Another creative approach which is achieving progress: the photonic laser thruster.
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The distinction is more important than you let on.
https://www.jerrypournelle.com/science/dean.html
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And I thought I was pedantic. 
Your disappointment in Boing Boing is noted.
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The difference between your number and the one by @DonatellaNobody (assuming a start from speed 0) is interesting. Can anyone confirm that Robert A. Heinlein actually said or wrote
Once you get to earth orbit, you’re halfway to anywhere in the solar system.
I have found several, slightly different versions of that quote, but it is missing from his wikiquote page.
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Since we’re vying for the pedant throne, I’ll point out that an ion thruster that is powered by solar cells would need consumable propellant rather than fuel, since it isn’t providing energy through chemical or nuclear reaction
And the suitability of solar sails for intersteller travel is limited by the fact that as you get further from the sun, the acceleration decrreases because there is less light falling on it. The proposals I’ve seen for this posit using lasers based in orbit to send more light to to the sail. Of course the lasers required to get to another star in ~100 years would require more power than our entire civilization consumes at the current time.
edited to add: which is definitely more efficient than carrying propellant with you, but as they say space is really, really big.
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“Second star to the right and straight on 'til morning.”
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Think of this way.
Satellites are solar powered.
Satellites also position themselves with thrusters.
Satellites are subject to orbital decay. In order to maintain a stable orbit, they must periodically use their thrusters to reposition themselves. Thrusters have a limited supply of propellant. When that propellant is completely used up. the satellite eventually falls into the atmosphere and burns up. (the effects of atmospheric drag eventually catch up to objects in LEO. One rather famous example of this is Skylab )
Even ion engines require reaction mass. The solar sail concept avoids this problem. As long as the sail survives, it can move in reaction to the sun, or a ground based laser, depending on how the sail is designed. It’s not pedantic, because this not a minor detail. Rather, it is the entire point of the exercise.
We don’t have Dean drives. If they worked, space travel would be far simpler.
Don’t know what Dean drives are, but I get that the commenter I replied to is correct for the technical use of the words powered and propelled; that’s why I went to the trouble to include their quoteblock within my quote of theirs. Colloquially for lay readers the terms are interchangeable.
It doesn’t work, of course, but if it did, it would be a massive fucking deal.
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