How Do You Harvest Energy?

Energy harvesting refers to capturing small amounts of energy from ambient sources like sunlight, wind, temperature differences, and vibration and converting it into usable electrical energy to power small devices or charge batteries. Energy harvesting provides an alternative to relying solely on batteries and can enable self-powered devices and wireless sensor networks. With the growth of the Internet of Things and proliferation of small electronic devices, energy harvesting is becoming increasingly important as a way to eliminate maintenance costs and minimize environmental impact. Renewable energy plays a crucial role in energy harvesting since many ambient energy sources are inherently renewable, like solar and wind. Transitioning from fossil fuels to renewable energy is critical for mitigating climate change and building a sustainable energy future.

According to the International Energy Agency (IEA), electricity generation from renewables accounts for about 40% of total renewable energy supply globally. The IEA projects renewables will supply 50% of global electricity by 2030 as countries continue to expand wind and solar capacity and improve energy storage solutions. The share of energy from renewable sources is increasing each year. Expanding renewable energy and harnessing ambient energy through harvesting techniques will help meet rising energy demand in a clean, efficient way.

Table of Contents

Solar

Solar energy harvesting refers to capturing the sun’s energy and converting it into useful forms of energy like electricity or heat. There are several methods for harvesting solar energy:

Photovoltaics (PV) use solar panels containing solar cells made from semiconducting materials like silicon to convert sunlight directly into electricity. When sunlight hits the solar cells, the photons excite electrons and generate an electric current that can power devices (Source 1).

Solar thermal systems use solar collectors like parabolic mirrors to concentrate sunlight and produce high temperatures which can generate electricity via a steam turbine or heat water. This thermal energy can also be stored for later use (Source 2).

Passive solar aims to harness sunlight through building and home design. Strategies include orienting windows and rooms to maximize solar gain for heating, installing thermal mass like tile floors to absorb and slowly release heat, and using overhangs or shade trees to minimize summer solar gain (Source 3).

Wind

Wind power is one of the fastest growing renewable energy sources in the world. As of 2023, over 650 gigawatts (GW) of wind power capacity has been installed globally. The total wind power capacity of the leading country, China, stood at 328,970 megawatts (MW) in 2023. The United States ranks second with 132,738 MW of installed wind capacity. Other top countries are Germany, India, Spain, the UK, France, Brazil, Canada, Sweden, and Italy.

Wind turbines convert the kinetic energy of wind into mechanical power, which is then converted into electricity by a generator. They are usually grouped together into wind farms or wind power plants to generate bulk amounts of power. Offshore wind farms located in coastal waters are becoming increasingly common as well. The power output of a turbine is proportional to the cube of the wind speed, so sites with strong and consistent winds are ideal locations for wind farms.

According to the U.S. Department of Energy, a single 1.5 MW turbine can power over 400 homes. Wind farms with hundreds of these turbines have the capacity to provide electricity to entire towns and cities. With technological improvements and growing capacity, wind power is poised to become one of the world’s leading renewable electricity sources in the years ahead.

Hydroelectric

Hydroelectric power is one of the largest renewable energy sources in the world. Hydroelectric dams use the energy from flowing water to turn turbines and generate electricity. Some of the largest hydroelectric dams in the world include the Three Gorges Dam in China, which has a capacity of 22,500 MW ¹, the Itaipu Dam between Brazil and Paraguay at 14,000 MW², and the Guri Dam in Venezuela at 10,200 MW³.

Dams are generally constructed on rivers to create large reservoirs. The water held in the reservoir has potential energy due to being at a higher elevation. When water is released from the reservoir through the dam and into turbines, the potential energy gets converted into kinetic energy and then into electricity by rotating the turbines. Dams provide a consistent and controllable source of electricity that can be dispatched on demand.

Tidal power utilizes the ebb and flow of ocean tides to generate electricity. Tidal stream generators capture energy from currents created by tides. Tidal barrages make use of the difference between high and low tides by filling up reservoirs at high tide and emptying them at low tide to spin turbines. Examples of tidal power projects include the Sihwa Lake Tidal Power Station in South Korea.

Wave power uses the energy from ocean surface waves to generate electricity through devices like oscillating water columns that use wave movement to spin turbines. Locations with high wave activity tend to be best suited for wave power. However, it remains a developing technology with limited installed capacity globally.

Geothermal

Geothermal energy comes from the natural heat inside the earth. It can be harnessed in a few different ways. Geothermal power plants use steam from reservoirs of hot water found a couple of miles or more below the Earth’s surface to turn turbines and generate electricity. Geothermal heat pumps transfer heat to and from the ground to heat and cool buildings.

At geothermal power plants, wells are drilled into underground reservoirs to tap steam and very hot water that drive turbines linked to electricity generators. Plants generate only about one-sixth of the carbon dioxide of a fossil fuel plant. Geothermal reservoirs have lifetimes of decades. With a geothermal heat pump system, pipes buried in the shallow ground use the earth’s natural heat to provide heating, cooling, and often hot water for homes and other buildings. Some systems also use the stable ground temperatures to heat and cool industrial processes.

