Artificial Photosynthesis: Creating Solar Fuel

SolarThermanPower

Over the long term, new energy sources will be needed to meet increasing energy demand, mitigate climate change, and provide energy self-sufficiency at the national and regional level. Ideal sources would be abundant, renewable, carbon neutral, portable, and affordable and make use of the existing energy infrastructure.

The energy needs of living organisms are met directly or indirectly through photosynthesis, a process that converts sunlight into fuel. Renewable energy strategies already convert sunlight to electricity with photovoltaic cells and convert biomass—a product of photosynthesis—to fuel such as ethanol.

But there are other paths to using the sun’s energy. An area of nascent research seeks to mimic photosynthesis itself—to convert sunlight directly to fuel. While the hurdles are daunting, the prospects for abundant, clean, renewable energy are intriguing.

3 WAYS TO CONVERT ENERGY FROM SUNLIGHT

It’s been estimated that 10 trillion watts of clean-energy generating capacity must be developed by 2050 if global warming is to be contained. The best hope for generating that much power is sunlight—as enough solar energy strikes the earth in an hour to supply humankind’s energy needs for a year.

But considerable technology development will be required to harness even a fraction of the sun’s power. And not all sun-based solutions may be equally effective. For example, land and water availability limit solutions based on biomass. On the positive side, solutions that create liquid fuels have the distinct advantage that they can use existing fuel-distribution infrastructure.

The majority of the energy consumed on Earth already derives directly or indirectly from sunlight; nuclear and geothermal energy are the exceptions.3 Most of the energy from sunlight is produced by photosynthesis; fossil fuel energy is ultimately derived from photosynthetic organisms.

There are a variety of ways to convert sunlight to energy without waiting for geologic processes to convert biomass to fuel. (Those that create fuel, as opposed to electricity, have been called “gas without the death or waiting.”) Some are in commercial use while others will require substantial development before they become commercially viable.

  • Converting sunlight to electricity. Photovoltaic materials convert light energy to electrical energy, using solid-state devices or dye-sensitized solar cells.7 Concentrating solar power (CSP) uses sunlight to warm a heat-transfer fluid; the hot fluid is used to generate steam; the steam drives a turbine that produces electricity. The key limitation of these processes is the need for energy storage—sunlight is available during only a portion of the day. CSP has the advantage that energy may be stored temporarily in the form of heated fluid rather than as electricity.
  • Converting plants to fuel. Biomass—e.g., corn, switchgrass, or algae—can be converted into biofuels such as ethanol or biodiesel. The key limitations of this approach are relatively low efficiency in terms of land, water, and fertilizer resources, and competition for agricultural resources used for food.
  • Converting sunlight to fuel. Direct solar-to-fuel conversion has the potential to solve two of the planet’s greatest energy- related issues—carbon emissions and energy security.9 There are a variety of ways to convert sunlight to fuel, directly or indirectly. These have the great advantage that energy can be stored and transported efficiently—as is already done today with fossil fuels. The various methods use electrochemical processes, biological catalysis, or chemical catalysis.

3 BUSINESS IMPLICATIONS

  • While there is considerable disagreement about which new energy sources to develop, the technological pathway to pursue, and how long it will take, it’s clear that everyone who consumes energy needs to prepare for changes in the way that energy is produced, how much energy costs, and possibly the way energy is delivered.
  • There is a sometimes-bewildering array of ways to harness the sun’s energy, each with passionate advocates. The shift in energy technologies will play out over decades, possibly with twists, turns, and false starts, before a new equilibrium is reached.
  • Artificial photosynthesis is realistically a decade or so from producing a viable device that can serve as the basis for development, and possibly two decades or more from commercialization at scale. Organizations that could benefit from the commercialization of this technology should continue to monitor progress and perhaps fund academic or startup research in order to stay abreast of new developments and involved in early-stage investment and exploration.