Emergency Power Sources Operating Based on Energy Harvesting Processes for Application in Crisis Situations

Abstract

This article discusses the use of energy harvesters as emergency power sources during emergencies, crises, and disasters. The climate crisis, population growth, social and political unrest, terrorism, wars, and information chaos all contribute to the increasing likelihood of populations suddenly being deprived of access to electricity. This threat is possible both locally and globally. Regardless of the size, source, or type of emergency, disaster, or crisis, rescue procedures and actions that enable people to function are essential. This requires, among other things, ensuring emergency power sources. Energy harvesting technology can be used to create both primary and supplementary sources of electricity. The authors of the article conducted a comprehensive analysis of this topic and reviewed existing research in this field. Based on literature studies, a number of conclusions were formulated defining the current state, future development directions, and challenges in the use of energy harvesters in crisis situations. The aim of the work is to draw attention to existing threats and to try to direct the interest of scientific teams towards intensifying research in this field, both in terms of the development of cognitive knowledge and the transition from the area of model research to final applications.

1. Introduction

Current global annual electricity consumption is approximately 30 PWh [1]. The unit of measurement prefix P–peta, denoting a multiplier of 10¹⁵, is rarely used in technical and economic matters. This means that the average daily electricity demand per person is about 10 kWh. Since the beginning of the 21st century, global electricity consumption has doubled [1]. Rapidly developing information processing technologies using generative artificial intelligence models are posing new energy challenges for humanity. Global technology companies are planning to use their own nuclear power plants to power their supercomputing centers [2,3]. Due to its properties, such as ease of transmission, distribution, and high-efficiency conversion into other forms of energy, electricity is one of the fundamental elements of modern civilization.

Primary uses of electricity, such as lighting, heating, and conversion to mechanical energy, have been expanded to include information processing and transmission technologies, which require power sources. The vast majority of the inhabitants of our planet cannot imagine even a short-term existence without the availability of electricity.

However, there are a number of threats, emergencies, crises, and disasters during which access to electricity can be partially or completely limited. The largest power outage to date, a blackout, occurred in India in 2012. As a result of grid overload, over half a billion people were left without access to electricity for two days [4,5]. However, smaller, localized emergencies related to power outages can also pose a threat to property, health, and life. Examples include power outages in hospitals [6], deep mines [7], and nuclear power plants [8].

Threats, crises, and disasters related to limited availability of electricity can have natural, anthropogenic, or mixed sources. They can be entirely random in nature, but there are also cases that can be predicted with a significant probability, as well as intentionally induced events. Natural disasters include earthquakes, volcanic eruptions, impacts from space, tsunamis, tornadoes, floods, fires, avalanches, epidemics, and droughts [9,10]. Human-related disasters include wars, terrorist acts, construction disasters, industrial accidents, ecological disasters, fires, nuclear threats, and land, sea, air, and space transportation accidents [11,12,13]. In many cases, the cause of a disaster is mixed, linked to both human activity and forces of nature [14,15].

Disasters have always been inextricably linked to the existence of our planet. A spectacular example is the extinction of the dinosaurs [16]. The causes of this disaster remain controversial and heatedly disputed, although one thing is certain: it was not caused by the actions of our species. However, in today’s world, with a human population exceeding 8 billion, social, political, and economic conflicts becoming increasingly extreme, civilizational, industrial, and technological development reaching unprecedented speeds, and the exploitation of our planet’s resources exceeding its natural regeneration capacity, human-induced crises are an integral part of everyday life. We are dealing with the consequences of undoubted climate change [17,18,19,20], nuclear disasters [21], destruction caused by armed conflicts and terrorism [22,23], ecological disasters [24,25] and many other threats.

Regardless of the source or type of emergency, disaster, or crisis, rescue operations are essential. One obstacle to these operations may be limited access or the complete absence of grid-based electricity sources. This energy is essential for powering rescue equipment, lighting, life support systems, communications, positioning, monitoring, signaling, and many other devices. Emergency services naturally have their own battery or photovoltaic power sources, as well as diesel generators of varying power, used during rescue operations [26]. However, in operations under difficult conditions, in areas with limited access, and during long-term operations, standard power sources may prove insufficient. Emergency power sources based on energy harvesting processes can be a supplement.

Energy harvesting is a technology that has been rapidly developing in recent years [27,28,29,30]. The idea behind this technology is to acquire and store relatively small amounts of electrical energy by converting other types of energy from the environment. This energy from environment sources, derived from natural or anthropogenic processes, is dissipated under natural conditions. The size of electrical power generated in the harvesting process is not strictly limited but is assumed to range from microwatts to single watts [31]. For example, a system for obtaining energy from photovoltaic panels to power a network of wireless sensors is an example of an energy harvester [32], while photovoltaic farm systems [33] significantly exceed the scope of this technology. These processes differ primarily in the amount of energy generated. Energy harvesters are self-sufficient power sources, eliminating the need for connection to the power grid or battery replacement. They are primarily used to power low-power devices, such as sensors, monitors, information systems, data transmission and communication systems, positioning, lighting, and many others. This is particularly true for powering devices used in hard-to-reach locations. This technology is also preferred for environmental and ecological reasons [34].

The authors of this article aims were to review and analyze emergency power sources based on energy harvesting processes for use in emergencies, crises, and disasters. The climate crisis, social and political unrest, ongoing wars, the ubiquitous information overload and uncertainty surrounding its truthfulness, make this issue particularly relevant today. According to the authors, research into technologies used in emergencies requires increased attention from research centers, both theoretically and in terms of application.

The introduction to this article outlines the relevance and importance of the topic. Chapter two is devoted to energy conversion processes in harvesting technology. Chapter three provides an overview of the concepts, current research, proposed solutions, and prototypes of harvesters for use in emergencies. The conclusions discuss the problems, challenges, and prospects of the technologies discussed.

