This comes from Robert Zurin's the Case for Mars What is a Terrawatt year? Is that 1 terrawatt produced in one year? I don't see why it's measured in terrawatts. Why not just terrawatts? Further down he says That's more understandable. Tell me if this calculation is correct. To get 120 millibars of oxygen you need to multiply 2200 by 120 since 2200 TW are needed for 1 millibar of oxygen. 2200 * 120 = 264,000 terrawatts It looks like he thinks you can produce 100 TW a year with 90 coming from reflectors and 10 coming from factories. If that's 100 TW a year that would take 2640 years, so there is something that I'm not understanding. But I should also point out that I don't really trust this guy. He has an agenda, going to Mars and quick, so he's motivated to minimize all the obstacles and make everything seem easier than it is.