Energy conservation is the practice of decreasing the quantity of energy used while achieving a similar outcome.
Energy efficiency is using less energy to provide the same level of energy service.
In the context of transportation, fuel efficiency commonly refers to the energy efficiency of a particular vehicle model, where its total output (range, or "mileage" in the US) is given as a ratio of range units per a unit amount of input fuel.
Geothermal power is energy generated by heat stored beneath the Earth's surface.
Green building is the practice of increasing the efficiency of buildings and their use of energy, water, and materials.
A green roof is a roof of a building that is partially or completely covered with vegetation and soil, or a growing medium, planted over a waterproofing membrane.
Hybrid Electric Vehicle
A hybrid electric vehicle is a vehicle which combines a conventional propulsion system with an on-board rechargeable energy storage system to achieve better fuel economy than a conventional vehicle.
Passive solar buildings aim to maintain interior thermal comfort throughout the sun's daily and annual cycles whilst reducing the requirement for active heating and cooling systems.
Photovoltaics, or PV for short, is a solar power technology that uses solar cells or solar photovoltaic arrays to convert light from the sun directly into electricity.
Plug-In Hybrid Electric Vehicle
A plug-in hybrid electric vehicle (PHEV) is a hybrid vehicle with batteries that can be recharged by connecting a plug to an electrical power source.