Another solar question???????

Today I purchased 8 AGM GPL CT6 Lifeline batteries for solar storage. How many 670 watt solar panels would I need to keep the battery bank charged?

Nearly none if you don't draw any power from them. You need to determine what your daily KWH consumption will be, and then take into consideration hrs. of sunlight available each day, to replenish them.
Loren

It takes about 1/4 amp per battery for maintenance. So you need 2 amps minimum for 8 batteries.. A solar panel only works for 1/6 -1/4 of the day. So 6 X 2 comes to 12 amps and if 12 volt panels - that comes to around 150 watts.

Why AGMs?

JDEM= "Why AGMs?"

The battery bank is going to be install in my enclosed cargo trailer and I was concerned about Hydrogen gas build up from the venting of the Flooded batteries. I could picture of a fireball engulfing everything.

WOWWWWWWWWWWWWw Greg, those are great batteries and AGM to boot which I told you I would recommend and would use when I upgrade YOU DONE GOOD but your wallet got lighter lol

Those are rated at 300 Amp Hours of energy storage so if wired in series parallel with four parallel banks of two in series that's a whopping 1200 Amp Hours !!!!!!!!!

So, you ask "How many 670 watt solar panels would I need to keep the battery bank charged?"


CORRECT ANSWER It depends on how much you discharge them which requires an energy audit.


Typical light duty use may be water pump and vent fans and small electronics and charging and that may well be less then 100 Amp Hours per day. If that were the case, heck a single 670 watt panel, subject to location and sun duration and tilt or flat panels, will most likely get you by.

FYI I run a small 120 VAC extra fridge 24/7 and a CPAP all night and usual fans and water pumps and electronics but no microwaves or hair dryers or AC (yeah right) via my Inverter and my 715 flat roof mounted solar watts (subject to sunlight) typically has my batteries (four 6 volt Trojans 450 Amp Hours) re charged to 100% SOC by early to mid morning SO THATS ALL I NEED.

Now if you wire up an Inverter (12 VDC to 120 VAC) and started using high energy appliances like maybe a microwave NOW YOU NEED MORE SOLAR


BOTTOM LINE PURE GUESS based on what you have told us so far and your whopping 1200 battery amp hours


1) I would start out with TWO of those 670 watt panels (even if one gets you by subject to loads) and if you need more you can add on later IT ALL DEPENDS ON YOUR LOADS AND SUN LIGHT AND TIME AND TILT ANGLE OR FLAT

2) I would use an MPPT solar charge controller but with 1340 solar watts of panels that requires OVER ONE HUNDRED AMPS !!!!!!

3) To make wiring easier I would use a COMBINATION INVERTER/CHARGER versus two separate pieces of equipment and wiring (IE a separate Charger and a separate Inverter) Take a look at Magnum

IMPORTANT NOTE when wiring all those batteries in series/parallel LOOK AT THIS WEBSITE as it makes a difference how they are wired: http://www.smartgauge.co.uk/batt_con.html

NOTE this is going to require huge copper cables you know

AGAIN ANSWER IS IT DEPENDS ON YOUR LOADS AND HOW THE PANELS ARE MOUNTYED AND SUNLIGHT TIME AND ANGLE

But Id start with two of those panels as a pure educated GUESS even if one gets by fine to allow for future expansion

John T Again retired EE but NOT a solar expert
Connecting multiple batteries

John T. Yhanks. I just bought the Midnite Solar Classic 150 Charge Controller 150VDC Input MPPT from a solar place across the road. I'm watching videos on u-tube about this controller. Looks like it might work pretty good.

As for the number of 270w panels...I was thinking of starting out with 4 or maybe 6.
Are these panels any count???

Greg, Now that you say 270 watt panels Id install at least three but 4 to 6 gives you more energy harvest ability HOWEVER the answer still depends on your energy requirements ?????????

FWIW I think Renogy is a decent brand. Some gents like Mono but mine are Poly and work fine.

On a solar charge controller, don't forget in addition to the input voltage the charging capacity needs to be adequate. If you had lets use four 270 watt panels and were charging at 13 volts that's 83 charging amps meaning a 100 amp controller

When connecting multiple panels parallel means less of a problem when partial shading is present but in series there's more voltage so less current flows down to the controller. My three 245 watt 24 volt panels are all wired in parallel

I like AGM because there's less venting concern of corrosive potentially explosive gasses then in conventional flooded lead acid YOU CHOSE WISELY

Don't forget you need a good (Id use Pure Sine Wave PSW versus the cheaper Modified Sine Wave MSW) Inverter and smart 3/4 stage charger but as I mentioned better yet a combination Inverter/Charger like Magnum makes

John T Hope to meet up on the road some day. Ive been dry camping the last 2 weeks and will the next few and my batteries stay charged fine yayyyyyyyyyyyy

AGMs require venting too.

I have a lot of solar panels from Renogy. Good prices and seem to be as good quality as any other panel I have ever owned.

I don't use MPPT controllers on my setups. No measurable advantage over the cheaper PWM types where I live and my array voltage is the same as my battery bank voltage.

On one setup, I had a $450 Outback MPPT 60 amp controller. It burnt out after 5 years. I replaced it with a pair of 30 amp PWM controllers for $12 each and it works just as well. I also like having two controllers so if one fails, I still get some charge.

JDEM- I understand your statement. My cargo trailer has a roof vent w/o a fan. The AGM batteries don't emit near the hydrogen that flooded lead acid batteries do, plus the AGM's require less maintenance. Am I correct?

I appreciate everyones help on this. I am a Newbie to this solar stuff.

AGMs have terminals that seem to corrode less over time and yes - emit less gas to free air unless overcharged.

I am not "anti-AGM." Just don't see any benefit when it comes to solar banks. They do not last any longer then standard FLA batteries yet cost a lot more. Sometimes, they fail earlier then the cheaper FLAs. Was a big problem when they first started getting used in solar banks because the "equalization" charge mode would ruin them.

You did not research and plan prior to purchasing panels and batteries ?

Lead acid batteries wether they be flooded starting , deep cycle flooded , gell or AGM. They should not be operated from 100% down to 0%.
Out of 1200amp hr of flooded deep cycle , using 400amp hr is about mad if you want long battery life . The AGM’s will take more abuse and discharges down to 50% prior to charging .
It is like having a 1200gallon water storage tank but only being able to use 400 or 600 gallons of the total capacity .