Energy technology is concerned with developing systems capable of producing, transporting, and delivering energy in a way that is safe, economical, and, increasingly, environmentally friendly. It is a field of many overlapping disciplines. Hard sciences such as physics and chemistry are crucial to understanding where energy may be available, engineering disciplines are required to design the systems that harness energy, and environmental science is used to measure the impact of energy technology on the natural world.
Energy technologies are the primary determinants of energy availability, fuel choice, end use efficiency, and the degree and nature of by-product emissions, and energy research and development (R&D) is the vehicle by which new technologies become available.
Most applications of energy technology for transportation purposes use the same basic process—burning fuel to produce heat, boil water, and create steam. Steam ships revolutionized shipping methods during the First Industrial Revolution and later began to replace sail-powered vessels as the primary ships of war. These steam ships used coal as fuel. During the Second Industrial Revolution, transportation energy technology began to utilize oil as the primary fuel. Oil-based internal combustion engines are used in every country of the world for transportation applications.
Any source of energy can be converted into electricity using energy technology. Sources of electricity in the United States include coal, natural gas, and nuclear power. The sources of electricity generation and fuels for transport often differ because of the different requirements for each application. Electricity power plants must be very efficient in generating the most electricity possible. Transportation energy systems, on the other hand, can get away with less fuel efficiency, because they also need to be small and light enough to fit into vehicles.
A growing concern is the development of alternative energy sources. Coal, oil and natural gas are all non-renewable energy sources, meaning that they exist in finite quantities in Earth and could one day be used up. Burning coal and oil have negative environmental effects, which are also a growing concern. Energy technology is being pursued to develop clean, efficient, and renewable sources of energy for both electricity and transportation applications.
Solar technologies convert sunlight into electrical energy either through photovoltaic (PV) panels or through mirrors that concentrate solar radiation. This energy can be used to generate electricity or be stored in batteries or thermal storage.
Solar radiation, also known as electromagnetic radiation, is emitted by the sun. While every location on Earth receives some sunlight over a year, the amount of solar radiation that reaches any one spot on the Earth’s surface varies. Solar technologies capture this radiation and turn it into useful forms of energy.
There are two main types of solar energy technologies—photovoltaics (PV) and concentrating solar-thermal power (CSP).
Photovoltaic solar energy is obtained by converting sunlight into electricity using a technology based on the photoelectric effect. It is a type of renewable, inexhaustible, and non-polluting energy that can be produced in installations ranging from small generators for self-consumption to large photovoltaic plants.
A semiconductor device called a photovoltaic cell is used for this purpose, which can be made of monocrystalline, polycrystalline, amorphous silicon, or other thin-film semiconductor materials. The cells made from monocrystalline silicon are obtained from a single crystal of pure silicon and achieve maximum efficiency, between 18% and 20% on average. Those made from polycrystalline silicon are made in blocks from several crystals, so they are cheaper and have an average efficiency of between 16 % and 17.5 %.
Finally, those made from amorphous silicon have a disordered crystalline network, which leads to a lower performance (average efficiency between 8% and 9%), but also a lower price.
There are two types of photovoltaic plants: those that are connected to the grid and those that are not. Within the former there are two sub-classes:
- Photovoltaic power plants: all the energy produced by the panels is fed into the electricity grid.
- Generator with self-consumption: part of the electricity generated is consumed by the producer (in a dwelling, for example) and the rest is discharged onto the grid. In addition, the producer takes from the grid the energy needed to meet their demands when the unit does not supply enough.
Grid-connected installations have three basic elements:
- Photovoltaic panels: these are groups of photovoltaic cells mounted between layers of silicon that capture solar radiation and transform the light (photons) into electrical energy (electrons).
- Inverters: they convert the direct electrical current produced by the panels into alternating current, suitable for consumption.
- Transformers: the alternating current generated by the inverters is low voltage (380-800 V), so a transformer is used to raise it to medium voltage (up to 36 kV).