2. Methods of Converting Primary Energy into Electricity in Harvesting Technology

Energy harvesters convert source energy from the environment into electric current. This current can be directly used to power low-power devices and systems or stored in supercapacitors and batteries. In emergency power sources using harvesting technology, source energy can be drawn from any source available in an emergency. These sources can be divided into three groups. The first is energy generated by humans, most often by emergency services in emergencies. This energy is available in the form of mechanical energy and thermal energy. The second group includes natural sources like solar energy and its derivatives, such as wind, water movement, biomass and biofuels, thermal energy, and geothermal energy. The third group comprises anthropogenic sources, such as sources from industry, communications, or transmitters of electromagnetic waves. Because the essence of harvesting is the conversion of energy forms, various methods of converting source energy into electrical current are used. Converting mechanical energy into electrical current is possible using electromagnetic, piezoelectric, and triboelectric methods. The electromagnetic (electrodynamic) method utilizes the phenomenon of electromagnetic induction, which involves the generation of an electromotive force in a conductor placed in a variable magnetic flux. The piezoelectric method is based on the phenomenon of inducing electric charges on the surfaces of certain materials during mechanical deformation. The triboelectric method, on the other hand, relies on the generation of charges on appropriately selected pairs of materials interacting with each other through friction, proximity, and direct contact.

Electromagnetic energy can be converted into electricity in photovoltaic cells and antenna systems. Photovoltaic cells constructed from semiconductor materials convert light into electricity. This process exploits the phenomenon of charge carriers moving within a semiconductor due to the energy of incident photons. This movement of charges creates a potential difference at the cell’s terminals. In the radio frequency range, electromagnetic energy can be collected from environment and converted into electricity in antenna systems. The use of resonant circuits and rectifiers cooperating with antennas allows for the conversion of high-frequency electricity into direct current. In such systems, it is possible to utilize electromagnetic energy from transmitters, as well as from lightning discharges.

The conversion of thermal energy into electricity can be achieved in thermoelectric and pyroelectric transducers. Thermoelectric transducers utilize the Seebeck effect. In this phenomenon, an electromotive force is generated in a circuit composed of junctions of different metals or semiconductors placed at different temperatures. Pyroelectric transducers, on the other hand, utilize a single source that changes temperature over time. The pyroelectric phenomenon involves the generation of an electromotive force in certain materials due to temperature changes. The materials most commonly used in this method are crystals similar to those used in the piezoelectric method.

There are also other methods for converting source energy into electrical current, which are not yet typically used in energy harvesters. These include magnetohydrodynamic method, thermal emission method, and direct conversion of chemical or nuclear energy into electrical current.

In energy harvesters, in addition to the basic method of converting energy into electrical current, a pre-conversion that changes the form of energy is also used. This can be a mechanical-mechanical conversion, for example, converting wind into the rotational motion of a turbine. Pre-conversion of thermal energy into mechanical energy of motion or conversion of infrared radiation into heat is also used. The type and design of such transducers depends on the creativity of the energy harvester’s designers.

Table 1. Characteristics of Energy Conversion Methods Used in the Harvesting Process.

Primary Energy	Conversion Method	Typical Efficiency	Typical Power Density	Internal Resistance of Current Source	Percentage Share in Publications	References
Mechanical Energy	Electromagnetic	60–95 [%]	30–200 [W/m2]	middle	17%	[28,30,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52]
	Piezoelectric	20–80 [%]	10–300 [W/m2]	high	19%	[28,30,40,49,53,54,55,56,57,58,59,60]
	Triboelectric	30–50 [%]	0.2–10 [W/m2]	high	15%	[28,30,38,39,40,41,46,48,61,62,63]
Electromagnetic Energy	Photovoltaic	15–47 [%]	30–220 [W/m2]	middle	16%	[28,30,64,65,66,67]
	Antenna Systems	50–90 [%]	0.002–10 [mW/m2]	low	11%	[28,30,68,69,70,71]
Heat Energy	Thermoelectric	5–20 [%]	1–10 [W/m2]	low	15%	[28,30,66,72,73,74,75]
	Pyroelectric	1.5–19 [%]	10–40 [mW/m2]	high	7%	[28,30,76,77]

presents the characteristics and properties of the methods of converting source energy into electrical energy used in the harvesting process, along with literature references.

The data in Table 1 are based on the publications analyzed in this article, which describe research on energy harvesters intended for use in crisis situations. Data from review articles on energy harvesting [28,30] were also used. The ranges of values for parameters such as efficiency and power density given in Table 1 should be considered representative of prototypes described by research teams in publications from the last twenty years. These data are not absolute; they are intended solely for comparative purposes. Due to the significant number of features and parameters that distinguish specific harvester prototypes, creating comparative graphs, for example, is practically impossible. Therefore, the author attempted to standardize two basic parameters of energy conversion in the harvesting process. These values were estimated based on data contained in individual publications. For comparison purposes, the generated power density was expressed in standardized units. This density expresses the ratio of the generated power to the harvester’s active surface area. This surface area is an arbitrary value, assumed by the author. For example, in the case of photovoltaic conversion, this is obviously the cell surface, while in other cases, it will be the conventional surface area where the source energy interacts with the converter. Strictly defining parameters for each converter separately would require considering numerous factors, using different units, and complicate comparisons of methods, which is the main task here. The percentage of energy conversion methods in publications describing the design and research of energy harvesters was determined based on the Google Scholar database, including articles from the last 20 years. A statistical Monte Carlo method with keyword search was used. For harvesters using hybrid processing, combining two or more processing methods, these publications were included in the class of each method used.

3. Review of Energy Harvesters Intended for Application as Emergency Power Supplies Using Various Primary Energy Sources

The review of concepts, prototype designs, and the results of theoretical, model, and experimental research on energy harvesters designed for use in crisis situations was based on an analysis of scientific articles published over the last two decades. An effort was made to select publications representative of the analyzed topic, which explicitly stated that the research subject was intended for use in emergency situations, such as rescue operations, crises, disasters, terrorist threats, or wars. Of course, there are also a number of articles presenting original concepts and designs of harvesters developed for other purposes that could also be used in these emergency situations. However, these publications are not included in this review. This is because the authors decided to frame this article strictly for intended crisis applications. This allows for an analysis of the interest of research teams in the challenge of addressing research topics related to the increasing occurrence of various threats.