According to ThinkGeoEnergy, the top geothermal power generation countries in 2022 were the United States, Indonesia, the Philippines, Turkey, and New Zealand (ThinkGeoEnergy). The United States had the most geothermal power capacity at 3,794 MW. Indonesia followed with 2,356 MW of capacity. The Philippines had 1,916 MW, while Turkey and New Zealand had 1,500 MW and 1,000 MW respectively.

Bioenergy

Bioenergy is energy derived from recently living biological material known as biomass. Biomass can come from plants or biological waste products like manure. Common sources of biomass used for energy production include corn, sugarcane, trees, grasses, algae, and waste from animals, plants, industries, and homes (https://www.energy.gov/eere/bioenergy/bioenergy-basics).

Biomass can be directly burned to produce heat or converted into transportation fuels like ethanol and biodiesel, combustible biogases, or thermoelectricity. In 2019, bioenergy accounted for almost 6% of global energy supply (https://www.iea.org/energy-system/renewables/bioenergy). Modern bioenergy applications include:

Biofuels like ethanol and biodiesel used for transportation
Biogas derived from organic waste used for electricity and heating
Solid biomass like wood, agricultural residues, and waste burned directly for heat and electricity generation

Bioenergy is considered renewable because biomass can regrow over relatively short timescales. It offers a renewable alternative to fossil fuels and can contribute to reduced greenhouse gas emissions when sustainably produced and used (https://www.nrel.gov/research/re-biomass.html). However, bioenergy also has limitations and sustainability concerns that must be managed, such as impacts on land use, biodiversity, and food production.

Thermoelectric

Thermoelectric generators (TEGs) are devices that convert heat directly into electrical energy using the Seebeck effect. They operate through thermocouples, which are made of two different conducting materials joined at one end. When heat is applied to one end, it creates a temperature difference across the thermocouple, causing electrons to move from the hot to the cold end and generating an electrical current.

TEGs capture waste heat from industrial processes, engines, or even body heat and turn it into useful electricity. They have no moving parts, operate quietly, and are highly reliable. The efficiency of TEGs is typically around 5-8%, although recent advances have enabled over 10% efficiency in some cases [1]. Ongoing research aims to improve materials and device architectures to enable efficiencies over 20%.

TEGs are used in niche applications like powering sensors in oil pipelines, space probes, and recovering waste heat from car exhausts. They can also charge batteries using ambient temperature differences. With further efficiency improvements, TEGs have the potential for more widespread adoption to recover waste heat and generate clean electricity.

Piezoelectric

Piezoelectric energy harvesting converts mechanical energy, such as vibrations or pressure, into electrical energy using piezoelectric materials. Piezoelectric crystals produce voltage when they are compressed or twisted – the piezoelectric effect. Common piezoelectric materials include lead zirconate titanate, quartz, and barium titanate. When these materials deform from vibrations or pressure, the crystal structure produces voltage that can be harvested.

Piezoelectric energy harvesting has many applications. It can power small sensors and electronics by harvesting ambient vibrations in the environment. For example, a piezoelectric harvester on a bridge can generate electricity from traffic vibrations (Li et al., 2014). Wearable devices can use piezoelectric materials to harvest energy from human motion. And piezoelectric elements can recover waste energy from equipment vibrations in factories or data centers. Ongoing research focuses on improving the efficiency and integration of piezoelectric energy harvesting devices.

Electrostatic

Electrostatic energy harvesting works by using capacitors and electrostatic induction. Capacitors are electrical components that can store energy in the form of an electric field. They consist of two conductors separated by an insulator or dielectric material. When the conductors hold equal but opposite charges, an electric field is created between them, allowing the capacitor to store energy.

Electrostatic induction enables energy harvesting through variable capacitors. When the capacitance of the capacitor changes due to external vibrations or motion, the charges on the plates get redistributed to equalize the voltage. This flow of charges can be harnessed to generate electricity through an external circuit. Electrostatic energy harvesters typically utilize a variable capacitor structure with movable plates that change capacitance when subjected to ambient vibrations [1].

One approach is to maintain a constant charge on the capacitor plates while allowing capacitance to vary. The changing voltage across the capacitor can then be used to drive current through an external load. Another technique keeps voltage constant while the motion causes charge transfer between the plates, generating electrical current [1]. Overall, electrostatic conversion enables effective vibration energy harvesting through capacitive transduction.

Conclusion

There are a variety of techniques used to harvest renewable energy sources. Solar power harnesses energy from the sun using photovoltaic panels or concentrated solar power. Wind power utilizes wind turbines to generate electricity from kinetic energy in wind. Hydroelectric power generates electricity from the flow of water, using dams or run-of-river systems. Geothermal energy taps into heat below the earth’s surface to produce steam for electricity generation. Bioenergy converts biomass from plants and organic waste into fuel and electricity through processes like combustion, gasification, pyrolysis, and anaerobic digestion. Thermoelectric generators can produce electricity from temperature differences between two sides. Piezoelectric materials generate voltage when mechanical stress is applied. Electrostatic generators use contact electrification to harvest energy from friction between two surfaces. In summary, renewable energy can be harvested from natural flows of sunlight, wind, water, heat, and organic matter through various ingenious techniques.