SUMMARY: Microbial power systems: Generating clean energy from dirt
The results of our research prompted us to consider using microbial fuel cells as energy generators for the developing world. To that end, we defined the criteria for a microbial energy generator using a systems approach. We began by determining that if microbes mediate 50% of the energy flux through terrestrial system (a conservative estimate), and humans occupy 35% of the Earths’ terrestrial surface, we could potentially access 9 tW of power annually via microbial processes alone.
PROBLEM SPACE: The Energy Crisis and poverty: humanity’s largest problem.
Over half of the world’s population, 2.8 billion people, live in rural areas of developing countries. The vast majority live without access to distributed electricity. In today’s electronics age, electricity is the key to improving quality of life. In a recent report, the World Energy Council (WEC) determined that the “lack of electricity reduces the potential for achieving the major changes in rural economies that lead to … the alleviation of global poverty”.
There is broad recognition that demand for electricity in the developing world is immense. 56% of Indians (India) live without continuous access to electricity, but rural Indians continue to be a major consumer of electronics. In 2006 alone, there were nearly 70 million new cell phone subscribers (2006) in rural India. To provide power for their devices, customers commonly use 12-volt car batteries to recharge phones (the batteries are hauled between the home and a recharging station, often kilometers away). This inefficient and dangerous practice underscores the length to which people will go for electricity.
To date, numerous alternative energy sources have been proposed or implemented to some degree in the developing world. By and large, these systems harness solar power, wind power, human power (hand cranks) or bio-fuels. Each of these technologies has serious practical limitations. As such, only a small percentage of people to date have continuous access to electricity.
Are we energy limited?
There is no shortage of energy in our environment. The Earth receives about 122,000 terrawatts (tW) of solar power annually. 2.5% of solar energy (3,050 tW) is is theoretically available as solar power. About 0.2% of this energy (244 tW) is theoretically available as wind power. Biomass captures nearly an equal amount of energy, circa 200 tW annually. Today, the world uses 13 tW of power per year (refs on Wikipedia), and is projected to use 30 tW by 2025. Thus, we are not energy limited, but rather limited in our means of harnessing energy.
To date, solar and wind power technologies are not readily accessible to the majority of people on Earth. They are costly and sophisticated, and manufactured in industrialized urban centers of wealthy nations. If we intend to make electricity accessible to all people, it is apparent that we must develop new affordable and accessible alternatives.
SOLUTION: Microbes: stewards of planetary energy
Despite their diminutive size, our biosphere is driven by microbes. Microbes are responsible for over half of Earth’s primary production, exist everywhere in our biosphere, and are the most physiologically tolerant life forms known.
Most important, a great many microbes in nature live without oxygen. Microbes in soil are even capable of using solid minerals instead of oxygen. Our research (Girguis et al 2005, Reimers, Girguis et al 2006, Girguis and McBride, 2006) has shown that a tremendous number of microbes in nature are capable of this extracellular electron transport (or EET). This allows microbes to deposit electrons onto solid surfaces. By analogy, this is akin to a person eating a cheeseburger and “breathing” by touching a metal file cabinet. While this capacity may seem exotic, it allows microbes to live in anaerobic environments and use minerals to generate energy.
Microbial fuel cells: harvesting electrons from microbes
Microbial fuel cells (MFC) are devices that directly harness the energy from microbial metabolism by fostering the growth of microbes onto a solid inert electrode, or anode (Figure 1). The anode is made of a conductive material such as graphite, and the energy from microbial metabolic processes --specifically the electrons harnessed via EET-- is conducted towards the cathode, directly converting microbial metabolic activity to electrical power.
To date, most MFC research has used pure bacterial cultures in the laboratory to produce power (Logan et al 2006). However, our recent research focuses on studying microbes capable of generating power in natural systems (Figure 2). Unlike prior research, we observed that numerous microbial species were capable of growing on the electrode and generating energy. We also observed that 2 to 15 watts of power are continuously produced daily (with the lower power output coming from very poor soil at freezing temperatures). Our field experiments were the first to demonstrate the ability to generate significant power in a variety of natural environments.
This fueled our desire to develop a microbial fuel cell that would directly harness electricity from the environment, in the most efficient manner possible, at the lowest cost possible, with the intent of providing electricity to the 1 billion people in Earth who live without electricity.
With support from the Lindbergh Foundation, we developed an three microbial power generators (MPGs) for the developing world. Our simplest version is the bucket light (Fig. 3). The fuel was soil, cow manure and fruit scraps. To minimize cost, I used low-grade charcoal as the anode and cathode. The power was stored in supercapacitors, which were then placed in series to boost the voltage and illuminate and LED. The bucket light provides approximately 2 hours of intense light (ca. 150 lumens) or four hours of mild light (80 lumens, sufficient to illuminate a room for reading or work). Most importantly, the bucket light runs for one year without refueling or servicing, runs continuously whether light or dark, hot or cold, rain or shine. After one year, the user replenishes that fuel, and the system is up and running within 6 hours. The bucket light MPG is designed to operate in excess of ten years, so long as fuel is replenished annually (note that we have one system deployed outdoors that has been running for six years straight!). Note that the market for lighting fuel alone in the developing world is $38 billion (for kerosene).
Our next system is an MPG cell phone charger (Fig. 4). Our MPG cell phone charger costs approximately $20, and has 9 times the energy density of our rudimentary cell due to patented electrode treatments and energy management circuitry which controls the population dynamics and evolution of microbes on the anode and cathode. We designed our energy management circuitry to poise the anode and cathode potential at that voltage which stimulates greatest power production. This in turn serves as a positive feedback loop, stimulating and sustaining the growth of microbes that perform better at EET. A variation in this theme is our waste/sewage-fed MPG for providing all the basic power needs of a family. We have built two prototypes and have been measuring power production during the last three months. We anticipate this system will cost approximately $40 USD. This system harnesses power from sewage or composting. It is deployed outdoors in a leach field or compost pile. The electronics are comparable to our cell phone charger, although the power output is 96 watts of power each day. This is sufficient to power enough solid-state lighting for a home, as well as provide more than sufficient power for cell phone charging, radios and computers (e.g. the $100 laptop from MIT).
MPGs: deploying a potentially disruptive technology
Currently, we are deploying prototypes in rural regions of India (with the Indian Embassy and the Indo-US Sci-Tech Forum), as well as Africa (via funds I’ve raised from family and friends). To date, we have received great enthusiasm for our product from both the end-users and potential distributors.
In consultation with Iqbal Qadir (founder of Grameen phone in Bangaldesh) and Amy Smith (developing world expert, winner of the MacArthur award, and lecturer at MIT), I have founded a company called Living Power Systems that has exclusive rights to the technology I have developed at Harvard. It is our intention to partner with Grameen phone and the rural electric company of India, to distribute our products through existing distribution networks. The net result is a business that is profitable to local distributors and manufacturers, as well as our company. This will sustain MPG technology development in the US.
MPGs represent a comprehensive approach to power production, and address the burgeoning needs for power in today’s world. They are eco-friendly, verifiable, replicable and achievable. If we truly intend to better all of humanity, it is apparent that we must develop alternative energy systems. We believe that MPGs present the single best opportunity to provide people with an opportunity to generate energy for themselves in an environmentally sustainable manner. As Bhagavad Gita once said “to the illuminated person, a clod of dirt, a stone and gold are all the same.” MPGs may soon prove that to be true.