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Scientists Develop New Dirt-Powered Fuel Cell That Runs Forever
(scitechdaily.com)
This is a most excellent place for technology news and articles.
They claim "68 times more than required to operate the sensors", then mention a sensor to measure soil moisture.
A basic soil moisture sensor, like say, the ones I have stacked on a shelf here, will work on 2 AA batteries. It runs on 2V at 10mA. So that's 20 milliWatts, and in willing to be a fair bit of that goes into the electronics that make a red, green or orange led light up at certain moisture levels, and the bit that beeps when below a certain level.
Still, this sets something of an upper limit at 1.3W, or maybe 680 mA? Those seem rather high, so I'm betting their moisture sensor is a bit more delicate than my model. It depends on the size and number of cells though.
Im pretty sure most soil moisture measurment devices just measure the capacitance to measure dielectric permittivity. U can design such a setup to use any arbitrary amount of power depending how close the electrodes are rogether etc etc.
Yeah, I am imagining the soil moisture things from the garden store, with the little needle gauge thing, that takes so little power that there's no battery slot. I feel like the amount of power this thing makes is extremely low.
Probably generates nanowatts