By Saya Kitasei Worldwatch’s new report - Powering the Low-Carbon-Economy: The Once and Future Roles of Renewable Energy and Natural Gas - argues that natural gas could form a powerful partnership with renewable energy in powering a low-carbon future. Just after four in the morning on July 2, 2008, winds began to pick up over part of Colorado. That morning, regional wind turbines were providing a modest 5 percent share of the power generated by the state’s largest electric utility. Over the next 90 minutes, however, wind generation quadrupled, from 200 MW to 800 MW, then fell rapidly back to 200 MW. The entire wind event was over by 8 a.m. But here’s the problem. Wind power in Colorado is treated as a “must-take” resource, which means that system operators had to rapidly ramp down at least four coal power plants and then ramp them up again just a few hours later in order to accommodate the surge in available wind power. Coal plants, which burn coal to turn steam turbines, can take days to reach full power from a cold start. They are not designed to ramp up and down quickly. Enter natural gas. Natural gas combined-cycle plants can typically achieve a cold start in about three hours, and they ramp up and down at a rate of about 7 percent of their capacity per minute. The steam turbines in coal power plants are also much less efficient when running at low capacity, while combined-cycle natural gas plants by contrast can still operate relatively efficiently at low capacity. And therein lies the potential. Natural gas can be used in a range of efficient, flexible, and scalable generating technologies, making it a natural partner for variable renewable energy sources such as wind and solar power. Because these renewable resources vary by the season, day, and even hour, wind and solar power plants cannot always generate electricity when it is needed, as other types of power plants can. Meanwhile, the coal and nuclear steam turbines that form the backbone of most electricity systems today are very slow to turn up and down and become much less efficient when they are running at less than full power. The inflexibility of these plants limits the amount of variable generation that the electricity grid can absorb. Renewable energy and natural gas can also power a transition away from inefficient centralized power. Natural gas power plants come in a range of scales, allowing them to generate electricity in both centralized and distributed power systems. Distributed power, produced from small generators located near electricity consumers, can reduce the expense and efficiency losses associated with long-distance transmission. Small solar, wind, and natural gas-fired cogeneration plants can be integrated directly into distribution lines and networked together to create a diffuse, flexible, local, and low-carbon grid. In order to play a sustainable role in a low-carbon future, natural gas itself can and must decarbonize. At the chemical level, natural gas consists primarily of methane, a molecule that can be produced or synthesized from a variety of renewable sources. Landfills and organic processes can create methane that otherwise enters the atmosphere, where it acts as a greenhouse gas some 25 times more potent than carbon dioxide. This methane or “biogas” can be used interchangeably with natural gas, and capturing and utilizing it can mitigate greenhouse gas emissions. In the future, methane supplies could be decarbonized further by blending in hydrogen gas, a zerocarbon fuel that can be produced from water through electrolysis using renewable energy. Working together, renewable energy and natural gas can accelerate the decarbonization of the world’s electricity system and form the foundation of tomorrow’s low-carbon economy. By Saya Kitasei, Sustainable Energy Fellow at the Worldwatch Institute