photovoltaic high voltage DC power supply

I am trying to build a solar powered catapult. Charge up four 45,000 uF computer caps, and that solenoid sucks that steel cylinder in like a mug! It works fine with 117VAC + full wave bridge recifier, but when I try using a Harbor Freight 5 watt photovoltaic battery charger (350 mA @ 12 V), it doesn't quite make it: It works with a small capacitor across the outputs (100 uF, 400V electrolytic--takes that puppy well above 200VDC!), but when I try to charge up even one of the 45,000 uF caps, it can't get above 30 volts, even though it is sending 200mA into the input side of a Hartley oscillator DC-DC converter. Any ideas out there? Bruce Ratcliffe, sunny Fresno