Last year the United States attracted more private investment in clean energy than any other country, according to a report released today by the Pew Charitable Trusts, “Who’s Winning the Clean Energy Race?” But the findings suggest this was largely because of tax incentives that either have just expired or will expire soon, so the U.S. might not carry this lead into 2012.

The report is a useful resource that outlines where clean-energy investment is going: which countries, which forms of energy, and what types of investment, whether early-stage funding to startups or large-scale project financing.

However, it does make one unfair comparison. It says that 565 gigawatts of renewable energy are installed worldwide, including sources such as solar, wind, and small hydroelectric power (but not large dams). It says this is 50 percent more than the total installed nuclear capacity, but that’s misleading. Renewable energy might have a higher rated capacity, but these technologies produce power only about a quarter of the time, because wind and sunlight are intermittent. Nuclear power plants, which run night and day, actually generate more electricity.

More broadly, the report could be faulted for the way it presents investment in clean energy as a competition between nations. If the goal is to reduce carbon dioxide emissions, does it really matter where the funding goes, as long as there is funding? And if the goal is to create jobs, is it clear that investment in clean energy is the best approach?

Whatever the goals, the most efficient approach would be to focus on those goals rather than on clean-energy investment by country. In the case of cutting carbon dioxide emissions, investment should be judged by how much emissions are reduced per dollar. Installing solar panels or wind turbines in China, where they could offset coal use, might make more sense than installing them in California, where they would offset natural gas; that energy source emits half as much carbon dioxide as coal.

Meanwhile, some clean-energy investments might generate a lot of jobs, but others do not. Installing solar panels on residential rooftops requires a lot of people, and the jobs often pay well. Solar-cell factories, however, don’t employ that many people for their cost.

If the goal is jobs, in fact, then the tax credits and other incentives that have driven clean-energy investment in the United States should probably not be tied explicitly to clean energy at all. Maybe investing in other kinds of energy projects would put more people to work.

The location of investments does matter in one way. The fact is that current renewable-energy technologies are too expensive to displace much fossil fuel. Solar panels must get much cheaper, and we need cheap ways to store or manage the intermittent electricity they generate. That will require major innovations, not just scaling up existing technology. And innovation isn’t just a matter of funding. It also requires less tangible conditions, such as an environment conducive to taking risks and a critical mass of skilled researchers. A dollar invested in a place with those intangibles will almost certainly yield more innovation than a dollar spent in a place without them.

Some countries, such as the United States, have been very good at inventing new things. Indeed, the Pew report shows that the United States has led in attracting investment by venture capitalists in early-stage clean-energy technologies. But while the U.S. has led in early-stage funding, it often hasn’t led in funding to build solar-panel factories and power plants. In the long term, that could hurt innovation in the U.S. Making better solar cells requires a good understanding of what works in factories and what doesn’t, and that’s hard to do if the factory is half a world away. Innovators must often leverage the experience and financial resources of manufacturers to succeed (see our recent cover feature “Can We Build Tomorrow’s Breakthroughs?”).

If U.S. policy fails to encourage investment in clean-energy factories and power plants, it may fall to countries such as China, India, and Indonesia (which saw the fastest growth in clean-energy investment last year) to develop the technologies that will have the biggest impact on carbon dioxide emissions and job creation.