The standouts among energy harvesting technologies

Today, embedded systems and smart IoT devices are asserting themselves as technological mainstays that are central to the way the world around us is organised. As IoT pushes into more and more remote locations, the big brains behind the tech world are busy scoping around for alternative sources of energy. 

This search has been on for a while and in all likelihood, isn’t going to stop anytime soon. The global mood around the topic of the impending energy crisis has been tense, bordering on grim, for a while now. We have an increasingly loud voice emerging from the global populace demanding a move away from fossil fuels and all the apparent damage that they are understood to unleash. 

Incredible advances

If you are at all invested in the pursuit of alternate energy sources, the last few years must give you a whole lot to feel satisfied about. We may not have figured out how to power our megacities and cars, en masse, using clean energy. But we have come a long way towards finding cleaner and greener ways to power our sensors, nodes, edge devices, microelectronics and consumer electronics.

What this means is that we have, over a relatively short period of time, been able to unplug embedded systems and IoT devices from the electricity grid. Today's IoT systems don’t need access to AC current. That may not be all that impressive in itself until you factor in the crazy bit about how these systems can make do without batteries either! 

This is by no means a small feat. We have essentially gone from accessing the internet exclusively through dedicated computing devices, to democratising internet access across a wide range of everyday objects, to setting said objects free from the tyranny of grids or batteries, all in a matter of a few years. This has truly made the unimaginable possible. The sky is truly the limit for IoT systems now. Sensors in a remote gas pipeline, weather monitoring systems in the middle of nowhere, underwater data-collecting systems, absolutely none of these is any challenge for IoT in it’s batteryless avatar. 

There was quite some apprehension about the growth trajectory of the internet of things falling short of the initially bullish predictions. However, the emergence of batteryless IoT has quashed these worries and put them to sleep. Thanks to energy harvesting technologies, IoT has truly been set free to realise its full potential - the massive potential which caused many an analyst to swoon and make predictions that left many an eyebrow quizzically raised. 

Better infrastructure for IoT

As the 2010s reached the halfway mark, newer technologies emerged that lent hope and much-needed sustenance to the IoT vision that was starting to garner doubts and nay-sayers aplenty. 

Better modalities of energy harvesting along with big leaps in the field of ultra-low power semiconductors meant that IoT could now go places that it couldn’t even dream of. Embedded systems, edge devices and smart operations based on big data could now be put in place no matter how remote the terrain, or how extensive the project. 

With energy harvesting, finding a viable source of power was no longer a concern that weighed down potentially visionary projects. As we entered the 2020s, the energy harvesting race was no longer a fad. Neither was it an exciting possibility for the future. It had well and truly been accepted as the future of IoT. The only hope if we were to bring to fruition the crazy predictions that were made about IoT in the halcyon days of its infancy.  

Today, we have a whole host of options within the realm of energy harvesting - depending on the nature of your project and its specific requirements, you can choose from a range of power sources such as solar, thermal , wind, piezoelectric, triboelectric, kinetic, tide and many more. Each of these options comes with its own list of ideally suited applications, pros and cons. In this post, what we set out to do was to offer our readers a rundown on what some of these considerations are and how various energy harvesting technologies stack up against each other. 

Solar energy harvesting

Here’s a simple way to wrap your head around why solar energy is such a good option (at least in principle) to power ultra low-power electronics. 

Think about it.

All life on planet earth is solar powered. All of it! There is not a single life form that does not owe its life, directly or indirectly to the sun. The sun singlehandedly holds together  the entire edifice of carbon-based life. 

So, it makes a lot of sense that this practically inexhaustible source of energy can be a great way to power miniscule semiconductors that barely need any power to do their jobs. 

Today, the market is witnessing some impressive solar energy harvesting propositions - For instance, a flexible, single-junction GaAs PV cell developed by the now defunct company Alta, came with a 28.9% conversion rating from the National Renewable Energy Laboratory.

Although the company went under, the cell was a great example of a design that could have seen at least some of the great potential of solar energy harvesting truly realised. 

Thermoelectric energy harvesting

Thermoelectric energy harvesting makes use of the Seebeck effect to produce an electric current from a temperature gradient between two unique types of conducting substances. 

Thermoelectric energy harvesters are not particularly known for their efficiency. In fact, thermoelectric energy harvesters tend to compare quite unfavourably to other types of energy harvesters in terms of energy efficiency. However, they are still the most preferred types of energy harvesters in certain applications because of how quietly they operate. 

Thermoelectric harvesters are solid state devices, which means that they don’t have many moving parts. Thermoelectric energy harvesters are increasingly being preferred for certain specific applications like in military aviation. They are also being preferred for wearable IoT devices and bio-medical devices such as implants because they can harvest energy from the surface heat or the internal body heat of the user. 

Solar and wind in tandem

Why make do with one when you can have two?

Scientists have begun experimenting in earnest with devices that contain more than one type of energy harvester. A notable example of this kind of a multi-energy-harvesting device is the one that scientists from the National Center for Nanoscience and Technology  came up with, which can harvest both wind and solar within a single framework.

Although tiny in size, the device is able to generate 8mW of power using solar and on the wind side of things, is able to produce 26 mW! That’s no mean feat!

This is just one example of how a device that uses more than one kind of energy harvesting can be highly practical and make a lot of sense in terms of its flexible functionality. 

Each energy source comes with its own set of limitations which devices like these are able to overcome by not having the entire embedded system depend on one source of power. 

RF energy harvesting

Radio frequency energy harvesting has emerged as one of the most trusted and reliable means of powering ultra-low power electronics and IoT sensors. RF energy harvesting scores heavily over its peers over a number of parameters.

Firstly, there is the near universal supply of radiofrequency waves - this one probably doesn’t come as a surprise for anyone. For better or for worse, our surroundings are rife with electromagnetic waves these days and this situation isn’t changing anytime soon. 

Then, there’s the incredible amount of control that is possible with rf energy harvesters. Think about it, you can’t really have much of a say in how sunny or windy it’s going to be on a given day but in the case of RF energy harvesting, it is possible to calibrate the exact amount of energy that goes in. This makes for a precise calibration of the reception according to the needs of the particular application. Moreover, RF energy harvesters are incredibly inexpensive to manufacture and maintain. 

Summing up

Ultimately, each energy harvesting technology has its own place. More importantly, we need to explore each and every lead we get when it comes to alternate sources of energy. We can’t afford to be lackadaisical when it comes to our approach. What may seem like a non-viable technology today might just be the lifesaver we were looking for when viewed in tandem with some new technological advancement in the future. 

Nevertheless, it pays to invest time and thought into choosing the right kind of energy harvesting technology for your system, depending on where it will be deployed, what kind of a load is it expected to handle and other pertinent variable such as weather conditions.