What is energy harvesting?

All the giant strides humanity has made in terms of civilization and technology can fundamentally be attributed to one capability that we have - the ability to harness and deploy energy. Globally, we use about 607 quintillion joules of energy each year. Our energy needs are only increasing, with our rapid population growth, and global energy expenditure is expected to be around 777 quintillion joules by the year 2040. These are mind-bending figures and it is no wonder then, that issues of energy and energy shortage feature so prominently in global policymaking. Amidst concerns of depleting fossil fuel reserves and the widespread panic about their environmental impact, it is an epic understatement to say that continuing to meet our energy demands is going to be a mammoth challenge.  

“The total installed base of Internet of Things (IoT) connected devices is projected to amount to 75.44 billion worldwide by 2025, a fivefold increase in ten years.” 

- Statista Research Department

However, despite all the panic and fear-mongering, human ingenuity and innovation continue to offer us hope that we will be able to find a way around this energy shortage. As such, there is a lot of hope that lies in large, environmentally sustainable sources of power such as nuclear and solar. In addition to this, we also have large amounts of energy all around us in the environment, that goes largely unused. This is where energy harvesting comes in - Energy harvesting offers a promising solution to our energy crisis - both economically and environmentally.

What is energy harvesting?

Energy harvesting (Also known as energy scavenging or ambient power) refers to the process of capturing and converting energy from the surroundings to electricity. The energy can either be used immediately or be stored for future use. Energy harvesting works by harnessing small amounts of ambient energy, which is otherwise dissipated or wasted in the form of heat, vibration, light, etc. Energy harvesting, as a technology, is still in a nascent stage of maturity. It is by no means the answer to all our energy woes. However, it does hold tremendous promise when it comes to powering low-power electronics. With the rapidly expanding IoT market, this spells massive potential for this technology.

So in ONiO's application running from any type of battery meant adding a step-down or boost circuit with the added cost of such regulator. Or one could have selected one of the honorably few microcontrollers that will run directly from a lithium cell or single-cell alkaline battery. Either way, a significant premium is added to your BOM due to additional components or from sourcing a premium-priced microcontroller.

What is ambient energy?

At any given point in time, there is energy all around us that is going to “waste”, as it were. For instance, given the preponderance of electronics and mobile devices, we are constantly bathed in an ocean of radio waves and Wifi signals. Our surroundings are rife with potentially usable energy that could power our electronics if harnessed and stored.

In fact, a new app launched by Dutch designer Richard Vijgen called Architecture of Radio, allows us to visualize this massive, invisible field of energy around us, at all times.

A quick energy-swipe at the ONiO headquarters using the "Architecture of Radio" app.

These signals represent just one form of ambient energy. Ambient energy could also be energy in the form of light, heat, sound or vibration. For instance, most power stations in the world employ a turbine which converts heat to mechanical energy, which is then converted to electricity. This process is very inefficient, with over 2/3rds of the energy input being lost to the surroundings in the form of heat, and only 1/3rd of the input being converted into usable electricity. Energy can potentially be harvested from any of these sources, although not all of them are technologically feasible at this point.

The basic technology of energy harvesting

There are many different types of energy harvesting technologies based on the type of energy source. However, all energy harvesting systems, in their simplest form, consist of three main components, in addition to a source of energy:

1. Transducer/Harvester: This is the part of the system that converts the ambient energy from the source into electrical energy.
2. Interface Circuit: The interface circuit extracts the maximum possible amount of energy from the transducer and makes the energy suitable for use by conditioning it into a suitable form for the desired application (through voltage rectification, voltage regulation, etc).
3. Load: The load is the part of the system that could either include electronic devices that consume the harvested energy (such as chips, circuits, actuators, sensors, etc.) or energy storage components such as capacitors, super-capacitors, etc.

Types of energy harvesting

These are a few common sources of ambient energy:

• Light Energy
• Kinetic Energy (Vibrations, mechanical stress, etc.)
• Thermal Energy
• RF Energy (Radio waves)

Harvesting solar energy

Solar energy is commonly harvested using photovoltaic cells (PV cells). Photovoltaic cells convert light energy (from the sun) directly into electricity using a principle known as the “photovoltaic effect”. The photovoltaic effect essentially refers to the process in which photons (units of light energy) excite electrons into a higher energy state thereby causing an electric current to be generated.

There are four categories of PV cells:

• Single and multi-junction cells
• Thin-film cells
• Crystalline Si cells
• Emerging PV technologies

PV cells generally tend to be expensive. Instead of using PV cells, LEDs (light-emitting diodes) and photodiodes can be used to harness light energy and provide energy for low-power devices such as IoT edge-devices. LEDs are relatively less expensive; Photodiodes are more expensive when compared to LEDs but supply more energy.

