12 MWe
Hi gb
The oft-quoted 85 days VASIMR to Mars mission (sans 30 days spiralling out of Earth's g-well) needs 12 MW of power. Beaming to Mars via laser might be doable, but it'd be quite a spread beam by then. Solar option would need 2.25 times 12 MW of collection power at apohelion. Landis designed a system using L'Garde inflatables as part of an SPS, and estimated it could get 100 kWe per individual 24 kg power-units. Thus the 12 MW at Mars power supply would mass ~270 x 24 kg = 6480 kg. Eminently doable, but it has to be pointed at the Sun and that might complicate matters. Might get 1 kW/kg specific power out of a solar-powered system, after accounting for structure, which for Mars missions would be adequate. Further afield will need nukes.