Hazardous waste - Waste characterized as being flammable, oxidizing, corrosive, toxic, radioactive, explosive or with the potential to threaten public health or the environment.

Heating, ventilation and air conditioning (HVAC) - Climate control system of buildings; it ensures that room temperature, humidity and air flow are adequate to sustain a comfortable living environment.

High temperature superconducting transformers - Transformers that use high temperature superconducting materials to improve efficiency and reduce losses in electrical transmission.

High voltage transmission - Movement of voltage over long distances (greater than 35,000 volts).

Horizontal-axis wind turbines (HAWT) - Most common type of turbine, with the main rotor shaft and electrical generator at the top of a tower and is usually pointed into the wind.

Hot-summer/cold-winter zone (aka transition zone) - Region in China characterized by hot, humid summers and cold, humid winters. Temperature difference between day and night is relatively little and there is usually large amount of precipitation in a year. Zone includes the whole of Hubei, Hunan, Jiangxi, Anhui, Zhejiang provinces, Shanghai, Chongqing, the eastern parts of Sichuan and Guizhou provinces, the southern parts of Henan, Jiangsu, Shanxi and Gansu provinces and the northern parts of Fujian, Guangdong and Guangxi provinces.

Hybrid electric vehicles (HEV) - Vehicles that combine an internal combustion engine with an electric motor to drive the vehicles, and rely on gasoline or diesel and electricity storage batteries as power sources.

Hybrid locomotives - Locomotives that utilize a conventional power source (typically a diesel engine) in conjunction with a rechargeable energy storage system (REES). The REES is charged using the surplus energy from the power source and/or from regenerative breaking, and can then be used to provide energy for propusion.