Reducing electricity use by lowering voltage?

tomstickland

This is a story I saw in the local rag. A council are planning to reduce their electricity bill by working at 230V, and if that's a success they're going to try 220V.

With a single resistor and DC voltage, then power consumed is proportional to voltage squared over resistance. I assume that this roughly translates to mains AC, though there are the complications of inductance etc.

However, a quick look round the internet didn't reveal any easy ways to implement this, so I'm a bit confused by their plans. Surely the reduction process would involve some losses.
http://www.thisisgloucestershire.co.uk/news/Rising-energy-bills-hit-Forest-Dean-District-Council/article-302161-detail/article.html

JayMT

Interesting theory, I wonder how they plan to regulate their mains supply? Legally it can drop down to 216V anyhow and still be in spec.

As for saving energy, it would depend on what the load is.

Old fashioned light bulbs - they would simply glow a bit more dimly so use less (and last longer!)
New CFL and fluorescents - dunno
Kettle - would stay on for longer to compensate, so no energy saving
Heating - same as kettle, would be easier to turn the thermostat down instead
For more complex power supplies as used in PCs etc - difficult to say, my guess would be as the voltage reduced the current consumption would go up to compensate so no energy saving.

markbloke

What on earth are they on about? If you put AC through a transformer you can jack it up or down to any voltage you please so that's not a problem. The problem is that you are charged by kwh, not volt-hours. If your appliances need a certain amount of power to function then they'll continue to use that power - if you're lucky. If you're unlucky they won't work at all. Surely there's got to be more to that story.

btr30

Sounds like a "voltage optimisation" device by Power Perfector or equivalent. Device is a low loss transformer (with thyristors I think) which works by lowering mains voltage from up to 250 v to European standard 220V. A 10% reduction in voltage would equate to 18% reduction in power consumption. Most equipment is rated for 220v so will work ok. Not any use for heating applications as equipment will have to be on for longer to reach temperature.
Best application would be in a large office type environment, which suffers from over-voltage, and has a high base load such as IT servers, with main electricity use of IT equipment and lighting.
Units were around £15k depending on size, so not appropriate for every building

mech_2

I think they've been had. I can't see it making a big saving in practice.

Switched mode power supplies in PCs etc actually tend to be slightly less efficient at lower supply voltages (Many of them will work on anything from US 120V to European 230V/240V so the efficiency curves are out there if you look for them).

At least we can deduce how much they paid. If they expect their electricity bill to be £13,000 and they expect to save 19% (from 1 - 0.9^2) and make their money back within two years, then whatever it was they're having installed cost no more than £4,940 at the most.

If this was being applied to street lighting in the small hours of the morning (slightly dimmer lighting when no one is about) I can see the sense to it, but not this. I think they will be disappointed.

tomstickland

There are also power factor optimisation devices out there.

markbloke

What they need is a monorail.

Cardew

tomstickland wrote: »

There are also power factor optimisation devices out there.

Not sure of your point here Tom.

Domestic customers pay for kWh not kva, power factor will have no effect.

Industrial customers get fined if their power factor drops below a certain level.

JohalaReewi

Presumably, the council are industrial customers so have to keep an eye on the power factor?