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.)

Disabling the LAN9512

The LAN9512 is the hardware device which controls Ethernet and USB ports. This chip consumes almost 200mA. The LAN9512 datasheet explains some states of the device to save energy - these modes are SUSPEND2, SUSPEND1 and SUSPEND0.

echo 0x0 > /sys/devices/platform/bcm2708_usb/buspower will effectively disable the device and wake up it again with echo 0x1 to the same file.

Details are at this StackExchage post.

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

Raspberry Pi Model A vs Model B

The SMSC LAN9512 USB Hub and Ethernet Controller.

http://www.smsc.com/media/Downloads_Public/Data_Sheets/9512.pdf http://www.daveakerman.com/?page_id=1294 http://www.bitwizard.nl/wiki/index.php?title=Reducing_power_consumption_of_a_raspberry_Pi http://www.youtube.com/watch?v=L1EihTxIdnQ http://traffic.integreen-life.bz.it/default/wiki/power-consumption http://raspberrypi.stackexchange.com/questions/8498/disable-lan9512