Energy Efficient and Grid-Interactive Datacenters

Exploiting workload flexibility in time and space to design energy efficient and grid-responsive data centers

Energy is the biggest constraint on AI and cloud data centers. Electricity grids are struggling to keep pace with rising demand and with data center demand patterns. Moreover, the electricity that powers these data centers is not always clean, and its cost and availability change frequently. By 2030, demand growth is projected to outpace grid decarbonization, and global data center emissions could rise by as much as 4.2x (Maji et al., 2025). My research exposes energy as a schedulable resource and exploits the flexibility of when and where workloads run to make data centers responsive to the grid.


Energy Virtualization

Today’s energy systems hide the unreliability of renewable power inside hardware, so software cannot see or manage it. Ecovisor (Souza et al., 2023) virtualizes the energy system the way a hypervisor virtualizes compute. Ecovisor gives each application software-defined control over its own energy, and each application decides how to handle the intermittency of clean power.

Ecovisor virtualizes the energy system (grid, renewables, storage) alongside the computing system, exposing software-defined control of both to applications.

Grid-Responsive Scheduling and Scaling

CarbonScaler (Hanafy et al., 2024) uses that visibility to chase cleaner electricity. It exploits the elasticity of cloud workloads, scaling them up during clean-energy windows and down during dirty ones, and it builds carbon signals directly into the autoscaling loop. It won Best Student Paper at ACM SIGMETRICS 2024.

Scaling compute isn’t the only lever. FM-CAC (Yang et al., 2026) adds a new dimension for battery-buffered edge AI. It treats the battery as an active temporal buffer that separates when energy is drawn from the grid from when it is consumed, and it jointly optimizes the software pipeline, the hardware operating point, and the battery schedule at each step.

The same elasticity ideas also apply to cluster-level provisioning across heterogeneous workloads (CarbonFlex (Hanafy et al., 2025)), jobs with unknown length (LACS (Bostandoost et al., 2024)), the choice of the best scheduling policy per job (FTL (Bostandoost et al., 2024)), and workloads with internal task dependencies (job-shop-based carbon scheduling (Bostandoost et al., 2026)).

Scaling cloud resources in response to grid carbon intensity, running more work during clean energy periods.

Spatial Shifting

Grid-responsiveness is also about where a workload runs. CarbonEdge (Wu et al., 2025) shows that carbon intensity varies significantly even at mesoscales, within a US state or among neighboring European countries, well below the continental scale that most cloud-region shifting exploits.

The same idea scales to CDNs. CDN-Shifter (Murillo et al., 2024) combines spatial load shifting with capacity shifting across a large CDN’s edge sites.

The principle extends to video streaming, where the network path matters as much as server placement (Go with the Flow (Murillo et al., 2026)).

Spatial shifting routes workloads toward geographic regions with lower-carbon electricity grids, complementing temporal shifting strategies.

Carbon–Cost–Energy Tradeoffs

Grid-responsive scaling raises a cost problem. Shifting a job to a cleaner window leaves already-purchased reserved capacity idle, which raises the effective cost of the work that does run. GAIA (Hanafy et al., 2024) co-optimizes carbon, cost, and performance together, and it uses real-time carbon-intensity data to decide how much reserved capacity to spend now versus shift later.

The War of the Efficiencies (Hanafy et al., 2024) exposes a deeper tension. Once the grid exposes time-varying carbon intensity, the most energy-efficient job is not always the most carbon-efficient one, so optimizing for one can work against the other.

Untangling the Carbon-Cost Tradeoffs (Hanafy et al., 2026) goes beyond single-application tradeoffs and quantifies the stampede effect at scale, where many independent schedulers converge on the same low-carbon windows or regions. That convergence creates the contention carbon-aware scheduling was meant to avoid and undercuts both cost and carbon goals.

On the left, GAIA trades carbon reduction against cost by choosing how much reserved capacity to use. On the right, the three-way tradeoff between carbon, cost, and energy in cloud scheduling.

