News Analysis

Tesco opts for flywheel power in energy-efficiency drive

Cliff Saran

Supermarket giant Tesco is using steam-age technology to keep its 21st century datacentre running during power failures.

The retailer is one of a handful of companies in the country using a flywheel to store electricity for powering down servers in an emergency.

The flywheel is one of the more radical elements in Tesco's 10-year blueprint to reduce the power consumption in its datacentre.

Nick Folkes, IT director at Tesco, has workedon the project for the past 18 months.

"Last year, we realised our electricity costs were going through the roof. We needed to do something radical. We were already using virtualisation for our mainframe and high-end Unix systems, but we had to tackle energy waste on our Intel servers."

Tesco was able to keep its existing datacentre fully operational as it installed the new hardware, cooling and software components. Tesco is deploying the final servers this month and the roll-out will be completed in April.

Environmentally-friendly option

Tesco is using the flywheel toreplace traditional uninterruptible power supplies, which require a bank of environmentally-unfriendly lead-acid batteries to supply back-up power to the datacentre.

The flywheel system claims to be 98% energy efficient. The wheels rotate at 7,200rpm to store energy, which is converted to electricity, when there is a power failure.

Folkes says the kinetic system is able to provide 25 seconds of power, enough to enable the servers to power down safely.

Tesco has invested in new power generators that can startup in less than 20 seconds, fast enough to power up the datacentre when there is a prolonged power cut."Our old generators were slow and took 60 seconds to start,"says Folkes.

Tesco has also upgraded its datacentre cooling, using a hot isle containment system supplied by APC to improve cooling efficiency. The system uses fans on the blade servers to expel air into a sealed area between rows of racks called "hot isles", making cooling more efficient and predictable because the hot air is contained in one place. Experts saythis reduces thelikelihood of hot spots developing in the datacentre, which can cause components to overheat and fail.

According to Folkes, the hot isle technology allows Tesco to run more blade servers per rack than is normally possible. "We can use 30kW per rack, compared with 2-3kW per rack with traditional datacentre cooling," he says.

 

Flywheel energy storage 

Flywheel energy storage systems store kinetic energy, ie the energy produced by motion, by constantly spinning a compact rotor in a low-friction environment. When short-term back-up power is required the rotor's inertia allows it to continue spinning and the resulting kinetic energy is converted to electricity via a generator.

Texas-based Active Power has developed an integrated UPS and DC power supply, CleanSource Flywheel, as an alternative to chemical batteries.

Source: Active Power

Server virtualisation

Tesco has refitted its datacentre with HP Bladeserver hardware, an HP SAN and Citrix networking.

It has used Citrix Xenserver as its virtualisation platform. Folkes says he selected Citrix over market leaderVMware because the Citrix product is licenced on a per server basis, whereas VMware uses per core licensing.

The Citrix technology has allowed Tesco to reduce the number of Intel servers to just over 180 - down from more than 1,500 when the project began. The servers are also running more applications, making them more energy efficient. Folkes says Tesco is now seeing 70% utilisation on its Intel servers, compared with 6% before.


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