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Concept discussion

Harvesting energy out of very bad weather conditions is an often neglected aspect of solar power. If you are on grid, the potential power that you can harvest is so ridiculous that it does not matter to try to optimize that. If you are off grid in a cabinet, where you live, you may have a generator to compensate the missing power.

But if you need to power an unattended instrument all year long from solar power, you need to be able to buffer the energy for weeks of bad weather. Even for just powering as less as a Raspberry Pi zero, requiring only 100mA, the steady power requirement of 2.4Ah a day is able to drain a fully charged 100Ah battery to it's cut-off at 50% in 20 days. Far less, if you were not able to charge the battery to 100% before the bad weather period.

So it becomes important to be able to harvest as much of the scarce energy a panel will provide, when it is permanently shaded. And it even becomes more important not to waste that scarce energy in powering the solar charge controller...

FAQ

This is the place to enter your experiences...

Q What is the shunt rating?

A External shunts will usually be marked with the Amp rating, typically at 75mV.

A module might have a rating, eg an INA3221 has a maximum Vshunt of 163.8mV with an R100 shunt Resistor. Calculate Amp rating with V=IR or V/R=I. 0.1638V / 0.1Ω = 1.6A The INA3221 is Rated at 1.6A.

Q How do I measure the R010 (10Ω) Shunt Resistor with my cheap multimeter?

A Put a low, medium and high amperage (within module capacity) across the shunt and measure the mV then calculate with V=IR or V/I=R. (Cheap multimeters can't measure very low Ohms.)

eg A measurement of 51mV at 5A is 0.051V / 5A = .010Ω, or a R010 shunt resistor. Average a few readings and enter a calibration factor if required.