Hybrid Cars - Explained

Hybrid Electric Vehicles

Solar Heat

As long as the sun is going to the trouble of heating up the earth, we may as well take advantage of its efforts wherever we can. Solar heat, or solar thermal energy, reduces the demand for fossil fuels or electricity generated by fossil fuels. There are three main methods for doing this:

1. Passive solar energy for buildings. By planning to use available incoming solar energy, a building can reduce its heating requirements significantly without much added cost. Passive solar design includes use of south-facing windows and overhangs that are sized to allow sun to enter the building in the winter but that will block the summer sun. Use of high-heat-capacity materials in the area where the sun strikes provides some storage of heat during the most intense periods of sun and minimizes the likelihood of overheating. Passive solar design usually makes the most sense in new construction and is most effective in well-insulated structures.

2. Active solar energy for buildings. Commercially available solar heating systems that circulate a fluid (usually water or air) through solar collectors mounted on roofs or in yards can contribute to the heating needs of a building. The fluid is driven by a pump or fan, with heat either going directly into the building or warming a storage medium such as rocks or water. For many parts of the world, this will be a supplement to a primary system that does not use solar energy. China currently leads the world in making use of solar heating, with an estimated 80 percent of all installations worldwide. The Chinese solar heating panels are made from evacuated tubes rather than the fl at-plate designs used elsewhere.

3. Hot-water heating. Domestic hot-water heaters are probably the simplest and most widespread application of solar energy. These are well suited to warmer locations, where added costs are not needed to provide for freeze protection.

Geothermal Energy

Geothermal energy refers to producing heat from the earth. Theoretically, this potential resource alone can supply all the world’s energy needs if fully exploited. Some geothermal sites are near the surface and are readily accessible. Other sites require drilling to the layers of heated rock 10 km (6.2 miles) or more beneath the earth’s surface. At least 20 countries around the world are using geothermal energy, including Iceland, the United States, Italy, France, New Zealand, Mexico, Nicaragua, Costa Rica, Russia, the Philippines, Indonesia, China, and Japan. Kenya will soon be able to provide close to one-quarter of its electrical requirements using geothermal energy.

Geothermal electricity is generated by steam produced from underground heat turning a turbine. If the underground heat is not hot enough to produce steam on being brought to the surface [182°C (360°F)], the water in the geothermal reservoir is passed through a heat exchanger that transfers the heat to a separate pipe containing fluids with a much lower boiling point. Systems using this form of heat exchange (known as binary-cycle plants) have the advantages of lower cost and increased efficiency. Most geothermal power plants planned for construction are binary-cycle plants.

An interesting tradeoff to explore is whether it is more cost-effective to retrofit an existing coal-fired electricity plant to run off geothermal power rather than to go to the effort of capturing and storing the carbon dioxide emissions.

The temperature of the earth slightly below its surface is close to 55ºF (13ºC).

Geothermal energy also can be used for heating homes directly, as is being done in about 30,000 locations in Canada. Use of an underground heat sink (instead of colder winter air) enables electric heat pumps to be much more efficient.

This approach also can be used for cooling in parts of the world where it is needed.

Transportation-The Problem with Oil

AUTOMOBILE EFFICIENCY-HOW MUCH OIL

IS REALLY NEEDED TO MOVE JUST ONE PERSON?

One-quarter of the greenhouse gases generated throughout the world are a byproduct of transportation. In the United States, each person consumes, on average, 1.3 gallons of gasoline each day. This is 10 times greater than the average for the world. America continues to exhibit an infatuation with the automobile. Just as adolescents in industrialized countries count the days until they are able to drive, a similar interest in becoming mobile exists, and understandably so, throughout the emerging world.

Today, more than 7 out of 10 people in the United States own cars. In Europe, this number ranges from between 2 and 5 people out of 10. In the rapidly developing countries of China and India, that number is much less than 1 person out of every 10. If the rest of the world consumed gasoline at the rate that it is consumed in the United States, 10 times the current amount of greenhouse gases would be generated. Standard spark-ignition internal combustion engines today are perhaps 35 percent efficient under ideal conditions and 10–20 percent efficient in typical urban driving.

