Sean James

No more electrical infrastructure: towards fuel cell powered data centers

We consider the use of fuel cells for powering data centers, based on benefits in reliability, capital and operational costs, and reduced environmental emissions. Using fuel cells effectively in data centers introduces several challenges and we highlight key research questions for designing a fuel cell based data center power distribution system. We analyze a specific configuration in the design space to quantify the cost benefits for a large scale data center, for the most mature and commonly deployed fuel cell technology, achieving over 20% reduction in costs using conservative projections.

SizeCap: Efficiently handling power surges in fuel cell powered data centers

Fuel cells are a promising power source for future data centers, offering high energy efficiency, low greenhouse gas emissions, and high reliability. However, due to mechanical limitations related to fuel delivery, fuel cells are slow to adjust to sudden increases in data center power demands, which can result in temporary power shortfalls. To mitigate the impact of power shortfalls, prior work has proposed to either perform power capping by throttling the servers, or to leverage energy storage devices (ESDs) that can temporarily provide enough power to make up for the shortfall while the fuel cells ramp up power generation. Both approaches have disadvantages: power capping conservatively limits server performance and can lead to service level agreement (SLA) violations, while ESD-only solutions must significantly overprovision the energy storage device capacity to tolerate the shortfalls caused by the worst-case (i.e., largest) power surges, which greatly increases the total cost of ownership (TCO). We propose SizeCap, the first ESD sizing framework for fuel cell powered data centers, which coordinates ESD sizing with power capping to enable a cost-effective solution to power shortfalls in data centers. SizeCap sizes the ESD just large enough to cover the majority of power surges, but not the worst-case surges that occur infrequently, to greatly reduce TCO. It then uses the smaller capacity ESD in conjunction with power capping to cover the power shortfalls caused by the worst-case power surges. As part of our new flexible framework, we propose multiple power capping policies with different degrees of awareness of fuel cell and workload behavior, and evaluate their impact on workload performance and ESD size. Using traces from Microsofts production data center systems, we demonstrate that SizeCap significantly reduces the ESD size (by 85%ofor a workload with infrequent yet large power surges, and by 50% for a workload with frequent power surges) without violating any SLAs.

Evaluating energy storage for a multitude of uses in the datacenter

Datacenters often are a power utilitys largest consumers, and are expected to participate in several power management scenarios with diverse characteristics in which Energy Storage Devices (ESDs) are expected to play important roles. Different ESD technologies exist, including little explored technologies such as flow batteries, that offer different performance characteristics in cost, size, and environmental impact. While prior works in datacenter ESD literature have considered one of usage aspect, technology, performance metric (typically cost), the whole three-dimensional space is little explored. Towards understanding this design space, this paper presents first such study towards joint characterization of ESD usages based on their provisioning and operating demands, under ideal and realistic ESD technologies, and quantify their impact on datacenter performance. We expect our work can help datacenter operators to characterize this three-dimensional space in a systematic manner, and make design decisions targeted towards cost-effective and environmental impact aware datacenter energy management.