shawname wrote:Why is that? It seems that current would flow from the higher voltage of the panels to the batteries. Is it because the panels see the batteries as a direct short?
Light pushes a fixed number of electrons through a nominal 0.5 volt potential barrier in each cell, or 18 volts in a 36 cell panel. Each electron has excess energy depending on the wavelength of the photon causing the push, that excess is dissipated within the cell on the high side of the barrier. With no load the small capacitance of the circuit will charge up to 18 volts, now the electrons have enough energy to fall back through the barrier and the current recirculates in each cell. Connect a 12 volt battery and that capacitance will quickly discharge to 12 volts, and the voltage across each PV cell will drop to 0.33 volts. The original current will begin to flow, but another 0.17 volts of energy is lost on the high side of the barrier (actually the current increases a little because the lower barrier allows longer wavelength photons to be effective).
shawname wrote:Would the magnetic field be a coil or a capacitor? It would seem like either of those would be able to handle quick fluctuations, but not fluctuations over the course of an hour. The KHz rates would allow for less amps, lighter circuitry?
A coil in series will continue to push electrons when the panel is disconnected, the collapsing field going to zero and generating whatever voltage is needed to drive current through the battery. The voltage across a capacitor would be decreasing so it would only provide current for a short time, until the voltage drops to battery equilibrium potential.
shawname wrote:The shunt being a small resistor in parallel?
In series, to measure the current through the battery. For most battery chemistries the voltage always increases with increasing current (not NiMH however) so a feedback loop that maximizes the voltage would work as well. But small changes in voltage would represent large changes in current, and higher precision ADCs would be needed to measure it. For less than 10 amps or so the watts lost across a < 1 ohm shunt are not important; for kWh battery banks it might make sense to measure voltage instead, or use a Hall device to measure the current.