Considering that in today’s cars roughly 300 pounds of people and gear are moved through traffi c in a vehicle that is 10 times that weight, the overall efficiency of the fuel in performing its primary function is only about 1–2 percent. From this, we can take heart in how much room there is for improvement.

GENERATING LESS CARBON DIOXIDE

Gas–Electric Hybrids

Hybrid vehicles have two motors-an electric motor powered by a battery and a significantly downsized gasoline engine. The battery is charged by the operation of the gasoline engine and by regenerative braking, which recaptures mechanical energy that otherwise would be lost during braking.

Hybrid designs save energy in the following ways:

• They use the electric motor to provide power during acceleration. This enables the gasoline engine to be much less massive.

• When the vehicle brakes, the energy is recovered as electrical energy, which is then stored in the battery.

• Shutting down the engine when the vehicle is stopped eliminates waste.

This is especially true during city driving, where there can be a lot of unproductive idling time in traffic.

• Use the electric motor instead of the gasoline engine at slow speeds eliminates engine operation when it is least efficient.

• Power steering and other accessories can be shifted to more efficient electrical operation.

Transmission improvements also reduce loss of power. Use of nickel–metal hydride batteries similar to those used in satellites instead of lead–acid batteries increase the amount of energy a battery can hold and enhances its performance. A hybrid, such as the Toyota Prius, just about doubles the fuel economy of comparable nonhybrid cars, with even better numbers under congested urban conditions.

How much will this help? Let’s assume that 2 billion cars are expected to be on the world’s roads by the middle of the twenty-first century and that all achieve 60 miles per gallon (mpg) instead of the 30 mpg or so that is typical of today’s cars. This will prevent 1 billion tons of greenhouse gas emissions each year.

 Of course, there are differences in how automobile gasoline mileage is measured. More “realistic” driving conditions result in lower numbers. Still, the best-performing gas–electric cars such as the Prius show a factor of 2 improvement over comparable cars that do not have an electric motor. Moreover, improvements in how much energy can be stored in a given battery mass (called the specific power of the battery) can be expected to translate directly to improved hybrid car performance.

Plug-in Hybrids—Producing Much Less Carbon Dioxide

How about taking a hybrid car and putting in an even higher-performance battery that can be charged when the vehicle is not in operation? A supersized battery would reduce the need for the gasoline engine substantially. Basically, this would be an electric car with a small gasoline motor to supplement the power of the electric motor the small percentage of the time that greater acceleration is needed.

The gasoline motor also would extend the range of the vehicle so that it could continue back home or to the nearest place to recharge the battery if the battery runs out. Mileage approaching 100 mpg is reasonable to expect from this approach and since most car owners drive less than 35 miles (16 km) per day recharging overnight may be very feasible. Mileage in the range of 100 mpg can be accomplished on some current commercially obtained hybrid cars by using a precharged lithium ion battery rather than the standard nickel-metal hydride battery (http://auto.howstuffworks.com/100-mpg-news.htm ).

In a Prius “hypermileage” marathon, a team drove 1397 miles along a 15-mile course on 12.8 gallons in just under 48 hours. The result: an average 109.3 miles per gallon setting an unofficial world record. 120.6 mpg was established on the best segment of the course. The improved mileage came from driving techniques that minimized the amount of time that the engine runs and minimizes power fl owing to and from the battery. Although these techniques are not practical for most driving conditions, it serves as a proof of concept that significantly higher mileage is possible.

While operating by the electric motor, plug-in hybrids would not generate any greenhouse gases or any form of pollution, for that matter. However, since plug-in hybrids get some of their energy from the electrical power grid, the opportunity to reduce greenhouse emissions depends on the sources of the electricity used to charge the battery. If the electricity comes from a coal-fi red electrical power plant that does not capture and store its carbon dioxide emissions, the benefit t of the cleaner operation of the plug-in hybrid would be greatly diminished. If the electricity is produced without carbon dioxide emissions, the impact of the plug-in vehicle can be significant in addressing the transportation part of this problem.

Automobile designs that use precharged batteries (such as plug in hybrids) contribute to reducing global warming only to the extent that the electricity they use to charge their batteries does not generate greenhouse gases.