Energy Storage News

Aquion Energy to manufacture low temperature sodium carbon batteries for large scale stationary storage applications

A company called Aquion Energy has developed a new type of sodium ion battery which it claims has superior performance and economic characteristics compared to NGK Insulator's molten salt sodium sulfur (NaS) batteries. They are targeting large scale grid storage applications with this technology.

Some information about the batteries taken from Dr. Jay Whitacre's presentation at the 2011 Electricity Storage Association Annual Meeting is listed below:

Some additional information taken from Aquion Energy's Applications web page is given below:

Attribute Demonstrated Targeted
Cycle Life at 100% DOD >5000 >20000
Calendar Life 2 years >20 years
Temperature Range -10°C - 60°C -40°C - 80°C
Round Trip Efficiency (DC to DC) 90% 95%
Temperature Range -10°C - 60°C -40°C - 80°C

The quoted energy density of 30Wh/l is comparable to lead acid batteries but is low compared to lithium ion batteries (160Wh/l). This low energy density explains why they are targeting stationary storage applications.

If they can really deliver the advertised 20,000 cycle life time then this battery will represent significant long term cost improvement over NGK insulators NAS batteries which have only a 4500 cycle lifetime at 90% DOD. A cost calculation ignoring interest is given below:

Cost/kWh = $300/20,000 = $0.015/kWh

One must add to this cost the efficiency penalty of:

Efficiency cost: base generation cost (1-η)/η

where η is the round trip efficiency. So, for example if the AC to AC efficiency is 0.8 and the energy being stored costs $0.10/kWh the efficiency cost is $0.025/kWh. These costs are certainly lower than those of NGK Insulator's batteries which cost more than $400/kWh and which have a life expectancy of only 4500 cycles. However, one must keep in mind that these are long term equilibrium costs applicable to a situation where storage capacity is constant and only worn out batteries are replaced as needed. During a situation of vigorous growth where lots of new capacity is being installed which will take many years to deliver full value (at 1 cycle per day 20,000 cycles represents 54 years!) the cost will be much higher than those calculated above.

The high range of operation temperature is good because it helps to avoid paristic energy loss due to temperature control measures.

Another good thing about this battery design is the electrode materials are earth abundant materials: Sodium(2.3%), Manganese (0.1%), Carbon, and Oxygen. Which the use of such abundant materials means that this technology is probably scalable to large production volumes.

The fact that Aquion is planning to start large volume manufacturing in 2013 indicates their belief that this battery design is far advanced. Of course a 'chicken or the egg' problem exists with technologies which are cheap due to long service lifetimes: In order to convince customers to pay the high up front costs you need to show field data demonstrating reliable performance, and in order to get this field data you need customers. Even if a potential market niche for your product at a particular price point exists it may take a long period of time to establish yourself in that niche.

Sep 04, 2011

Energy Storage News

rogerkb [at] energystoragenews [dot] com