Electronic – Free Piston Stirling Engine Tuning Capacitor – Series Vs Parallel

It's better to use just the generator so you don't have to tolerate the variability of the PV.

If, when fully charged, each cell is at 1.2 volts, then you'll need a current-limited source with greater than a 3.6 volt output to charge them, the current limit being determined by the cells' specifications.

If your generator can't generate more than 3.6 volts, then the PV should be connected in series with it.

Unless there's some compelling reason to do so, the PV and the generator shouldn't be connected in parallel, directly, since the one with the higher voltage will feed current into the one with the lower voltage, possibly starving the battery or increasing its charge time.

Also, since more voltage will cause more charge (current) to flow into the battery, it's better to arrange things so that the charger's output voltage only pushes the allowed current into the battery. That is, neither excess voltage across nor current into the battery is a Good Thing.

Without the capacitor, the source has to provide all the energy (St): the actual energy consumed by the load (Pt) and the energy stored in the inductive part of the load (Qt). The inductive part makes the source supply a lot more current than necessary, since a lot of that current goes into setting up a magnetic field that stores some of the energy generated by the source.

With the capacitor in parallel, there is now an additional source of energy, which can take up some/all of the burden of supplying current to the inductive load (when it resists changes in current till it sets up its field), after which the source takes over again and recharges the capacitor. So the apparent power S (and thus energy) drawn from the source is reduced and is much closer to the true power P actually being used by the load.