Efficient energy use, or energy efficiency, is the process of reducing the amount of energy required to provide products and services. There are many technologies and methods available that are more energy efficient than conventional systems. For example, insulating a building allows it to use less heating and cooling energy while still maintaining a comfortable temperature. Another method is to remove energy subsidies that promote high energy consumption and inefficient energy use.[1] Improved energy efficiency in buildings, industrial processes and transportation could reduce the world's energy needs in 2050 by one third.[2]
There are two main motivations to improve energy efficiency. Firstly, one motivation is to achieve cost savings during the operation of the appliance or process. However, installing an energy-efficient technology comes with an upfront cost, the capital cost. The different types of costs can be analyzed and compared with a life-cycle assessment. Another motivation for energy efficiency is to reduce greenhouse gas emissions and hence work towards climate action. A focus on energy efficiency can also have a national security benefit because it can reduce the amount of energy that has to be imported from other countries.
Energy efficiency and renewable energy go hand in hand for sustainable energy policies.[3] They are high priority actions in the energy hierarchy.
Energy productivity, which measures the output and quality of goods and services per unit of energy input, can come from either reducing the amount of energy required to produce something, or from increasing the quantity or quality of goods and services from the same amount of energy.
From the point of view of an energy consumer, the main motivation of energy efficiency is often simply saving money by lowering the cost of purchasing energy. Additionally, from an energy policy point of view, there has been a long trend in a wider recognition of energy efficiency as the "first fuel", meaning the ability to replace or avoid the consumption of actual fuels. In fact, International Energy Agency has calculated that the application of energy efficiency measures in the years 1974-2010 has succeeded in avoiding more energy consumption in its member states than is the consumption of any particular fuel, including fossil fuels (i.e. oil, coal and natural gas).[4]
Moreover, it has long been recognized that energy efficiency brings other benefits additional to the reduction of energy consumption.[5] Some estimates of the value of these other benefits, often called multiple benefits, co-benefits, ancillary benefits or non-energy benefits, have put their summed value even higher than that of the direct energy benefits.[6]
These multiple benefits of energy efficiency include things such as reduced greenhouse gas emissions, reduced air pollution and improved health, and improved energy security. Methods for calculating the monetary value of these multiple benefits have been developed, including e.g. the choice experiment method for improvements that have a subjective component (such as aesthetics or comfort) and Tuominen-Seppänen method for price risk reduction.[7] [8] When included in the analysis, the economic benefit of energy efficiency investments can be shown to be significantly higher than simply the value of the saved energy.
Energy efficiency has proved to be a cost-effective strategy for building economies without necessarily increasing energy consumption. For example, the state of California began implementing energy-efficiency measures in the mid-1970s, including building code and appliance standards with strict efficiency requirements. During the following years, California's energy consumption has remained approximately flat on a per capita basis while national US consumption doubled.[9] As part of its strategy, California implemented a "loading order" for new energy resources that puts energy efficiency first, renewable electricity supplies second, and new fossil-fired power plants last.[10] States such as Connecticut and New York have created quasi-public Green Banks to help residential and commercial building-owners finance energy efficiency upgrades that reduce emissions and cut consumers' energy costs.[11]
See main article: Energy conservation. Energy conservation is broader than energy efficiency in including active efforts to decrease energy consumption, for example through behaviour change, in addition to using energy more efficiently. Examples of conservation without efficiency improvements are heating a room less in winter, using the car less, air-drying your clothes instead of using the dryer, or enabling energy saving modes on a computer. As with other definitions, the boundary between efficient energy use and energy conservation can be fuzzy, but both are important in environmental and economic terms.[12]
See main article: Sustainable energy.
Energy efficiency—using less energy to deliver the same goods or services, or delivering comparable services with less goods—is a cornerstone of many sustainable energy strategies.[13] [14] The International Energy Agency (IEA) has estimated that increasing energy efficiency could achieve 40% of greenhouse gas emission reductions needed to fulfil the Paris Agreement's goals.[15] Energy can be conserved by increasing the technical efficiency of appliances, vehicles, industrial processes, and buildings.[16]
If the demand for energy services remains constant, improving energy efficiency will reduce energy consumption and carbon emissions. However, many efficiency improvements do not reduce energy consumption by the amount predicted by simple engineering models. This is because they make energy services cheaper, and so consumption of those services increases. For example, since fuel efficient vehicles make travel cheaper, consumers may choose to drive farther, thereby offsetting some of the potential energy savings. Similarly, an extensive historical analysis of technological efficiency improvements has conclusively shown that energy efficiency improvements were almost always outpaced by economic growth, resulting in a net increase in resource use and associated pollution.[17] These are examples of the direct rebound effect.[18]
Estimates of the size of the rebound effect range from roughly 5% to 40%.[19] [20] [21] The rebound effect is likely to be less than 30% at the household level and may be closer to 10% for transport. A rebound effect of 30% implies that improvements in energy efficiency should achieve 70% of the reduction in energy consumption projected using engineering models.
See also: Domestic energy consumption and power usage effectiveness.
