Issues and responses
Clean-energy vehicles are vehicles that use energy sources other than petroleum such as natural gas (CNG), electricity, methanol, hydrogen, or solar energy. These vehicles offer the advantages of reduced emissions of CO2 and other exhaust gases. Many clean-energy vehicles have been developed and some are already in operation, but they still present certain problems such as short traveling ranges and high operational costs. For this reason, they are at present used only for a limited number of applications and within limited areas. In order to increase their use, it will be necessary to resolve the various technical issues still outstanding and to build the fuel-supply stations and other infrastructural elements they require.

Electric vehicles

Electric vehicles guarantee zero emissions, almost no vehicle noise, and excellent energy efficiency. The source of the electricity they use, however, is mostly thermal power stations (60% in Japan) which emit large amounts of CO2. There is therefore a need to reevaluate the use of electric vehicles on the basis of their power source. Currently some 2,300 electric vehicles, ranging from scooters to small trucks, are in operation on public roads in Japan. Though their use is limited due to their restricted running performance and traveling distance, we can expect the range of application for electric vehicles to increase once high-performance, low-cost batteries are developed, more recharging stations are built and systems for recycling batteries are established.

Hybrid vehicles

Hybrid vehicles make efficient use of both an engine and another source of motive power, such as electricity or pressure. For example, a hybrid vehicle may use an electric motor for starting up and traveling at low speeds and a combination of electric motor and engine for accelerating and traveling at high speeds; it may store the energy generated by braking or slowing down as electricity or pressure and then use this stored energy as supplemental power for starting up and accelerating (parallel hybrid); or it may use an engine for charging and run on an electric motor (serial hybrid). Hybrid vehicles provide substantial advantages in terms of environmental protection, including outstanding fuel economy and a dramatic reduction in CO2 and other exhaust emissions.

CNG vehicles

Natural gas consists primarily of methane and automobiles generally use compressed natural gas (CNG). Natural gas also enables significant reductions in CO2 emissions. Although the distance traveled on one full tank is short, CNG vehicles offer the additional advantage of significantly reduced nitrogen oxide (NOx) and particulate matter (PM) emissions compared with vehicles powered by diesel fuel. For this reason, natural gas vehicles are being developed and used particularly for commercial purposes, such as in city bus transport and freight delivery. Some 1,400 CNG vehicles are currently in use in Japan.

Fuel cell-powered vehicles

Fuel cell-powered vehicles are electric vehicles equipped with fuel cells that function as power generators. Pollution-free fuel-cell vehicles fueled by hydrogen stored in a hydrogen-occluding alloy and only emitting water are now being developed. With respect to infrastructure requirements, in future fuel cell-powered vehicles running on methanol (the methanol is transformed into hydrogen) will likely be more feasible. However, a number of technical issues still need to be resolved in this regard.

Methanol vehicles
Methanol is a liquid fuel produced from natural gases and other elements which offers excellent storage and transportation properties for use in automobiles. The Otto-type methanol engine is being developed as an alternative to the conventional gasoline engine and a diesel-type methanol engine is also being developed as a way of reducing NOx and PM emissions. Some 300 methanol vehicles, mostly small trucks running on diesel methanol, are currently in use in Japan. Issues that have yet to be resolved include the need for improvement in the durability of injectors and spark and glow plugs, improved low-temperature starts and reduced aldehyde emissions on ignition.

LPG vehicles
PG (liquefied petroleum gas) is either propane or butane gas which is used in automobiles in liquid form. It has in fact been used for many years in taxis because of its low cost, but now LPG engines are increasingly being mounted in small trucks as an alternative to diesel engines in order to reduce NOx and PM vehicle emissions. Despite the lack of fuel-supply stations, LPG-powered vehicles offer many advantages over other types of clean-energy vehicles.

Solar cars

The solar car is a type of electric vehicle which uses solar cells to generate electricity to drive its motor. Japanese vehicle manufacturers have had great success in international solar-car races. In addition, some solar cars have been developed specifically for use on public roads. Solar cells do not yet offer sufficient performance for widespread use as energy sources for automobiles. They are also costly and take up considerable space. Nevertheless, solar cars are extremely attractive because they use the cleanest source of energy available--the sun. It is therefore hoped that the performance of solar cells will be significantly improved in future.