Zero emission refers to an engine, motor, or other energy source, that emits no waste products that pollutes the environment or disrupts the climate.
Zero emission engines
Vehicles and other mobile machinery used for transport (over land, sea, air, rail) and for other uses (agricultural, mobile power generation, etc) contribute heavily to climate change and pollution, so zero emission engines are an area of active research. These technologies almost in all cases include an electric engine powered by an energy source compact enough to be installed in the vehicle. These sources include hydrogen fuel cells, batteries, supercapacitors, and flywheel energy storage devices.
In some cases, such as compressed air engines, the engine may be mechanical rather than electrical. This mechanical engine is then powered by a passive energy source like compressed air, or a combustible non-polluting gas like hydrogen.
The above engines can be used in all vehicles, from cars to boats to propeller airplanes. For boats, energy sources such as nuclear power and solar panels can also be a viable option, in addition to traditional sails and turbosails.
Zero emission energy production
Current technology for power plants
Renewable energy sources, including solar power, wind power, tidal power and hydroelectric power. are often referred to as zero emission power, since their operation produce very few, or zero, emissions. On the other hand, the construction of such plants may involve emissions if the materials are created or assembled using equipment that produces emissions. For example, the production of high purity silicon for photovoltaic cells consumes large quantities of carbon, contributing to CO2 emissions, and this is also true for the production of steel and concrete for wind turbines and hydroelectric dams.
Similarly, Nuclear power plants do not emit significant amounts of pollutants during their operation, but the extraction of Uranium ore and construction of waste repositories usually involves machinery powered by gasoline. The construction of the plant itself also requires materials similar to those for renewable energy sources, tho because of nuclear powerplants large output per station, less so per amount of energy produced. All in all, emissions due to the operation, fuel production and waste management from nuclear powerplants are similar in magnitude to those of the renewables. However, though nuclear powerplants do not emit large amounts of pollution during normal operation, they do produce large quantities of radioactive waste, which has to be stored for several centuries before it's radioactivity has decreased to that of the uranium ore ( see Nuclear waste ). There is also concern that flawed designs or operation can lead to nuclear accidents, emitting radioactive pollutants, as happened during the Chernobyl disaster.
Potential future technologies
Many technological improvements have been suggested to reduce emissions from various energy sources. Carbon dioxide could be captured from fossil plants and stored underground rather than released into the atmosphere ( a technology known as carbon capture and storage ). Improved efficiency for solar cells, or cells made from novel materials, could offset the emissions associated with silicon production. New reactor technology could enable nuclear reactors to produce orders of magnitude more energy without increased emissions, and recycled or new materials could reduce the emissions associated with construction of windturbines and hydroelectric dams.
Non-zero-emission future technologies
To complement today's current zero-emission technology, many new energy sources with low emissions are being researched, including among others: Wave power, Nuclear fusion and Bio fuel. These non-zero-emission technologies, despite still emitting some degree of pollution are used to bridge the gap between the highly polluting technology (coal, fossil oil, ...) and the zero-emission technology. The reason why these technologies are used is often because they are in some cases cheaper or because they can be integrated faster (less machinery to alter).
A concept like vegetable oil economy produces emissions; however, the only emissions are things that were first taken out of the atmosphere when the plants were growing. So there is no net emission.