I’m thinking this would be less a conventional laptop and more of an e-ink device that could also save word processing documents, spreadsheets, etc., and serve primarily as an e-reader/commuter tool that’s a little more type-friendly than the current generation of eReaders and iPads.

What do you think?

My figure was for the oldish laptop I’m currently using – it’s what the power gauge is reading. I could imagine the power consumption being reduced to a tenth or less, say to that of a PDA-type device, smart phone or MP3 player. This would make energy harvesting easier: now we are only three orders of magnitude away, i.e. we need to type at an average of 1,000 keystrokes per second. It helps.

However, reducing the power requirement now makes it easier to achieve satisfactory operating life using a battery: in our example, it increases battery life by a factor of ten, from 4 hours to 40 hours. A further factor of ten reduction in consumption gives a battery life of 400 hours; somewhere near this point power stops being a major issue!

Kindle-type devices with passive E Ink screens already have a battery life in weeks if not months, with no need to type continually on some Keyboard of Death.

Anyway, eReaders and iPads don’t have keyboards.

The difficulty with the laptop application is that there is not enough power going into the keyboard by typing, however it is harvested. Our fingers simply don’t deliver enough power, just a millijoule or so per keystroke. And the lower the power consumption of the computer, the more attractive (i.e. smaller, cheaper, longer lifed) batteries become.

This is the bind in which energy harvesting technology so often finds itself. On one side, the energy available in the environment tends to be rather too scarce to be useful, that is, it is too widely dispersed and therefore has to be gathered over too large an area or volume to be convenient and cost effective.

On the other hand, if the power requirement is lower, then batteries start to look more attractive. Usually they can deliver more power at less cost in a smaller package. But they do need to be recharged or changed periodically.

There are definitely niches where energy harvesting works very well, though they are quite rare. Wireless sensors are an example, as there is no wire to power the device. But the power consumption of modern chipsets can be so low that the sensor may have served its purpose or become obsolete before its battery is flat.

Anyway, the abstract refers to ‘integrated microscale energy scavenging systems’; ‘micro’ i.e. millionths, very little. I’d guess that early applications for the thin piezoelectric films that RMIT University is developing are more likely to be as integrated sensors for motion detection and other sensing, and maybe for generating a few microwatts for very low-powered circuits.

First, Dr Bhaskaran has not invented a product for charging laptops or anything else. What she has done is develop a nanoindentation technique to assist in the characterisation of thin piezoelectric films. No doubt this is very useful research, but it is nowhere near being a product.

Next, a typical keyboard key force is 45g and key travel is about 3.5mm. The energy from a single key press is therefore F x s = 1.5mJ. My laptop is currently consuming about 15W. Therefore, assuming all the energy from each keystroke is converted into useful power, which it can’t, I would need to average 10,000 key strokes per second. I can’t type that fast.

Even with reduced power consumption and stiffer keys with greater travel, it is clear from this simple sum that this is several orders of magnitude away from a feasible invention.

For example, if the keys had 35mm of travel and required a key force of 450g (i.e. about one pound-force), and the laptop used only 1.5W, it would require ‘only’ 10 keystrokes per second, still assuming no losses. But at 1.5W, my existing batteries would last 40 hours instead of 4.

The energy harvested from the environment (after all the losses) must exceed the power consumption of the device.

Many energy harvesting ideas fail as soon as this basic arithmetic is done. Too often there is simply not enough energy in the environment available to be harvested. If there were, the world would be unbearably noisy, shaky, lossy, windy, hot, bright or whatever.

Reducing the device power consumption of course reduces the energy that needs to be harvested. However, this then makes it easier to achieve acceptable life from batteries. Thus there is a rather narrow window of opportunity for energy harvesting where it is not more cost effective, compact and reliable to use batteries instead.

I am not against energy harvesting in principle. Sometimes there are reasons why energy cannot be stored (e.g. plants that are subject to explosive atmosphere regulations) and battery changing or charging is difficult, that create an overwhelming case for energy harvesting.

There are some good products where energy harvesting works well: PV powered calculators, torches with solar battery chargers, bike lights with dynamos, where the power requirements and duty cycle match the available energy. But in practice, good opportunities are scarce and most do not stand up even to basic engineering scrutiny. Like this one.