It's such an easy, relevant question to ask that it boggles the mind that investors don't have their own engineers to ask it. I know you're money people not tech, but how do you know you're not being ripped off if you can't check figures that basic?

Anyway, apparently 3 MWh/tonne is a not-unrealistic claim, so they're only demanding 1.5 MW (on average, though if solar-powered it would make sense to oversize) and a km2 of solar panels could reasonably generate 50-100 MW on average (this is conservative for most places, though not for Iceland). A km2 of tress, by their calculations, gets 1,000 tonnes, so DAC comes out ahead, although you're right to observe that trees do have a synergistic use for the carbon they capture.