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The Energy Hierarchy is a classification of energy options, prioritised to assist progress towards a more sustainable energy system. It is a similar approach to the waste hierarchy for minimising resource depletion, and adopts a parallel sequence.
The highest priorities cover the prevention of unnecessary energy usage both through eliminating waste and improving energy efficiency. The sustainable production of energy resources is the next priority. Depletive and waste-producing energy generation options are the lowest priority.
For an energy system to be sustainable: the resources applied to producing the energy must be capable of lasting indefinitely; energy conversion should produce no harmful by-products, including net emissions, nor wastes which cannot be fully recycled; and it must be capable of meeting reasonable energy demands.
The top priority under the Energy Hierarchy is energy conservation or the prevention of unnecessary use of energy. This category includes eliminating waste by turning off unneeded lights and appliances and by avoiding unnecessary journeys. Heat loss from buildings is a major source of energy wastage, [1] so improvements to building insulation and air-tightness can make a significant contribution to energy conservation. [2]
Many countries have agencies to encourage energy saving. [3] [4]
The second priority under the energy hierarchy is to ensure that energy that is used is produced and consumed efficiently. Energy efficiency has two main aspects.
Energy efficiency is the ratio of the productive output of a device to the energy it consumes. [5]
Energy efficiency was a lower priority when energy was cheap and awareness of its environmental impact was low. In 1975 the average fuel economy of a car in the US was under 15 miles per gallon [6] Incandescent light bulbs, which were the most common type until the late 20th century, waste 90% of their energy as heat, with only 10% converted to useful light. [7]
More recently, energy efficiency has become a priority. [8] The last reported average fuel efficiency of US cars had almost doubled from the 1975 level; [6] LED lighting is now being promoted which are between five and ten times more efficient than incandescents. [9] Many household appliances are now required to display labels to show their energy efficiency.
Losses are incurred when energy is harvested from the natural resource from which it is derived, such as fossil fuels, radioactive materials, solar radiation or other sources. Most electricity production is in thermal power stations, where much of the source energy is lost as heat. The average efficiency of world electricity production in 2009 was c.37%. [10]
A priority in the Energy Hierarchy is to improve the efficiency of energy conversion, whether in traditional power stations [11] or by improving the performance ratio of photovoltaic power stations [12] and other energy sources.
Overall efficiency and sustainability can also be improved by capacity- or fuel-switching from less efficient, less sustainable resources to better ones; but this is mainly covered under the fourth level of the hierarchy.
Renewable energy describes naturally occurring, theoretically inexhaustible sources of energy. [13] These sources are treated as being inexhaustible, or naturally replenished, and fall into two classes.
The first class of renewables derive from climatic or elemental sources, [14] such as sunlight, wind, waves, tides or rainfall (hydropower). Geothermal energy from the heat of the Earth's core also falls in this category.
These are treated as being inexhaustible because most derive ultimately from energy emanating from the sun, which has an estimated life of 6.5 billion years. [15]
The other main class of renewables, bioenergy, [16] derives from biomass, where the relatively short growing cycle means that usage is replenished by new growth. Bioenergy is usually converted by combustion, and therefore gives rise to carbon emissions. It is treated as carbon neutral overall, because an equivalent amount of carbon dioxide will have been extracted from the atmosphere during the growing cycle. [17]
Bioenergy sources can be solid, such as wood and energy crops; liquid, such as biofuels; or gaseous, such as biomethane from anaerobic digestion.[ citation needed ]
The next priority in the hierarchy covers energy sources that are not entirely sustainable, but have a low environmental impact. These include the use of fossil fuels with carbon capture and storage. [18]
Nuclear energy is sometimes treated as a low impact source, because it has low carbon emissions.
