Dakota wrote: The reason I sometimes have trouble understanding alternative energy is that any alternative energy comes from another source of energy. How can you end up with more energy? I do understand downhill driving and braking as those external sources. I guess eliminating idling helps too. I was surprised that the city and highway mileage for Prius are so close. I thought it shines in city driving.
Good point. A major concept that most people don't understand is that gasoline automobile engines, despite all their technogeewhizdoodads, are horribly inefficient. This is because the wide range of conditions a car is under (acceleration, coasting, idling, etc) make it impossible to have the engine running for any period of time at high efficiency, not to mention that much of the energy goes into heat (that's why your engine is super hot to touch and you need a big radiator and cooling system to get rid of the heat without the engine melting into a puddle of iron and aluminum). Only about 15% of the energy in gasoline actually gets to the wheels to move the car. Even much of that 15% gets turned into heat by the braking, so if you recover any of the braking energy at all you can dramatically increase the efficiency, which is what the Prius does (though it only recovers about 15% of the braking energy). The Prius also shuts down the engine when it's not needed and avoids running it in low efficiency modes through computer switching of the engine/motor system.
You see, it's not that hybrids produce "new" energy. It's just that they don't waste such a massive amount of energy. Also note that when you are talking hybrids, you are NOT talking about alternative energy. A hybrid (i.e. Prius) still uses fossil fuel 100%. However, it doesn't waste as much energy as a regular gasoline car. "Alternative energy" refers to energy sources that are alternatives to fossil fuel energy sources. Fossil fuel is finite and therefore will run out. The earth only holds so much of it and we are fast using it all up. Alternative energy sources are those that have essentially infinite amounts of renewable energy (the sun, the tides, river systems, waves, etc). They won't run out until the sun-earth system disappears.
The Prius does in fact shine in city driving compared to other cars. Regular cars typically get 20 city, 35 highway. The Prius gets something like 45 city, 45 highway. This indicates that it does just a tiny bit better on the highway but is a massive improvement in the city.
Furthermore, the Prius will never come close to approaching electric cars or "plug in" hybrids in efficiency. In comparison to gasoline engines, electric motors are roughly 85% efficient at obtaining energy from batteries, and stationary natural gas power plants are better than 50% efficient. This means that any way of getting your wall socket electricity to power your car will make it hugely more efficient to a gasoline engine. This is why there is absolutely no doubt that electric cars are the future.
