> She didn't understand that he has already made his point. (1 kilometre² ==> 1GW).

I always feel Musk is a little bit too one-sided in his presentations. I mean I'm obviously on his side, and it does make sense for certain audiences to present solar as this amazing solution that is a TOTAL no-brainer... because you have to fake it 'till you make it, and if you genuinely believe that solar is an awesome (part of the) solution at the end of the road (as many do, including myself and Musk) then these white lies can be warranted. But still it irks me a bit.

For example he'll say 1 km2 is 1 GW, because 1 m2 is 1000 watts of solar energy. Here's an excerpt from McKay's (free) book Without the Hot Air, a Cambridge physicist professor wrote it and I can recommend it.

> The power of raw sunshine at midday on a cloudless day is 1000W per
square metre. That’s 1000 W per m2 of area oriented towards the sun, not
per m2 of land area. To get the power per m2 of land area in Britain, we
must make several corrections. We need to compensate for the tilt between
the sun and the land, which reduces the intensity of midday sun to about
60% of its value at the equator (figure 6.1). We also lose out because it is
not midday all the time. On a cloud-free day in March or September, the
ratio of the average intensity to the midday intensity is about 32%. Finally,
we lose power because of cloud cover. In a typical UK location the sun
shines during just 34% of daylight hours.
The combined effect of these three factors and the additional compli-
cation of the wobble of the seasons is that the average raw power of sunshine
per square metre of south-facing roof in Britain is roughly 110 W/m2,
and the average raw power of sunshine per square metre of flat ground is
roughly 100 W/m2.

So you get a raw power of 100 w/m2, already an order of magnitude less. Then you take that energy and hypothetically apply PV panels to it, say averaging 20% (20% panels obviously exist but they're a bit more expensive and therefore this is already a rate that's a bit higher than today's average, but doable in the long-term) and you end up with 2% of his 1 GW per km2 in practice. (at least this is for a typical UK square metre, can be higher in a sunny US area), and only 0.5 kwh per average day per square metre of panel.

If you then add to that installation / maintenance costs, and costs of new infrastructure (from transportation to storage) and look at the inefficiencies there, it's not quite true to say 200 km2 will simply do it, hell even if you ignore all that.

With the figures above you get 100 gwh per day of electricity from 200km2 of panels (before storage or transportation). Now he said 'power the US', not 'power cars' or 'power homes' or 'power businesses', but the US, unless I missed something.

Now the US uses about 100 quadrillion BTUs, which is, rounding quite a bit, very roughly 30 million gwh per year, or about say 80k gwh per day. We just established that based on typical UK land with nice panels you get about 100 gwh on 200km2 per day. Yet he says that these panels can power the entire US? It's off by a factor of 800x. Even if you say instead of powering the US, let's power only homes, or just transportation, so you're now off by say a factor of 200x, and then you say well let's put these panels in much better circumstances than the UK, and get 4x more sunhours on average, you're still off by a factor of 50x. I'm sure I've made a few mistakes here and there but I don't think any of this order of magnitude.

Another comparison is the Topaz farm, which has about 0.12 gwh per km2 of daily average generated power. To generate the 80 thousand gwh we use every day, we'd need 664 thousand km2, not '150 to 200 km2 to power the US'. It's insanely wrong to the extent I keep double checking my numbers cause the odds are far bigger than I'm wrong, not him, but I'm not seeing any real mistakes here. Agua Caliente solar project has about (very roughly) 0.18 gwh per km2 generated daily, similar story. Huanghe solar park in China has a 0.15 daily gwh per km2 rate, similar story. Even if you consider that yes, not every single metre is covered and a bunch of other factors etc (many offset by other factors by the way), you need orders of magnitude different results to get anywhere near Musk's figure so I'm not seeing how adjusting for slightly more accurate numbers gets anywhere close to his story.

Anyway I'm not a big energy guy so I'd love for others to enlighten me. Cheers.

tl;dr I really like Musk, I'm a big fan of solar, but I think he's doing a ton of hand waving in his 'we only need xyz and we could go fully solar' to the extent it's just completely false and I've seen it too many times now. Part of that is fine because I'm of the opinion we can at times be allowed to present things better than they are to get the ball rolling and I'd love to get the solar ball rolling (faster), but there are limits.