I recently sat down with Yogesh Ramadass, a design engineer with Texas Instruments. Heís as much of an expert on the subject of energy harvesting as anyone I know, so I asked him some pertinent questions on the subject.
Whatís the real definition of energy harvesting?
In the broadest sense, any situation where one uses freely available energy from the ambient to get useful work done should be classified as energy harvesting. That raises the question, doesnít most of the useful energy on earth come from the sun? And the answer would be yes, the earth is one big energy harvester, harvesting the available heat and light energy from the sun. Plants and animals on the earth harvest the sunís energy for everyday living.
For a more specific definition of energy harvesting as it applies to electronics, energy harvesting refers to the conversion of ambient energy available in the form of heat, light, wind, and mechanical energy into useful electrical energy to power electrical and electronic items. This ranges from the megawatts of power harvested using big wind, tidal, and solar farms to the relatively tiny microwatts and milliwatts of power harvested by small solar cells, thermal harvesters on vents, and vibration harvesters on machines.
What can we do today with energy harvesting, specifically in the very low power space?
Today, we have energy harvesting systems that can reliably harvest from tens of microwatts to a few milliwatts of power, depending on the ambient surroundings. For example, small solar-cell-powered systems in indoor surroundings can typically harvest a few tens of microwatts. Taken outdoors, that same system can increase its power capability to a few milliwatts. With this amount of power, we can run small temperature, humidity, and chemical sensors, which can relay vital information to a central hub. With the ability to be self-powered, the shackles of a fixed energy source like a battery can be removed, paving the way for widespread adoption.
What can we expect energy harvesting to look like in the next five years?
In the next five years, the energy harvester and the storage technologies required in these systems will be more mature. The electronics within these systems will also be pushing new lower power regimes, making it more viable to use energy harvesting to replace batteries, both from technology and cost perspectives. When this happens, we will see harvesting devices all around us, in home-automation devices, wearable devices monitoring our health, industrial sensors, and many others.