Off-grid facilities operate in isolation and are often located in remote locations and on farms to meet lighting demands, support telecommunications, and run pumps in irrigation systems. These isolated plants require two additional elements to function:
- Batteries: to store the energy produced by the panels that is not used when it is generated, the stored energy can then be used when needed.
- Controllers: to protect the battery from overcharging and prevent inefficient use of the battery.
Photovoltaic technology has a number of benefits which makes it useful as a renewable energy source. These include:
- 100% renewable, inexhaustible and non-polluting.
- Modular, meaning it can be used in installations ranging from large plants on the ground to smaller roof panels.
- Enables battery installation for storing excess electricity.
- Suitable for rural and isolated areas with low-or-no existing power lines or energy infrastructure.
Concentrating solar-thermal power (CSP) systems use mirrors to reflect and concentrate sunlight onto receivers that collect solar energy and convert it to heat, which can then be used to produce electricity or stored for later use. It is used primarily in very large power plants.
Concentrating solar-thermal power (CSP) technologies can be used to generate electricity by converting energy from sunlight to power a turbine, but the same basic technologies can also be used to deliver heat to a variety of industrial applications, like water desalination, enhanced oil recovery, food processing, chemical production, and mineral processing.
Solar energy technology companies
The majority of wind energy technology uses wind to produce electricity, using the kinetic energy created by air in motion. This is transformed into electrical energy using wind turbines or wind energy conversion systems. Wind first hits a turbine’s blades, causing them to rotate and turn the turbine connected to them, changing the kinetic energy to rotational energy by moving a shaft which is connected to a generator. This produces electrical energy through electromagnetism.
The amount of power that can be harvested from wind depends on the size of the turbine and the length of its blades. The output is proportional to the dimensions of the rotor and to the cube of the wind speed. When wind speed doubles, wind power potential theoretically increases by a factor of eight.
Wind power is one of the fastest-growing renewable energy technologies, with increased worldwide use, in part due to falling costs. Global installed wind-generation capacity onshore and offshore has increased by a factor of almost 75 in the past two decades, jumping from 7.5 gigawatts (GW) in 1997 to approximately 564 GW by 2018. Production of wind electricity doubled between 2009 and 2013, and in 2016 wind energy accounted for 16% of the renewable electricity generated.
The best locations for generating wind power are sometimes remote ones, with offshore wind power also offering large potential for the future.A U.S. Departent of Energy research survey in April 2021 states that wind turbines will be two to three times larger by 2013, with a median of 5.5MW for land-based turbines and 17MW for offshore turbines. This is expected to drive cost decreases between 35% and 50% by 2050 for both locations.
Wind-turbine capacity has increased over time. In 1985, typical turbines had a rated capacity of 0.05 megawatts (MW) and a rotor diameter of 15 meters, but current wind power projects have turbine capacities of about 2 MW onshore and 3 to 5 MW offshore.
Commercially available wind turbines have reached 8MW capacity, with rotor diameters of up to 164 metres. The average capacity of wind turbines increased from 1.6 MW in 2009 to 2 MW in 2014.
Wind energy technology companies
Geothermal technology harnesses the Earth’s heat, which maintains a near-constant temperature. Farther below the surface, the temperature increases at an average rate of approximately 1°F for every 70 feet in depth, with tectonic and volcanic activity bringing higher temperatures and pockets of superheated water and steam much closer to the surface.
Geothermal energy is considered a renewable resource. Ground source heat pumps and direct use geothermal technologies serve heating and cooling applications, while deep and enhanced geothermal technologies generally take advantage of a much deeper, higher temperature geothermal resource to generate electricity.
A ground source heat pump takes advantage of the naturally occurring difference between the above-ground air temperature and the subsurface soil temperature to move heat in support of end uses such as space heating, space cooling (air conditioning), and even water heating.
A ground source or geoexchange system consists of a heat pump connected to a series of buried pipes. One can install the pipes either in horizontal trenches just below the ground surface or in vertical boreholes that go several hundred feet below ground. The heat pump circulates a heat-conveying fluid, sometimes water, through the pipes to move heat from point to point.