Energy harvester designs were reviewed based on the primary source of processed energy. Included were energy generated by humans or groups of humans, energy derived from natural sources such as sunlight, wind, water movement, and thermal sources, and energy of anthropogenic origin, such as electromagnetic wave emissions or vehicle traffic. Harvesters utilizing multiple primary energy sources were also considered.

3.1. Utilization of Human-Generated Energy

During rescue operations and other emergency services related to ensuring human safety and saving lives, a significant problem is powering mobile electrical devices constituting personal equipment. Batteries serve as the primary power supply, but their energy decreases during operations, and replacing or recharging power sources is not always possible. Therefore, ensuring the ability to recharge energy storage devices during operations is crucial. Article [55] proposes a solution to this problem by using a piezoelectric transducer. The authors developed a buckle for a backpack strap used as personal equipment that transduces electrical energy using forces acting between the user and the backpack during movement. The buckle was designed to convert the forces acting on the backpack strap during movement into significantly higher forces acting on a piezoelectric stack located inside the buckle. This increased the voltage on the transducer and mechanically protected it from damage. The article presents the results of model tests of the piezoelectric buckle and experimental results of energy harvesting efficiency. However, the power generated by this system is small, on the order of 0.4 mW during a typical backpack user’s walk. The idea of placing the energy harvester in the backpack buckle seems original. It utilizes the variable tension of the strap used to secure the backpack. However, the resulting output power is low. Therefore, the economic feasibility of this solution should be considered.

The heat generated by the human body’s metabolism can be used to generate electricity. Under typical thermal comfort conditions, the heat loss of an adult human is approximately 100 W. Article [74] presents a system designed to wirelessly signal a patient’s fall. The system is powered by a thermoelectric transducer that utilizes the temperature difference between the patient’s body and the environment. The prototype thermoelectric transducer is equipped with two heat exchangers. One is in contact with the patient’s body, the other in contact with the air. For a temperature difference of 15 K, the maximum transducer power of over 500 microwatts was achieved. This energy is stored and then used to sequentially power the patient’s accelerometric position transducer and the wireless data transmission system. However, the article does not provide information on many key parameters of the prototype, such as the surface area or type of thermoelectric transducer. The advantage of this solution, as declared by the authors, is battery-free operation, meaning it requires no maintenance or periodic replacement of the power source. However, with a small temperature difference between the patient’s body and the surrounding environment, the harvester’s output power is very low. This calls into question the economic viability of this solution. Furthermore, the device’s heat sink is adjacent to the patient’s body, which acts as a source of higher temperature. This poses problems related to installation of the device on the patient, discomfort in use, and the need for disinfection when changing users.

The authors of the article [37] proposed a system for autonomously powering low-power devices equipped with a keyboard. These devices could include laptops, for example. The authors propose a special design for individual keys within the keyboard. Each keystroke deforms a piezoelectric element located beneath it, generating a burst of energy. This energy recharges the battery powering the device. The authors’ state that the resulting output power is 1.2 W, but do not provide detailed test and measurement results. It is possible that the reported power value represents the peak pulse value. Analysis of this solution shows that its application is very limited. The authors report significant output power, but the average power of the device is likely negligible; the value of this parameter is not provided. It is difficult to expect significant amounts of energy to be obtained even from intensive typing on a computer keyboard while maintaining an ergonomic level of required keystroke pressure.

The article [38] describes a power supply system for a self-sufficient rescue helmet equipped with an illuminating lamp. This system utilizes energy obtained from mechanical vibrations induced by the movement of the person wearing the helmet. The conversion of mechanical energy into electrical energy was implemented using a hybrid generator consisting of a triboelectric nanogenerator (TENG) and an electromagnetic generator (EMG). The power density achieved in the tested system is up to 167.22 W/m³. This is sufficient to ensure good ambient lighting in an emergency. The system can also be used to generate electricity from human movement to power other devices used in emergency situations, such as signaling, communication, or rescue devices. The research results presented in this article expand the application area of energy harvesters derived from human biomechanical movement, but also significantly expand the use of TENGs as power sources for autonomous electronic systems. Autonomous, maintenance-free powering of personal devices, such as a safety helmet integrated with lighting, is certainly an interesting solution worth expanding. The hybrid energy converter used by the authors allows for greater power output compared to a standard converter, but this is associated with significant complexity of the harvester. Further research should consider the economic aspects and reliability of operation in difficult conditions.

Article [39] analyzes the possibilities of using human generated energy to power devices necessary for ensuring safety, such as lighting, communication, and life support systems. The human body generates thermal energy and can generate mechanical energy. Thermal energy can be converted into electrical energy using thermoelectric transducers. Mechanical energy, on the other hand, can be converted using various types of electromagnetic generators and the increasingly popular triboelectric generators. The article analyzes examples of systems that provide power to electrical devices in crisis situations using energy generated by the human body. This article is a review, presenting commercially available designs of energy generation systems utilizing a human-generated source. This publication can be a source of information on the possibilities of using human-generated energy both in crisis situations and in locations remote from standard power sources, such as during tourist or survival activities.

Article [40] presents an interesting solution for an autonomous power source, shaped like a cylinder with the dimensions of a standard battery. This source can be used in many crisis situations. The idea behind this solution is to convert mechanical vibration energy into electrical energy using three integrated transducers: an electromagnetic transducer, a triboelectric transducer, and a piezoelectric transducer. The power supply system is constructed as a cylinder with a wound coil, in which a cylindrical permanent magnet moves under the influence of vibrations. These elements constitute the electromagnetic transducer. Additionally, the magnet impacts two piezoelectric transducers placed on both bases of the cylinder, and friction against the walls is used to create the triboelectric transducer. The energy from all the transducers is combined and stored. The authors analyze in detail the amount of energy delivered from each transducer depending on the frequency and amplitude of vibrations. The prototype’s efficiency is sufficient to power a GPS module for half an hour after the source is activated by vibrations induced by a 10 min run. This type of power source can be an alternative to battery power in many emergency situations. The presented harvester represents an original technical solution that can be described as a “self-charging battery.” This type of power source can be used as emergency equipment by rescue services, as well as in shelters, mountain huts, and deep mines. Further research should be focused on testing the reliability and service life of such a harvester, as well as the technological feasibility of implementing it in large-scale production.

