Alex W.'s Blog

Solar Panel - Day 7 Later On

June 27, 2010

I’ve measured the amperage across the solar panel throughout the day, at 9:00 AM (.3 amps); 12:00 PM (.7 amps); 5:00 PM (.3 amps); or about .4 amps averaged from 9:00 to 3:00. So, (0.4 amps) * (12 volts) =  (4.8 watts) * (6 hours) = (28.8 watt hours / per day)

The inverter takes a consistent 1 watt. Which comes to, (1 watt) * (24 hours a day) = (24 watt hours / per day)

(28.8 watt hours / per day) - (24 watt hours / per day) = (Only 4.4 watt hours to charge my devices with)

I have hooked a Kill-A-Watt EZ into the line between my chargers and the extension cord. When charging an iTouch and a Droid it draws 7 watts, and when there just plugged in they draw 2 watts.

(4.4 watt hours) / (2 watt hours) = (2.2 hours of charging) and thats if their fully charged! In reality:

(4.4 watt hours) / (7 watt hours) = (38 minutes of charging)

My Droid gets around 10% charge per 15 minutes. So about 25% charge per device over one day.

Now I get why the solar panel can’t support my setup. The only solution I can think of is to setup a relay on the inverter so I have to flip a switch in the house to allow power to go to it.

Other: (216 watt hours “battery capacity”) / (28.8 watt hours per day) = (7.5 Days of charging for full battery)

Alex Wendland

Written by Alex Wendland, who is currently studenting at Harvard College. Here's a Twitter handle, a GitHub, some LinkedIn, ol' Facebook, or a hip Instagram if you're interested.