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Cutting the Electric Bill for Internet-Scale Systems
Kevin Leeds
The Concept
Energy costs differ by location Reroute customer requests to
cheaper locations
$50/MWh $30/MWh
Customer
CloserCheaper energy
Why This Is Possible
Electricity prices vary per region Price variation between coal and hydro
Also by hour (up to factor of 10) Solar power, wind power, tide
Trends are detectable Power grids may be over/under-
utilized
Potential Savings
Google spends over $38M on electricity per year.
3% energy cost reduction saves ~ $1M
Energy Elasticity
Energy Consumed / Load on cluster
Idealistic: 0 load = 0% peak power Realistic: 0 load ~ 60% peak
power (current state-of-the-art) Without energy elasticity, no
savings can be gained
Constraints Affect Outcomes
Elasticity Existing systems: ~2% savings Fully-elastic system: ~13% savings
Bandwidth constraints on fully-elastic No constraints: ~30% savings 95/5 constraints: ~13% savings
Client-server distances Constrained: ~45% max savings Non-constrained: ~35% max savings
Wholesale Electricity Markets
Regional Transmission Organization (RTO) Runs several parallel wholesale markets
Day-ahead markets (expectations for the day) Real-time markets (real-time price calculations)
Changes in price Demand rises, more expensive sources of
energy are called upon (congestion exists)
Price changes per hour
Price Differences Between Regions
Cluster Power Calculations
Variables F = Fixed power V = Variable power E/r = Derived Constants PUE = Power Utilization Efficiency n = # of servers in cluster u = average CPU utilization
What about routing energy increases?
Shouldn’t be significant 1 kJ/Google Query 2 mJ/Packet passing through router
Savings Experiment Findings
Cost Savings Experiment (Change in Per-Cluster Cost)
Reaction Delays
Faster reaction to changes = lower cost
Future Work
Weather Differentials Cool centers with outside air (AZ vs
MN) Implementing Joint Optimization
Systems already reroute traffic based on bandwidth costs, performance, and reliability – add local energy costs
Questions/Comments
Thank you!
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