Energy Harvesting

This post originally appeared as part of the official Nobel Week Dialogue blog. For my first #NWD13 blog post, I wanted to introduce the readers to the concept of Energy Harvesting (EH)

The event will stream live on the homepage tomorrow (from 9am GMT – the site will switch to a new “streaming” format at 8am). If you’re interested in energy, I think you’ll really enjoy this event. Available on mobile devices too, and all day, so drop in at any time!

The world is still dependent on fossil fuels, which are both finite and environmentally costly. And we also know that we can’t just depend on so-called “renewable” technologies. Beatrice’s post showed just how complex it is to get a country’s energy balance right! Sustainable and so-called “carbon-neutral” energy can be derived fromnuclear fission or captured from ambient sources.

The first of these is ever-present in the media, often for the ‘wrong’ reasons (nuclear power will be discussed in Session 3B of the programme). And most of us are familiar with some large-scale ambient energy capture, such as collecting sunlight using solar cells, wind from turbines and tidal energy from tidal generators. But at the other end of the scale, there are small amounts of ‘wasted’ energy that could be useful if captured. Recovering even a fraction of this energy would have a significant economic and environmental impact. This is where energy harvesting (EH) comes in.

So, what is energy harvesting? Well, I hope that this meeting will show that the energy crisis is about more than fossil fuels versus renewables: it’s also about gettingmore from what we already use… and this is where energy harvesting comes in. It is a process that captures small amounts of energy that would otherwise be lost as heat, sound, vibration or motion. It can use this captured energy to improve the efficiency of systems, by reusing some of the waste energy, or even to power new technologies, such as wireless sensors.

  • VIBRATION, movement and sound can be captured and transformed into electrical power using piezoelectric materials. Piezoelectricity literally translates as ‘electricity resulting from pressure’. In these materials, electric charge is produced in response to applied mechanical strain. Human motion, low-frequency vibrations, and acoustic noise are just some of the potential sources that could be harvested by piezoelectric materials.

One area of interest is in harvesting the kinetic energy generated by the footsteps of crowds to power ticket gates and display systems – this technology has already been implemented in Japan’s busiest train stations, and UK companies are testing energy-harvesting tiles in the corridors of schools around the country. This technology can be used to power wireless sensors too – replacing the need for batteries.

  • HEAT can be captured and transformed into electrical power usingthermoelectric materials. When there is a temperature difference across one of these materials (i.e. one side hot, the other cold), it causes a voltage across the material. If the temperature difference is kept constant, this voltage can be used to provide electrical power.

Heat represents the biggest energy loss in industry. Heat engines generate nearly all of the world’s electrical power. These are gas or steam-powered turbines that convert heat to mechanical energy, which is then converted to electricity. But approximately two-thirds of the energy input is not converted to electrical power but lost as heat. And in the car industry, the figures are just as bad – almost 70% of the energy produced by a car engine is lost, and most of that, in the form of heat.Thermoelectric materials can capture some of this heat, and produce electricity. Cars and trucks equipped with thermoelectric generators (TEGs) would have significant fuel savings (especially with the increasing cost of petrol). In 2012, BMW demonstrated this proof of concept – Their prototype TEG was placed on the exhaust line of a BMW X6, and it produced about 500W from running on a highway, reducing fuel consumption by 5%.

The important thing to note about energy harvesting is that its aim is not to generate large-scale power, but to capture small amounts of energy that is ‘wasted’ during industrial and everyday processes. So it is only part of the “energy solution”, but I think a fascinating one!

Would you like to learn more about each of these technologies? Here are a few news stories I wrote on recent research papers

  1. VIBRATION: a generator that can convert footsteps into electrical power, maybe offering a large scale solution for urban areas: (Power) Walk this Way
  1. HEAT: Scientists from Northwestern University have developed a new nanostructured thermoelectric material which they claim converts heat to electricity more efficiently than any existing material: Thermoelectrics Go Nano