Microbial Battery Grid-Scale Storage CellVolt: Gene-Edited Bacteria Store Grid-Level Energy

CellVolt, jointly released by the MIT Center for Synthetic Biology and bioenergy startup CellGrid Energy, is a new energy storage technology that uses gene-edited bacteria to store grid-level energy. The technology redesigns energy storage with a synthetic biology approach: bacteria discharge when in use and store energy when charging, enabling long-duration, large-capacity, low-cost grid-level storage.

The project grew out of reflection on the limitations of lithium batteries. Although lithium batteries have high energy density, they suffer from cycle life and cost issues for grid-level long-duration storage scenarios (continuous discharge for more than eight hours). The MIT team explored a completely new approach: using gene-edited bacteria as the energy storage medium. The metabolic processes of bacteria can be precisely controlled, allowing them to store organic molecules when powered and break down these molecules to release electricity when discharging.

The core technology is the engineered Geobacter. The MIT team made a series of genetic modifications to Geobacter: knocking out three genes that reduce electron transfer efficiency, inserting two genes that enhance conductive pilin protein expression, and optimizing the key cytochrome c. These modifications boost the electrochemical activity of Geobacter about eightfold, allowing cell density to reach about 1 billion per milliliter.

On the storage principle, the CellVolt system consists of two large bioreactors. When charging, current is fed into the reactor, and the Geobacter convert electrical energy into acetate stored within the cells. When discharging, the Geobacter break down the acetate, and the released electrons are collected on the electrodes as current. The entire process involves no rare metals, requiring only organic culture medium (molasses works), water, and air.

For measured performance, the Energy Research Center at the University of California, Berkeley tested the CellVolt prototype system for 18 months. In simulated grid peak-shaving scenarios, the system achieved a cycle efficiency of 82 percent, significantly higher than the 65 percent of mainstream lithium-ion battery packs. More importantly, CellVolt has a cycle life exceeding 10,000 charge-discharge cycles, far above the lithium battery pack's ceiling of about 3,000 cycles. Daniel Nocera, CTO of CellGrid Energy, said this long life stems from the self-healing ability of bacteria. Damaged cells can divide and reproduce to replace themselves.

On the commercialization path, CellGrid Energy will build the first CellVolt commercial storage station near Sacramento, California in the second half of 2026, with an installed capacity of 50 megawatt-hours. The station will interconnect with the California grid, taking on the task of storing excess solar power during the day and dispatching it during nighttime peak hours. The company also announced a 10-year agreement with Pacific Gas and Electric (PG&E) for PG&E to purchase a total of 500 megawatt-hours of CellVolt storage. Professor Nocera said the cost target for CellVolt is 80 dollars per kilowatt-hour, about 40 percent below lithium batteries.

On safety and environmental aspects, CellVolt has significant advantages. Geobacter is a completely non-pathogenic environmental microbe, unable to reproduce in the human body or cause infection. The system does not produce any toxic byproducts during operation, and the final culture medium can be used as agricultural fertilizer. Professor Christopher Voigt, who directs the MIT Center for Synthetic Biology, said this kind of biological storage represents the most important application of synthetic biology in the energy field, with potential future extensions to carbon capture and hydrogen production.