A hybrid is a vehicle that can run on two or more sources of energy, typically gasoline and electricity. The Toyota Prius is an example of a gas/electric hybrid, also referred to as a Hybrid Electric Vehicle (HEV). The Prius recovers energy from the braking system when the brakes are applied. Acceptance of HEVs was initially very slow due to the high price tag. Now, a decade later, more than 250,000 HEVs are manufactured per year. The Prius delivers over 40 mpg and is the most popular HEV. Honda, Ford and Chevy have marketed hybrids with various levels of success. All of the major players are now planning on producing green car hybrids. This is likely due to government imposed standards. A spokesman for GM predicted that 4 out of 5 cars sold in 2020 will be hybrids as a result of increasingly tougher emissions standards.
Although there is much hype about HEVs the environmental benefit tends to be somewhat overstated. HEVs are best suited for city driving where 10%–20% fuel can be saved, depending on driving conditions, the driver and car maintenance. On the highway fuel economy is slightly lower than traditional vehicles.
Look for Toyata to continue to lead the hybrid technology in the future. The longer term goal for the Prius is to deliver fuel efficiency up to 90 mpg. This will be achieved by making the vehicle lighter by using carbon fiber and aluminum.
Expect plug-in Lithium-Ion batteries within several years from most car manufacturers. Plug-ins can be charged at night when electricity demand is low. There are still battery issues to be worked out (safety, temperature, performance) before we can expect mass-production. Recently a fleet of Google Prius Hybrids were converted to plug-ins.
Prius Plug-In (converted)
Micro-Hybrids
An initiative similar to the HEV, but without the large battery, is called micro-hybrid. The micro-hybrid, also called “stop-start”, causes the engine to stop idling during car slow down and stop conditions. This technology saves an estimated 5% - 15% for city driving and comes with a much lower price tag than full blown hybrids. Stop-start was introduced by Peugeot-Citroën on the Citroën C3 in 2004 and will be installed on most Peugeots and Citroëns in the EU on or around 2010. 2008 Smart Fortwo Micro Hybrid
Supercapacitor Hybrids
Another variation of the gas/electric design is being developed by BMW. Instead of using a stack of rechargeable batteries, BMW is investigating use of super-capacitors, making the car lighter, 
faster and more efficient. As with hybrids, super-capacitors are charged by energy recovered by regenerative braking. The capacitors store less power but unlike rechargeable batteries, all 100% of what is stored can be utilized. The electricity is used during standing-start acceleration where an electric motor has an advantage over the internal combustion engine. The prohibitive price of the super-capacitors has prevented other manufacturers from entertaining this solution. 20% improvement in fuel efficiency has been reported.
BMW X3 Supercapacitor Hybrid
Copyright 2008