Math Check-Number of PV Panels (Watts) to Fully Recharge a standard 100Ah (1280Wh) LFP Battery?

[PopDBop]

I'm operating in an area with an average 5.5 peak solar hours per day (panels tilted to the area's latitude facing 180° due south).

So, if I assume 95% charging efficiency of the MPPT solar charge controller, then I get the following for numbers of Watts/Panels I need to fully charge a single 100Ah/1280Wh LiFePo4 battery:

(1280Wh/5.5h)/95% efficiency = 245 Watts, or ≈ 250 Watts of PV panels.

Correct?

Of course, I'm not draining and recharging that battery 100% every day. But if I were, I'd need 250 Watts of panels.

If I was using about 50% capacity daily, then I'd only need 125W of panels to keep that same battery recharged. At 80% usage (keeping battery state of charge between 10% and 90%), I'd need about 240W of panels (.8 * 250W= 200W).

 

[MisterSandals]

(1280Wh/5.5h)/95% efficiency = 245 Watts, or ≈ 250 Watts of PV panels.

Math looks good.

How does this work in the winter when your solar hours are reduced?
What SCC do you have that operates at 95%?

Panels are cheap, build up your array as much as possible. Knowing what SCC you have may allow others to elaborate on how to do this best.

 

[PopDBop]

Works fine in winter months (15% lower irradiance) at my latitude. My main power usage is AC, which I don't need in the cooler months anyway.

You have to go on the assumptions provided. MPPTs claim even higher efficiencies than 95% I'm using. I'm not designing a specific system per se, not yet. Just developing a general rule-of-thumb sizing metric for my location.

So based on this simple exercise, I'm good with between 200W to 250W of solar panels for each standard sized 1280Wh LiFePo4 battery in my bank. I can tweak the specifics when it comes to actual system design time.