Energy harvesting means taking energy that would be otherwise lost into the surroundings as heat, light, vibration and movement, capturing and utilising it, allowing for more self-sustaining high efficiency technologies in small scale applications with low power requirements.
Why harvesting energy can help us and the environment?
We all use energy in everything that we do, whether that be gas and electricity, or the physical energy needed to carry out daily tasks, such as walking to work, hoovering the carpet or lifting weights at the gym. Each of these activities, including the usage of gas and electricity, requires both the creation and output of the energy required to carry them out.
In both cases, there is a lot of energy lost in the process, which generally goes to waste. One of the biggest examples of this is when electricity is generated in power stations, in which almost two thirds of the potential energy conversion is lost, primarily through heat that is released into the environment. This level of efficiency is just not good enough, which is why much research and development has been put into energy harvesting devices.
How does it work?
Energy harvesting is very much in its early developmental stages. Its full potential has not yet been reached and is only being used by a limited set of industries. The main aim for energy harvesting is to improve reliability to the point where devices can be self-sustaining, using the energy lost in their functionality to power themselves in a circular process.
There are several forms of energy harvesting but the end result is always generating electricity. Below you’ll see some of these methods, and although their names may sound extremely complex, they can be explained in basic terms:
Certain materials generate electricity when pressure is applied to them. The quartz crystal and certain ceramics are considered piezoelectric materials. With the piezoelectric effect, we can target sources of energy such as human motion, low frequency vibrations or acoustic noise, where pressure on an actuator creates a small voltage. Piezoelectric harvesting can be applied to electronic devices such as entry systems and control surfaces such as your tv remote. The same principle can also be used by ultrasonic inductors for remote sensing applications where sensors can activate doors without needing to be powered.
Batteryless remote control
The force that is used in order to press down a button on the remote control has enough capacitance potential, to enable a self-powered tv remote. A great example of this is the batteryless remote developed by Arveni in Grenoble, France.
Reducing our reliance on batteries for small electronic devices does not just make environmental sense but will also help bring down consumption costs and improve efficiency in the long run.
Piezoelectric floor tiles
When pressure by form of footsteps is applied to the kinetic tile, its structure is disturbed at a nano level and electrical potential is therefore created. Technology is now being developed that can harvest this electrical voltage and turn its potential into usable electricity. Kinetic tiles, or piezo tiles as they are sometimes called, have been installed in festivals and concerts in order to power things such as ticket gates. A good example of piezoelectric floor tiles being used was at the Paris Marathon in 2013, when 4.7 kWh of electricity, enough to power a laptop for two days, was generated solely from the runners steps on the floor.
Pavegen, the british company developing these kinetic tiles, has moved away from this piezoelectric material approach because of cost. Their latest design is based on a triangular tile that flexes with each step as it drives a flywheel converter installed on each corner of the triangular surface. By converting vertical mechanical vibrations into revolving mechanical energy, it can much more easily be turned into usable electricity.
Wristwatches have a piezoelectric crystal power source made of quartz that electrically keeps time accurately over long stretches of time. In fact, most inexpensive consumer watches will lose a dozen seconds per month. Some more advanced quartz time mechanisms are able to compensate this with semiconductor silicon time circuits that reduce the variance.
This method harvests the voltage created by the difference in temperature between two dissimilar objects. This method of energy collection requires multiple materials that create a voltage by means of their temperature opposition. Harvesting this charge, we can develop technologies such as:
Temperature powered phone charger
The ‘onE Puck’ thermoelectric charger developed by Epiphany Labs is a fantastic example of how thermoelectric harvesting can be used to create a self-sustaining electrical system. By placing a hot or cold item, ideally a drink, on the coaster-style product, you’ll be able to charge your phone due to the conversion of the voltage created by material temperature. As you can see in the image below, this small device is proof of what thermoelectric harvesting can achieve.
Thermoelectric generator for cars and lorries
Generators that use thermoelectric harvesting convert the heat that is created in the general operation of cars and lorries and convert it into electricity. This puts less pressure on the engine and battery, meaning fuel efficiency can be increased. Studies have shown that installing cars and lorries with these generators reduced fuel consumption by around 5%. This does not create a self-sustainable model; however, it does increase efficiency and reduces the amount of fuel needed to power the car.
The method of pyroelectric harvesting relies on the creation of a temporary voltage caused by temperature change in some materials. Its main usage at the moment is in sensors. It is worth noting that this method is not quite ready for commercial systems.
A good example of this is in a passive infrared (PIR) sensor that can be used in such scenarios as outdoor lights that will turn on when motion is detected. The pyroelectric element uses the small voltage created from the heat emitted by the person approaching to power the light. This creates a self-sustainable model from the most unlikely of sources.
What about large scale energy loss?
The above examples of energy harvesting are, at present, very much generating electricity on a small scale. However, what about the 173 trillion kilowatts of energy that hit the earth from the sun and the endless amounts of wind that has enough energy to blow down trees? Well, although most of it, predictably, goes to waste, more and more effort is going into harvesting these energy sources as time goes by. Millions and millions of pounds worth of investment has gone into the development of renewables, and solar and wind are two of the main methods.
On a large scale, wind turbines are a form of energy harvesting, using energy that would otherwise go to waste to power our homes and businesses. The difference is, the waste energy is not coming from a man made process like the heat loss from power stations. Increasingly, renewable energy companies all around the world are investing more and more time and energy into capitalising on wind energy generation. In the United Kingdom, electricity generated through wind turbines accounted for around 11% of all electricity used in 2015. One wind farm alone, like the Whitelee Wind Farm in Glasgow, has the capability of generating 539,000 kW, enough to power 761,000 homes.
On a smaller scale, wind harvesting is being used for such things as camping stoves and phone chargers. Like the below example, the iFan phone charger designed by Tjeerd Veenhoven uses wind to power its small generator and therefore charge up your iPhone. These sorts of small innovations are baby steps towards integrating renewable, self-sustaining technologies into our daily lives.
The earth receives roughly 173 trillion kW of energy from the sun at any given moment, which is 10,000 times more than the whole world’s population uses; however, at present, just a miniscule amount of that energy is actually being converted into useful electricity for the earth’s usage. The main problem with solar energy at present is that the equipment needed to convert the sunlight is extremely expensive. Not only this, but the amount of money spent does not reflect the amount of return; as of yet, the efficiency of most solar panel systems is still quite poor; however, with time this is improving gradually. At the moment, electricity coming from solar energy generation represents around 1.2% of all electricity used in the United Kingdom, the largest amount of which coming from Chapel Lane Solar Farm in Bournemouth, which covers an astounding 310 acres, the size of 175 football pitches.
On a small scale, solar power has been powering everyday appliances such as calculators and torches for years; however, huge advances in solar technology have seen some incredible products being developed, namely those with regards to remote usage scenarios, such as camping. Large remote solar panel systems can now be transported and used wherever you are, accompanied by solar integrated devices too such as skylights, phone chargers and speakers.