banner by Sarah Burns
Growing Energy Demands: How to Hack Photosynthesis
by Samantha Grimes
We need a smarter energy system. The United States Energy Information Association predicts global energy consumption will increase by 56 percent between 2010 and 2040. This means that annually, the world will exhaust over 8.65 x 1020 joules of energy, the equivalence of burning 820 quadrillion matches, which translates to more than 103 million matches for each person on the planet. Compounding this daunting reality, annual carbon dioxide (CO2) emissions are anticipated to continue increasing through 2040, even with international agreements to begin reductions.
While transitions away from fossil fuels and toward cleaner, more sustainable energy sources are already underway, in order to be truly proactive in the future of energy, new solutions must be incorporated into everyday life. Solar, wind, hydroelectric and geothermal energy each have benefits, but none can function as a singular solution to global energy demands. Thus, combinations of sustainable energy technologies could lead to more security in providing the greatest amount of clean energy, while mitigating risks or inconveniences to communities. The aforementioned technologies might not be the only sources of renewable energy in the near future, however, as two new technologies might provide novel methods for harnessing energy. As with all searches for energy, their conception ultimately leads back to the sun.
The Artificial Leaf
Photovoltaic cells and panels, another name for solar panels, have recently gained notoriety in the United States for several reasons. Decreasing costs of panels, subsidies offered for households installing them, the increasing ease of installing them and the potential to bring power to rural areas have all made solar power more attractive. However, photovoltaic cells are not the only way to directly harness solar energy– artificial photosynthesis has recently become a reality with the “artificial leaf.”
In nature, photosynthesis is surprisingly inefficient. The process rarely exceeds 1 percent efficiency in most plants, though occasionally peaking at 3 percent efficiency in some algal species. Artificial photosynthesis, as reported by the Joint Center for Artificial Photosynthesis at Caltech, runs at an efficiency between 3 to 4 percent, consuming just CO2 present in the atmosphere, to 10 percent efficiency with the addition of pure carbon dioxide gas.
Composed of three main components, two electrodes and a membrane, the artificial photosynthesis system uses sunlight to oxidize water molecules at one electrode to produce protons, electrons and oxygen gas, while recombining protons and electrons at the other electrode to produce hydrogen gas. A plastic membrane prevents the oxygen and hydrogen gas from mixing, and a nanometer-thick coating of titanium dioxide on the electrodes increases stability and keeps them from corroding. Though this system is currently less efficient than photovoltaic panels, which normally operate between 12 and 17 percent efficiency, the 2015 model is still in its preliminary stages of successful application and has plenty of room to grow, so to speak.
What’s more, the artificial leaf still faces a financial barrier in entering commercial production. While it is slightly more cost-efficient than solar panel systems rigged with electrolysis to produce hydrogen fuel, it still costs $6.50 to produce a kilogram of hydrogen with the artificial leaf, whereas fossil fuels only cost between $1-2 for the same output. Nonetheless, new designs are constantly being tested to find the most efficient methods of light absorption. Ultimately, the artificial leaf might still sit on the precipice of revolutionizing energy production.
Energy from Plants
If commercialized systems of artificial plants are not yet viable options for mass energy production, perhaps the next step in the search for alternative energy is harvesting energy from plants we already grow as food sources. In 2007, global agriculture resulted in over 1.2 billion hectares of crop cultivation, a land area that will most likely increase in the coming decades in order to account for increased demand on the agricultural industry. The natural resource exists, and the question simply stands as to how best it can be utilized.
Researchers at the University of Georgia have developed a method for interrupting the photosynthetic process in order to capture the electrons flowing in photosynthesis. This is done by isolating thylakoids, structures containing pigment which captures light for photosynthesis, in plant cells, and subsequently modifying and immobilizing thylakoid proteins on carbon nanotubes. The carbon nanotubes then function as electrical conductors, capturing electrons as they are produced by the plant cells.
Inspired by this and similar research, a Dutch company called Plant-e has developed a different functional system that also captures electrons, but is unique in that it does not have any measurable impact on the overall process of photosynthesis or otherwise harm the plant. In this system, called a Plant-Microbial Fuel Cell, electrodes are inserted in the soil surrounding the plant roots and take up the electrons and protons released from the microbial breakdown of the excess sugars released through the roots. The Dutch system specifically focuses on utilizing marshy plants and grasses and is currently being implemented to power lower energy demands, such as street lights and WiFi, because the energy output is not particularly high.
Even when optimized with the current design, a Plant-Microbial Fuel Cell will average producing just over three watts per square meter.[ Nonetheless, the system is easy to install and maintain, and can be used with relative ease across large swaths of agricultural land, something Plant-e intends to make the most of in order to bring sustainable energy to rural areas. Though no large-scale units are currently for sale through the company, and research is ongoing, Plant-e currently sells small-scale educational units that power LED lights.
Though both the synthetic leaf and energy harvested directly from plants are in the beginning stages of development, exciting progress has been made in pushing these technologies toward usable forms that can provide sustainable energy to more communities. While the synthetic leaf is more efficient than directly harvesting energy from plants, and has the benefit of taking in CO2 and releasing oxygen gas, the drawbacks, namely its cost and singular function of creating energy make direct-harvest, which makes use of an existing resource, an attractive option. Integrating energy collection and storage capabilities into agricultural land plots could bring sustainable energy to rural populations without disrupting plant growth or placing additional demands on the community through difficult upkeep. Furthermore, Plant-e’s design could encourage the implementation of sustainable energy systems into urban agriculture in order to produce multi-purpose green spaces that will complement other forms of sustainable energy. While neither artificial plants nor real plants are the global solution for an energy overhaul, their implementation might encourage more cohesive systems that remain mindful of the ever-growing need for energy.