Q. What is 'Energy Harvesting'?
A. Energy harvesting is a term associated with capture and storage of energy for small power requirements. It is frequently used for power capacity in milliwatt, microwatt, nanowatt to picowatt power range. For a gauge of scale of power-producers, solar panels are easily able to produce tens of watts of power on a sunny day. A typical device like a light bulb consumes 60W of power.
Q. Then why do we need small power 'Energy Harvesting'?
A. There are lots of markets. For example, present day medical problems like diabetes, pacemakers, and other implantable biomedical devices can benefit from such small 'Energy Harvesting Devices'. Another example is live-patient monitoring chips. These chips with sensors implanted within the body can provide the medical examiner with live heartbeats, pulses, sugar, blood pressure, even fats and cholestrol, haemoglobin levels, remotely, i.e. the patient need not be in the clinic.
Another potential markets is electronics. The capacity to produce extremely small electronics also opens the door to extremely low power electronics. Although so far the benefit of scaling (reducing the size of transistor) has led to more computation-efficient and capable hardware, the power scaling with size scaling is yet to see its full potential. Lot of wireless technologies are focussing on this aspect (see here).
An interesting example is the Contact lens LED projector and sensor (here).
Q. What are the typical 'Energy Harvesting Devices'?
A. We dont call Solar panels as energy harvesters in the conventional sense, although literally they are. However, more interesting concepts involve use of microwave, radio wave and other electromagnetic energy that surrounds us all the time in the modern world because of cell-phone towers, TV towers, radio waves etc.
Another dimension of energy harvesting is through human being themselves. We daily produce a large amount of energy to enable us to do many tasks. However, there is potential to harvest part of this energy by transduction (conversion of energy).
Consider a person wearing a body suit which has flexible solar panels and at every human body joint there is a piezo. Thus while walking in the sun one could be harvesting solar energy, and motion of the limbs producing extra energy through the piezo. But this is just the tip, there is lot of effort dedicated to harnessing the chemical energy from within our bodies (see our post here) and thermal energy our body generates throughout the day.
Q. Is Energy Harvesting green?
A. Yes, and thats the whole point. To harvest energy from what is around us and within us. It embodies the concept of traditional rural farming (hence the term harvesting) by using available resources (electromagnetic waves, solar energy, body heat, internal chemicals within the body, small mechanical motions) and by energetically favourable simple transduction (conversion) process yield a produce (power).
The research community has already demonstrated tools like solar panels, piezos, low power sensors, GBFC's (glucose bio-fueld cells), most of which are highly commercial. So its a matter of time.
The research community has already demonstrated tools like solar panels, piezos, low power sensors, GBFC's (glucose bio-fueld cells), most of which are highly commercial. So its a matter of time.
Q. What are the challenges for 'Energy harvesting'?
A. The biggest challenge is low power devices, the entire electronic and technical industry is focussed on highly complex and more processing capacity whereas, the most useful products to humanity require low power, small size, moderate computation-ability. Consistent effort is needed in this direction.
Another critical thing is that the lifetime of energy harvesting products. If energy harvesting products are to become BIG then they must provide the advantage of longer life of products even if they have low power capacity. Further, a critical requirement is small size rechargeable batteries so that the power produced may be stored. And there is a lot of room for system level innovation at this stage.