Photosynthesis-like technologies offer a sustainable future even as world populations grow by generating and storing the energy to run homes and cars on-site, according to the inventor of a new renewable personal energy system at the Massachusetts Institute of Technology.

Personal energy (PE) is the goal of professor Daniel Nocera, director of both the Solar Revolutions Project and the Eni Solar Frontiers Center at MIT. According to Nocera, PE systems emulate the way a plant transforms solar energy into a fuel that can be used at night and on cloudy days. PE aims to enable a renewable, sustainable future, even as the world's energy needs double by 2050.

PE works by creating a self-contained energy generation and storage system at its point-of-use location. As the world population grows by another 3 billion by 2050, demand for energy can nevertheless be kept carbon-neutral by adopting a PE model for energy generation, as opposed to the centralized energy generation and distribution grids used today. PE generates electricity with solar panels during sunny days that is stored as liquid fuel on-site, then converted into electricity by fuel cells that are drawn upon at night to power homes and recharge plug-in hybrid vehicles.

According to Nocera's new report titled "Chemistry of Personalized Solar Energy," rival methods of storing solar energy do not offer high enough energy density to realize PE, including current proposals by others to use compressed air, flywheels, super-capacitors, pumped water and batteries.

Battery technology is advancing with regard to increased lifetime and power density—the rate at which a charge can flow in and out of the battery. However, Nocera claims that the needed energy density—the amount of energy stored per unit volume—required to realize PE can only be met by storing energy in liquid fuels during the day at their point of use, the way a plant does using photosynthesis.

Key to success of such a system is the efficiency of a photosynthesis-like method of splitting water molecules into oxygen and hydrogen that can be stored in separate tanks, then recombined by a fuel cell to provide electricity to the home and car when sunlight is not available.

According to the report, a deeper understanding of the water-splitting catalysts that emulate photosynthesis has been sought by chemists over the last several decades. Nocera claims his team has now discovered a cobalt-based catalyst that realizes this dream for the first time. Using his cobalt-based catalysts provides a manufacturable, efficient and inexpensive method of splitting water into hydrogen and oxygen for PE.

By emulating the functional elements of photosynthesis, Nocera's team is currently working toward realizing the potential of personal energy systems for creating a renewable, sustainable future.