The lowest priority under the energy hierarchy is energy production using unsustainables sources, such as unabated fossil fuels. Some also place nuclear energy in this category, rather than the one above, because of the required management/storage of highly hazardous radioactive waste over extremely long (hundreds of thousands of years or more) timeframes [19] and depletion of uranium resources. [20]
There is a consensus that the share of such energy sources must decline. [21]
Within this tier, there are possibilities for limiting adverse impacts by switching from the most damaging fuel sources, such as coal, to less emissive sources, such as gas. [22]
Many suggest that when such high impact energy usage has been minimised, the effects of any unavoidable residual usage should be counterbalanced by emissions offsetting. [23]
The Energy Hierarchy was first proposed in 2005 by Philip Wolfe, [24] when he was Director General of the Renewable Energy Association. This first version had three levels; energy efficiency, renewables and traditional energy production. It was endorsed and adopted in 2006 by a consortium of institutions, associations and other bodies in the Sustainable Energy Manifesto. [25] Subsequently, the concept has been adopted and refined by others in the energy industry [26] and in government. [27] [28]
Biogas is a gaseous renewable energy source produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste, wastewater, and food waste. Biogas is produced by anaerobic digestion with anaerobic organisms or methanogens inside an anaerobic digester, biodigester or a bioreactor. The gas composition is primarily methane and carbon dioxide and may have small amounts of hydrogen sulfide, moisture and siloxanes. The methane can be combusted or oxidized with oxygen. This energy release allows biogas to be used as a fuel; it can be used in fuel cells and for heating purpose, such as in cooking. It can also be used in a gas engine to convert the energy in the gas into electricity and heat.
Biofuel is a fuel that is produced over a short time span from biomass, rather than by the very slow natural processes involved in the formation of fossil fuels such as oil. Biofuel can be produced from plants or from agricultural, domestic or industrial bio waste. Biofuels are mostly used for transportation, but can also be used for heating and electricity. Biofuels are regarded as a renewable energy source. The use of biofuel has been subject to criticism regarding the "food vs fuel" debate, varied assessments of their sustainability, and ongoing deforestation and biodiversity loss as a result of biofuel production.
A non-renewable resource is a natural resource that cannot be readily replaced by natural means at a pace quick enough to keep up with consumption. An example is carbon-based fossil fuels. The original organic matter, with the aid of heat and pressure, becomes a fuel such as oil or gas. Earth minerals and metal ores, fossil fuels and groundwater in certain aquifers are all considered non-renewable resources, though individual elements are always conserved.
Energy development is the field of activities focused on obtaining sources of energy from natural resources. These activities include the production of renewable, nuclear, and fossil fuel derived sources of energy, and for the recovery and reuse of energy that would otherwise be wasted. Energy conservation and efficiency measures reduce the demand for energy development, and can have benefits to society with improvements to environmental issues.
Electric power systems consist of generation plants of different energy sources, transmission networks, and distribution lines. Each of these components can have environmental impacts at multiple stages of their development and use including in their construction, during the generation of electricity, and in their decommissioning and disposal. These impacts can be split into operational impacts and construction impacts. All forms of electricity generation have some form of environmental impact, but coal-fired power is the dirtiest. This page is organized by energy source and includes impacts such as water usage, emissions, local pollution, and wildlife displacement.
Alternative fuels, also known as non-conventional and advanced fuels, are fuels derived from sources other than petroleum. Alternative fuels include gaseous fossil fuels like propane, natural gas, methane, and ammonia; biofuels like biodiesel, bioalcohol, and refuse-derived fuel; and other renewable fuels like hydrogen and electricity.
Energy is sustainable if it "meets the needs of the present without compromising the ability of future generations to meet their own needs." Definitions of sustainable energy usually look at its effects on the environment, the economy, and society. These impacts range from greenhouse gas emissions and air pollution to energy poverty and toxic waste. Renewable energy sources such as wind, hydro, solar, and geothermal energy can cause environmental damage but are generally far more sustainable than fossil fuel sources.
Bioenergy is a type of renewable energy that is derived from plants and animal waste. The biomass that is used as input materials consists of recently living organisms, mainly plants. Thus, fossil fuels are not regarded as biomass under this definition. Types of biomass commonly used for bioenergy include wood, food crops such as corn, energy crops and waste from forests, yards, or farms.
