U.S. climate change legislation now before Congress would mandate that by 2020, 15 to 20 percent of the nation's electricity supply would come from renewable sources like wind and solar.
Currently wind and solar contribute only about 2 percent, with hydropower providing an additional 6 percent.
Can these renewable sources meet the nation's energy needs? A new report from the Pew Center on Global Climate Change finds that wind and solar can be a major source of electricity in the United States. But the report says that will happen only if the United States adopts new policies that promote renewable energy and put a price on climate-changing carbon emissions.
Paul Komor, professor of environmental studies at the University of Colorado and author of the Pew report, says there's theoretically enough sun and wind to meet all U.S. energy needs. The good news, he says, is that the country is already tapping these unlimited resources.
"This isn't a question where we need huge amounts of new research for a brand new technology which doesn't even exist yet. That's not the case here. These things exist. They are reliable. You can buy them from different vendors."
Most of the electricity the United States produces comes from fossil fuels - such as coal or natural gas - which are abundant and still relatively cheap. A major barrier to adding wind or solar is cost, although wind has become more competitive with natural gas. Komor says solar is a different story.
"Current technologies with what you can buy today, it's quite expensive to make electricity directly from the sun. These technologies work quite well, but the costs are quite high."
According to the Pew Center report, if wind is to supply 20 percent of the U.S. energy needs, it will require investments in transmission-line construction of $3-4 billion per year, or a 40 to 50 percent increase over current expenditures, to deliver electricity from remote wind turbines to urban users. And, says Komor, there's the additional challenge of where to put those transmission lines.
"It's a site[ing] challenge, to getting all the landowners and those with jurisdiction over the land to agree to accept that line on their land. Many people don't want this."
Another issue, says Komor, is variability. Wind and solar power are both subject to natural conditions.
"Some people have seen the variability of these resources as making this electricity system unstable… like the lights are going to go out when the wind doesn't blow. Well, that's not going to happen. We do have to pay for this, but the costs are not that high."
The climate change legislation passed by the House of Representatives would also establish a federal renewable electricity standard. It would require utilities in every state to get 15 to 20 percent of their electric power from renewables by 2020. It also puts in place a system of trading credits that would allow states to buy renewably generated power to meet the requirement. Part of that standard could also be met with more efficient use of electricity. Komor says 30 states have already adopted similar measures.
"Every state has its own numbers, its own definition of renewables, but that's the concept. It's a straightforward idea."
The Pew report finds that under current policies, the solar and wind share of the nation's energy mix will increase, but not that much. A business-as-usual forecast predicts that overall, renewables will supply 14 percent of U.S. electricity by 2030, with non-hydro renewables like solar and wind providing only 8 percent.
Yet Komor says the more ambitious goals envisioned by the U.S. Congress are still attainable, especially if congressional plans to put limits on climate-changing carbon emissions succeeds in making renewables more competitive.
"So the bottom line is, the technology - particularly for wind - is there. The barriers are neither trivial nor insurmountable. This is something that is technically feasible, economically reasonable. Politically that is the challenge that the Congress is facing right now."
Komor says he doesn't expect the law that emerges from Congress to be perfect, but he believes it's a good first step toward meeting the challenges of America's energy future.