Modern appliances, such as, freezers, ovens, stoves, dishwashers, clothes washers and dryers, use significantly less energy than older appliances. Current energy-efficient refrigerators, for example, use 40 percent less energy than conventional models did in 2001. Following this, if all households in Europe changed their more than ten-year-old appliances into new ones, 20 billion kWh of electricity would be saved annually, hence reducing CO2 emissions by almost 18 billion kg.[22] In the US, the corresponding figures would be 17 billion kWh of electricity and 27000000000lb CO2.[23] According to a 2009 study from McKinsey & Company the replacement of old appliances is one of the most efficient global measures to reduce emissions of greenhouse gases.[24] Modern power management systems also reduce energy usage by idle appliances by turning them off or putting them into a low-energy mode after a certain time. Many countries identify energy-efficient appliances using energy input labeling.[25]
The impact of energy efficiency on peak demand depends on when the appliance is used. For example, an air conditioner uses more energy during the afternoon when it is hot. Therefore, an energy-efficient air conditioner will have a larger impact on peak demand than off-peak demand. An energy-efficient dishwasher, on the other hand, uses more energy during the late evening when people do their dishes. This appliance may have little to no impact on peak demand.
Over the period 2001–2021, tech companies have replaced traditional silicon switches in an electric circuit with quicker gallium nitride transistors to make new gadgets as energy efficient as feasible. Gallium nitride transistors are, however, more costly. This is a significant change in lowering the carbon footprint.[26] [27] [28]
See also: Building performance and Green building.
A building's location and surroundings play a key role in regulating its temperature and illumination. For example, trees, landscaping, and hills can provide shade and block wind. In cooler climates, designing northern hemisphere buildings with south facing windows and southern hemisphere buildings with north facing windows increases the amount of sun (ultimately heat energy) entering the building, minimizing energy use, by maximizing passive solar heating. Tight building design, including energy-efficient windows, well-sealed doors, and additional thermal insulation of walls, basement slabs, and foundations can reduce heat loss by 25 to 50 percent.[29]
Dark roofs may become up to 39 °C (70 °F) hotter than the most reflective white surfaces. They transmit some of this additional heat inside the building. US Studies have shown that lightly colored roofs use 40 percent less energy for cooling than buildings with darker roofs. White roof systems save more energy in sunnier climates. Advanced electronic heating and cooling systems can moderate energy consumption and improve the comfort of people in the building.[25]
Proper placement of windows and skylights as well as the use of architectural features that reflect light into a building can reduce the need for artificial lighting. Increased use of natural and task lighting has been shown by one study to increase productivity in schools and offices.[25] Compact fluorescent lamps use two-thirds less energy and may last 6 to 10 times longer than incandescent light bulbs. Newer fluorescent lights produce a natural light, and in most applications they are cost effective, despite their higher initial cost, with payback periods as low as a few months. LED lamps use only about 10% of the energy an incandescent lamp requires.
Leadership in Energy and Environmental Design (LEED) is a rating system organized by the US Green Building Council (USGBC) to promote environmental responsibility in building design. They currently offer four levels of certification for existing buildings (LEED-EBOM) and new construction (LEED-NC) based on a building's compliance with the following criteria: Sustainable sites, water efficiency, energy and atmosphere, materials and resources, indoor environmental quality, and innovation in design.[30] In 2013, USGBC developed the LEED Dynamic Plaque, a tool to track building performance against LEED metrics and a potential path to recertification. The following year, the council collaborated with Honeywell to pull data on energy and water use, as well as indoor air quality from a BAS to automatically update the plaque, providing a near-real-time view of performance. The USGBC office in Washington, D.C. is one of the first buildings to feature the live-updating LEED Dynamic Plaque.[31]
Industries use a large amount of energy to power a diverse range of manufacturing and resource extraction processes. Many industrial processes require large amounts of heat and mechanical power, most of which is delivered as natural gas, petroleum fuels, and electricity. In addition some industries generate fuel from waste products that can be used to provide additional energy.
Because industrial processes are so diverse it is impossible to describe the multitude of possible opportunities for energy efficiency in industry. Many depend on the specific technologies and processes in use at each industrial facility. There are, however, a number of processes and energy services that are widely used in many industries.
Various industries generate steam and electricity for subsequent use within their facilities. When electricity is generated, the heat that is produced as a by-product can be captured and used for process steam, heating or other industrial purposes. Conventional electricity generation is about 30% efficient, whereas combined heat and power (also called co-generation) converts up to 90 percent of the fuel into usable energy.[32]
Advanced boilers and furnaces can operate at higher temperatures while burning less fuel. These technologies are more efficient and produce fewer pollutants.[32]
Over 45 percent of the fuel used by US manufacturers is burnt to make steam. The typical industrial facility can reduce this energy usage 20 percent (according to the US Department of Energy) by insulating steam and condensate return lines, stopping steam leakage, and maintaining steam traps.[32]
Electric motors usually run at a constant speed, but a variable speed drive allows the motor's energy output to match the required load. This achieves energy savings ranging from 3 to 60 percent, depending on how the motor is used. Motor coils made of superconducting materials can also reduce energy losses.[32] Motors may also benefit from voltage optimization.[33] [34]
Industry uses a large number of pumps and compressors of all shapes and sizes and in a wide variety of applications. The efficiency of pumps and compressors depends on many factors but often improvements can be made by implementing better process control and better maintenance practices. Compressors are commonly used to provide compressed air which is used for sand blasting, painting, and other power tools. According to the US Department of Energy, optimizing compressed air systems by installing variable speed drives, along with preventive maintenance to detect and fix air leaks, can improve energy efficiency 20 to 50 percent.[32]
See main article: Energy efficiency in transport.