TY - CONF
T1 - Should we dual-purpose energy storage in datacenters for power backup and demand response?
AU - Narayanan, Iyswarya
AU - Wang, Di
AU - Mamun, Abdullah Al
AU - Sivasubramaniam, Anand
AU - Fathy, Hosam K.
N1 - Funding Information:
In this paper, we have examined provisioning energy storage for two important purposes - Power Backup (PB) and Demand Response (DR) - in the datacenter. These two purposes have very different characteristics in terms of their needs (power vs. energy), mandates (hard guarantees vs. best effort), and frequency of usage (a few times a year vs. multiple times in a day). Using actual power traces of a datacenter, we have evaluated different configurations that consider dual purposing batteries for both PB and DR, having separate sets of batteries, and soft-partitioning them. We have also considered under-provisioning the batteries, and the effect of battery wear on overall-TCO. The study gives the following key insights that are useful for a datacenter designer: • Despite the differences, dual-purposing is a better op-tion than maintaining separate sets of batteries, when batteries are the only choice. • This is mainly because (peak) power demands to han-dle an outage for PB really dominates when provision-ing. The consequent energy, that we literally get for free, is more than adequate for power capping in DR. • Such dual-purpose provisioning does not compromise on the ability to handle a power outage before the load can be transferred to Diesel Generators. • Given the non-orthogonality between the power and energy dimensions of batteries, and the different needs of PB and DR, hybrid ESD technologies which use a power-efficient option (such as Flywheels and Ul-tracapacitors) for PB, and use batteries just for DR, are much more cost-effective than any battery-only so-lution. They can reduce TCO by half compared to the dual-purposed battery-only options that have been studied until now, without compromising on the abil-ity to handle power outages 5 Acknowledgements This work was supported, in part, by NSF grant 1302225 and a research gift from Google. We would also like to thank Sriram Govindan from Cloud Server Infrastructure Team in Microsoft for his help in collecting datacenter power traces.
PY - 2014
Y1 - 2014
N2 - Prior work has shown the benefits of Energy Storage Devices (ESDs), such as batteries, to smoothen/flatten power draws in Datacenters, for reducing demand during peak tariffs (for op-ex savings) and under-provisioning the power infrastructure (for cap-ex savings). Until now, all prior studies for such smoothening, referred to as Demand Response, have considered re-purposing existing UPS unit batteries for demand response. It is not clear if such dual usage - handling power outages and demand response - is the most effective option since the needs (energy and/or power), mandates (best effort vs. hard stipulations), costs, availability and health degradation considerations could be very different. In this paper, we study the design space of choices for provisioning ESDs for these dual purposes - separate ESDs for each purpose, common pool of ESDs for both purposes, and soft-reservations in this pool with possible re-purposing dynamically based on demand. Our evaluations show that: (i) provisioning lead-acid batteries for a peak “power” load needed to handle power outages already comes with sufficient energy capacity that is more than adequate to automatically supply the energy needs for demand response; (ii) this makes it economically attractive to use the same UPS batteries, originally intended for Power Outages, for Demand Response as well, despite any consequent health degradation (due to repeated discharges); (iii) the ability to handle the needs during a power outage is not compromised despite the dual-purposing of these UPS batteries; and (iv) the non-orthogonality of the power and energy capacities of these batteries (i.e. provisioning for the high power needs during an outage automatically comes with a lot of energy capacity) suggests the possibility of having different Energy Storage Technologies for the two purposes and we show that a heterogeneous/hybrid option using Ultra-capacitors or Flywheels for Power Backup and batteries for Demand Response is a more cost-effective option.
AB - Prior work has shown the benefits of Energy Storage Devices (ESDs), such as batteries, to smoothen/flatten power draws in Datacenters, for reducing demand during peak tariffs (for op-ex savings) and under-provisioning the power infrastructure (for cap-ex savings). Until now, all prior studies for such smoothening, referred to as Demand Response, have considered re-purposing existing UPS unit batteries for demand response. It is not clear if such dual usage - handling power outages and demand response - is the most effective option since the needs (energy and/or power), mandates (best effort vs. hard stipulations), costs, availability and health degradation considerations could be very different. In this paper, we study the design space of choices for provisioning ESDs for these dual purposes - separate ESDs for each purpose, common pool of ESDs for both purposes, and soft-reservations in this pool with possible re-purposing dynamically based on demand. Our evaluations show that: (i) provisioning lead-acid batteries for a peak “power” load needed to handle power outages already comes with sufficient energy capacity that is more than adequate to automatically supply the energy needs for demand response; (ii) this makes it economically attractive to use the same UPS batteries, originally intended for Power Outages, for Demand Response as well, despite any consequent health degradation (due to repeated discharges); (iii) the ability to handle the needs during a power outage is not compromised despite the dual-purposing of these UPS batteries; and (iv) the non-orthogonality of the power and energy capacities of these batteries (i.e. provisioning for the high power needs during an outage automatically comes with a lot of energy capacity) suggests the possibility of having different Energy Storage Technologies for the two purposes and we show that a heterogeneous/hybrid option using Ultra-capacitors or Flywheels for Power Backup and batteries for Demand Response is a more cost-effective option.
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M3 - Paper
AN - SCOPUS:85078535430
T2 - 6th Workshop on Power-Aware Computing and Systems, HotPower 2014
Y2 - 5 October 2014
ER -