Article [41] presents the concept and research results of a portable electrical power source that utilizes human biomechanical energy. The concept is based on the integration of a nonlinear electromagnetic generator with two triboelectric nanogenerators operating in contact mode. The system is housed in a rectangular prism-shaped body with a square base. Inside the body is a permanent magnet mounted between two springs attached to the bases of the body. A coil, which is part of the electromagnetic transducer, is wound on the outside of the body. Additionally, contact triboelectric transducers are placed on both bases of the body. The system converts vibration energy induced by walking, running, or manual shocks induced by humans into electrical energy. This hybrid transducer is designed to power personal electronics such as smart wristbands, smartphones, or health monitors. In the prototype tests, an output power of 40 mW was obtained during walking, 60 mW during slow running and 120 mW during manual excitation by shaking the hand. The presented device is another example of a system employing hybrid processing. With such a solution, the ratio of energy gain to the complexity of the system’s design must always be considered. A complex design always carries the risk of reduced reliability and increased production and operating costs.

In the event of natural disasters and other emergencies, a significant problem is, among other things, ensuring energy sources for communications, monitoring, and lighting. In large population centers, significant amounts of energy can be extracted from the movement of people. An interesting solution was proposed in [42]. An energy harvester utilizes the changes in ground pressure generated by moving people. The design comprises flexible containers of liquid placed in the ground, connected by a system of pairs of tubes with one-way flow valves. The tubes contain miniature electromagnetic transducers equipped with turbines. The flow of liquid between the containers, caused by the pressure change, causes the turbines to rotate and generates electricity. A prototype consisting of two connected containers was built and subjected to laboratory testing. An average output power of 1.4 W was achieved, enabling the powering of a small LED-based lighting system. Solutions similar to the one described by the authors are presented in numerous publications, as energy harvesters placed in floors, sidewalks, or stairs. When using such a device in continuous operation, in addition to energy parameters, operational, ergonomic, economic, and even aesthetic parameters must also be considered. To date, such systems have not found widespread application in the application phase.

The authors of [43] proposed an electrical power source mounted on a backpack, utilizing load mass vibrations induced by human movement. The load mass is mounted on a spring system, and its vibrations are converted into unidirectional rotational motion via a system of gear train. This rotational motion is converted into electrical current via electromagnetic conversion. A series of laboratory experiments were conducted with the prototype placed on the back of a person running on a treadmill. Using a 5 kg load mass and a treadmill speed of 10 km/h, an average power of approximately 0.8 W and a peak power of 2.4 W were achieved. The proposed system can be used as an emergency power supply during physical activity in open spaces, particularly for autonomous powering of communication, positioning, and monitoring systems. Significant power output was achieved with this harvester. The developed system therefore has the potential to advance to the application phase. However, this should be preceded by a series of tests related to reliability, long-term operation in harsh conditions, and optimization of dimensions, weight, and ergonomic parameters.

Article [44] describes an efficient electrical power generation system that utilizes the force of a person’s foot pressing against the ground. Due to its small size, the system can be placed in footwear, and according to the authors, the designed harvester, unlike many other designs, does not restrict a person’s freedom of movement. This is an advantage when used as a power source for portable devices used in emergency situations by rescuers, firefighters, or other services. The Harvester’s mechanical system converts the vertical reciprocating motion caused by the foot pressing against the ground into a unidirectional rotational motion that drives an electromagnetic transducer. This allows for continuous energy generation while walking, marching, or running. At a walking speed of 7 km/h (4.3 mph), i.e., brisk walking, an average output power of 2 W was achieved. This is sufficient power to power positioning devices, radio communications, or night lighting. Energy generation using human foot pressure, using a system embedded in footwear, is commercially available, for example, in sports shoes or children’s shoes. In such applications, the generated power is low and is used to power lighting effects. The system described in this article delivers significantly higher power, allowing for a wider range of potential applications. Further development of the system should pay attention to the durability and reliability of the device, as well as the level of user comfort and additional energy expenditure during use.

In warfare or other crisis situations, continuous power supply for communication, positioning, and monitoring equipment is a challenge. Batteries have a limited lifespan, so it is crucial to ensure the possibility of powering them from alternative sources. The authors of [56] propose an energy source that utilizes the variable pressure exerted by a person walking on transducers. They analyze the potential of using a piezoelectric generator stimulated by human gait to power low-power electronic devices. In the prototype solution, ceramic piezoelectric elements were placed on shoe soles. The energy generated by the transducers during human movement was measured. The average energy obtained was 875 microjoules per step. A person testing the prototype harvester walked for an hour at a step frequency of 0.66 Hz, accumulating 2.1 J of energy in the battery. This amount of energy is sufficient to power a device drawing 33 mW for one minute. This allows it to power an emergency communication device to transmit its position or call for help. In the presented solution, the power of the electric current generated during walking is low. This limits the system’s application area to low-power devices. However, if production costs are low and reliability is high, such devices could be common equipment in footwear used in various services, for example, for personal identification or determining a person’s position and movement path.

