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.

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 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.^[19]

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 ^[20] and depletion of uranium resources.^[21]

There is a consensus that the share of such energy sources must decline.^[22]

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.^[23]

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.^[24]

The Energy Hierarchy was first proposed in 2005 by Philip Wolfe,^[25] 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.^[26] Subsequently, the concept has been adopted and refined by others in the energy industry^[27] and in government.^[28][29]

• Energy law
• Energy policy
• Green transport hierarchy
• List of books about energy issues
• Maslow's hierarchy of needs
• Soft energy path
• Waste hierarchy