I don't think this is a reflection on the amount of usable sunlight on that hits the surface of the earth. It sounds more like a vague, general statement and isn't backed by calculations in the article.
The late Professor McKay (whose book on information theory and ML is neat by the way) published a great book full of climate back of the envelope calculations, Whithout the Hot Air, which is available online[1]. He clearly disagrees with this statement, as seen in the recap figure on page 103[2].
"This theoretical potential represents more energy striking the earth’s surface in one and a half hours (480 EJ) than worldwide energy consumption in the year 2001 from all sources combined (430 EJ)."
Not back of envelope. Energy calculations worked through.
EDIT: Solar is a better investment than the S&P500. If US corporations were looking for some place to invest those trillions of dollars they won't repatriate [1], seems like renewables would be a perfect fit.
"Eight of the biggest U.S. technology companies added a combined $69 billion to their stockpiled offshore profits over the past year, even as some corporations in other industries felt pressure to bring cash back home.
Microsoft Corp., Apple Inc., Google Inc. and five other tech firms now account for more than a fifth of the $2.10 trillion in profits that U.S. companies are holding overseas, according to a Bloomberg News review of the securities filings of 304 corporations. The total amount held outside the U.S. by the companies was up 8 percent from the previous year, though 58 companies reported smaller stockpiles."
McKay uses something very close to this (as you said) theoretical value as the starting point of its calculations for how much can effectively be extracted.
The late Professor McKay (whose book on information theory and ML is neat by the way) published a great book full of climate back of the envelope calculations, Whithout the Hot Air, which is available online[1]. He clearly disagrees with this statement, as seen in the recap figure on page 103[2].
[1] http://www.withouthotair.com/Contents.html
[2] http://www.withouthotair.com/c18/page_103.shtml