A system for emergency power generation for portable electronic devices with a power output of 10 W is presented in article [45]. The primary energy source is the movement of both the human arms and legs. The developed backpack-shaped harvester is placed on the user’s back. Four cables connected to the limbs extend from the system. The limb movement is converted via the cables into the rotational motion of pulleys, on which the cables are wound. The pulleys are equipped with a return spring mechanism. The bidirectional rotation moving of the four pulleys is converted into the unidirectional motion of the central pulley, which drives an electromagnetic transducer. Laboratory tests of the prototype achieved an output power of nearly 10 W. The authors anticipate the potential use of the developed harvester, for example, in fire rescue operations, underground mining rescue, or during natural disasters. The output power achieved in this solution is significant and can be used to power a wide range of personal devices for rescuers and other services. However, this is achieved at the cost of burdening and restricting the movements of the person operating this type of harvester. The degree of difficulty in moving and performing other activities by the user requires research and optimization for ease of use. Furthermore, the device is a complex mechanical system with many moving parts, and therefore may be susceptible to damage, especially when operated in harsh environmental conditions.

The development of nanotechnology and advances in the field of nanomaterials are leading to increased efficiency in energy harvesting methods. Article [63] presents an energy transducer using a material with a three-dimensional cellular structure in the form of elastic, deformable foam. Based on the triboelectric phenomenon and moisture-induced energy generation, the developed material generates electrical energy upon deformation. The authors envision using the developed transducer to generate electrical energy using the pressure exerted by moving people. The transducers can be installed in shoe soles or in the ground. The energy generated using these transducers is small, not exceeding 10 milliwatts. This amount of energy could be used, for example, to power emergency signaling systems. Although the energy amounts generated in the described transducer are small, solutions based on innovative advances in materials technology have future potential. Converting various forms of energy into usable electric current directly within the structure of specialized materials can provide a basis for the design of reliable, ergonomic, and efficient harvesters of human-generated energy.

3.2. Harnessing Natural Energy

The article [75] presents the concept, prototype, and test results of an independent power source utilizing the temperature gradient occurring in a natural environment. The system utilizes a thermoelectric cell, which uses the temperature difference between the environment and the substrate. The system design utilizes a higher-temperature external heat sink, heated by solar radiation or warm ambient air, and a lower-temperature heat sink, in the form of an elongated aluminum cylinder, embedded in the substrate. Long-term tests of the prototype recorded the temperature of both heat sinks and the generated electrical power. During the day, the temperature difference between the heat sinks can reach up to several dozen kelvins, while at night, this difference is much smaller, on the order of 5–10 kelvins. The generated power has a variable diurnal pattern, reaching up to 0.4 W during the day and 10 milliwatts at night. The article tested various heat sink designs and demonstrated that the system can be used in both summer and winter. Of course, the generated power is significantly lower in winter. The authors consider the possibility of using the system as an autonomous power source, for example, in disaster-stricken areas. This type of harvester, utilizing thermoelectric processing, has high application potential wherever significant temperature gradients occur. Such systems are characterized by the absence of moving parts, which contributes to their high reliability. Research and development in this class of converters should be focused on optimizing heat exchangers and heat pipes. The use of new materials with unique thermal properties in this area can ensure high energy conversion efficiency.

Environmental monitoring in the event of natural disasters is an important issue related to the protection of life and property. The monitoring process can be implemented using a network of sensors wirelessly connected to a base station. However, powering these sensors with conventional batteries requires constant maintenance, associated with significant costs and labor. Therefore, article [46] presents the concept of a hybrid wind-powered electricity generator. The rotor’s rotational motion-to-electricity converter utilizes two conversion methods: electromagnetic and triboelectric. Hybridization allows for greater energy efficiency across a wide range of wind speeds. Furthermore, the autonomous sensor power supply system is equipped with photovoltaic cells, and the entire system is housed in a weather-resistant housing. The hybrid energy generator powers environmental sensors and wireless data transmission systems. Example applications of the developed system include monitoring forest fires, earthquakes, and emergency and crisis notification systems. The original element of this article is the design of a hybrid mechanical-to-electrical energy converter. For such converters, it is important to consider whether the energy gain associated with hybridization is sufficient relative to the system’s complexity. The authors point to increased energy efficiency associated with the use of wind energy at both low and high speeds. However, verifying this claim requires comparative studies with conventional systems. Another important element is the reliability test of the harvester during long-term operation.

Article [47] presents the design and testing of a portable generator for generating electricity using available natural resources, such as flowing water or wind. The device was developed to meet the demand for electricity during rescue activities away from power supplies. The system consists of a turbine, a generator, and a battery energy storage system. The DC generator generates a voltage of 0.7–11.1 V at a rotational speed of 117–1434 rpm. Laboratory tests confirmed the system’s effective operation for water velocities of 4.8–5.9 m/s and wind speeds of 4.0–10.3 m/s. The presented solution utilizes hybridization, allowing for the use of air or water movement as a primary energy source. The problem of developing an efficient turbine capable of operating in both environments requires further research and optimization. The authors of the article limited their research primarily to laboratory tests, making it difficult to assess the harvester’s potential for application in natural conditions.

Article [66] analyzes the problem of using renewable energy to provide emergency power to nuclear power plant systems. In particular, the system is responsible for ensuring the operation of cooling and safety systems after an unplanned shutdown. A hybrid system integrating photovoltaic, wind, and battery storage sources was developed. The developed emergency power system was subjected to model tests during test operations involving interruptions in power from standard sources, planned and unplanned shutdowns, start-ups, and standard operation. The results confirmed the hypothesis that renewable energy could be used to ensure the safe operation of a nuclear power plant during emergency conditions. The system was developed for Egypt’s first 1200 MW nuclear power plant in El-Dabaa. The issue of emergency power sources for nuclear power plants, discussed in the article, is a key element in ensuring the operational safety of such facilities. A power outage during emergency situations can be a source of unimaginable disaster. When designing nuclear power plants, multiple energy sources should be considered for emergency situations. Expanding these sources with renewable energy is an important element of the safety optimization process and is environmentally friendly.

