Solar Lighting

mosfet123

Junior Member level 1
Hi;

I have 30W 18V 1,6A solar panel and I have 12,8V 36Ah LiFePo4 battery. I want to use for lighting fixture (about 25W). is this solar panel enough for charging to battery ? and ıt should be work 3 days at cloudly days . Does anyone have an idea ? Finally is this system ok ?

KlausST

Super Moderator
Staff member
Hi,

Calculate the energy you need for the light. (over 10 days) I gues it wont be on for 24/7...
Calacualte the (expected, but low) energy you get from the solar panel. (over 10 days). Search the internet, there will charts for expectable power for your region)
--> If you get less than you need: either change the solar panel or the light.

Calculate the energy you need for the light. (over 3 days)
Calacualte the (worst case) energy you get from the solar panel. (over 3 days)
--> the difference energy needs to be supplied by the battery.
--> calaculate Ah of Battery

Klaus

Easy peasy

If we assume no charge for 3 cloudy days, the light, 25W has to work over at least 3 cloudy nights, say 12 hrs per night, this is 900 watt hours.

Say the battery is a 12.8V Li-ion, 900 watt / 12V = 75 amp hour minimum.

If you want a full recharge of the system on the next sunny day, again you need to input 900 W-hrs into the battery in say 8 sunny hours

thus the solar cell output needs to be 900 / 8 = 112.5 watts for 8 hours solid ( say 13V @ 8.7 amps )

To allow for inefficiencies in the system, provide for longer actual useable life of the system components, and the weather, it would pay to double these amounts, i.e. 12V 150 A-hr battery

and 2 x 150 watt solar panels. ( 13V @ 23 amps )

you're welcome ...

points: 2

Kripton2035

points: 2

mosfet123

Junior Member level 1
I see. Thanks. I will use with motion sensor to %50 load for 8 hours at nights and 4 hours it will run full load 25W (2-8-2) I have calculated its will spend 600W in 3 days so i would need 12,8 V 46Ah , if I multiply to 2 I would need 12,8V 92Ah

Easy peasy

600 watt-hours over 3 days, not 600W. What is the average battery volts from full to flat, these are the volts to use in the calcs.

mosfet123

Junior Member level 1
Peak 14,6 , Undervoltage protection 10,8V , Undervoltage protection recovery 12V