NaS Energy StorageCindy Zhang and Lisa Li

Why is Energy Storage Important Growth in renewable energy technologies requires better energy storage solutions.

Many renewable energy resources are intermittent. - ie. Solar, Wind, and Wave

Mismatch between power availability and demand.

Electricity demand vs wind supply graph [1]

NaS Batteries as Energy Storage

PEAK SHAVING

● Storage discharges when demand is above the upper limit.

● Storage charges when demand is below the lower limit.

Peak Shaving Case [1]

NaS Batteries as Energy Storage

LOAD LEVELING:

● Storage charges excess power during lower demand.

● Storage discharges during higher demand.

Load Leveling Case [1]

Comparison of Energy Storage Technology NaS POSITIVE CHARACTERISTICS:

● High power and energy density ● High efficiency ~ 90%● Utility scale application:

- Power rating: 1 - 100 MW - Capacity: 10- 1000 MWh

● Sodium and Sulfur: abundant materials

Comparison of Energy Storage Technologies [2]

How NaS Batteries Work

NaS Battery Diagram [3]

Electrodes:- Anode: liquid sodium

- Cathode: liquid sulfurElectrolyte: beta alumina ceramics

System is completely sealed to:- Prevent liquid sodium from spontaneously

burning when in contact with air and moisture.- Maintain the high operating temperature

needed for the electrodes to remain molten, and to promote desired reaction mechanisms.

How NaS Batteries Work

NaS Battery Operating Principles [3]

Discharge: Na donates electron to the external circuit. Na ions then pass through the electrolyte to the positive electrode, and form Na polysulphide (Na2Sx).

Charge: Na2Sx decomposes, and Na ions migrate back through the electrolyte.

● Operating temperature:○ 300-500 °C

● Temperature varies:○ Charging - Temp ~

constant○ Standby - Temp drop○ Discharging - Temp rise

High operating temperature can cause short circuiting, and is a fire hazard [4].

NaS Challenge: High Operating

Temperature

Case Study: Tsukuba Fire Incident in 2011NGK has temporarily halted production of NaS batteries.

Restricted and suspended usages of existing NaS batteries in 174 locations in Japan and 5 other countries.

Priority on reforming NaS batteries until the end of 2012.

NaS module layout [5]

Case Study: Prevention of Future Incidences

Fire prevention methods [5]

Operations and productions resumed in 2012 after modifications were implemented.

NaS Challenge: High Cost● NaS batteries are cheaper

than other batteries, ie. Li-ion, and can serve a longer expected lifetime (~ 15 yrs).

● Sodium and sulfur are abundant and relatively inexpensive.

Cost comparison of common battery technologies [6]

NaS Challenge: High CostProduction cost makes up over 66% of the NaS battery’s total cost:

● High operating temperature:○ Equipments: thermal insulation, heaters,

temperature control, thermal enclosure, etc.○ Expensive ceramic electrolytes

● Corrosive sodium polysulfides: insulators corrode and become gradually conductive, increasing the self-discharge rates, or crack.○ Expensive thermal spraying coatings of Cr-Fe

alloys [8]Typical NaS Cost Distribution [7]

NaS Challenge: High Cost

CURRENT COST REDUCTIONS:

● Mass production can reduce production costs.

● Larger scale applications reduce cost per kWh and more economical.

Cost vs Production [7]

Next Step: Low Temperature NaS BatteryCURRENT R&D:

● Reduce operating Temp: 300 to 80 °C by replacing anode with a sodium potassium alloy.

● Cost reduced by ~ 50%, mostly from battery equipment.

Installed cost estimates [9]

Conclusion● NaS batteries have positive prospects of becoming a popular energy storage

device due to:○ High efficiency ~ 90%○ High power/energy density○ Abundancy of raw reactants (Na and S)○ Significantly cheaper compared to other batteries, including flow batteries

● R&D for areas of improvements:○ Eliminating fire hazards

■ Implement safety measures and reduce the operating temperature○ Reducing cost

■ Mass production ■ Large scale applications■ Reducing operating temperature

Thank you for listening.

Questions?

References [1] Sean Leavey. “The Future of Electricity Supply and Demand: Smart Devices Responding to The Grid’s Health”. 01-Nov-2013. [Online]. Available: http://attackllama.com/2013/11/the-future-of-electricity-supply-and-demand-smart-devices-responding-to-the-grids-health/ [15-Mar-2016].

[2] “Energy Storage Technologies”. Energy Storage Technologies. [Online]. Available: http://energystorage.org/energy-storage/energy-storage-technologies [15-Mar-2016].

[3] “NGK Insulators requests customers to stop using NAS batteries,” Semiconductor Portal. [Online]. Available: https://www.semiconportal.com/en/archive/news/main-news/111026-ngk-nas-battery.html [15-Mar-2016].

[4] Zahrul Hussien et al. “Modeling of Sodium Sulfur Battery for Power System Applications”. Electrika, vol. 9, no. 2, 2007.

[5] “Q&A Concerning the NAS Battery Fire | NAS Battery Fire Incident and Response”. NGK Ltd. 15-Jun-2012. [Online]. Available: http://www.ngk.co.jp/english/announce/111031_nas.html. [Accessed: 15-Mar-2016].

[6] Peter Singer. “Energy Storage: The Basics”. Energy Storage Trends. Nov-2010. [Online]. Available: http://energystoragetrends.blogspot.ca/2010_11_01_archive.html [15-Mar-2016].

[7] Zhaoyin Wen. “Study on Energy Storage Technology of Sodium Sulfur Battery and it's Application in Power System”. International Conference on Power System Technology. 2006. [Online]. Available: http://www.apmaths.uwo.ca/~mdavison/_library/natasha/batterytechnologies4.PDF [15-Mar-2016].

[8] A. Okuno et al. “Development of plasma sprayed corrosion protective coatings for sodium sulfur battery cell containers”. 12-May-2004. Materials Information Society. Pp. 70-75. 15-Mar-2016.

[9] Gao Liu et al. “A Storage Revolution”. University of Berkeley. 12-Feb-2015. [Online]. Available: http://ei.haas.berkeley.edu/education/c2m/docs/Sulfur%20and%20Sodium%20Metal%20Battery.pdf [15-Mar-2016].