Solar Design

GOALS

1. Operate through a week of rain (battery life of 10 days).
2. One day of sun provides 2 days of operation (operate unit 1 day and charge batteries 1 days worth) so need an average of 50% sunny days.
3. Low profile (solar array fits on the top of a 10 frame Langstrough hive.)
4. Affordable. Readily available parts.
5. Simple. Easy to build and maintain.

DESIGN

Power calculations

Average power consumption

Pi A: 200 ma @ 5V = 1 W Scale: 50 ma @ 12V = .6 W (The actual measured Pi power consumption is 120 Ma.) Assume PS efficiency is 85% 2 watts/.85 = 2.4 watts 2.4 watts / 6 VDC = .4 amps .4 amp x 24 hours = 9.6 AHr derate 200 AHr battery to 100 AHr 100 AHr / 9.6 AHr/day = 10.4 days

Charge rate

Goal: 4.8 watts (2x consumption) 5 watts x 24 hours = 120 watt hours 120 watt hours / 20 watt = 6 hours at maximum output (12 hours at 50% output Derate panel to 15 watts = 7.6 hours (note: 20 watts is maximum output and that probably won't ever happen - especially if the panel is flat on the top of the hive. I would feel more comfortable using a 40 watt solar panel 2.3 amps max output.)

NOTES

1. Battery Amp Hour ratings are theoretical. A 200 AHr battery in theory would supply 200 amps for 1 hour or 1 A for 200 hours. In practice this is far from true - there is a better chance of getting closer to 1 A for 200 hours than 200 amps for 1 hour. The point is, the AHr rating of the battery must be derated (depends on the rate of discharge and temperature). 2. 6 V golf cart batteries are better deep cycle batteries (thicker plates) than 12 V marine deep cycle which are a compromise. Battery life depends mostly on Depth of Discharge (DOD) - the bigger DOD, the shorter the battery life. 3. A solar "Charge Controller" probably won't work - DO NOT USE THIS: http://www.amazon.com/Sunforce-7-Amp-Charge-Controller/dp/B0006JO0XI/ref... Hardware: 40 Watt solar array: http://www.ebay.com/itm/40w-New-40-watt-Module-Sun-Solar-Panel-PV-Poly-c... $54 on ebay Battery: http://www.ebay.com/itm/Trojan-Black-Box-6-Volt-210-Amp-Hour-Deep-Cycle-... $95 on ebay, probably find locally (Sam's Club) Solar Charger/PS: http://www.prodctodc.com/dc-auto-boost-buck-converter-25w-315v-to-0530v-... $7 WiFi Adapter: http://www.amazon.com/Importer520-Wireless-Adapter-Antenna-54Mbps/dp/B00... $10 (This is about $170 not counting shipping/taxes.) May need gain antenna: http://www.mfjenterprises.com/Product.php?productid=MFJ-1800 $30