Beatrice Lang
The efficiency of electric power transmission is a critical aspect of modern infrastructure. Electric power can be transmitted through overhead power lines or underground cables, with the choice of transmission method impacting energy loss. High-voltage transmission lines can carry electricity over long distances with minimal losses of around two percent. On the other hand, low-voltage distribution lines may experience higher losses of about four percent. Various factors, such as weather conditions and power consumption, influence the variability of losses in transmission and distribution. While the exact percentage of energy lost within the wiring of our homes is unknown, it could range from negligible to a few percent. Power plants also play a role in energy loss, with about 65% of energy from raw materials making it to the grid as electricity.
| Characteristics | Values |
|---|---|
| Percentage of energy lost in power plants | 65% or 22 quadrillion Btus in the U.S. |
| Percentage of energy lost in transmission and distribution | 6% (2% in transmission and 4% in distribution) or 69 trillion Btus in the U.S. in 2013 |
| Energy lost in the wiring inside walls | Negligible or a few percent |
| Voltage of transmission lines | Hundreds of thousands of volts |
| Distance covered by transmission lines | Dozens or hundreds of miles |
| Distance covered by low-voltage distribution lines | A few miles or less |
| Technology to reduce transmission and distribution losses | Superconducting materials |
| Alternative technology to reduce transmission and distribution losses | Change how and when power is used |
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What You'll Learn
Energy loss in power plants
Energy loss is a significant issue in today's electricity systems. The process of converting energy from one form to another often results in only a fraction of the original energy being available for its intended purpose. This is true for both internal combustion engines and power plants. While fossil-fuelled power plants are more efficient than car engines, they still experience considerable energy loss.
In conventional thermal electricity generation, around 60% of the energy input is typically lost as waste heat. This means that for every 100 units of energy input, 60 units are lost as waste heat, and only 40 units are converted into electricity. This phenomenon is not limited to thermal power plants; it also affects other types of power plants that utilise fossil fuels, such as coal and natural gas.
The efficiency of a power plant is measured by its heat rate, which calculates the amount of energy required to generate one kilowatt-hour (kWh) of electricity. For example, a natural gas plant with a heat rate of 44% efficiency would lose 56% of the energy in the gas during the conversion process, resulting in only 44% of the energy being transformed into electricity. This loss occurs due to the inherent inefficiencies in converting energy from one form to another.
The energy loss in power plants can be attributed to several factors. Firstly, the process of generating electricity itself is inefficient. The most common method of electricity generation involves producing heat to boil water and create steam, which then spins a turbine to generate electricity. This process inherently loses a significant portion of the initial energy. Additionally, there are minor losses from the energy used to operate the power plant itself.
Furthermore, the type of fuel and technology used also impact the efficiency of a power plant. For instance, a typical coal power plant has an energy yield of around 35%, resulting in a loss of 65% of the energy content of the coal. On the other hand, a modern combined-cycle gas plant may achieve a loss of around 55%, while the best-in-class plants can reduce losses to below 40%. The introduction of higher-efficiency natural gas plants and the increased direct generation from renewable sources have contributed to improving overall efficiency.
To mitigate energy loss, various approaches can be considered. One method is to implement Combined Heat and Power (CHP) systems, which utilise the waste heat generated during electricity production. By combining heat and power generation in a single combustion process, CHP plants can achieve higher efficiency than traditional boilers and power stations. Additionally, the physical proximity of CHP plants to their users further reduces transmission losses. Another approach to reducing energy loss is to focus on electrification and improving efficiency through better housing insulation, the adoption of electric vehicles, and the support of public transportation.
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Transmission and distribution losses
The process of converting raw materials into electricity and transmitting that electricity to consumers results in some energy loss. This loss is referred to as transmission and distribution loss.
Electricity is typically generated in power plants by burning energy-dense materials to produce heat, which boils water into steam, spins a turbine, and ultimately generates electricity. This process is subject to thermodynamic limits, resulting in only about two-thirds of the energy in the raw materials being converted into electricity.
Once electricity is generated, it needs to be transmitted to consumers, often over long distances. This transmission is primarily done through high-voltage transmission lines, which help reduce energy loss due to resistance over long distances. However, there are still some losses associated with this transmission process. Smaller power lines result in relatively larger losses. High-voltage direct current (HVDC) technology is employed in submarine power cables and to stabilize power distribution networks, but it also comes with higher installation costs and operational limitations.
Technological advancements, such as superconducting materials, have the potential to significantly reduce transmission and distribution losses. However, the current cost of implementing such technologies is often higher than the monetary losses incurred by utility companies through their existing power lines. Alternative solutions, like reconductoring, which involves replacing existing transmission lines with higher-capacity lines, have been explored to handle the increasing electricity production and reduce transmission losses.
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Voltage and energy loss
The percentage of energy lost during transmission and distribution is dependent on a variety of factors, including the voltage, the distance travelled, the type of power line, and the weather and power consumption at the time of transmission.
Electricity is transmitted at high voltages to reduce energy loss due to resistance over long distances. The use of high voltage power lines results in lower losses than low voltage lines. For example, electricity may travel dozens or hundreds of miles on high-voltage transmission lines with losses of around two percent, whereas electricity travelling a few miles or less on low-voltage distribution lines may experience losses of around four percent.
