Solar battery charging

Have been looking at the instructable on the micro solar generator, and wondering if there is a formula to calculate how big a solar panel is needed to charge a battery. I'm looking at maybe using a car battery to run some LED globes such as the one below on my deck, they run at 1w 8mA 12v. Any ideas?

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lazza10 years ago
First how long do you want to run the leds,how many,then calculate amp hours required,size the battery amp hours required,how quick you want the battery recharged,then calculate the s/panel wattage required,try not to discharge the battery below 60% Thats the basics for your requirements.
robbtoberfest10 years ago
I found exactly what we need here. http://www.sunelco.com/commo.aspx
It's too long to explain, but basically you need to figure out how many amp hours your lights will be pulling, add some more for battery and wire inefficiency, then figure out the battery size based on those numbers along with battery inefficiency in cold weather. Then you calculate the size of the photovoltaics or whatever input is needed to keep up the system.
murzilka10 years ago
Another reviews-resource on solar panels and solar energy products Solar Panels
trebuchet0310 years ago
It's not how big to charge a battery..... Any panel will charge a battery (assuming you've got the voltage). The question is... How fast do you need to charge it versus how much load will you be using?
I guess first you have to figure out how often/much you will be running the lights. Something about amp hours. How many amp hours the battery has, and base your charge input on that. I'll get back to you later because I've been trying to learn this too.
I found this article "Solar Power 101"
You'll also want to use a battery that will not be destroyed by completely discharging or a system that will shut down the system before the battery setup reaches a critical discharge point.