References

2026

  1. ISLPED
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    FM-CAC: Carbon-Aware Control for Battery-Buffered Edge AI via Time-Series Foundation Models
    Kang Yang, Walid A. Hanafy, Prashant Shenoy, and 1 more author
    In 2026 IEEE/ACM International Symposium on Low Power Electronics and Design (ISLPED), 2026
  2. GreenSys
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    Quantifying the Carbon Reduction of DAG Workloads: A Job Shop Scheduling Perspective
    Roozbeh Bostandoost, Adam Lechowicz, Walid A. Hanafy, and 2 more authors
    In Proceedings of the 2nd International Workshop on Systems and Methods for Sustainable Large-Scale AI (GreenSys), 2026
  3. e-Energy
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    Go with the Flow: Analyzing the Carbon Footprint of Green Streaming
    Jorge Murillo, Walid A. Hanafy, David Irwin, and 2 more authors
    In The 17th ACM International Conference on Future and Sustainable Energy Systems (e-Energy ’26), June 22–25, 2026, Banff, Canada, 2026
  4. IEEE TC
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    Untangling the Carbon-Cost Tradeoffs and Stampede Effect Challenges in Cloud Computing
    Walid A. Hanafy, Thanathorn Sukprasert, Abel Souza, and 2 more authors
    IEEE Transactions on Computers, 2026

2025

  1. HotCarbon
    Data Centers Carbon Emissions at Crossroads: An Empirical Study
    Diptyaroop Maji, Walid A. Hanafy, Li Wu, and 3 more authors
    ACM SIGEnergy Energy Informatics Review, 2025
    Presented in HotCarbon’25
  2. Arxiv
    CarbonFlex: Enabling Carbon-aware Provisioning and Scheduling for Cloud Clusters
    Walid A. Hanafy, Li Wu, David Irwin, and 1 more author
    2025
  3. HPDC
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    CarbonEdge: Leveraging Mesoscale Spatial Carbon-Intensity Variations for Low Carbon Edge Computing
    Li Wu, Walid A. Hanafy, Abel Souza, and 5 more authors
    In Proceedings of the 34th International Symposium on High-Performance Parallel and Distributed Computing (HPDC ’25), 2025

2024

  1. SIGMETRICS
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    🏆 CarbonScaler: Leveraging Cloud Workload Elasticity for Optimizing Carbon-Efficiency
    Walid A. Hanafy, Qianlin Liang, Noman Bashir, and 2 more authors
    SIGMETRICS Performance Evaluation Review, Jun 2024
  2. e-Energy
    LACS: Learning-Augmented Algorithms for Carbon-Aware Resource Scaling with Uncertain Demand
    Roozbeh Bostandoost, Adam Lechowicz, Walid A. Hanafy, and 3 more authors
    In The 15th ACM International Conference on Future and Sustainable Energy Systems (e-Energy ’24), June 4–-7, 2024, Singapore, Jun 2024
  3. HotCarbon
    Data-driven Algorithm Selection for Carbon-Aware Scheduling
    Roozbeh Bostandoost, Walid A. Hanafy, Adam Lechowicz, and 3 more authors
    ACM SIGEnergy Energy Informatics Review, Apr 2024
    Presented in HotCarbon’24
  4. SoCC
    CDN-Shifter.jpg
    CDN-Shifter: Leveraging Spatial Workload Shifting to Decarbonize Content Delivery Networks
    Jorge Murillo, Walid A. Hanafy, David Irwin, and 2 more authors
    In Proceedings of the 2024 ACM Symposium on Cloud Computing, Redmond, WA, USA, Apr 2024
  5. ASPLOS
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    Going Green for Less Green: Optimizing the Cost of Reducing Cloud Carbon Emissions
    Walid A. Hanafy, Qianlin Liang, Noman Bashir, and 3 more authors
    In Proceedings of the 29th ACM International Conference on Architectural Support for Programming Languages and Operating Systems, Volume 3, La Jolla, CA, USA, Apr 2024
  6. HotCarbon
    The War of the Efficiencies: Understanding the Tension between Carbon and Energy Optimization
    Walid A. Hanafy, Roozbeh Bostandoost, Noman Bashir, and 3 more authors
    ACM SIGEnergy Energy Informatics Review, Sep 2024
    Presented in HotCarbon’23

2023

  1. ASPLOS
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    Ecovisor: A Virtual Energy System for Carbon-Efficient Applications
    Abel Souza, Noman Bashir, Jorge Murillo, and 4 more authors
    In Proceedings of the 28th ACM International Conference on Architectural Support for Programming Languages and Operating Systems, Vancouver, BC, Canada, Sep 2023