Thursday, May 21, 2009

EnerVault, Flow Batteries, and the need for Energy Storage

Most renewable energy technologies are intermittent. Solar power comes from sunshine, Wind power comes from wind, etc. Some renewable energy technologies are constant though, like the flow of rivers through a dam or the flow of tides. It is Solar and Wind power that has the brightest promise but it's difficult to envision powering a city only when the wind is blowing. What if it's a hot day with no wind and everyone wants to crank up the air conditioners? Thus relying on intermittent wind power doesn't pass the Aunt Millie test. Society has grown to expect electricity to always be there in abundant quantities. Hence for renewable energy technologies to fill that role, there must be affordable energy storage systems.

EnerVault is a stealth mode startup company working on on "Flow Batteries" for large scale energy storage. Unfortunately there is very little information out there so this article has to do some detective work.

First, what the heck is a flow battery? Flow battery (Wikipedia) says:

A flow battery is a form of rechargeable battery in which electrolyte containing one or more dissolved electroactive species flows through a Electrochemical cell that converts chemical energy directly to electricity. Additional electrolyte is stored externally, generally in tanks, and is usually pumped through the cell (or cells) of the reactor, although gravity feed systems are also known.[1] Flow batteries can be rapidly "recharged" by replacing the electrolyte liquid (in a similar way to refilling fuel tanks for internal combustion engines) while simultaneously recovering the spent material for re-energization.

Fuel cells are electrochemical energy conversion devices that convert chemical energy directly to electrical energy in which a fuel and an oxidant undergo electron transfer reactions at the anode and cathode of an operating electrochemical cell respectively, separated by an ion exchange membrane. These devices are not subject to Carnot's limitations and can ideally generate electricity as long as they are supplied with fuel and an oxidant. They differ from batteries in that the active chemical species are stored inside the battery where as they are supplied externally in the case of fuel cells. So, power and energy specifications can be scaled up independently for a fuel cell where as the energy density of a battery is limited by the amount of active material that it can stored inside it.

Flow Batteries: EnerVault Quietly Building Energy Storage for the Grid

Claim: $100 per kWh compared to $500 per kWh for Lithium-ION batteries

EnerVault is in a round of raising capital to build a demonstration unit.

Their CEO gave a presentation at the CleanTech conference at UC Berkeley on May 6, 2009. ( unfortunately it seems they don't publish video anywhere. This is the bio given for him:

Craig Horne: Chief Executive Officer, EnerVault

Dr. Craig R. Horne is CEO and Co-Founder of EnerVault Corporation, a start-up company developing next generation energy storage solutions for the grid and renewable energy installations. Craig's long commitment to a better planet has guided his 20 year career in cleantech spanning solid oxide fuel cell, Li-ion battery, Pb-acid battery, and Redox Flow Battery technologies. During his career he has served leadership roles at NanoGram Corporation, NeoPhotonics, Kainos Energy, and World Energy Labs. Craig currently serves on the Technical Advisory Boards of NanoGram and Amprius and previously was an Advisor to NanoGram Devices. Craig has over 15 publications and has been awarded 14 US patents in equipment, processes, and nanomaterials-based components for lithium ion batteries, photonic devices, and fuel cells. Craig earned degrees in Materials Science and Engineering from University of Florida (B.S. with High Honors), UCLA (M.S.), and UC Berkeley (Ph.D.). While at Berkeley, he minored in Energy and Resources and received several awards for his work in Li- ion battery active materials. Craig has twice served as Chair of the San Francisco Section of the Electrochemical Society, currently serves on the Sunnyvale Mayoral Green Ribbon Committee, and is an active volunteer in Sunnyvale community organizations and schools.