Energystorage– you can't do electric vehicles without it, and it sure would make renewable solar and wind energy a lot more useful.

That's the imperative behind 2009's push into energy storage – from the fast-moving world of batteries for electric and plug-in hybrid vehicles to the slower development of a variety of technologies for storing power on the electricity grid.

1. A123, Green Tech's First IPO of 2009: A123 Systems broke the green tech IPO drought in September, when it debuted its shares to the public markets and was immediately rewarded with a doubling of their price. But the lithium-ion battery maker has since seen shares fall to close to their initial offering price of $13.50, perhaps linked to the scaling back of electric vehicle plans by customer Chrysler. A123 is also making batteries for grid energy storage, bridging two worlds that have until now been mostly separate.

2. The Government Boosts Vehicle Batteries" Next-generation batteries wouldn't be where they are today without the billions of stimulus dollars the federal government has aimed at the sector. In August, the Department of Energy handed out $2.4 billion to such companies as EnerG2, A123 Systems, Johnson Controls, eTec, EnerDel, Saft and Chrysler and General Motors, most of it to build battery factories in the United States – a key goal of the grants, given Asia's dominance in battery technology and manufacturing.

3. Fuel Cells' Waning Fortunes? What the federal government has given to batteries, it has taken away from a once-favored alternative - fuel cells. Technologies to convert hydrogen into electricity and water are clean, but they also require a massive infrastructure to deliver hydrogen - which is mostly made today by cracking natural gas - to millions of vehicles. Energy Secretary Steven Chu has said he will cut back drastically on DOE funding for vehicular fuel cell research, which he described as decades away from commercial viability. In the meantime, fuel cells soldier on in the stationary power generation market, and are finding niches in forklifts and other short-range heavy vehicles, as well as in military applications.

But wait? Panasonic has started to deliver fuel cells that burn natural gas to produce heat and electricity in Japan and Bloom Energy is expected to come out of its hidey hole soon to talk about devices that pretty much do the same thing for industrial customers. By exploiting heat and power, these fuel cells can be 80 plus percent efficient.

4. The Promise, and Problem, of Lithium Ion: Lithium-ion batteries are the hands-on favorite for the next generation of electric and plug-in hybrid vehicles. They're also known for overheating and catching on fire – a problem when they're powering your car. They also rely on a metal with a limited supply chain, which could cause problems in the future. Researchers are hard at work on new iterations of lithium-based battery technologies, including lithium-sulfur and lithium-air batteries, and startups aimed at discrete pieces of lithium-ion batteries continue to make advances.

5. Old Battery Techs Get Facelifts: There are cheaper materials than lithium to use in batteries. The trick is tweaking them to deliver equivalent performance. Several varieties of lead-acid batteries hope to overcome the chemistry's problems to meet niches in transportation and grid energy storage. Zinc battery technologies are staking claims, including nickel-zinc, silver zinc and zinc air. Then there are untested technologies, such as Xtreme Power's dry cell batteries, promising breakthroughs.

6. Grid Energy Storage Takes Center Stage: New battery technologies have typically made the move from powering portable electronics to powering vehicles. Could they move up to even larger applications – storing power on electricity grids? Industry watchers have high hopes, but say lithium-ion has a way to go to catch up to incumbent forms of storage.

7. Batteries For The Grid: Battery technologies that have taken the lead in grid energy storage include sodium sulfur batteries, the focus of Japan's NKG Insulators and a new project for General Electric, as well as various forms of flow batteries, which share characteristics with fuel cells. But all of these technologies will be hard-pressed to compete for large-scale energy storage with the old-fashioned method of pumped hydro – pumping water uphill, then letting it flow downhill to spin a turbine.

8: Hot and Cold Running Grid Storage: Storing electricity can mean shifting its use to when it's cheaper and more plentiful. That's the goal of a host of thermal storage technologies aimed at turning air conditioned buildings into icemakers at night and ice-melters by day, using that cold to replace hot afternoon power demand. Calmac, Ice Energy, IceCycle, Coolerado, and a host of others have devised ways to do it, and Congress is considering tax incentives. Meanwhile, electric hot water heaters can also store energy by super-heating at night and dispensing with power draws in the morning, and could be a target of utility smart-meter enabled demand response programs.

9. The DOE Funds Experiments: The Department of Energy's $3.9 billion in smart grid stimulus grants included only $185 million specifically earmarked for storage. But that funding included a wide range of storage technologies, including compressed air energy storage to back up gas turbines, flywheels to provide brief bursts of frequency regulating power to the grid, and batteries ranging from warehouse-sized to those small enough to be mounted on power poles.

10: Virtual Power Plants, Microgrids, Other Storage Concepts: Duke Energy CEO Jim Rogers has said he'd like to see "virtual power plants" enable by the smart grid, making the entire grid a giant storage device of sorts. High-speed, integrated communications and intelligence could make the grid more responsive to voltage sags and surges, outages and other disruptions, which makes up a small but significant portion – about 5 percent – of the power utilities generate today. Microgrids could turn office parks and college campuses into stand-alone sources of power, and that power could be sold back to the grid.