The future of energy is the mobile phone.

The short version

If every household device was as good an energy manager as the mobile phone, energy consumption and carbon emissions would fall.  The 240 volt AC ring main is a good way of servicing devices which consume lots of energy, but in a modern home many devices work with DC at 12 volts or less.  The conversion of high AC voltages to low DC voltages is often inefficient (less than 50%), thus having a low voltage household distribution system could reduce energy consumption and emissions.  From a sample of one, our household consumes approx. 8 kwh/day from a 240 Volt AC supply, say, 50% of this is converted to low voltage DC, if the conversion efficiency is raised from 40% to 80%, there is a saving of 2kwh/day.

Moving to a low voltage distribution is not simple and requires research to ensure systems are safe, can handle variations in device voltage, and can be implemented in a way that equipment manufacturers can work with - In short a sizeable technical challenge.  The availability of cost-effective LED lighting could provide the incentive.

The longer version

Back in 2006 , our household cut its electricity consumption from 20 - 25 kwh/day to 8 - 10 kwh/day by doing little more than swapping incandescent lamps for CFLs and dumping some ageing computers.  As electrical items have come up for replacement, we've considered of the energy consumption of the new items before purchase.  However, short of of adopting the lifestyle of the house's original inhabitants in 1901 when the house was lit by a combination of gas and colza (rapeseed oil) lamps, 8 - 10 kwh/day seems as low as we can go.

To go further, we need a technological breakthrough, which, according to Chemistry World is now within sight, this is LED lighting.  Incandescent lamps emit a broad spectrum of radiation (roughly 100 - 4,000 nm), however, visible light (roughly 390 to 750 nm) is only a small proportion of this.  The total output of fluorescent lamps is more or less in the visible light range (often with a few spikes in the spectrum), thus  they consume less electricity for a given light output. However, a fair chunk of the electricity that they consume ends up as heat (working CFL's are hot to the touch and should be allowed to cool before handling).

LED's offer low energy lighting.  A couple of years ago I purchased a 12 volt LED which had an output of approx. 30 lumens for about £10.  The good things about this device were that it was always cold to the touch, claimed less than 100 mA and showed no signs of degradation in more than 1,000 hours.  The downside was the high cost and luminous performance not much better than the CFLs which we now use to light the house.  The difference between the LED and the CFL is that the LED is evolving and within a few years could be a cost and energy effective form of lighting.  Companies like Philips are backing this future with large R&D budgets.  LED lamps (increasingly called solid-state lighting) are low voltage DC devices (12 Volts or less) and like other semiconductor devices will need some form of voltage conversion to operate from the standard 240 volt AC Mains.

Back to the mobile phone.  For all practical purposes, the mobile phone is a small computer for which ever-more diverse applications are being developed.  Many of these things can not only guide you to the pub using GPS, but estimate the benefit to your health of walking there.  They are also good energy managers.  A typical mobile phone has a 3.3 volt battery with a capacity between 1 and 2 amp hours (i.e. not a lot of energy).  It's convenient to use a mains charger to keep them working, but a small solar panel with appropriate protection could to the job just as well.  This leads to the question, if all the devices in the home were as good at energy management as the mobile phone, by how much would electricity consumption be reduced and with it, carbon emissions.

I chose the mobile phone as an example because it is a device we're all familiar with which could be run on renewable energy (solar is the most practical option) and need not be connected to a mains supply.

The old order changes, yielding way to new

Our house was completed in 1901.  It was lit by a combination of gas lights and oil lamps, the remains of the gas pipes can be found in places around the house.  Whilst this might sound romantic, even when used with care, they required regular cleaning and maintenance (a job which invariably fell to the women of the household).  Electricity arrived in the 1920s, initially its principal use was lighting.  Looking at the remains of the wiring, I doubt it was safe with more than 5 amps.  As the decades have passed, all sorts of labour saving devices came into common use, such as vacuum cleaners, fridges and washing machines and in the 1950s, a modern ring main was installed.  Until the start of the 21st century, energy was cheap, energy efficiency either to cut costs or reduce emissions was not a high priority for many people and electricity consumption increased year on year as the number of electrical devices in the home increased.  There was little incentive to question the 240 volt AC distribution system.

