America needs lots of clean, low-cost, secure electricity. Unfortunately, renewable sources don't fill the bill, and a national requirement wouldn't change things.
Renewables (excluding hydroelectric dams) produce less than 3% of U.S. electricity, much of which is hardly clean. About two-thirds comes from burning scrap vegetation ("biomass") and garbage, which produce the same pollutants and carbon as coal. The real job is to produce fewer of them, rather than changing fuels from fossilized to non-fossilized vegetation.
Geology limits geothermal opportunities, biomass is environmentally questionable, and solar remains prohibitively expensive. That leaves wind power, but efficient wind turbines pollute in their own way taller than the Statue of Liberty and maddeningly noisy. A national requirement would engender the same environmental resistance as conventional generators and transmission. Opposition to California's requirement is so strong that today, it gets a smaller percentage of power from renewables than in 2001.
Wind generates only when it is blowing, and it blows least when power is most valuable. At peak demand hours in 2006, wind plants in both California and Texas produced below 3% of their potential. To maintain reliability will require continued investment in full-scale backup generation. Wind generation is itself expensive even at today's fuel prices, it requires a massive federal tax credit to survive.
A national policy that creates jobs in renewables destroys them elsewhere. Forcing people and businesses to buy expensive power leaves them less to spend on other goods and investments in future productivity. If unemployment is a national problem, attack it with a national policy rather than special-interest legislation for the renewables industry.
That industry is already big enough worldwide that a U.S. requirement is not needed to bring forth better renewable technologies. And renewables don't matter for national security or energy independence; these are about oil, which produces about 2% of our electricity.
If pollution and climate change are problems, attack them directly. Don't confuse this special-interest legislation with an efficient solution to them.