Different materials have different spectral signatures.
Is the spectral signature different for a given solar panel, depending on whether it is charging a (spacecraft's) batteries or there is a full charge and the panels are heating up? I would expect that certain wavelengths be absorbed more when charging and either reflected or contributing more to increasing temperature once the batteries are fully charged. I am neglecting any system to dissipate the surplus power (e.g. a nanosatellite with a simple power subsystem). I would also expect this effect to be fairly small for the overall spectral signature of a particular satellite, given the other materials composing the satellite.
Thank you in advance for contributing to this discussion.
Alex,
No. The emissivity and albedo (and more particularly) the spectral reflectance profile are not influenced by the state of charge (SOC) of a craft's internal batteries.
Several reasons lead me to this.
1) The batteries are, in general, 'hidden' from the PV arrays - there are DCDC chargers between the arrays and the batteries.
2) The movement of electrons in a PV junction does not alter the optical characteristics of the array.
Certainly, if the arrays are generating current, they will warm from Joule heating - but they're in sunlight (otherwise there's no current...) and have a low albedo - so solar insolation will dominate (probably) that source of power.
In any case, a hot PV array is well-modelled (I reckon) as a blackbody - and so all you'll know from a spectral emission profile is the temperature of the array.
There's probably a body of literature out there on the reflectance spectra of various array types.
Reflectance varies more with angle of incidence than it does with back EMF from the charged system. A high voltage on the panels can affect the reflectance, but such voltage is abnormal and would likely damage the PV junctions.
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