DC computer network reduces library’s energy usage

A university library has markedly reduced its energy demand after installing and running what is claimed to be Britain’s first local direct-current (DC) computer network.

The pilot scheme is the culmination of an EPSRC-funded research project by Bath University’s Department of Electronic and Electrical Engineering, with industrial support from RWE Npower.

The network uses specially adapted desktop computers, which use less energy than traditional machines powered by the alternating current (AC) that supplies houses and businesses.

Although the researchers are still gathering data on the system, they say they have largely succeeded in achieving their efficiency goals since the installation was competed at the end of December.

‘With 50 computers installed along with monitors we’re using about 2kW of power, so the average computer on that is at roughly 40W. We were expecting 35W, but the previous computers were drawing about 140W on average,’ said project leader Dr Miles Redfern of Bath.

In addition, the network uses a battery stack that has been delivering 12 hours of storage, an improvement on the predicted four hours, which opens up cost-saving potential.

For many commercial companies, electricity is billed at a higher rate in the day than during the night, meaning there is benefit in converting AC power, charging the batteries at night and running the network independently from the grid during the more expensive peak daytime hours.

Nevertheless, there were challenges to overcome on the project: the team had to move the one-tonne AC converter through the university library and into the roof space, removing and rebuilding walls to transport it.

The next stage will be to roll out the network, which is currently only on the fifth floor of the library, to other parts of the university.

There is also potential for renewable solutions: wind turbines and solar panels output a DC current, which normally calls for an inefficient conversion from DC to AC for usage.

‘We’re investigating having photovoltaic cells on the library roof… they produce direct current and we can pump that straight into the network. When the energy is not being used then obviously it can be used to recharge the batteries, but when the clouds go over, the system doesn’t stop because the batteries are there to support it,’ Redfern said.

A full cost-benefit analysis is due in the summer, after the trial period, and the partnership is currently in talks with several commercial companies and one large government affiliate that relies heavily on computers.