Energy Testing

It turns our winter is a great time to test renewable energy systems. Both on a state scale - like in Texas last week and on a private [smart] home scale.

Last year I upgraded all my battery powered sensors and light switches to photovoltaic with the goal to have them running forever. I opted for supercapacitors rather than rechargeable batteries, as supercapacitors supposedly have infinite life span. A 5F capacitor at 4.5V (discharging down to 3.6V) is able to power a radio transceiver for two days. The sun rises everyday - I thought - so that would be 100% extra margin. Which turned out not to be enough. 

My mistake was making the upgrade in springtime and it all worked beautifully throughout Summer towards Autumn... In November problems started popping up. As the days were shorter and I stopped getting any direct sunlight (I live in a valley) and the sensors started falling out of the network. Quick voltage check showed there was not enough charge to keep them going. In most cases replacing a photovoltaic panel to a bigger one solved the problem but there were a couple which were in and out despite being fitted with relatively large panels.

And these few problematic cases I solved by adding a backup battery. A coin battery keeps a sensor running for a year. So if this is only 20 days a year when the battery is needed for a solar-powered device, it should last for 15 years. 15 years is not forever, but it seems to be a good balance between the size of the solar panel and the once-in-fifteen-years inconvenience of replacing the battery.

Whether or not the Texas case ends up being blamed on renewables, all systems, big and small should be designed for the worst case scenario. And tested. 

This is not to say Summer is a bad time for stress testing. Far from that! Many years ago when I put an Android tablet as my permanent car multimedia screen, I did it in Winter. And it started failing in summer. The problem was also power-budget related. In Winter it was statistically operating less on full brightness (more driving in the dark). When Summer came in, it turned out the battery was not charging fast enough to support extended operation at full brightness. This time it was the consumption that varied and not tested at peak demand....