Roof mounted solar panel trickle charger for 2 batteries?

[Zimm]

My new plan for my shed is to put a roof mounted solar panel on and some type of dual bank trickle charger to keep my 2 tractor batteries topped off. Basically a solar powered battery tender. I'm lost on finding a simple system. I don't want the tiny dash board mounted vehicle ones, and the marine systems are way too big. I just want to keep the 2, 12 volt tractor batteries topped off in the off season without having to run power to the shed.

 

[12VoltInstalls]

So you need to have a pair of ‘small jumper cables’ wired to the output of a ~20 amp solar charge controller from at least 100W of solar panel. And always turn off solar panel disconnect before disconnecting one or both of the batteries.

see the WindyNation kit on Amazon for ~$160

 

[Zimm]

My follow up question is will a solar charge controller keep 2 separate batteries topped off? seems like it'll overcharge one of them. Maybe dual 20 amp chargers and 2 panels?

 

[Rednecktek]

I just use the Load ports on my cheaper PWM controllers, a panel, and a small 35Ah battery for control voltage. Set the low voltage cutoff on the Load ports to higher than the control battery needs to be (I set mine for 12.4v cutoff) and just clamp it to the battery terminals or (like I did) wire in a couple SAE plugs to the mowers and a plug on the end of the Load ports. Since the Load ports and the control voltage battery are always the same voltage, if the main battery is being charged then the mower battery is being charged. When winter hits and there isn't enough sun to charge, the Load ports get shut of so they don't drain the control battery. When the sun comes out and the control battery starts charging, it'll kick on the Load terminals and start charging the mower.

Since the Load ports are only good for 5a on my cheap controllers, it's a native trickle charger and can keep both my motorcycle and my riding mower fed at the same time in theory.

Now in reality, it never worked because I get so little solar radiance that the batteries would all self discharge before the panels could get enough sun to recharge anything. Yes, so little sun that the power draw of a PWM SCC has killed 120Ah batteries before, even with 200w of south facing 45deg panels.

 

[12VoltInstalls]

My follow up question is will a solar charge controller keep 2 separate batteries topped off? seems like it'll overcharge one of them. Maybe dual 20 amp chargers and 2 panels?

Dual SCCs would be ‘better’ empirically but in practical terms they are both similar batteries.

Being lead acid batteries, you would be charging/floating to ~13.8V+ to charge nominal 12V batteries that probably “rest” around 12.6-12.8, maybe even 13V.
13.8V is roughly the static no-load charging of a vehicle alternator while the motor is running so no practical harm will come anyways.

Just do it

I get so little solar radiance that the batteries would all self discharge before the panels could get enough sun to recharge anything. Yes, so little sun that the power draw of a PWM SCC has killed 120Ah batteries before, even with 200w of south facing 45deg panels.

For most regions- even here in Vermont- to merely maintain a battery or two 200W of panels should work.
But one would have to be diligent about snow removal, OR do what I do and simply locate the panels vertically oriented; other than freezing rain (rarely) you will always be able to receive some irradiance.

 

[Zimm]

Okay so my shed is done and I'm ready to buy a solar kit. What's a good system that will be a few hundred watts (2 panels maybe?), an inverter to run my dual battery trickle charger, and a 12 volt light? I have a good amount of roof (12x16 shed) that gets full sun all day long.

I'm eyeing something like this Renogy 200 watt kit with 700 watt inverter. https://www.renogy.com/new-200-watt-12-volt-solar-premium-kit/

Or since my roof is so big, maybe one larger panel instead of two smaller ones?