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Penn State University

Energy Storage in Datacenters: What, Where, and How much?. Di Wang (CSE) C huangang Ren (CSE) Anand Sivasubramaniam (CSE) Bhuvan Urgaonkar (CSE) Hosam Fathy (MNE). Computer Science &Engineering (CSE) Mechanical & Nuclear Engineering (MNE). Penn State University.

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Penn State University

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  1. Energy Storage in Datacenters: What, Where, and How much? Di Wang (CSE) Chuangang Ren(CSE) • AnandSivasubramaniam(CSE) • Bhuvan Urgaonkar(CSE) • Hosam Fathy (MNE) Computer Science &Engineering (CSE) Mechanical & Nuclear Engineering (MNE) Penn State University

  2. Datacenters Are Heavy Power Consumers • Increase in number/size of datacenters due to heavy reliance on Internet services • Datacenters, if treated as a country, fifth in the world for electricity use • Datacenter electricity usage expected to double in next 5 years and requires 12 new power plants

  3. Monthly Costs for a 10MW Datacenter Peak power draw Other Utility Bill 8% Servers Power draw (W) 24% Energyconsumption (area under this curve) Power Infrastructure 30.5% Month Chart: Source: Book by Barroso et al., Assumption: 20,000 servers, 1.5 PUE, 15$/W Cap-ex, Duke Energy Op-ex, 4yr server & 12 yr infrastructure amortization (Tier-2) 37.5% All cost are amortized at a monthly granularity

  4. Monthly Costs for a 10MW Datacenter Other Cost is heavily impacted by peak power draw. (Barroso, Ranganathan, Hamilton, Bandarkar) Utility Bill (Op-ex) 8% Servers 24% Power Infrastructure (Cap-ex) 30.5% 37.5% All cost are amortized at a monthly granularity

  5. Peak Power Impact on Op-ex 15-min Peak power draw 12 $/KW Average draw Power draw (W) Peak to Average ratio 3:1 5 c/KWh Energyconsumption (area under this curve) Month Duke Utility Tariffs (12 $/KW, 5 c/KWh) 5 Note: Tariff rates collected from Duke Energy Utility.

  6. Peak Power Impact on Cap-ex Power Infrastructure Utility Substation Diesel Generator (DG) Auto Transfer Switch (ATS) UPS Power Distribution Unit (PDU) … … Server Racks 6

  7. Peak Power Impact on Cap-ex Utility Substation Rated Peak capacity Diesel Generator (DG) Auto Transfer Switch (ATS) UPS Power Distribution Unit (PDU) … … Server Racks

  8. Peak Power Impact on Cap-ex Utility Substation Power (W) Rated Peak capacity Time Auto Transfer Switch (ATS) UPS Power Distribution Unit (PDU) … … Server Racks 8

  9. Peak Power Impact on Cap-ex Utility Substation Power (W) Rated Peak capacity Time Auto Transfer Switch (ATS) UPS Power Distribution Unit (PDU) … … Server Racks

  10. Key Lesson • Reducing peak power draw helps • Lower Op-ex • Lower Cap-ex How do we reduce peak draws ?

  11. Demand Response Knobs in a Datacenter DVFS throttling: Fan et al., [2007], Felter et al., [2005], Meisner et al., [2011] Consolidation: Chase et al., [2001], Pinheiro et al., [2001], Lim et al., [2011] Migration/Scheduling: Moore et al., [2005], Ganesh et al., [2009], Lin et al., [2011] Peak Original draw Power Cap How realize energy storage in datacenters? New draw Energy storage: Govindanet al. [2011,2012], Urgaonkar et al. [2011], Culler et al., [2012], Power consumption (W) Energy Storage Device (ESD) Time

  12. Energy Storage Device (ESD) in Current Datacenters Utility Substation Diesel Generator (DG) Auto Transfer Switch (ATS) Cost Saving ESD Power Distribution Unit (PDU) … … Server Racks

