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Power Hungry

A keynote at the recent MEMS Executive Congress by TI’s Ajith Amerasekera discussed, among other things, power and battery requirements for handling our increasingly digital, distributed world. The conclusion he came to – that there’s still lots that needs to be invented – isn’t particularly surprising, but some of the facts regarding how he got there caught my attention.

We talk about the cloud and the use of the internet to ship digital goods like movies as being an environmental boon – no nasty, soot-producing trucks rumbling around the countryside. Just nice, neat, clean bits traveling invisibly through the ether from their cloud to yours.

Well, if the cloud ever gets organized enough to secede from the Internet and become its own country, it will immediately register on the power meter: it would be the fifth largest energy consuming country behind the US, China, Russia, and Japan and just ahead of India, Germany, and Canada, which are more or less tied.

And that’s based on 2007 data.

And that DVD you have decided to forego in favor of digital streaming? It does have a bigger power footprint than the downloaded version, but not by nearly as much as you would think: only around 20% less.

The ways in which the energy is consumed are, of course, vastly different. When shipping by truck, it’s easiest to see the truck as the big power hog – but it’s actually the smallest slice of the stack. The big part is the actual DVD itself at about 70% of the overall power footprint. The paper sleeve is next, then the plastic case. Rounding things out are warehouse costs and, coming in last, the trucks. So the two most obvious consumers are the least significant.

For digital streaming, the big consumer is, of course, the server farm. Then internet routers, then home routers, and lastly, data storage. (And that’s assuming a simple path from the server to the home – clearly, the farther afield those bits have to roam en route, the more energy they require.) His point is partly that optimized streaming could cut that streaming footprint by over half. Those optimizations include sleeping, link-rate adaptation, rate adaptation, and dynamic voltage scaling.

For mobile – or perhaps better to say untethered devices (you can manually recharge a phone, but a remote wireless sensor: not so much) – he sees power consumption levels needing to go from 100s of µW today to around the 1 nW level for a 10-year device lifespan.

His major conclusion from all of this: lithium ions aren’t going to cut it; we need a new technology. They’ve taken us a long way from the NiCd and NiMH days, but they’re running out of big improvements. So something new is needed for the 2020s.

Energy harvesting has promise, of course, but the traditional sources we look to now range from 0.001 µW/cm3 for scavenging WiFi RF energy to around 100 mW/cm3 for using outdoor light. He says we need to look for non-traditional sources of energy, including biological and micro-fuel-cell approaches.

So as interesting as some of those data points are, it is fair to say that the conclusions aren’t news… we’ve got work to do.

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