President Obama gave his first major speech on climate change today at the United Nations, part of a special session convened by U.N. Secretary General Ban Ki-moon. The reason for the session? Lack of speed in international negotiations to address climate change.

You can see the president's speech here:

In addition to reaffirming the U.S. commitment to addressing climate change, the president listed some recent accomplishments: new efficiency standards for all vehicles, billions of dollars for renewable energy development, and the nation's first mandatory greenhouse gas reporting system. He even noted a plan to work with the world's other largest economies, known as the G20, to "phase out fossil-fuel subsidies so that we can better address our climate challenge."

Here's a seemingly simple solar power fact*: the sun bathes Earth with enough energy in one hour (4.3 x 10²⁰ joules) to more than fill all of humanity's present energy use in a year (4.1 x 10²⁰ joules). So how to convert it? In the world of solar energy harvesting, there's a constant battle between cost and efficiency. On the one hand, complex and expensive triple-junction photovoltaic cells can turn more than 40 percent of the (specially concentrated) sunlight that falls on them into electricity. On the other, cheap, plastic solar cells under development convert less than 5 percent.

In between, ubiquitous photovoltaics—the multicrystalline silicon solar panels cropping up on rooftops across the country and, indeed, the world—struggle to balance the need for (relatively) easy manufacturing and low cost with technology to get the most electrons for your solar buck.

Mining is the second most dangerous occupation in the U.S., averaging roughly 27 deaths for every 100,000 workers per year. That's nearly nine times higher than the overall fatality rate for U.S. industry as a whole, according to data from the U.S. Census Bureau (pdf).

So it stands to reason that energy derived from renewable resources such as the sun and wind might cause fewer workplace deaths than energy industries—coal, oil and natural gas—that rely on mining, drilling and otherwise extracting fossil fuels. And that's exactly what doctors from Medical College of Wisconsin and Duke University Medical Center found in an analysis published in JAMA The Journal of the American Medical Association on August 19.

If solar power is ever going to take off—and the world needs it to—photovoltaic cells will have to become a whole lot cheaper to produce.

Making solar cells from silicon, the most common approach, can be expensive and relatively inefficient at turning sunlight into electricity. As semiconductor manufacturer Applied Materials chief technology officer Mark Pinto told me last year: "With solar, it's all about cost."

But there are signs of improvement, writes Richard Swanson of SunPower Corp. in this week's Science. Last year, manufacturers made 5 gigawatts of photovoltaic panels. And some of these panels required just under six grams of silicon per watt of power—down from 15 grams at the turn of the century. And that watt of power now costs around $1.40 to produce compared with $2 or more in the 1990s.

Duke Energy wants to put a power plant on your house.

Over the next year, the utility plans to spend $50 million to plop a variety of photovoltaic panels on commercial buildings, the roofs of private homes, and other property in North Carolina.

Once installed, the 10 megawatts worth of solar panels are expected to produce enough alternating-current electricity to power 1,300 homes. But the utility’s main goals for the demonstration project are to gain experience with distributed generation—putting the power plant closer to the customer—and with integrating intermittent, renewable resources like sunshine into the grid.

When it comes to energy policy in the U.S., not very much has changed since President Jimmy Carter declared more than three decades ago that achieving energy independence was "the moral equivalent of war."

Today, Carter had his “I-told-you-so-moment” in testimony on energy policy before the Senate Foreign Relations Committee, giving lawmakers a bit of a history lesson (while acknowledging that some of them were also in government then).

Two weeks after becoming president, Carter famously appeared in a cardigan and urged energy conservation on a resistant American public. Ultimately, that and other efforts led to a more energy-efficient economy as well as cutting oil imports in half by 1982.

Do the potential benefits of plants that use renewable sources such as wind and solar to generate energy outweigh the environmental damage that could be caused to make way for them? Californians are grappling with that very question as the state moves ahead with Gov. Arnold Schwarzenegger's plan to have utility companies generate one-third of the state's energy from renewable sources by 2020; today renewables account for 12 percent of their output.

The facilities and infrastructure needed to meet the governor's goals, however, require the state to turn over acres of previously undeveloped land (to install fields of solar panels, for example), something residents near the Carrisa Plains region (about 170 miles northwest of Los Angeles) fear may destroy the area's natural beauty, not to mention habitats of endangered animals such as the San Joaquin kit fox, Time reports.

American research firm SRI International and Japan's Hyper Drive Corporation today are testing the latest generation of their jointly developed buoy-mounted, ocean wave-powered generator off the coast of Santa Cruz, Calif. As the generator bobs up and down, an accordionlike device inside, made of artificial muscle called Electroactive Polymer Artificial Muscle (EPAM), stretches and contracts, creating mechanical energy that is converted into electricity.

SRI is hoping to demonstrate its ability to generate at least 10 Watts of power in waves about 3.3 feet (one meter) in height, a stepping stone to the 100-Watt capacity the researchers hope to be able to generate within a few years. One of their goals is to replace the 25-Watt batteries that navigation buoys use today with a source of renewable energy that can power additional equipment such as cameras and storm warning sensors.

Among the many pressing issues that President-elect Barack Obama will face when he takes office in January is climate change, which he has called an “immediate threat” and warned has made Earth a “planet in peril.” In an effort to prevent and reverse the problem, he supports a so-called cap-and-trade scheme similar to one now in effect in the U.S. Northeast and the European Union.

Under such a plan, the government sets an overall limit on the amount of pollution allowed and polluters, such as power companies, are sold or given permits to pollute. Those who emit less pollution thanks to a new wind farm, for example, can then sell their excess pollution permits to other companies struggling to meet their quotas. That ensures that the industry stays within the overall emission limit, which declines over time.