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Full Cell
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3) Fuel Cell Benefits
A) Environmental
B) High Efficiencies
C) Combined Cooling, Heat & Power (CCHP)
D) Reliability
E) Power Quality
F) Permitting Ease
G) Modularity
H) "Distributed Generation-ness"
4) Challenges
A) Cost Reduction
B) Fuel Flexibility
C) Endurance and Reliability
D) Infrastructure
E) Non-Technical Barriers
F) Innovative Technical Development
G) Other Issues: Government Regulation, Insurance, etc.
While the technology for these electrochemical power plants has existed since 1839, only recently have fuel cells gained popular recognition and come under serious consideration as an economically and technically viable power source.
Further more, fuel cells are considered a prime candidate for 'green' energy production: clean, quiet, and efficient.
1) What is a Fuel Cell and How Does It Work
Fuel cells are electrochemical devices that convert a fuel's chemical energy directly to electrical energy with high efficiency. With no internal moving parts, fuel cells operate similar to batteries. An important difference is that batteries store energy, while fuel cells can produce electricity continuously as long as fuel and air are supplied. Fuel cells electrochemically combine a fuel (typically hydrogen) and an oxidant without burning, thereby dispensing with the inefficiencies and pollution of traditional energy conversion systems.
Fuel cells forego the traditional fuel-to-electricity production route common in modern power production, which consists of heat extraction from fuel, conversion of heat to mechanical energy and, finally, transformation of mechanical energy into electrical energy. In a sense, our bodies operate like fuel cells because we oxidize hydrocarbon compounds in our food and release chemical energy without combustion.
Fuel cells function on the principal of electrolytic charge exchange between a positively charged anode plate and a negatively charged cathode plate. When hydrogen is used as the basic fuel, "reverse hydrolysis" occurs, yielding only water and heat as byproducts while converting chemical energy into electricity, as shown in Figure 1. Pollutant emissions are practically zero.
2) Fuel Cell Types
Fuel cell types are generally characterized by electrolyte material. The electrolyte is the substance between the positive and negative terminals, serving as the bridge for the ion exchange that generates electrical current.
While there are dozens of types of fuel cells, there are six principle kinds in various stages of commercial availability, or undergoing research, development and demonstration. These six fuel cell types are significantly different from each other in many respects; however, the key distinguishing feature is the electrolyte material.
They are:
1. Alkaline Fuel Cell (AFC)
2. Molten Carbonate Fuel Cell (MCFC)
3. Phosphoric Acid Fuel Cell (PAFC)
4. Proton Exchange Membrane Fuel Cell (PEMFC)
5. Solid Oxide Fuel Cell (SOFC)
6. Direct Methanol Fuel Cell
3) Fuel Cell Benefits
A) Environmental
B) High Efficiencies
C) Combined Cooling, Heat & Power (CCHP)
D) Reliability
E) Power Quality
F) Permitting Ease
G) Modularity
H) "Distributed Generation-ness"
A) Environmental Acceptability
The environmental benefits of fuel cells are some of the main motivating forces in their development. These benefits include the zero- or near-zero-emission of criteria pollutants (NOx, SOx, CO, and hydrocarbons) and very low noise emissions.
Environmentally friendly fuel cell properties could eliminate consumer contempt for power generation close to their houses and businesses. While most consumers probably would prefer to have conventional electricity generated at a location far from their homes due to the noise and pollution, the benign nature of fuel cells makes them non-offensive even if placed in residential communities.
B) High Efficiencies
Depending upon fuel cell type and design, fuel-to-electricity efficiency ranges from 30 to 60 percent (LHV). For hybrid fuel cell/gas turbine systems, electrical conversion efficiencies are expected to achieve over 70 percent (LHV). When byproduct heat is utilized, the total energy efficiency of fuel cell systems approaches 85 percent.