  13. Rack level UPS Distributed UPS Configurations Why should we restrict ESDs to any one level of the datacenter power hierarchy (e.g., central or server)? Server level UPS … Utility Substation PDU Utility Substation Diesel Generator (DG) Diesel Generator (DG) ESD Server Racks Auto Transfer Switch (ATS) … Auto Transfer Switch (ATS) Why should we be restricted to single ESD technology (e.g., Lead acid battery)? … Cost Saving … Similar to the ones in Google, Microsoft and Facebook datacenters

  14. Talk Outline • Motivation • Efficacy of Different ESDs • Framework for Provisioning and Control • Evaluation • Conclusions

  15. Which ESD to choose for peak shaving? Power Power Power E E E Time Time Time

  16. Which ESD to choose for peak shaving? power Time

  17. Which ESD to choose for peak shaving? power power Time Time

  18. Ragone Plot 10,000 0 Compressed Air (CAES) Specific Energy (Wh/kg) 1,000 Fuel Cell Combustion Engine, Gas Turbine Flywheels (FW) LI 100 Batteries 10 LA Specific Power (W/kg) 1 Ultracapacitors (UC) Supercapacitors 0.1 Capacitors 10 100 1,000 10,000 100,000 1,000,000

  19. Ragone Plot 10,000 0 Specific Energy (Wh/kg) Compressed Air (CAES) 1,000 Flywheels (FW) LI 100 10 LA Specific Power (W/kg) 1 Ultracapacitors (UC) Supercapacitors 0.1 10 100 1,000 10,000 100,000 1,000,000

  20. # 1: Capital Cost (Energy and Power) Lithium ion battery Lead-acid battery Compressed air Ultracapacitor Flywheel 20

  21. # 2: Volume Density (Energy and Power) Compressed air Lead-acid battery Lithium ion battery Ultracapacitor Flywheel

  22. # 3: Discharge Time vs. Charge Time Peak cap Peak cap Compressed air Lithium ion battery Lead-acid battery Flywheel Ultracapacitor Power Power Time Time

  23. # 4: Lifetime • ESD Health • Charge-discharge life cycles • Depth of discharge () Dead Depth of discharge Lithium ion battery Lead-acid battery Compressed air Ultracapacitor Flywheel 23 23

  24. # 4: Lifetime • ESD Health • Charge-discharge life cycles • Depth of discharge () Dead Depth of discharge Lithium ion battery Lead-acid battery Compressed air Ultracapacitor Flywheel 24 24

  25. # 5: Energy Efficiency Energy Wastage Input > Output Lithium ion battery Lead-acid battery Compressed air Flywheel Ultracapacitor

  26. # 6: Self-Discharge Losses Lose charge even not being discharged Lithium ion battery Lead-acid battery Compressed air Flywheel Ultracapacitor

  27. # 7: Ramp Time Start up time to change the power output Power output Ramp time Lithium ion battery Lead-acid battery Compressed air Flywheel Ultracapacitor Time 27 27

  28. Given a workload, which ESD is best suited for reducing its peak?

  29. “No Single ESD to Shave Them All !” Cost-effective ESD for Different Demands 32 8 Peak cap Power Inter-peak distance: D (hour) 2 D 0.5 UltraCapacitor Flywheel Lead Acid CAES Time 0.1 W 1 10 100 Peak Width: W (min)

  30. “No Single ESD to Shave Them All !” 32 8 UC Power Inter-peak distance: D (hour) 2 UC Time 0.5 UltraCapacitor Flywheel Lead Acid CAES 0.1 1 10 100 Peak Width: W (min)

  31. “No Single ESD to Shave Them All !” 32 Ultracapacitor 8 CAES Power 2 Inter-peak distance(hour) CAES Power Time 0.5 UltraCapacitor Flywheel Lead Acid CAES Time 0.1 1 10 100 Peak Width (min)

  32. “No Single ESD to Shave Them All !” Ultracapacitor 32 LA 8 CAES Power Power 2 Inter-peak distance(hour) Time (W=100min) FW Time (W=1min) Power FW 0.5 UltraCapacitor Flywheel Lead Acid CAES Time (W=10min, D=0.5h) LA 0.1 Power 1 10 100 Peak Width (min) Time(W=10min, D=5h)

