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University DC network could save money and energy

Researchers at Bath University are attempting to resurrect low-voltage direct-current power transmission in order to save money and energy.

The university is building a DC local network in part of its library to power specialised desktop computers, which use less energy than traditional machines powered by the alternating current that supplies houses and businesses.

The DC system prevents the power supply from being distorted, a common problem with AC computers that causes greater energy losses. Utility companies often fine organisations with many computers for causing large distortion problems.

Using DC will also allow the university to add batteries to the network, charging them at off-peak times when tariffs are lower and using the cheaper electricity during peak times.

‘The biggest opportunity to do this will be in the commercial sector, on sites where there is a lot of computing equipment,’ project co-leader Dr Miles Redfern from the university’s electronic and electrical engineering department told The Engineer.

‘We don’t see this going into the mass market where people want convenience and the 13A AC socket is too well established. But doing it in this concentrated way doesn’t demand a radical change of assets.’

While DC networks were the first form of commercial electricity distribution, AC quickly became the near-universal way of transmitting power because it tends to lose less energy as heat and the voltage can be easily stepped up or down with transformers.

DC is used to transmit power at high voltage over large distances and other local DC networks have existed in the past but almost all have now disappeared from the UK, according to Redfern, because of the historical dominance of AC.

The DC computers, supplied by Stafford-based Stone Group, have a better power-management system than typical AC computers, reducing peak power usage from around 350W to 35W and average usage by 50 per cent.

Traditional computers also tend to draw power intermittently, which distorts the AC power supply’s waveform and increases its frequency, causing more energy to be lost as heat.

‘The DC computers are less noisy, are better for the environment and smaller,’ said Redfern.

With the help of electricity firm RWE npower, the university has already begun installing the 50 computers and new wiring system, which will operate alongside the traditional network so that staff can continue using other appliance that run on AC.

Redfern and his colleague Professor Raj Aggarwal have received £80,000 from the university to install and run the network for six months to test its feasibility and potential energy, financial and environmental benefits.

Using DC could also make it easier to integrate solar-power generators and LED lighting, which produce and run on DC, respectively, into the network.

‘If it were rolled out across the university it could immediately save around £25,000 in efficiency,’ said Redfern. ‘It’s not earth-shattering science, it’s just re-engineering.’

Bath University library

Bath University library Photo credit: Nic Delves-Broughton

Readers' comments (4)

  • Quote "Traditional computers also tend to draw power intermittently, which distorts the AC power supply’s waveform and increases its frequency, causing more energy to be lost as heat."
    I don't think it is the "drawing power intermitently" that effects the AC waveform, rather the large quantity of transformers and AC-DC converters used in appliances (PCs) creating non-linear loads (i.e. the current drawn is not proportional to the voltage applied). My understanding is that lots and lots of these small appliances distort the AC sinusiodal wave by generating harmonics at different frequencies. These harmonics, if intense enough cause faulty trips and fry other components in the distribution system, if you aren't able to filter them out or isolate them. Hence the electric companies charging extra to solve these problems.

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  • Manchester University, in the late 1950’s, had a fairly new suite of Electrical Laboratories, under the likes of Prof. FC Williams and ER Laithwaite (who was later at Imperial College). I remember (not being an electrical eng’g graduate) that these laboratories were supplied with 100V DC. I think I was told, this was provided from a bank of lead-acid cells.

    Is there anyone who can corroborate, and whether this is relevant to the above? Also, how the cells were kept topped up?

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  • UMIST certainly had a DC network in the 'New Building' - and in the 'Old' as far as I remember - I was there from about 1978, and it was still (albeit intermittently) active. Don't know if it was battery-backed, though.

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  • They're apparently alluding to a need for power factor correction. The intermittent nature of the distributed loads, say disc drives spinning up in a "server farm", draw an inductive load at the AC mains. Ideally one wants the load to appear as pure resistance, thus no AC standing wave on the copper, in otherwords 100% of the power delivered to the load. Conversely, with DC one must consider Joule Heating or "I^2R loss" when drawing a large current across the copper. Ultimately it sounds like a power budgeting exercise: power factor corrector (PFC) circuit effeciencies to determine a central or distributed AC/PFC topology; and determining DC-DC converter efficiencies and accordingly choosing a sufficiently high DC voltage to mitigate said I^2R loss. The innovation of renewable energy (PV-DC) integration enhancing efficiency is commendable. Design of the overall system presents a considerable number of power accounting permutations to find an optimal solution, but hardly requiring the brainpower of senior academicians...

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