The relationship between voltage and energy loss is such that as voltage increases, power loss decreases. This is because, for a given transmission line, carrying the same power at a higher voltage will reduce loss percentage. For instance, if the voltage is increased by a factor of 10, the power loss will decrease by a factor of 100.
However, there are other factors to consider when increasing voltage. Higher voltages require increased insulation and larger towers, which can be costly. Additionally, the type of power line used can impact energy loss. Underground power transmission, for example, has a higher installation cost and greater operational limitations compared to overhead power lines, but it lowers maintenance costs.
The weather and power consumption can also affect energy loss. Losses are higher when demand is high, such as during hot summer days when many people are using air conditioning. In contrast, losses are lower during periods of low demand, such as in the middle of the night.
Overall, the percentage of energy lost during transmission and distribution can vary, but it is generally around six percent in total, with about two percent lost in transmission and four percent lost in distribution. To reduce these losses, grid engineers are working on developing technologies such as superconducting materials, although the current cost of implementing these solutions is high.
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Electric power transmission history
The history of electric power transmission began in the 19th century, with the use of hydraulic transmission systems in cities, which employed high-pressure water mains to deliver power to factory motors. London's system, for example, delivered 7,000 horsepower (5.2 MW) over a vast network of 180 miles (290 km) of pipes. However, these hydraulic systems were eventually replaced by cheaper and more versatile electrical systems.
In the early days of electric power, there were two main obstacles to widespread transmission. Firstly, devices requiring different voltages needed specialised generators with separate lines. Examples include street lights, electric motors in factories, power for streetcars, and lights in homes. Secondly, generators had to be located relatively close to their loads, typically within a mile for low-voltage devices.
Researchers at the time understood that increasing voltage was the key to overcoming these challenges. They knew that by doubling the voltage and halving the current, the same amount of power could be transmitted over a longer distance. This principle was demonstrated at the Paris Exposition of 1878, where electric arc lighting was installed along the Avenue de l'Opera and the Place de l'Opera, powered by Yablochkov arc lamps and Zénobe Gramme's alternating current dynamos.
The foundation of modern electric power transmission was laid in 1882 with Thomas A. Edison's Pearl Street Station in New York City. This DC generator and radial line transmission system were primarily used for lighting. In 1881, Lucien Gaulard and John Dixon Gibbs invented the "secondary generator," an early transformer that enabled the transmission of alternating current (AC). The first long-distance AC line was constructed in 1884 for the International Exhibition of Electricity in Turin, Italy, spanning 34 kilometres (21 miles).
The first transmission of single-phase alternating current using high voltage occurred in Oregon in 1890, delivering power from a hydroelectric plant at Willamette Falls to Portland, 14 miles (23 km) away. The following year, in 1891, the first three-phase alternating current using high voltage was demonstrated during the International Electricity Exhibition in Frankfurt, Germany, with a 15 kV transmission line stretching 175 km from Lauffen on the Neckar to Frankfurt.
Throughout the 20th century, transmission voltages continued to increase. By 1914, there were 55 transmission systems operating at over 70 kV, with the highest voltage reaching 150 kV. The development of extensive regional grids and interties in the 1950s and 1960s led to the creation of computerized supervisory control and data acquisition (SCADA) systems for improved coordination and control.
Today, electric power transmission relies on high-voltage transmission lines to reduce energy loss over long distances. Most North American transmission lines use high-voltage three-phase AC, while DC technology is employed for greater efficiency over longer distances, typically hundreds of miles. Underground power transmission is more common in urban areas or environmentally sensitive locations, but it has higher installation costs and greater operational limitations compared to overhead power lines.
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Underground power cables
The transmission of electricity from power plants to homes is a complex process. Power plants use energy-dense materials such as coal, natural gas, petroleum, or nuclear fuel to generate electricity through heat and steam. However, due to thermodynamic limits, only about two-thirds of the energy from these raw materials makes it onto the electrical grid.
Electricity is typically transmitted through overhead power lines, but underground power cables are also a viable option. Underground power cables have several advantages over their overhead counterparts. They have a lower risk of starting wildfires and are less susceptible to interruptions during high winds, thunderstorms, or heavy snow and ice storms. Underground cables are also less affected by weather conditions and have a reduced range of electromagnetic field (EMF) emissions into the surrounding area. Additionally, they improve the aesthetic quality of the landscape and are safer in natural disaster-prone regions, such as areas prone to wildfires.
However, one of the main drawbacks of underground power cables is their significantly higher installation cost, which can be up to ten times more expensive than overhead power lines. This is due to the superior insulation required for underground cables, which must be resistant to soil, weather, and chemicals. Additionally, underground cables are harder to replace and upgrade, making them more challenging to maintain. They are also limited by their thermal capacity and are more subject to damage from ground movement, such as earthquakes.
Despite the higher initial cost, underground power cables may offer long-term economic benefits. They have lower maintenance costs and can reduce the overall lifetime cost of power transmission and distribution, especially in densely populated or environmentally sensitive areas. Underground cables also eliminate the need for wide clearance corridors, saving space.
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Frequently asked questions
About 6% of electricity is lost in transmission and distribution, with 2% lost in transmission and 4% lost in distribution.
Only two-thirds of the energy in raw materials used in power plants make it onto the grid in the form of electricity. About 65% of energy is lost in power plants.
Losses aren't a constant quantity. They change based on factors like the weather and power consumption. Losses are higher when demand is high and lower when demand is low.
