Solar Power, Batteries Included

Solar power has long provided the near-constant power generation needed to run satellite transmitters, some of them decades old by now. And some day solar power will drive the robotic arms of Mars landers.

But the electricity it generates must be stored onboard in rechargeable batteries. Researchers say that making these batteries denser, thinner and lighter can translate into spacecraft that fly farther and faster, are smaller and less expensive, and can carry space-based lasers.

So it’s not surprising that the U.S. government spends a lot of money researching and developing batteries. Much of the research focuses on lithium-ion polymer, a solid or gelatinous electrolyte critical to the chemical reaction that creates electricity. Lithium polymer, as it’s usually called, tops good battery performance with a high degree of malleability-which may allow it to be integrated into solar panels and other useful locations.

Proponents note that lithium polymer has proved safer than its sometimes-volatile predecessor, liquid lithium ion, and is now showing up in cell phones. Lithium polymer also has three times the energy density of the nickel cadmium (NiCad) rechargeables now ubiquitous in notebook computers, cell phones and toys.

The solid electrolyte’s malleability particularly intrigues people in the space and defense communities. “You can put it in small places or wrap it around things,” says Sheila Bailey, an expert in photovoltaics at the NASA Glenn Research Center in Cleveland.

Photovoltaic Finish

Bailey is the technical monitor for a $64,614 research grant awarded in July to Lithium Power Technologies of Manvel, TX, by the Ballistic Missile Defense Organization. (BMDO is the Arlington, VA-based group overseeing the Bush administration’s “Star Wars” missile defense program.)

Lithium Power will attempt to build a hybrid that combines thin-film lithium polymer with existing photovoltaic technology.

The combination could be shaped to form the main structural panels of spacecraft, saving space and allowing lighter weight or more power, claims Lithium Power president Zafar Munshi. BMDO is interested because of the potential to build lightweight micro- and nano-satellites, a key component in future versions of the missile defense system.

Eventually, cars might have similar surfaces generating power for their electrical systems (though not electric motors), Munshi says.

The first phase of the project aims at proving the feasibility of combining solar technology with thin-film polymers. “We’re going to be building some hardware to demonstrate the basic concept,” Munshi says. If the second phase is funded, commercial products, such as global positioning system (GPS) devices with roll-up solar cells that provide power in remote areas, could arrive within two years, Bailey predicts.

Jeff Bond, program manager with the BMDO’s small business innovation research group, cautions that combining thin-film batteries with existing photovoltaics is no easy task. “What Lithium Power is proposing in this phase is extremely high risk,” he says. “We’re looking to fund the wild ideas, if you will. We don’t have any specific requirement right now to use the technology.”

The main hurdles, Bailey says, are improving the energy efficiency of thin-film photovoltaic cells and lithium polymer batteries, reducing heat and developing the needed systems for power management and transmission. Building batteries that are more resistant to cold is another challenge.