Saturday, 9 September 2017

The Itinerant Solar Panel

Sometime back we visited Bernard Ng's orchard where he showed me his solar power rig, and I know I got to have one. I bought the same make of solar panel, SC Origin's 100W SPM100-M. I was quite pleased with it; so pleased that after two years in the guest room it was time it got mounted.

Solar panel facing west

I did not want a permanent mounting yet- the idea was to experiment with different locations and angles and collect data on the amount of charge I can collect from it. It needed to be stable enough not to get blown over, yet portable enough to be moved. At first I got a solar mounting frame:

But moving it was a little fraught. I found myself wrapping the panel in bubble wrap before moving it.

I finally settled on a very cheap (about RM60) plastic table, very common in Malaysia.

I simply unscrewed the table top from its metal base and mounted the solar panel in its place. The plastic table top disappeared under my 1969 Volkswagen Beetle as an oversized oil pan.

The solar panel needed to be mounted at an angle sometimes, and I nailed together a few bits of wood to hold it in place (otherwise the table tends to snap shut in the fully-folded position). To hold everything down, I made the wooden brace to fit the base of the battery. I used an NS60 sealed lead acid car battery.

Lastly the panel and battery needed to be connected to a solar charge controller, the 5A Gamma 2.0.
And mounted in place:

The Gamma came with an after-dark timer, so I connected a 35mA 12V LED night light to it.

Here is a charging graph, over some three days and two nights. The panel faced west so the morning charging starts slow, ramping up from 2pm until 6pm. The battery voltage here is seen to go well over the maximum 13.8V.

The discharging slope corresponds to the 35mA nightlight as well as a Raspberry Pi Model A (the original one) as well as a derivative of the Microchip Low Pin Count Development Board, probably 200mA or so in total.

By adding a WiFi USB dongle, the Wi Pi by Element14, we get a very rough-and-ready first version of an Internet of Things Solar Battery Voltage Monitor, which is the subject of the next post, so stay tuned!

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