If the ground temperature is warmer than ambient air temperature, the heat pump can move heat from the ground to the building. The heat pump can also operate in reverse, moving heat from the ambient air in a building into the ground, in effect cooling the building.
Ground source heat pumps require a small amount of electricity to drive the heating/cooling process. For every unit of electricity used in operating the system, the heat pump can deliver as much as five times the energy from the ground, resulting in a net energy benefit. Geothermal heat pump users should be aware that in the absence of using renewable generated electricity to drive the heating/cooling process (e.g., modes) that geothermal heat pump systems may not be fully fossil-fuel free (e.g., renewable-based).
Direct use geothermal systems use groundwater that is heated by natural geological processes below the Earth’s surface. This water can be as hot as 200°F or more. Bodies of hot groundwater can be found in many areas with volcanic or tectonic activity.
The water from direct geothermal systems is hot enough for many applications, including large-scale pool heating; space heating, cooling, and on-demand hot water for buildings of most sizes; district heating (i.e., heat for multiple buildings in a city); heating roads and sidewalks to melt snow; and some industrial and agricultural processes.
Direct use takes advantage of hot water that may be just a few feet below the surface, and usually less than a mile deep. The shallow depth means that capital costs are relatively small compared with deeper geothermal systems, but this technology is limited to regions with natural sources of hot groundwater at or near the surface.
Deep geothermal systems use steam from far below the Earth’s surface for applications that require temperatures of several hundred degrees Fahrenheit. These systems typically inject water into the ground through one well and bring water or steam to the surface through another.
Other variations can capture steam directly from underground (“dry steam”). Unlike ground source heat pumps or direct use geothermal systems, deep geothermal projects can involve drilling a mile or more below the Earth’s surface. At these depths, high pressure keeps the water in a liquid state even at temperatures of several hundred degrees Fahrenheit.
Deep geothermal sources provide efficient, clean heat for industrial processes and some large-scale commercial and agricultural uses. In addition, steam can be used to spin a turbine and generate electricity. Although geothermal steam requires no fuel and low operational costs, the initial capital costs, which include drilling test wells and production wells, can be financially challenging.
Steam resources that are economical to tap into are currently limited to regions with high geothermal activity, but research is underway to develop enhanced geothermal systems with much deeper wells that take advantage of the Earth’s natural temperature gradient and can potentially be constructed anywhere. Enhanced systems can use hydraulic fracturing techniques to engineer subsurface reservoirs that allow water to be pumped into and through otherwise dry or impermeable rock.
Geothermal energy technology
Flowing water creates energy that can be captured and turned into electricity. This is called hydroelectric power or hydropower. The most common type of hydroelectric power plant uses a dam on a river to store water in a reservoir. Water released from the reservoir flows through a turbine, spinning it, which in turn activates a generator to produce electricity.
Hydroelectric power doesn’t always require a large dam, however, with some hydroelectric power plants using only a small canal to channel river water through a turbine.
Another type of hydroelectric power plant is called a pumped storage plant. This type of hydropower can store power, and send electricity from a power grid into electric generators. The generators then spin the turbines backward, which causes the turbines to pump water from a river or lower reservoir to an upper reservoir, where the power is stored.
In order to use the power, water is released from the upper reservoir back down into the river or lower reservoir. This spins the turbines forward, activating the generators to produce electricity.
Hydropower energy technology companies
The movement of the ocean's waves, tides, and currents carries energy that can be harnessed and converted into electricity to power homes, buildings, and cities.
This movement occurs naturally when waves crash against coastlines and tidal currents ebb and flow. The energy available in this moving water is called kinetic energy, and it can be used to generate electricity.
A buoy can harness energy from the vertical rise and fall of ocean waves, as well as the back-and-forth and side-to-side movements, while currents and tides can generate electricity by spinning a turbine. Devices use to capture hydrokinetic power must be able to withstand turbulent and harsh conditions and be designed to preserve the integrity of the marine environment.
With oceans covering 75% of the planet and many water resources located near the most populated areas, ocean energy has great potential as a plentiful renewable resource.
