Written in Montreux, Switzerland, and despatched to TechRepublic at 2Mbps over an open wi-fi hub..
Over the past 18 months a number of articles and scientific papers have hit my screen describing various energy-harvesting schemes. Bluntly, these have spanned the vaguely feasible to the purely nonsensical.
At the unlikely end of the spectrum is the idea of using keystrokes, button presses and screen swipes to power mobile phones, tablets and laptops. Equally problematic schemes include collecting energy from cycling and rowing machines at health clubs and gyms.
Even at the apparently obvious end of these endeavours, which involve collecting energy from vehicles and people excercising, success depends on bad design and incomplete thermodynamic accounting. The best description I can come up with for the misplaced enthusiasm focused on this topic is:
These people want to fill a swimming pool with a tea spoon when it makes more sense to plug the leak.
Let’s just examine the incomplete analysis and wrong-thinking on this topic by probing the health-club example.
Here we have people expending energy to keep fit and well by exercising on running, cycling and rowing machines. But, you may ask, where the harvested energy is coming from. It certainly doesn’t come for free.
The true cost of energy
To create this power, these gym habitués have to eat food that has cost energy and materials to produce, transport, store and prepare. And those modified exercise machines have required materials, production, transport, installation and maintenance in materials and energy. Do you suppose for a moment that the energy collected is somehow green after all this? I don’t think so. It has a cost.
So what about the vibration caused by engines and road movement in vehicles? There is definitely energy to be collected here, but better design that dampens engine vibration and improves suspension systems saves more energy than can be harvested.
Obviously, collecting energy from existing vehicles could make sense, but new ones should not be designed with that in mind.
How can we be so sure that my argument is all true? The laws of thermodynamics. They mean there is no free lunch. You never get something for nothing. No matter what you do, entropy always increases.
In most areas we can get a far better outcome by concentrating on better design and greater primary efficiency.
Implanted electronics in human beings
Collecting μW, mW and watts when the object of our attention should be the consumption of kW is not very smart. However, there are a few areas where the trade-offs might just work well. One such is the powering of implanted electronics in human beings such as pacemakers, respiratory and brain stimulators.
Inserting batteries into people and then sewing them up, or having wires protruding through the skin is far from ideal. Energy harvesting from arterial blood flow, heart or muscle movement is therefore very attractive. Better still, the numbers actually make sense.
Watts of energy are available but only μW and mW are required – and better still a life is saved, improved, and extended.
But on another level batteries are always nasty in terms of the materials used, manufacture processes, their disposal and recycling. For me, this is one equation that works.