A wind turbine whereby the rotor is connected to the generator through a series of gears. This method can provide faster speeds at the generator allowing for smaller generators.

Indirect costs are costs that are not directly accountable to a cost object (such as a particular project, facility, function or product).

An indicator diagram is a chart used to measure the thermal, or cylinder, performance of reciprocating steam and internal combustion engines and compressors.

Incineration is a waste treatment process that involves the combustion of organic substances contained in waste materials.

An incident ray is a ray of light that strikes a surface.

The inchworm motor is a device that uses piezoelectric actuators to move a shaft with nanometer precision.

An incandescent lamp or incandescent light globe is an electric light with a wire filament heated until it glows.

In-situ leaching, also called in-situ recovery or solution mining, is a mining process used to recover minerals such as copper and uranium through boreholes drilled into a deposit, in situ.

Impulse turbines change the direction of flow of a high velocity fluid or gas jet.

Electrical impedance is the measure of the opposition that a circuit presents to a current when a voltage is applied.

The effect that a particular energy source has on the environment.

In photometry, illuminance is the total luminous flux incident on a surface, per unit area.

Igneous rock, or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic.

IEC 61400 is an International Standard published by the International Electrotechnical Commission regarding wind turbines.

The ideal gas law, also called the general gas equation, is the equation of state of a hypothetical ideal gas.

An ideal gas is a theoretical gas composed of many randomly moving point particles that are not subject to interparticle interactions.

Ice storage air conditioning is the process of using ice for thermal energy storage.

An Ice house, or icehouse, is a building used to store ice throughout the year, commonly used prior to the invention of the refrigerator. Some were underground chambers, usually man-made, close to natural sources of winter ice such as freshwater lakes, but many were buildings with various types of insulation.

An ice cap climate is a polar climate where no mean monthly temperature exceeds 0 °C (32 °F).

Hywind Scotland is the world's first commercial wind farm using floating wind turbines, situated 29 kilometres (18 mi) off Peterhead, Scotland.