not keep you from using your generator.

Also, I recommend you set your inverter/charger or converter-charger to 20A if you have shore power and 3+ days at an RV park. This is because a slowly charged FLA battery will reach a higher SOC vs. a fast charge battery. ...But again your first day on the road will produce the longest use of stored battery Amp-Hours (AH).

Other's may use a different methodology to figure out battery useful storage, but thinking in terms of amps works far better then tracking watts. And BTW, 400W of solar is only good for up to 5A/panel and then you lose efficiency depending the percent of sunshine and angle of the sun in the horizon. Just read the amps your solar controller is putting out and then average it for the amount of sunshine you are getting that day!

[Elkman]

I found with my Lithionics lithium phosphate batteries that they charge 4x as fast as the lead acid batteries and these made the solar panel output much more effective. More battery charging taking place during daylight hours with the new batteries.

The solar charge controller will limit the charging output depending upon the type of battery it is charging. Not all chargers will have a setting for lithium phosphate batteries so this may need to be upgraded as well.