NaS Energy Storage (3)

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].