From a technology perspective, things have changed a lot since the first Earth Days of the 1970s.
After barely moving for decades, there's been a surge in innovation in energy the past five years, fueled both by society's growing interest in clean energy and by the technology revolutions in other industries, like IT and biotech. That has expanded the definition of clean energy from solar and wind to many other areas.
Yergin is someone who should know. As the author of "The Prize," a book about the history of the oil industry, and co-founder of Cambridge Energy Research Associates, he advises CEOs of giant oil and gas firms on energy strategy. Like many people in green tech, he's not a typical 1970s-era tree hugger but a hard-boiled business man who sees technology change driven by economic, environmental, and national security reasons.
Innovation "runs across all sectors and it has a very strong climate change focus," Yergin said. "Clearly, one of the areas of major innovation is the nexus of transportation, smart grid, and renewable and alternative" energy.
Which technologies specifically have a good shot at making the biggest impact? As part of our Earth Day 2009 coverage, we try to handicap technologies that bear watching.
Utility-scale solar. Despite all the press around solar energy, its contribution to national electricity generation is barely a blip. But after a multi-decade hiatus, utility-scale solar power is back on the agenda, led in the U.S. by sun-blessed California's renewable energy mandates.
Over the past five years, several start-ups have designed concentrating solar thermal systems that generate heat by focusing the sun's light to make steam. The steam then turns a traditional turbine to make electricity. Desert areas like the Southwest region of the U.S. are tailor-made for this technology.
After racing forward for the last few years, concentrating solar upstarts have had to hit the brakes or change plans because of the cost and complexity--from environmental permitting, building transmission lines and the like--of these projects.
eSolar and BrightSource Energy stand out for having announced programs to move ahead with their solar tower technologies. Other relevant technologies in utility-scale solar are flat solar panels mounted on racks that follow the sun and concentrating photovoltaics from companies like Cool Earth Solar and SolFocus.
Energy storage. If solar was the technology that venture capitalists loved in 2007, last year and this year it's energy storage. For investors and entrepreneurs who like a tough problem, they picked a good area.
Why are electric vehicles so expensive? The batteries. What will transform wind and solar power from variable to reliable sources? Storage. How do we make our power-hungry electronic gadgets last all day? You get the picture.
There are a dizzying number of technologies to store electrical energy but they just can't seem to be too cheap, light, or environmentally benign.
The breakthrough for electric vehicles has roots in consumer electronics where lithium ion batteries have become the standard. U.S. companies on the forefront of making lithium ion batteries for cars and other portable electronics, like power tools, are Ener1 and A123 Systems, which signed a deal to supply Chrysler earlier this month.
Companies to watch in electric vehicles are, once again, high-profile Tesla Motors, Fisker Automotive, which will release its plug-in electric later this year, and Bright Automotive, a company founded by the former head of General Motors' EV1 program.
Meanwhile, a handful of progressive utilities are quietly dipping their toes into grid storage, installing one or two megawatt banks of batteries the size of tractor trailers or a small building. Although the lithium ion battery makers tend to get most of the attention, this is an area where alternative chemistries, such as zinc, or even stationary fuel cells are creeping in.
Efficiency. Ask nearly any clean-energy expert about the best way to lower greenhouse gas emissions in the most economical way and they'll say efficiency. An investment in efficiency, whether it's your home or your data center, will typically be the quickest payback when it comes to energy.
From a technology perspective, efficiency takes many forms, from Ford's EcoBoost to deliver better mileage on gasoline engines to LED lighting. For the power grid, efficiency means smart-grid technologies that help utilities better match the supply of electricity with demand and give homeowners ways to cut their monthly bills.
Although the grid will get a major upgrade from the stimulus plan, it's still unclear how many utilities can successfully make the financial case for investing in smart-grid technologies or how much consumers are willing to pay for home energy monitoring.
During a speech at last week's MIT forum on clean-energy policy, John Holdren, the director of the president's Office of Science and Technology Policy, said carbon capture and sequestration is a technology that deserves more research as a way to mitigate climate change.
Right now, though, technology for pumping large amounts of carbon dioxide underground is still not commercial. There are some companies, including GreatPoint Energy and Tenaska Energy, devising ways to make cleaner-burning natural gas from coal and to store carbon dioxide from that process underground.
The Department of Energy's budget--which has not yet been passed--calls for $3.4 billion in research for "low-carbon coal technologies" to study whether it can be done safely and economically.
Disappointments and a reality check
Looking back at our coverage of Earth Day 2008, perhaps the biggest disappointment, economically and environmentally, was the biofuels area. Because of fluctuating commodity prices, corn ethanol providers got clobbered last year with at least two declaring bankruptcy.
Meanwhile, cellulosic ethanol made from wood chips or prairie grasses hasn't yet been done at commercial scale as some in the industry had hoped. It's still a goal worth pursuing because cellulosic ethanol has a better environmental profile than corn ethanol, but the economic turmoil has slowed progress.
The great hope--and perhaps the sleeper--for the biofuels industry remains the lowly algae, although even the most optimistic say that it will be three years before it can be produced at large scale.
Another disappointment on my list is roof-mounted small wind turbines for homes. It's not that the technology doesn't work, but two studies in the U.K. and Massachusetts have shown that the available wind on people's homes is typically below manufacturers' minimum requirements.
Finally, water technologies attract very little investment even though awareness of water problems continues to rise, fed by high-profile droughts in California and Australia.
Sum it all up and it's clear there's a flowering of innovation in energy and environmental products, from people's homes to businesses. At the same time, we shouldn't fool ourselves: technology alone won't magically create a low-carbon economy and more sustainable lifestyles.
A healthy green-tech industry requires a healthy financial system and supportive policies. Many people are aiming for technology breakthroughs and, no doubt, there will be surprises along the way. But given the scope of the problem, it's clear the road to a greener economy will be long, expensive, and will need a different set of rules.