Article [48] proposed the design of an electricity generator using wind energy. The system could be used in the event of natural disasters or catastrophes as an outdoor power source. It consists of a small, cup-shaped wind turbine driving a hybrid, coaxial system of two electricity generators. Electromagnetic and triboelectric generators were used in this system. The electromagnetic system is conventional, but the main focus of the research was on the design of the triboelectric generator. A novel sliding-gear structure was used, enabling the implementation of twelve operating cycles during a single rotation. Friction materials were also optimized to improve efficiency and extend the duty cycle. At a rotor speed of 90 rpm, a stable output power of approximately 55 mW was achieved. The system can be used to power low-power systems, such as earthquake, fire, and wind speed monitoring. Test results indicate the significant potential of the developed system in terms of efficiency and long-term operational reliability. The described harvester is another example of the use of hybrid converters. Therefore, in this case, the degree of efficiency gains relative to system expansion should also be assessed. The authors of the study devoted effort to developing a design that will ensure high efficiency and operational reliability. A comparison with a conventional system would be an important element of verification.

Harnessing the energy of water flow in natural streams enables emergency power supply for electrical devices during various emergencies. To effectively utilize this energy, converted into rotational motion in the turbine, the authors of [49] developed a hybrid transducer combining piezoelectric and electromagnetic conversion. The system has two transducers of each type, and their operation is synchronous. The energy harvester rotor consists of a disc with alternating permanent magnets arranged around its circumference. The disc rotates over a stationary base on which two elastic beams with attached permanent magnets are placed. The rotating disc causes alternating deformation of the beams to which the piezoelectric transducers are attached. Additionally, permanent magnets are placed at the ends of the beams, moving in the coils of the electromagnetic transducers. The energy from both sources is combined and stored in capacitors. In the laboratory model of the harvester, a total output power of 23 mW was achieved, with the piezoelectric transducer being the dominant source. The solution described is innovative, but the output energy level is low. This depends on the harvester’s size and the parameters of the primary energy source. However, the efficiency of the developed and tested prototype limits its application area. Furthermore, assessing the system’s reliability and economic viability is crucial. This should be the subject of further research.

A low-power energy harvester utilizing the oscillating motion of the water surface is presented in [57]. It can be used in crisis situations to illuminate a set of signal buoys on the water. The advantage of the described harvester is the use of energy from omnidirectional oscillating motion. The system uses a system of three piezoelectric transducers excited by a massive disc placed above them. The disc is centrally mounted with an articulated joint so that it can tilt in all directions and strike one of the three piezoelectric transducers. The disc’s tilt is caused by water ripples, while the excitation force of the transducers is supported by free balls placed within the disc, which change its center of gravity. The prototype system was tested on the water surface, generating ripples with a predetermined amplitude and frequency. The maximum electric power generated in these experiments was approximately 1.5 mW. This solution utilizes an original energy conversion method. However, when developing innovative energy harvester concepts, their energy efficiency should be considered in relation to the complexity of the design. Because the prototype delivers negligible power, it is worthwhile to consider optimizing the system’s design in terms of the ratio of energy harvested to structural complexity in further research.

3.3. Utilization of Anthropogenic Energy

In many disaster-related situations, it is necessary to ensure the exchange of information via a wireless communication network. During prolonged operations, the power sources powering individual components of the communication system become depleted. To ensure long-term operation of the communication system, article [70] analyzes a network model in which information is exchanged between a base station and mobile network nodes, and the base station supplies energy to the nodes wirelessly via a radio signal. Mobile nodes are equipped with systems for harvesting electromagnetic waves and supporting power systems using the collected energy. This solution allows for extended uptime of the communication network, which is crucial in crisis situations. Powering low-power devices with energy supplied externally in the form of an electromagnetic wave is one alternative power supply method. This method is used in many specialized applications where wired power supply methods or local battery power cannot be used. The disadvantage of this method is low efficiency, as most of the electromagnetic wave energy is dissipated. Therefore, special attention should be paid to optimizing the system’s efficiency.

A vibration transducer, described in article [58], can be used to provide emergency power to low-power devices. The transducer can be mounted on any object whose vibrations are the primary energy source. These could be industrial facilities or mobile vehicles, for example. The processing is performed using a piezoelectric method, using a transducer in the shape of a beam loaded with a mass. The beam is additionally equipped with an adjustable mechanism for tuning the beam’s resonant frequency to the vibration frequency. Optimal tuning is achieved thanks to an indicator of the maximum output power achieved. The output signal from the piezoelectric transducer is converted to a lower voltage in an electronic pulse transducer, and the energy is stored in a supercapacitor. The system’s output power depends on the frequency and amplitude of the vibrations. In the implemented prototype, output power ranges from single milliwatts to approximately 33 mW, achieving an output voltage of 3.3 V and a continuous output current of 10 mA. The presented harvester achieved a relatively low level of output power. The output power in this case depends on the primary source of vibration energy and the dimensions and processing method used in the harvester. The authors of this paper paid particular attention to optimizing the processing process, and achieving higher output powers could be the subject of further research. An advantage of this type of harvester is the ability to house it in a sealed enclosure, enabling use in harsh environments.

The authors of the article [50] developed and tested a prototype of a vibration energy harvester. Its primary application is powering devices operating in the Internet of Things technology, but the developed power source can be used in crisis situations to power low-power emergency equipment. Vibrations of the object on which the harvester is mounted are converted into electrical current in an electromagnetic transducer. The transducer consists of a coil wound on a cylindrical body and a permanent magnet attached to a spring, moving within the coil. The electrical current generated in the transducer is converted in an electronic circuit, which provides energy to charge the battery. Modeling studies allowed optimizing the transducer’s resonant frequency to obtain maximum energy for the intended vibration pattern. The output power of the harvester prototype during testing was approximately 30 mW. This output can be used to charge a 4.2 V 100 mAh lithium-ion battery in approximately 24 h. In this study, the authors also emphasized optimizing processing efficiency. These harvesters can be used as power sources for monitoring systems in facilities exposed to significant vibration levels during operation. The harvester’s small dimensions and compact design, housed in a sealed enclosure, allow for the construction of a system of multiple point sensors connected to a wireless network.

