The most probable development that would put an end to our battery addiction is energy harvesting. Sometimes called also energy scavenging, it means using energy which is “freely” available in the environment to power up the devices that would traditionally rely on batteries to function. As we will see, this notion has been around for much longer than conventional electric batteries.

Energy harvesting has been around us for centuries. Before electricity was invented people used the windmills and watermills to ease up their work, or even the solar energy to heat water in metallic cisterns. Besides being eco-friendly, these methods would have provided free energy and virtually inexhaustible source.


Closer to our times (and somewhat closer to the modern notion of energy harvesting), the automatic watches and then wristwatches started to use ambient energy (mechanical energy in this case) to put into motion a self-winding mechanism. Contrary to the general opinion (I personally was surprised to find about it about 6-7 years ago) the technology exists since the early 1770s, when Swiss watchmaker Abraham-Louis Perrelet invented a mechanism that automatically winded a pocket watch. The mechanism used the mechanical energy generated by the movement of the human body and used it to wind the spring inside the watch. The technique stagnated until the 1920s when it was enhanced and applied to the wrist-watches that would have started to become popular at the time. Now-a-days, the automatic wristwatch is an ordinary existence in our lives and one of the most common examples of energy harvesting in action.


Electrical systems, however, are omnipresent today. Many scientists and engineers are looking into developing reliable solutions that would be capable of generating power with the ultimate goal of creating the device that will require no human intervention to replace batteries or recharge accumulators. Ever.
Much effort has been invested into creating harvesters capable of operating in remote and continuously changing environments. A typical application would be that where a system would be dropped in a remote location, it would gather data from sensors, it would gather energy from the environment to power itself and the sensors (for instance it could convert ocean wave motion to electric power) and then it would use this energy to also wirelessly transmit the data to a centralized location.


Based on the way they provide energy to the consuming elements of the system, harvester may be categorized as tricklers and bursters.


The tricklers provide small amount of energy in a rather continuous manner. The best example of a trickler is the solar cell, which has a low efficiency and can only provide small quantities of energy (especially in low light) but it does that as long as light is present.


The burster relies on ambient energy sources that are only available from time to time, but when that source is available, the harvester is capable of generating a reasonable amount of power to the system. The best example of a burster is the dynamo. Energy created in such a manner is usually stored in a capacitor, or a super capacitor , from where it is taken in a controlled manner by the system that is being powered.


Another classification of the harvester can be based on the type of energy it converts. They can use ambient energy which is available in the environment as movement, light, temperature difference or radio waves. The efficiency of such a harvester vastly varies based on this criterion. A table may be found below (courtesy of Texas Instruments) detailing their typical power output:

The cheapest solution is to use the solar cell. The technology is rather well known at this stage and has been successfully implemented in many applications across the globe. It is suited not only to power small devices that would otherwise employ batteries, but also to provide supplements of energy for households and for other use, in areas where there is no shortage of sunlight. Their drawback is that no matter how much light there is during the day, there will always be the night period when no energy is available to systems powered this way…

The solar cell

Peltier elements (which would also classify as tricklers) use the Seebeck and Peltier effects to gather energy from objects having different temperatures on their sides. They are the basis for modern thermoelectric modules which come as two metalized ceramic plates. Such a system can take great advantage of the warm walls of a house heated on the inside, or of the various temperature differences that generally exist in the urban environment. Compared to the solar cells, however, Peltier elements are rather expensive and their energy source (temperature difference) is difficult to control.

The Peltier element

The harvesters that convert motion to electric energy are the most divers. The dynamo is the oldest available and thus the most well known burster. It is actually a type of reversed electric motor that creates electricity from a rotary motion, rather than rotary motion from electricity. Generally speaking, the dynamo generates quite significant amounts of energy when a source of rotary motion is available, but its output is nil in its absence.

The dynamo

Other motion converters are generally employed in remote oceanic locations to operate as totally independent weather “stations”. They are not really complete stations, but rather sensors that can measure atmospheric pressure, wind speed, humidity, rainfall, fog presence etc. All this information is then wirelessly transmitted to the central station which is a conventional processing lab. These buoys, however, completely operate based on energy harvesters that convert the ocean wave motion in electric energy.


The piezoelectric element is another example of motion driven energy burster. They generate output power when subjected to mechanical torsion. Although quite expensive to manufacture, their application are endless, because human life and activity is based on movement. They generate a few miliwatts of power, which is quite enough for handheld applications. Researches are currently undergoing to determine how they can be implanted in sidewalks, to generate energy from the vibration of footsteps or how they can be integrated in shoes, to recover the walking energy. Piezoelectric elements have also been used to power up the modern versions of self-winding wristwatches or to build tiny brushes attached to clothing that would generate energy when the man would take the clothes off or would put them on.

The piezoelectric element

Another “free” energy source available in the environment would be the radio waves used by other applications. The RF harvester is generally tuned on a frequency known to be available in the area where the powered device is to be used and it generates sufficient amounts of energy if it operates in the vicinity of the transmitter. One of the most common applications using this kind of harvester is RFID (a technology which itself has many applications).


Biomechanical harvesting is also possible taking advantage of the energy radiated by the human body. A very good example is the knee strap designed by Max Donelan:
http://physicsworld.com/cws/article/news/32812
It can apparently generate quite a significant amount of energy, depending on both the movement of the man wearing the strap and on the metabolism.


Some companies try to integrate as many as possible of these existing solutions in order to make energy harvester solutions capable of operating in continuously changing environments (where no energy source is thus available in a predictable manner) and of providing significant amounts of energy to make a difference on your electricity bill (so these are not necessarily for battery powered applications, but also function on the principles of energy harvesting). A company called SolarBotanic has recently developed the nanoleaves, which are basically trees or brushes whose leaves incorporate a multitude of energy harvesters which draw energy from the sun, wind or ambient heat. The idea behind the concept is that it is a significant probability that the weather is either sunny, or windy or rainy etc. Such a tree or bush can be neatly planted in your backyard, nicely blending in with the landscape, while continuously generating small amounts of energy that trickles in the system of your household. If such a paradigm is combined with an energy efficient house, which uses the minimum amount of electricity, energy