Pellet fuels are a type of solid fuel made from compressed organic material. Pellets can be made from any one of five general categories of biomass: industrial waste and co-products, food waste, agricultural residues, energy crops, and untreated lumber. Wood pellets are the most common type of pellet fuel and are generally made from compacted sawdust and related industrial wastes from the milling of lumber, manufacture of wood products and furniture, and construction. Other industrial waste sources include empty fruit bunches, palm kernel shells, coconut shells, and tree tops and branches discarded during logging operations. So-called "black pellets" are made of biomass, refined to resemble hard coal and were developed to be used in existing coal-fired power plants. Pellets are categorized by their heating value, moisture and ash content, and dimensions. They can be used as fuels for power generation, commercial or residential heating, and cooking.
In the context of energy production, biomass is matter from recently living organisms which is used for bioenergy production. Examples include wood, wood residues, energy crops, agricultural residues including straw, and organic waste from industry and households. Wood and wood residues is the largest biomass energy source today. Wood can be used as a fuel directly or processed into pellet fuel or other forms of fuels. Other plants can also be used as fuel, for instance maize, switchgrass, miscanthus and bamboo. The main waste feedstocks are wood waste, agricultural waste, municipal solid waste, and manufacturing waste. Upgrading raw biomass to higher grade fuels can be achieved by different methods, broadly classified as thermal, chemical, or biochemical.
The energy policy of the European Union focuses on energy security, sustainability, and integrating the energy markets of member states. An increasingly important part of it is climate policy. A key energy policy adopted in 2009 is the 20/20/20 objectives, binding for all EU Member States. The target involved increasing the share of renewable energy in its final energy use to 20%, reduce greenhouse gases by 20% and increase energy efficiency by 20%. After this target was met, new targets for 2030 were set at a 55% reduction of greenhouse gas emissions by 2030 as part of the European Green Deal. After the Russian invasion of Ukraine, the EU's energy policy turned more towards energy security in their REPowerEU policy package, which boosts both renewable deployment and fossil fuel infrastructure for alternative suppliers.
Low-carbon electricity or low-carbon power is electricity produced with substantially lower greenhouse gas emissions over the entire lifecycle than power generation using fossil fuels. The energy transition to low-carbon power is one of the most important actions required to limit climate change.
Energy in Finland describes energy and electricity production, consumption and import in Finland. Energy policy of Finland describes the politics of Finland related to energy. Electricity sector in Finland is the main article regarding electricity in Finland.
Bioenergy with carbon capture and storage (BECCS) is the process of extracting bioenergy from biomass and capturing and storing the carbon dioxide (CO2) that is produced.
Energy in Switzerland is transitioning towards sustainability, targeting net zero emissions by 2050 and a 50% reduction in greenhouse gas emissions by 2030.
The environmental impact of the energy industry is significant, as energy and natural resource consumption are closely related. Producing, transporting, or consuming energy all have an environmental impact. Energy has been harnessed by human beings for millennia. Initially it was with the use of fire for light, heat, cooking and for safety, and its use can be traced back at least 1.9 million years. In recent years there has been a trend towards the increased commercialization of various renewable energy sources. Scientific consensus on some of the main human activities that contribute to global warming are considered to be increasing concentrations of greenhouse gases, causing a warming effect, global changes to land surface, such as deforestation, for a warming effect, increasing concentrations of aerosols, mainly for a cooling effect.
The energy mix is a group of different primary energy sources from which secondary energy for direct use - such as electricity - is produced. Energy mix refers to all direct uses of energy, such as transportation and housing, and should not be confused with power generation mix, which refers only to generation of electricity, as electricity only accounts for 20 % of the world's final energy consumption.
Greenhouse gas emissions are one of the environmental impacts of electricity generation. Measurement of life-cycle greenhouse gas emissions involves calculating the global warming potential (GWP) of energy sources through life-cycle assessment. These are usually sources of only electrical energy but sometimes sources of heat are evaluated. The findings are presented in units of global warming potential per unit of electrical energy generated by that source. The scale uses the global warming potential unit, the carbon dioxide equivalent, and the unit of electrical energy, the kilowatt hour (kWh). The goal of such assessments is to cover the full life of the source, from material and fuel mining through construction to operation and waste management.
Energy in Sweden is characterized by relatively high per capita production and consumption, and a reliance on imports for fossil fuel supplies.
Approximately 44% of primary energy is from renewable energy sources in New Zealand. Approximately 87% of electricity comes from renewable energy, primarily hydropower and geothermal power.
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