When [knight-of-ni] bought an Acurite Atlas weather station to replace his earlier 5-in-1 model, he was initally happy with its performance. However, after just ten months the batteries in the outdoor unit died; since the previous model would happily run for several years on one charge, this was a bit of a bummer. Climbing up on the roof more than once a year just to replace batteries was becoming inconvenient as well, so [knight-of-ni] designed a solar power system with supercap backup and remote monitoring that should keep the sensors running 24/7, come rain or shine.
The heart of the new power system is a pair of supercapacitors totalling 250 Farads, with an integrated protection circuit that limits the voltage to 5.4 Volts. The caps are charged by a 12 V solar panel; this means that quite a bit of power is dissipated in the protection circuit when the supercaps are fully charged, but since this is completely free solar power that is not much of an issue. A 6 V panel would have worked as well in full sunlight, but might have struggled on a cloudy or snowy day.
[knight-of-ni] wasn’t content with just letting the new power system run unattended however, and decided to integrate a remote monitoring tool as well. For this he used a Moteino, which is an Arduino-type board with an integrated 915 MHz transceiver. The data coming from this board is received by a Raspberry Pi running Linux and presented through a nice web interface. Thanks to this data [knight-of-ni] was able to confirm that the supercaps were fully charged in just an hour and a half on a sunny morning, and maybe three or four times that on a dark and rainy day.
If you’re interested in solar-powered weather stations, we’ve featured a few: some very simple, some more comprehensive, and one built into an IKEA lantern. If you’d like a recap on the working principle of supercapacitors and how they compare to batteries, look no further than our in-depth article on supercaps.
Thanks for the tip, [felix]!