  33. Hybrid ESD solution may be desirable Battery Compressed Air Ultracapacitor/flywheel Power Time

  34. Utility Diesel Generator Multi-level Multi-technology ESDs Battery ATS Flywheel ESD Compressed Air … PDU PDU PDU Battery ESD ESD ESD Capacitor … … … … ESD Server H/W Rack Rack Rack

  35. Talk Outline • Motivation • Efficacy of Different ESDs • Framework for Provisioning and Control • Evaluation • Conclusions Which ESDs? How much capacity? Where in hierarchy? Linear program Object: Optimize cost S.T. : ESD and workload constraints

  36. Methodology Max. Demand () Powercap () Power (W) Time t=30s

  37. Methodology , i=1

  38. Optimization Problem: Objective • Max (CapExSaving + OpExSaving – ESDCost) • CapExSaving = ( • OpExSaving= b ( + Dk,l,i,t- R)) • ESDCost = k,l,ik,l,i)

  39. Optimization Problem : Constraints • State of charge is bounded by depth of discharge and maximum capacity: • (1 - ≤ k,l,i,t≤

  40. Optimization Problem : Constraints • State of charge is bounded by depth of discharge and maximum capacity: • (1 - ≤ k,l,i,t≤ • Discharge/charge power are bounded by maximum capacity and discharge/charge rates: • 0 ≤ ≤ • 0 ≤ R≤

  41. Optimization Problem : Constraints • Net power draw at each Li is bounded by the cap: • 0 ≤ P + - ≤

  42. Optimization Problem Formulation: Constraints • Net power draw at each Li is bounded by the cap: • 0 ≤ P + - ≤ • Account for energy losses due to self-discharge • k,l,i,1 + δ - δ - μk

  43. Optimization Problem : Constraints • Net power draw at each Li is bounded by the cap: • 0 ≤ P + - ≤ • Account for energy losses due to self-discharge • k,l,i,1 + δ - δ - μk • Constrained by ramp rate of discharge

  44. Optimization Problem : Constraints • Net power draw at each Li is bounded by the cap: • 0 ≤ P + - ≤ • Account for energy losses due to self-discharge • k,l,i,1 + δ - δ - μk • Constrained by ramp rate of discharge • Volumetric constraints (10% server-level, 20% rack-level, no datacenter-level constraint) • ≤ • ≤

  45. Talk Outline • Motivation • Efficacy of Different ESDs • Framework for Provisioning and Control • Evaluation • Conclusions

  46. Realistic Power Profiles (a) TCS (Indian IT Company) (b) Google (c) MSN (d) Streaming Media

  47. Cost Savings for Google Workloads (Savings, ESD cost) Datacenter: FW+CAES Server: LA Server: LA Server: UC + LA Datacenter: CAES Savings ($/day) (5.2k, 0.3k) (4.9k, 0.4k) 30% (4.7k, 0.3k) 25% 20% Single-tech, Server-level Multi-tech, Server Level Single-tech, Datacenter-level Multi-tech, Multi-level Total cost without ESD is $12k/day

  48. Cost Savings for MSN Workloads (Savings, ESD cost) Datacenter: FW+CAES Server: UC Server: UC + LA Rack: LA Server: LA Datacenter: LA Rack: UC + LA Savings ($/day) (4.4k, 0.3k) (4.3k, 0.3k) (4.2k, 0.2k) (4.0k, 0.5k) (3.8k, 0.3k) (3.4k, 0.1k) Multi-tech, Single-level Multi-tech, Multi-level Single-tech, Single-level Total cost without ESD is $15k/day

  49. Charge/Discharge Control for MSN demand • CAES takes a bulk of the gap for significant portions of time • Ultra-capacitor is used for sudden spikes and gets charged from CAES

  50. Concluding Remarks • Framework for holistic energy storage based Cap-ex and Op-ex optimization • Representative results • ESD technologies beyond battery also useful in datacenter context • ESD technologies employed at multiple-levels of datacenter • Multiple technologies at multiple level

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