... wind alone is that it implies substantially more than 20% by 2020 for sustainable renewable energy.

If the US is going for 20% wind by 2020, then the portfolio standard would have to be something like 30% renewable or higher by 2020. The next "natural" (that is, small fraction) shares are 25% and 33%. There is also 35%, which allows pollies to say "more than a third".

I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.