Terence, I think that the solid state may perform better. I am not sure if this is correct but I have found that my sg doesnt charge as well as the run battery gets low. I think this is because the radiant seeks the impedance of the flat battery and as your run gets low and your charge gets high it doesnt transfer as efficiently. Capturing into a cap would Isolate this effectively. My window motor with sg circuit has a cap and scr on the back end and it will charge great, even when the run batt is low.

Please correct my simpleton explaination if someone knows better.