Over the last few years, Congress and the states have slowly cranked up support for renewable energy, especially wind and solar power. Likewise, more and more public dollars are going toward the creation of "smart grids" that would juggle demand more efficiently and reduce waste in the electricity sector. These are all grand ideas. But, as Katie Fehrenbacher points out today, the overall impact of both renewables and smart grids will be severely limited unless we find good ways of storing energy. This is still a big technical challenge. And energy storage hasn't gotten much attention from policymakers—at least until recently.

It's easy to see why large-scale renewable power depends on storage. The wind's not always blowing, and the sun's not always shining. What's more, in many areas, the wind's often whistling through only during the nighttime, when no one's even using electricity, so figuring out how to store that excess power is vital. (Denmark, for instance, manages to get 20 percent of its power from wind by dishing off the excess to Sweden and Norway, which then send back hydropower during breezeless hours—a clever storage set-up, but one that's not necessarily always available.)

Better storage could also help smooth out energy demand. A remarkable fact about the U.S. electricity sector is that, at the moment, nearly 14 percent of the country's 2,300 power plants are "peaking plants," expensive gas turbines that only get flicked on during those relatively rare hours when electricity demand really spikes. It's an inefficient and costly system. If we had a smart grid that could juggle demand (say, by electronically shutting down household dishwashers and other non-necessities when demand peaks) as well as better energy storage, we could reduce the need for those costly peakers and lower overall volatility.

The problem is that no one has yet devised a cost-effective way to store energy on a large scale. Oh, sure, there are all sorts of promising ideas out there. Molten salt pits for concentrated solar-thermal plants. Pumped hydro. Compressed air. (Earth2Tech has a good list here.) But experts say that most existing storage techniques have drawbacks and limitations. "We need scalable energy storage at an acceptable cost, and we still don't know how to do that yet," CalTech energy chemist Nate Lewis told me. "If we're hoping to someday get half our energy from intermittent sources, we need a lot more R&D to break through that barrier."

Yet there's still not much federal support for electricity storage. As Fehrenbacher notes, most of the storage-related money in the stimulus package went toward batteries for electric vehicles, which, while important (and another daunting obstacle), isn't the only issue. So it's encouraging that the Senate's now crafting a bill, introduced by Ron Wyden, to offer tax credits for grid-connected energy storage. This could apply to everything from plug-in hybrids (which could provide a form of storage, if they charged up in the middle of the night, rather than during early evening) to thermal cooling systems that "would make ice at night when electricity is cheaper and use the ice to cool the building during the day." It's not a bad start.

For more TNR, become a fan on Facebook and follow us on Twitter.