[I ran out of room to include this topic in my recent IET talk]
As late as the 1880’s a debate was raging about whether to distribute electricity to our homes by Direct Current (DC), where the current always flows in one direction as from a battery, or Alternating Current (AC), where the current reverses direction many times a second. The prolific American inventor Edison advocated DC, while European genius Tesla advocated AC. It was called the War of the Currents (what is it with all these “war” analogies? Enough already!).
Tesla won. Sending electricity a long way requires the use of high voltages (to allow low currents and therefore conductors cheap-enough and thin-enough to string along pylons). At the time the only practical way of stepping these high voltages back down to practical household levels was with transformers, which only work with AC.
So the grid connection to our homes is now AC – 230VAC across Europe and 110VAC in the Americas. And AC is fine for lots of the “grunty” things we’ve done in our homes for decades: running the motors in our fridges, washing-machines and dishwashers, and providing the heat for washing-machines, dishwashers, ovens and tumble-driers.
But as the following chart from DECC shows, our usage is changing. Since the 1970’s we’ve more than doubled our overall electricity consumption per home. In most categories of product, the average consumption rose simply because those products became widespread in homes. For example, consumption of the “Cold” and “Wet” categories rose just because gradually every home bought a fridge and a washing-machine.
However sometime around 1990 the consumption in these categories started to level-off. Everyone already had fridges and washing-machines, the market was now saturated. Lighting likewise levelled-off, and cooking hadn’t changed for a long while. This neatly shows that in the lives of us consumers there is indeed such a thing as “enough”: enough light, enough cold, enough washing – at least in the presence of moderate pain from high energy prices.
Good news, bad news
On the above chart it’s interesting to see that from around the year 2000 (for fridges) and 2005 (for lighting) there is clear evidence that consumption in those categories has started to fall. This has happened as old devices have gradually been replaced by ones with hugely increased efficiency – new fridges are now generally all A++, and new lighting all compact fluorescents – and in both cases technological advances mean that these use several times less energy than their primitive forebears.
That’s the good news.
The bad news is the huge rise in “gadgets” – consumer electronics and computers. As we can see, the biggest culprit is TV’s, the set-top-boxes under them, the black box PSUs (power supply units) which power all our gadgets, and computers of various sorts. Clearly this is an area where we really need to focus on reducing our consumption.
What will happen next? Well PC’s, TV’s etc. have all become dramatically more power-efficient over the last decade, and will probably continue to do so as long as pressure is kept up by rising energy costs and legislation. But this is being counteracted, perhaps more than counteracted, by a rise in the number of gadgets in our lives. And it seems likely that innovation and marketing will continue to drive a steady stream of new gadgets into our lives. Bad news from an energy standpoint.
But equally, just as there is such a thing as “enough light” or “enough heat”, there must be such a thing as “enough media”. Once you spend 24 hours a day in front of the goggle-box, you can’t spend any more.
Gadgets are mainly about pushing data to and fro (including to and from our brains) and the theoretical limits on how little energy computation and data transport require are very small. So the consumption of today’s gadgets is very far above where the laws of physics say they could be. As an example of just what is possible in reducing gadget consumption, witness the mobile phone. 20 years ago the first “carphone” users got a few hours talk time with a huge battery. Then only 10 years later we had 2 weeks of talk time with a tiny battery. Miracle! But then today we’re lucky if you get a day. Disaster! What’s going on? It is simply down to which problem engineers are currently focussed on. When they’re given a huge shopping list of features then energy-efficiency drops right down to the bottom of the list and talk time shrinks. But when efficiency becomes a must-have (e.g. because its mandated, or you suddenly can’t get a day’s battery-life), or feature innovation slows giving engineers more time to focus on talk-time, then it bubbles right back up to the top again, and engineers work their miracles on power consumption. So it will be with all our gadgets.
War of the Currents part 2 – Rise of the (DC) Machines
Meanwhile in the background there is a gradual shift going on. With the rise of gadgets, and of course the transition from compact fluorescent lighting to LED lighting, more and more of our electricity consumption is becoming low-voltage DC, rather than the high voltage AC of old. Powering a tiny computer chip from our massive mains 240VAC supply has been likened to trying to drink from a firehose – it can be quite difficult to do that conversion really efficiently. And of course if we have solar panels on our roof, they create low voltage DC too. So more and more we are converting DC to AC and then back to DC again, which is inefficient (witness how much power is lost in PSUs in the DECC chart above).
This has led some people to ask whether we wouldn’t be better-off keeping it all in DC. We’d still keep all our “grunty” machines running off AC from the grid, but then we’d just convert (once) down to low-voltage DC and then run that as a separate ring-main around the house for all our gadgets. Many LED lighting systems effectively already do this – one mains converter typically drives many lamps on a 12VDC spur.
And the thinking goes beyond even that, because of course one of the things that you can more easily do with DC is to store it, since batteries are inherently DC. This means that you can shift the timing of your consumption, charging the battery when electricity is cheap (at night). And of course if you have solar panels, charging it too whenever the sun is shining. So creative companies like Moixa are designing systems to manage all of this: the generation, the storage and the distribution of DC.
As the chart above shows, the net effect could be that a big fraction of our household DC consumption (gadgets and lighting) can be made cheaper, using off peak electricity. And if we have solar panels then a substantial further fraction can be run entirely off free solar electricity.
Your gadgets could become free to power – and perhaps more importantly guilt-free to power.
Quite a thought.