Disasters in underground mines can destroy communication systems with the crew. This communication is essential for situation analysis and coordination of operations. Article [71] proposes an emergency network system that provides both communication and power transmission to individual transceiver devices constituting network nodes. The system is based on radio transmission on two frequencies. Electromagnetic energy is transmitted at 860 MHz, converted into electrical current in the receivers and stored in supercapacitors. This energy is used to power an information transmission system operating at 915 MHz. The prototype device achieved a power transmission range of 35 m. This solution eliminates the need for batteries in emergency communication devices, ensuring they are constantly ready for use and do not require periodic charging. Operational safety in mines and other industrial facilities is a crucial element of industrial process. The presented original solution for powering the wireless communication network is an important element of research aimed at improving crew safety. This system could find a wide range of applications in many emergency services during disasters, ensuring long-term communication and supporting wireless data transmission from personal sensors.

3.4. Utilizing Energy from Mixed Sources

Energy harvesters often use an electromagnetic method for converting motion energy into electricity. Article [51] describes a hybrid electromagnetic transducer that utilizes both rotational motion and oscillatory motion from vibrations, as an energy source. Such a transducer can be used in emergency power sources utilizing various primary energy sources. For example, rotational motion from a wind or water turbine, or from a drive generated by human muscle power, can be utilized. Vibratory motion, on the other hand, can originate from natural sources, such as water ripples or air pulsations, or from vibrations of vehicles or human or animal movement. The hybrid electromagnetic transducer with two modes of operation described in the article is composed of an external, cylindrical coil system and an internal rotor with permanent magnets. In addition to its rotational motion, the rotor can also reciprocate in the direction of the rotation axis. This type of motion is supported by a spring system. During testing, the prototype transducer achieved a power output of 3.8 W from rotational motion, and approximately 100 mW from vibrations. The presented solution uses an innovative electrodynamic transducer operating in two modes: rotary and reciprocating. However, tests have demonstrated a significant efficiency ratio of approximately forty times in both modes. Therefore, it is necessary to verify the system’s effectiveness and reliability under various operating conditions, due to the complexity of the design. Determining the durability of the rotation axis mounting system is particularly important.

The design and experimental results of an energy harvester that converts strong, short, pulsed airflows into electrical energy are presented in [52]. The harvester can be used, for example, to power road signaling devices in emergency situations. Natural phenomena such as strong gusts of wind or airflows generated by passing vehicles can serve as the source energy. The prototype is constructed as a pendulum with a sail, deflected from its equilibrium position by the pulsed airflow. The pendulum is equipped with a magnetic system that increases the frequency of vibrations and improves the conversion efficiency. The pendulum’s motion is converted into electrical energy using an electromagnetic transducer. In a single pendulum cycle, electrical energy ranging from 0.24 to 4.44 mJ was generated, with air speeds in a short pulse ranging from 11.3 to 24.9 m/s. The authors propose implementing a matrix of this type of harvesters and energy merging. The energy generated by the engines of vehicles traveling at high speeds on roads and highways is largely used to overcome air resistance and, as a result, dissipated. Recovering even small portions of this energy in harvesters allows for cost-free powering of signaling and monitoring devices. Therefore, it is worth considering the development and construction of harvesters that utilize this energy. Optimizing the efficiency of these devices, which is low in the system described here, is particularly important.

In crisis situations, a key issue is ensuring sufficient power supply for portable devices. Extending the continuous operation time of battery-powered devices is possible by recharging them using an energy harvester. Article [67] describes the concept of a hybrid battery charging system for portable devices using a photovoltaic and thermoelectric converter. Combining energy from photovoltaic and thermoelectric sources enables effective and efficient energy harvesting from sunlight and human body heat. Ultra-energy-efficient boost converters, optimized for each source individually, were used to condition the energy from the converters. Under the operating conditions of the prototype, a power of approximately 380 mW was achieved, of which 80% came from the photovoltaic source and 20% from the thermoelectric source. The primary energy sources used in the harvesting process are characterized by temporal instability. Therefore, the concept of using complementary primary energy sources, described in this article, is worth exploring and exploring further. This is certainly one of the important development directions for this energy generation technology.

The original design of a vibration energy harvester was proposed in [59]. The design consists of two pairs of opposite buckled piezoelectric beams. The beam pairs are arranged in series along a straight line and rigidly mounted at their extreme ends. The center point of the beam pairs is attached to a spring. This original design allows for high vibration amplitudes, which allows for increased output power. Furthermore, operating in this configuration of piezoelectric beams produces negative stiffness in the vibration direction. The experiments achieved an output power of 8.31 mW. The device enables the processing of vibration energy from both natural sources, such as wind-induced tree branch vibrations, and anthropogenic sources, such as bridge vibrations. The concept presented in the article is an excellent example of progress in the design of new transducers dedicated to energy harvesting.

The vibration energy harvester presented in [60] combines two functions in its design: it converts the mechanical energy of vibrations to electrical energy and additionally acts as a vibration damper. The harvester is constructed from a rectangular platform mounted on springs at its four corners. A permanent magnet pendulum is mounted beneath the platform, which can move over a set of coils in which an electromotive force is induced. The 1:2 internal resonance enables energy transfer from the platform to the pendulum. This optimizes the harvester’s efficiency while simultaneously damping vibrations. The source vibrations can be caused by vibrations of mechanical structures such as machines or vehicles. Vibrations can also originate from natural sources, such as wind-induced vibrations of objects. The developed harvester is an interesting example of a system that, in addition to energy conversion, also serves as a vibration damper.

A summary of the review of articles describing the design and testing of energy harvesters intended to power devices in crisis situations is presented in

Table 2. A summary of the review of harvester’s prototypes.