With the advent of semiconductor devices, the pattern of electricity usage in the home has changed.  Much of the energy consumed is not in the form of high AC voltages but as low DC ones.  If LED lighting becomes viable, then it is possible, that most domestic electricity consumption will be by things using 12 volts DC or less.  At present, such devices are supplied by individual power supplies (wall warts etc.) often with efficiencies of 40% or less.  Thus it is a legitimate to consider an alternative low voltage domestic system.  Such systems when used with micro-generation might allow genuine electrical self-sufficiency, rather than the "carbon neutral" version currently on offer.

Many electronic devices consume very small amounts of energy, say, a mobile phone or small radio might consume less than 0.05 kwh/day.  A significant part of the cost is providing a power supply.  The energy source does not have to be a 240V AC supply.  A very nice alternative is device with wind-up generator.  30 seconds of gentle exercise can provides BBC Radio 4's Today, PM and The World Tonight programmes (but that is no reason to dismiss the technology).  Having acquired such a device, I'll attempt to dump some mains connected devices.

Research Plan

Using only an Edwardian semi and a sceptical family, I've attempted to advance the frontiers of urban energy research by measuring the amount of energy consumed in our household at low DC voltages and standard mains 240 Volt AC.

The pie chart has five slices.  The first of these is the amount of energy consumption which remains which could not be classified.  The second is the energy which is consumed by high load devices such as the washing machine, electrical kettle etc. which can only operate with a 240 Volt AC supply.  next is the devices which could feasibly work with a low voltage DC supply, an example is the fridge which requires less than 100 mA.  The final slice is for items which work internally at low DC voltages.  The amount absorbed by lighting was the total consumption less anything connected to the mains by a plug.  Out lighting is all 240V CFLs.

Low voltage distribution is not that simple

For high current devices, 240 volts AC is a good idea, and low voltage DC a very bad one.  During the spin and heating cycles, a washing machine can draw up to 1,200 watts or more.  At 240 volts, this is is about 5 amps, which is well within the safety limits of the 2.5 mm2 cable commonly used in ring mains, at 12 volts this becomes 100 amps which requires heavy cabling and appropriate safety measures, in short not what you want in your home.  The electricity supply system is based on high voltage AC for a reason, but technology moves on.

Discussion

As with all good science, we can make some conclusions before we start.  The first is a negative, some devices in their current form are simply not going to work at 12 volts, the list includes, but is not limited to washing machines, dish washers and vacuum cleaners.  Most of these devices are only used in short bursts (a washing machine cycle is typically an hour or less).  Potential solutions include dual 240 volt AC and low voltage DC circuits, using a laundry (energy savings from economy of scale).  If three men and four women can venture into space, we should be able to devise a way of getting clean socks without destroying the planet.

Secondly, there is the potential savings from economies of scale, if all the wall warts in our house (a geek term for plug mounted transformers which take in 240 volts AC and give forth 12 volts DC (or less) with varying degrees of regulation) were replaced by a single well regulated 12 volt power supply, the savings could be significant.

The actual choice of voltage for a low voltage main is an open question, I've opted for 12 volts because micro-generation devices like solar panels often work at 12 volts as do the lead acid batteries which can be used for buffer storage.  A 12 volt supply is adequate to meet the needs of lighting and small electric motors.  However, in many devices, the logic circuits work at 3.3 or 5.0 volts and components such as motors work at 12 volts.

The savings expressed wind turbine installations

A typical onshore wind turbine produces approx. 5 million kwh/year.  There are approx. 20 million households in the UK.  If each household reduces its consumption by 2kwh/day (approx. 700 kwh/year) by adopting low voltage technology, the savings are the equivalent of installing 3,000 wind turbines or a corresponding reduction in fossil/nuclear generating capacity.

Comment

I doubt is any of these ideas is original.  It would be nice to think that somewhere a university department of urban energy is evolving them.  Much of the energy and climate change debate is focussed on generation, but the way we use energy is equally important.  If emission reductions are to capture the popular imagination, the solutions most be cost-effective for there to be an incentive for the general population to adopt them.

As I have become more familiar with micro generation and urban energy, the more I am convinced that the way forward is, where practical, to start again.  Adding solar panels with a capacity of 2,000 kwh/year (cost £10 - £15k?) to a south facing roof and tying them back to the grid is, maybe, a good thing.  An attractive alternative is to reduce household consumption to less than 500 kwh/year and meet this demand from solar panels, using a grid connection as back-up during the winter months.  And don't forget the wind-up radio.

Page updated: 06-July-2010