Biomass is renewable organic material that comes from plants and animals. Biomass was the largest source of total annual U.S. energy consumption until the mid-1800s. Biomass continues to be an important fuel in many countries, especially for cooking and heating in developing countries.
The use of biomass fuels for transportation and for electricity generation is increasing in many developed countries as a means of avoiding carbon dioxide emissions from fossil fuel use. In 2020, biomass provided nearly 5 quadrillion British thermal units (Btu) and about 5% of total primary energy use in the United States.
Biomass sources for energy include:
- Wood and wood processing wastes: firewood, wood pellets, and wood chips, lumber and furniture mill sawdust and waste, and black liquor from pulp and paper mills, etc.
- Agricultural crops and waste materials: corn, soybeans, sugar cane, switchgrass, woody plants, and algae, and crop and food processing residues, etc.
- Biogenic materials in municipal solid waste: paper, cotton, and wool products, and food, yard, and wood wastes, etc.
- Animal manure and human sewage
Biomass is converted to energy through various processes, including:
- Direct combustion (burning) to produce heat
- Thermochemical conversion to produce solid, gaseous, and liquid fuels
- Chemical conversion to produce liquid fuels
- Biological conversion to produce liquid and gaseous fuels
- Direct combustion is the most common method for converting biomass to useful energy. All biomass can be burned directly for heating buildings and water, for industrial process heat, and for generating electricity in steam turbines.
Thermochemical conversion of biomass includes pyrolysis and gasification. Both are thermal decomposition processes in which biomass feedstock materials are heated in closed, pressurized vessels called gasifiers at high temperatures. They mainly differ in the process temperatures and amount of oxygen present during the conversion process.
Pyrolysis includes heating organic materials to 800–900oF (400–500 oC) in the near complete absence of free oxygen. Biomass pyrolysis produces fuels such as charcoal, bio-oil, renewable diesel, methane, and hydrogen.
Hydrotreating is used to process bio-oil (produced by fast pyrolysis) with hydrogen under elevated temperatures and pressures in the presence of a catalyst to produce renewable diesel, renewable gasoline, and renewable jet fuel.
Gasification entails heating organic materials to 1,400–1700oF (800–900oC) with injections of controlled amounts of free oxygen and/or steam into the vessel to produce a carbon monoxide and hydrogen rich gas called synthesis gas or syngas. Syngas can be used as a fuel for diesel engines, for heating, and for generating electricity in gas turbines.
Syngas can also be treated to separate the hydrogen from the gas, and the hydrogen can be burned or used in fuel cells. The syngas can be further processed to produce liquid fuels using the Fischer–Tropsch process.
Biomass energy technology companies
Energy can be stored in several ways, such as batteries or ultracapacitors. Alternatively, energy can be converted into a gas such as biogas, biomethane or hydrogen and stored as a fuel rather than as electricity.
There are numerous applications for energy storage technologies, including providing support services to the electricity grid, or to an individual consumer “behind-the-meter”. Energy storage technology may be deployed as stand-alone systems or with power generation as part of a hybrid or micro-grid scheme.
"E-fuels” can be utilized in high-efficiency decentralized reciprocating gas engine plants to produce both electricity and heat, at point of use, in order to save money and decarbonize utility supplies.
Energy resilience has become an essential consideration when evaluating power supply. Unexpected events such as extreme weather incidents, technical failures or even pandemics can put their toll on the power network.
Due to growing concerns about fossil fuels' environmental impacts and the capacity and resilience of energy grids around the world, engineers and policymakers are increasingly turning their attention to energy storage solutions. Energy storage can help address the intermittency of solar and wind power, and in many cases can respond rapidly to large fluctuations in demand. This makes the grid more responsive and reduces the need to build backup power plants.
The effectiveness of an energy storage facility is determined by how quickly it can react to changes in demand, the rate of energy lost in the storage process, its overall energy storage capacity, and how quickly it can be recharged.
Energy storage systems can be deployed in parallel with other technologies as a hybrid power plant or as part of a micro-grid. These modern, flexible solutions can combine the benefits of ultra-fast battery response with the longevity of a gas engine, whilst also balancing with renewable power generation for complete site optimization.