This blog contains a brief description of the current situation on the energy harvesting market, current trends, and examples of solutions with the key operating parameters.
Technological advances in minimizing power consumption and increasing efficiency of energy harvesting from external sources have made it possible for current low-energy devices to operate as battery-free. (Figure 1).
Figure 1: The Concept of Energy Harvesting
Deployment of energy harvesting technologies from independent sources has been taking place for more than a decade. The main obstacle preventing development of market was the efficiency of such solutions and the consumption of electricity by "pseudo" low-energy solutions. Currently, energy harvesting solutions market, regarding all the problems with the availability of raw materials and increase in optimization and technological efficiency, stands at the brink of its greatness.
Technology giants and innovative companies have started to incorporate this type of solution into their products to eliminate batteries or extend device life. On a mass scale, this move will significantly reduce the need for batteries as an energy source and produce "autonomous" and maintenance-free solutions.
The innovation aspect of a maintenance-free product will certainly be important for end customers when choosing this type of solution.
Energy conversion and management from thermal, light and AC sources
The first aspect in energy recovery is efficient conversion and management of the acquired energy. For this purpose, DC-DC converters with very low losses and high efficiency are used. Much higher market expectations have led to the development of a separate group of products dedicated exclusively to energy harvesting.
A strong player in the market of solutions dedicated to energy harvesting is E-peas Semiconductors, a company specialized in systems for processing and management of recovered energy. The manufacturer offers solutions dedicated to the acquisition of energy from thermal, light and RF sources (Figure 2). E-peas special PMIC solutions are designed for easy and efficient management of extracted energy. Depending on a design of the device resulting mainly from energy demand, different topology variants are available (Boost / Buck-Boost / Buck-Boost Battery Charger / Boost Battery Charger Wearable). Specifying the nature of the device's operation as well as selecting the right PMIC solution should be done based on an energy analysis of the device's operating plan and the amount of energy that can be recovered.
Figure 2: E-peas PMIC solutions
Another aspect relevant to the decision is a type of source used for energy recovery, where each individual source requires different selection criteria. The main factors characterizing the different sources are their efficiency and daily energy availability. Currently, the widest application in practice, mainly due to efficiency and effectiveness, are solutions dedicated to solar sources.
In the manufacturer's portfolio there are solutions with different topologies of work, this allows to consider different variants of a device operation. A block diagram of the most advanced solution is shown in Figure 3, while Table 1 presents key parameters of solar solutions.
Figure 3: Block diagram of the AEM10941 chip configuration
A very important criterion when selecting a solution is the operating conditions and critical (edge) parameters that define operation of a system and the achievable efficiency.
Table 1: Summary of key parameters of the AEM10xxx family
Light energy harvesting with photovoltaic (PV) cells
An important part of energy generation unit for light sources is a PV cell. When it comes to low-power, battery-operated and indoor devices, artificial light is used as an energy source.
Compared to the solutions available on the market, Epishine products stand out for their high efficiency and adaptability to the application. The manufacturer's portfolio includes six standard solutions with different number of PV cells for indoor light applications and active surface area, which define achievable output parameters (Table 2).
Table 2: Summary of available PV module solutions
Depending on the active area of selected PV module (number of cells) as well as the energy storage element, the final device will be characterized by specific functionality, price, and possibility of operation in a specified environment. Table No. 3 shows examples of photovoltaic module applications along with examples of storage elements in terms of their advantages and disadvantages of operation.
Table 3: Selected examples of PV module applications
The operating conditions of the PV cell module such as illumination intensity, ambient temperature and active surface will define the electrical characteristics of the modules. A summary of the main characteristics, shown in Figure 4, allows for the proper selection of a solution for powered circuit and a light intensity available in the room.
Figure 4: A summary of the main PV characteristics
The sensitivity and efficiency of PV cells is crucial in hard conditions such as low light intensity, changes in temperature, light angle, and light color. Comparative tables and graphs provided by the manufacturer illustrate the efficiency and sensitivity of solutions depending on changes in operating conditions.
In low-light conditions, where condition for minimal level of lightning can't be guaranteed, the sensitivity of the PV cells will play an important role. An example power output comparison for selected PV modules and very low illumination values is collected in Table 4.
Table 4: Comparison of output power at low light levels
Another important environmental factor affecting the PV cell efficiency is the ambient temperature, which affects the power and voltage losses (Fig. No. 5). The power and voltage variations did not exceed +/-20% over the full spectrum of the tested temperature range for the selected LEH3_50x50_6_10 module solution.
Figure 5: Ambient temperature affects the power and voltage losses
The angle of incidence is also of great importance in terms of maintaining efficiency, which, when exceeded, causes a drastic drop in efficiency. Figure 6 shows the dependence of module performance on the variation of the incidence angle, from which it can be deduced that the modules should operate at values of +/-30⁰.
Figure 6: Dependence of module performance
The last important factor is the color of light produced by a particular type of source. Figure 7 illustrates how photovoltaic modules can work with different light sources and colors. The cells operate in the light wavelength range of >300 nm to >700 nm, while maintaining a virtually constant and maximum conversion factor.
Figure 7: Photovoltaic modules work with different light sources and colors
The electronics market and the demands placed on companies supplying end products creates new challenges and forces changes. Technology-driven changes are often slow and less effective in their outcomes. In the case of energy harvesting and battery-powered devices described above, raw material issues will drive faster decisions and actions. The number of battery-powered devices is growing rapidly, creating additional demands on power supplies and problems with servicing each device after its declared operating time.
Considering current technology, component allocation issues, and the need for redesign, it is a good idea to (consider alternatives) take a correction on a topic of powering devices. Innovative approaches to a topic of power supply solutions with the development of energy harvesting technology will have an increasing impact on minimizing energy demand.