Energy Harvesters Application	Source of Primary Energy	Maximum Available Output Power	Reference
Powering portable personal devices: monitoring, lighting, communication, positioning	human movement–vibrations	0.4 mW	[55]
		160 mW	[38]
		120 mW	[41]
		2.4 W	[43]
	human movement–leg pressure	33 mW	[56]
		5 mW	[63]
	human movement–hand pressure	1.2 W	[37]
	human movement–all limbs	10 W	[45]
	human body heat	0.5 mW	[74]
Powering stationary local devices: lighting, communications, environmental monitoring	pressure of people and vehicles on the ground	1.2 W	[42]
		2 W	[44]
	vibrations of mechanical devices, vehicles, infrastructure facilities	33 mW	[58]
		30 mW	[50]
		8.31 mW	[59]
	air movement, wind	55 mW	[41]
		3.8 W	[51]
		5 mW	[52]
	water movement, flows, waves	23 mW	[49]
		1.5 mW	[57]
	temperature gradient in the environment	400 mW	[75]
		380 mW	[67]
Powering local wireless communication networks	electromagnetic waves	0.02 mW	[70]
		1 mW	[71]

. It contains data on potential applications of harvesters, primary energy sources and maximum obtained power of prototypes, along with an indication of the literature reference.

4. Conclusions

This article reviews current research and developments in the field of emergency power supply development using energy harvesting technology. This relatively narrow focus was chosen due to the ever-increasing threats associated with both human activity and natural processes. The article discusses existing and potential local and global threats in the context of the need to develop emergency power supplies. It reviews primary energy sources and methods for processing them in energy harvesting processes, with particular emphasis on crisis situations. A detailed analysis of this issue, based on a review of representative scientific articles, leads to the following conclusions:

• Electricity generation based on harvesting technologies is an important power source that can be used in crisis situations. Energy harvesters can constitute a primary power source in many cases, but they are more often used as a supplementary source. An important feature of harvesters is that they are distributed sources, much less susceptible to damage or global outage than centralized sources [78,79,80,81]. However, the literature analysis shows that this issue, despite ongoing and ever-increasing threats to civilization, has not yet been a priority area of research interest. This article aims to draw greater attention from research teams to the need to develop methods and technologies for emergency energy generation during crises.
• Research should consider potential primary energy sources specific to a specific type of threat. For example, during a forest fire, large areas are covered in heavy smoke, so access to energy from photovoltaic sources is limited. However, thermal energy may be a primary energy source in such a situation [82,83]. Perhaps our imagination is still very limited, and we are unable to predict possible energy sources in future disasters. Therefore, it is necessary to predict scenarios for various types of crisis situations and explore potential opportunities for obtaining primary energy for harvesting processes. It is also possible to use energy from multiple sources simultaneously or in a time-shared manner in a single harvester [84,85,86]. Furthermore, special attention should be paid to identifying the parameters and characteristics of potential energy sources by developing dedicated measurement systems and metrological procedure methodologies [87,88,89,90,91].
• An important issue is the search for effective methods for converting primary energy into electricity. An interesting area here is the hybridization of conversion methods, used in many of the designs analyzed. However, such a combination of several methods should be supported by a thorough analysis, both in terms of effectiveness and taking into account economic and operational factors. Innovative materials technology can play a crucial role in the development of conversion methods. Interdisciplinary collaboration between specialists from many fields is essential here. Developments in the pre-conversion of energy forms are also a significant area of energy harvesters [92]. For example, optimization and the development of innovative solutions for converting various forms of energy into mechanical energy of rotational motion are crucial. This allows the use of electromagnetic power generators, which have high efficiency, effectiveness, and output signal quality and are readily commercially available in a wide range of parameters.
• When designing energy harvesters for use in crisis situations, special attention should be paid to the potential operating conditions encountered during an emergency. Many of the designs described are in the prototype laboratory testing phase, where not all possible external influences are considered. In real-world conditions, the effects of high temperatures, precipitation, pollution, shocks, electromagnetic interference, and many other negative factors are possible [93,94,95]. In addition to examining the main energy conversion process itself, it is necessary to pay attention to potential factors that negatively affect the harvester.
• Some scientific publications contain only selected elements of the proposed solution description and incomplete research results. A scientific publication should include all the necessary elements for reproducing the research by other teams and verifying the results. It should also present results enabling a reliable assessment of the design, its performance, efficiency, and other parameters. This allows for direct comparison of different designs and solutions. A common mistake in presenting harvester research is presenting output signals as electrical voltages without specifying the output loads and the resulting power and energy. Furthermore, the authors of this article believe that the presentation of negative results should be not only allowed but even encouraged in scientific publications, which is currently very rare [96]. The main value of reliable negative results is that they demonstrate to other teams which paths of possible solutions are not worth pursuing.
• More attention should be paid to the transition from the prototype phase to commercial implementation [97,98]. Such efforts should be conducted in collaboration with research teams, commercial companies, and governments. Unfortunately, it appears that many developed solutions with application potential do not progress beyond the prototype or even laboratory model phase. This problem is difficult to solve, and it seems necessary to broaden the dissemination of research results to society and for scientific authorities to speak out more widely in public discussions.

Benjamin Franklin, a pioneer in electrical research, conducted an experiment in 1752 that today can be considered the archetype of energy harvesting. Using a kite tied to a damp thread, he collected lightning charges into a Leyden jar. Franklin is credited with the words, “Failure to prepare is preparation to fail” [99], which remain remarkably relevant in today’s turbulent times. In the 21st century, in our constant rush, we do not think about our daily dependence on electricity. Ubiquitous energy sources and countless energy devices accompany us almost everywhere and at all times. They enable both simple activities like brushing our teeth and incredibly complex processes based on generative artificial intelligence models. Taking advantage of these civilizational achievements, let us not forget to prepare contingency plans to secure emergency energy sources that enable our existence and rescue operations in crisis situations. This article reviews such sources based on energy harvesting technology. These sources provide relatively small amounts of energy, so they are not the primary source of emergency power. However, in many cases, they can be a supplement, or even the only possible solution in a given situation. Further challenges lie ahead for energy harvesting, and research in this field will undoubtedly continue and expand. However, it is important not to attempt to use energy harvesting where there is no substantive, pragmatic, and economic justification. Complex energy harvesting systems that utilize irrational energy sources or combine multiple processing methods in an unjustified manner represent a dead end in this field. This is especially true when they can be effectively replaced by simpler systems with significantly better application parameters.