Here's a renewable energy source most of us haven't thought of: dirt.
Living Power Systems, a company being spun out of Harvard University, has made a microbial fuel cell that is able to tease a trickle of electricity from garden-variety bacteria in the ground.
The ability to generate a tiny flow of electrons from organic material has been understood for decades and is a staple at elementary school science fairs.
Living Power Systems has developed a system that it says can create a useful amount of power, at least for specialized uses.
Its technology consists of a material that encourages microbes in the ground to grow across the surface of an electrode and specialized circuitry that siphons off the electricity microbes create during metabolism.
"There are terawatts moving through our biosphere. Solar energy ends up in our soil and sediment," Peter Girguis, the founder and chief scientist of Living Power Systems and professor of microbiology at Harvard. "Think of it as underground solar energy."
The company, which is now looking for funding, has built prototypes of a few products for low-wattage applications.
One, called the Light Bucket, will provide enough electricity for an LED light and a cell phone charger to people in the developing world who are not connected to an electricity grid. The company is also designing a power supply for wireless sensors and outdoor lighting.
These devices only need to plug into the ground to operate, according to Girguis, who made a presentation along with other clean tech companies at the Conference on Clean Energy in Boston on Tuesday.
Although the company is targeting a few specific markets initially, Girguis said that microbial fuel cells have the potential to provide 15 percent to 20 percent of household energy by tapping into the electricity in people's yards or septic systems. The technology could be used to power a cell phone tower today, he said.
Right now, its devices can generate about one half a watt per day from a square meter of ground, or 12 watt-hours per day. In its labs, it's been able to generate 10 times that amount, according to Michael Keating, the company's co-founder and acting CEO.
That kind of power generation won't run a refrigerator or even a PC screen, but it does make sense in the developing world, Keating said.
Company executives call microbial fuel cells the "bicycle of electricity" because they are simple to operate and can be manufactured locally in developing countries.
Natural versus designer microbes
Wireless sensors, too, are compelling use for microbial fuel cells because of the high costs involved in replacing sensor batteries, company executives said.
For the past two years, a device using the company's technology has been drawing electricity from the sediment at the bottom of Monterey Bay in California. The sonar navigational beacon for nuclear submarines was deployed as part of a military grant. A device in a lab has been operating for six years.
"The best implementation of this is to use it in a setting where you want to deploy a device and leave it alone," Girguis said.
A number of organizations are researching microbial fuel cells, including universities that are designing microbes specifically to generate electricity. Synthetic Genomics, headed by genetics pioneer J. Craig Venter, and other firms are looking to make by manipulating microorganisms.
By contrast, Living Power Systems is focused on trying to harness energy from naturally occurring bacteria rather than those specially designed for power generation, said Girguis.
Next year, the company intends to have products for a combined light and cell phone charger aimed at the developing world. It expects to have its garden light and wireless sensor power supply next year as well, according to Keating.