Harvesting kinetic energy

Kinetic energy is harvested using piezoelectric transducers. Piezoelectric transducers produce electricity from kinetic energy in the form of vibrations, sounds or movements. The transducer converts the kinetic energy into an AC current which is then conditioned into a suitable form and stored in a thin-film battery or super-capacitor.

A few examples of piezoelectric harvesting:

• Pressure sensors on car tires: Piezoelectric energy-harvesting sensors are installed inside the tires of cars. They monitor the air pressure in the tires and relay this information to the dashboard.
• Batteryless remote control units: Remote control units where piezoelectric transducers convert the force of the buttons being pressed into energy that powers the remote’s IR signal.
• Piezoelectric floor tiles: Pavements that are lined with piezoelectric floor tiles that convert the kinetic energy from the steps of pedestrians into usable electrical energy that is then used to power any number of applications like displays and ticketing systems.

Harvesting thermal energy

Almost all electrical systems emit heat. This accounts for a huge proportion of energy that is dissipated. Thermoelectric energy harvesting is based on a principle called the Seebeck Effect, which refers to the phenomenon where a temperature difference at the junction between two semiconductors/conductors, gives rise to a voltage.

A thermoelectric harvesting system consists of a thermoelectric generator (TEG) which consists of several thermocouples that are connected in series to a common heat source. This heat source could be a water heater, engine, solar panel, etc. The amount of energy generated is directly proportional to the temperature difference as well as the size of the TEG.

Thermoelectric harvesting finds application in powering wireless sensor nodes in industrial settings and other high-temperature environments where large amounts of heat are lost.

Harvesting RF energy

RF energy is literally all around us. RF waves are constantly broadcasted into the environment by mobile phones and other electronic devices that have become such an indispensable part of our lives.

RF Energy harvesting technology holds a tremendous amount of promise and the reason for its massive appeal is very simple - In a world where the number of radio transmitters is increasing at a ridiculous rate, RF waves essentially represent “free energy” waiting to be tapped into. ABI Research estimates that the number of mobile phone subscriptions has exceeded 5 billion. And to this already alarming figure, add the numbers of other radio-emitting devices such as Wifi routers, laptops, and microwave ovens, etc, and you can somewhat wrap your head around just how much energy is around us, in the form of RF waves, waiting to be harnessed.

Wireless Energy Harvesting (WEH) has emerged as the most trusted RF harvesting technology, because of its simplicity and ease of implementation - RF waves are picked up through an antenna, causing a potential difference across its length. This potential difference causes charge carriers to move along the length of the antenna. The RF-DC integrated circuit is then able to convert the energy from this movement into a stable DC current which is then used to power sensors or is stored in a capacitor.

RF harvesting has a number of potential applications - At close range to a transmitter, RF energy can be used in low-power devices such as GPS/RTLS tags, wearable battery-free medical sensors and to wirelessly charge low-power consumer electronics. At a longer range, there could be a number of other applications such as building automation, structural monitoring, and industrial control.

Why harvest energy?

The IoT (Internet of Things) market is poised to explode in a massive way. In just a few years, IoT sensors will number in the high billions. The IIoT (Industrial Internet of Things) is mainly aimed at automating processes and making them more efficient. However, if the billions of sensors and edge-devices that will be deployed are to be powered by batteries, this would actually result in a host of other problems.

These sensors might be deployed in places that are hard to reach and therefore, replacing the batteries might be a herculean task. Not to mention, replacing the batteries represents a long-term cost that is absolutely limiting and will be seen as a massive pain point by adopters.

Energy harvesting promises to solve this bottleneck - Especially in places that are very remote, and do not have a power source nearby. It also negates the need for man-power based management.

It also promises to be environmentally more sustainable and reduce the carbon footprint.

Summing up

The Internet of Things (IoT) is dramatically altering the landscape of our everyday lives. IoT devices are changing our lives in myriad ways - be it how we shop, work out or even drive our cars, IoT devices have now made their way into our lives in umpteen different configurations. And going by recent estimates, they are only set to continue rampantly on this upward trend. In the near future, there will easily be over a hundred billion IoT devices around us, integrated into our gadgets, appliances and in remote stations, sending us valuable data.

Energy harvesting technologies show great promise in powering this IoT explosion. With more and more IoT devices being deployed in very remote and hard-to-reach locations, batteries don’t represent a very efficient solution for powering edge devices. Moreover, using batteries is also not very ecologically sustainable. Technologies like RF harvesting open up new doors in our quest to power our MCUs and sensors.

ONiO.zero, a self-powered microcontroller, offers a unique solution for any IoT device by eliminating the need for batteries. No batteries mean no maintenance, lower BOM cost, and smaller designs. Read more about ONiO.zero here.