Creating Renewable Energy from Living Organisms

In recent years, researchers have more aggressively explored how plants, animals, fungi and bacteria can help us develop next-generation fuels and electricity. Nature, it seems, has much to teach about the efficiency of energy conversion and consumption.

Take photosynthesis, for example. When a plant’s pigment molecules absorb photons, they enter an excited state that is moved to the “reaction center,” a chlorophyll molecule called the protein complex. The reaction center is where the plant first generates chemical energy. This energy transfer is instantaneous and happens with almost 100 percent efficiency. Now researchers are trying to figure out how to design photovoltaic cells that mimic this virtually flawless process.

Greg Engel, an assistant professor of chemistry at the University of Chicago, is a researcher looking at this first stage of photosynthesis on the quantum level. He and other researchers have found that the energy transfer is actually a wave-like process, which allows the excitation to “feel” it’s way to the reaction center and sample many different pathways at once. That, says Engel, is why the process is so efficient.

“We need to start tweaking the system and understand how delicate a balance this is so that we can begin to get a feel for how we may build a similar system ourselves,” says Engel.

In a plant, the pigment molecules and the reaction center make up an antenna complex, which harvests the sunlight. One way to recreate the energy transfer is to build a large “living antenna” around a photovoltaic (PV) cell, says Engel. Because the average monocrystalline PV cell is around 11-15 percent efficient, modules must be bigger to collect more photons. However, with an antenna that collects more of the photons available, future modules wouldn’t have to be as big.

“Understanding how to do this with synthetic biology is still yet unclear,” says Engel. “This is probably a technology that is still decades away, but it stands to revolutionize the efficiency of solar collection.”
 
While the solar industry may be far away from mimicking photosynthesis, some bioenergy companies are mastering the process to grow algae specifically for fuels. These prolific plant-like organisms have the potential to produce massive amounts of oil that can be converted into ethanol and biodiesel. In fact, 40-50 percent of the body weight of certain algal strains can be oil. And if grown in the proper conditions, algal colonies can double in volume overnight. These factors explain why there are now over 30 companies around the world harvesting algae for fuel.

Sure, algae seem to be everywhere — in the neighborhood pond, lake or swimming pool. But it takes a very methodical, scientific approach to growing the right kind of algae that carry high amounts of oil.

“Everyone thinks, how tough can it be to grow algae? But in fact, in order to get high enough productivity, we really have to do some tricks to get the algae to grow at a fast enough rate to be commercially viable,” says Brian Willson, chief technology officer at Colorado-based Solix Biofuels.

Willson oversees the progress of Solix’s “biophotoreactor,” a closed-production system (as opposed to an open pond) made up of long plastic ribbons filled with algal colonies. Light is spread throughout the reactor at mid to low intensity levels, allowing for higher photosynthetic efficiencies. Then carbon dioxide is pumped in, giving the algae more “food” for growth. Once harvested, the algal oil can be converted into biodiesel and the carbohydrates can be made into ethanol.

According to Willson, Solix may be able to produce 7-8,000 gallons of oil per acre within the next 4 to 5 years. By comparison, palm only produces around 650 gallons of oil per acre. However, creating the optimal conditions to grow that much algae is still an issue. The company is currently experimenting with sunlight levels, salinity, water temperature, and nutrient levels, trying to get the process perfect in order to achieve high yields, says Willson.

“All the companies out there are still figuring these [growing conditions] out. I think you’re going to see more production this year, but it’s going to be a couple of years before you see significant quantities. It’s my view that it’s probably going to be 2012, 2013 before this becomes a contributor in terms of anything close to interesting levels of production,” says Willson.

In the meantime, the cellulosic ethanol industry is trying to get to meaningful levels of production too. One of the big issues facing producers is how to get the best mix of enzymes to cost-effectively break down cellulose, hemicellulose, and lignin from biomass into sugars for fermentation. Again, researchers in this sector are turning to various organisms for the answers.

One of the biggest enzyme producers, San Diego-based Verenium Corporation, is looking at extracting enzymes from the stomachs of termites. The enzymes inside a termite’s digestive system help it break down 95 percent of the biomass material it consumes within a 24-hour period. That fact, says Bill Baum, general manager of Verenium’s Specialty Enzymes Business Unit, led the company to explore what could be done to turn these pests into heroes.

“These guys are just like little biorefineries…so we wanted to go in and identify a lot of these enzymes that are doing this. So we extracted the DNA and we were able to identify hundreds of new cellulase enzymes that we’d never seen before,” says Baum.

The result has been a “cocktail” of enzymes that are able to efficiently break down a variety of biomass feedstocks. However, the product is still much more expensive than Verenium’s other enzymes mixes, says Baum. It may be a few years before termite guts start eating away the market share of traditional sources of fuel.

Steve Hutcheson, CEO and President of the start-up company Zymetis, says that his company is developing a mix of enzymes that will significantly lower the cost of breaking down cellulosic material. Zymetis is working with a bacterium found on marsh grasses in the Chesapeake Bay that produces the most diverse culture of cellulose-eating enzymes known. In addition, says Hutcheson, the bacterium can be coaxed into making more enzymes that are better suited for cellulosic ethanol production.

“Having the diversity of enzymes and the ease of being able to extract enzymes from the culture makes it very inexpensive to produce,” says Hutcheson. “We think this is a big step for the industry.”

Zymetis says that the growth and preparation of the enzymes will cost ethanol producers around 30 cents per gallon of fuel. The average cost today is around 35-50 cents per gallon. Hutcheson says that the Zymetis process could lower to around 15 cents per gallon over the next couple of years.

“Wait a few years” seems to be the common theme as companies try to develop these new forms of energy. It could be decades before PV cells mimic photosynthesis; it could be five years before we start growing meaningful amounts of algae for fuel; and it may be a few years before cellulosic ethanol makes its way onto the market. But compared with the tens of millions of years it took to make the dirty fossil energies we use today, waiting a few years for clean, renewable energy doesn’t seem that long to these companies.

“It’s not about if we can commercialize these technologies, but when,” says Verenium’s Bill Baum. “It won’t be overnight, but I’m hopeful that the next-generation of energies from these organisms is upon us.”