Stand-alone fuel cell systems have the capability of reaching efficiencies greater than 50 percent, even at relatively small sizes (e.g., 10 kW). Hence, fuel cell systems could reduce the impact of electricity production on global climate change by reducing the amount of greenhouse gases emitted into the atmosphere per kilowatt-hour of power. They would also reduce resource depletion and dependence on fossil fuels by allowing more power to be harnessed from the same amount of fuel.
Combined Heat and Power (CHP) or Combined Cooling, Heat and Power (CCHP) Capability
C) Combined Cooling, Heat & Power (CCHP)
High-quality heat is available for co-generation, heating, and cooling. Fuel cell exhaust heat is suitable for use in residential, commercial, and industrial co-generation applications.
The heat from a fuel cell can be used for a variety of purposes:
• Boilers: Two thermal loads for a boiler plant are make-up water and return water.If a boiler distribution system is maintained properly, make-up water requirements will likely be low.For high make-up water requirements, pre-heating boiler make-up water represents a good application for a fuel cell power plant. Load characteristics will depend on the loads on its thermal loop, time of year, and site specific factors.
• Domestic Hot Water(DHW) is used for a variety of purposes including showers, laundry, kitchen loads, etc.In dormitories or hotels, thermal loads typically peak in the morning and evening periods with little or no demand in the middle of the day and night.
• Space Heating Loops. Hot water space heating loops generally operate at temperatures that require the high-grade heat exchanger Thermal utilization is to the months where space heating is required.
• Swimming pools have both make-up water requirements (due to evaporation and spillage) and pool reheat requirements.The thermal load demand will vary depending on whether the pool is indoors or outdoors, the ambient temperature and humidity, the wind velocity, whether the pool is covered or not, the pool size and other site specific variables.
• Absorption Cooling Thermal Loads: Using a high-grade heat exchanger option, the fuel cell power plant can provide heat to an absorption chiller to provide cooling to a building. Absorption chillers create a thermal load for a fuel cell when no other loads are available. If electric rates are high in the cooling season, then displaced cooling using an absorption chiller can be cost-effective. Sites with longer cooling seasons or requiring continuous cooling (hospitals, etc.) are the best candidate sites for this technology
D) Reliability
Fuel cells are assumed to be superior to the grid because they are on site and subject to fewer disruptions (e.g. storms knocking down wires). With no moving parts, fuel cells will have less instances of failure than mechanical systems.
Today, the long-term performance and reliability of many of the fuel cell systems has not been significantly demonstrated to the market. Research, development and demonstration of fuel cell systems that will enhance the endurance and reliability of fuel cells are currently underway.
E) Power Quality
Fuel cell electrical output can be configured to be computer grade. For example, systems have been configured to provide 99.9999+ percent uptime. Furthermore, fuel cell power plants can be set up in a range of electrical outputs. Individual fuel cell systems also can be arranged in series to meet increasing load demands.
F) Permitting Ease
Permitting and licensing schedules are short due to the ease of siting. Furthermore, fuel cell power installations are exempt from air emission permitting requirementsin many U.S. states and provide flexibility under many federal, state and local air pollution standards.
G) Modularity
The fuel cell is inherently modular. It operates at near constant efficiency, independent of size and load. The fuel cell power plant can be configured in a wide range of electrical outputs, ranging from single kilowatt sizes up to multi-megawatt systems.
H) Distributed Generation
Distributed Generation (DG) refers to generation at or near the site of use (for example, at a near a building requiring power). Fuel cells are a form of DG, and can contribute to the establishment of a DG market because of their characteristics as described above. Instead of an electricity distribution infrastructure based on centralized power plants routing power through wires over long distances, fuel cells and DG make it attractive to spread small power plants throughout an electrical grid or a geographic area.
Such a configuration could:
• Reduce pollution
• Increase local and system reliability
• Increased power quality due to a potential freedom from troublesome frequency variations, voltage transients, dips, and surges. A fuel cell can be an attractive alternative to expensive uninterruptible power supplies, power-line filters, or energy storage systems used to condition grid electricity.
• Increase efficiency by reducing the distance electricity would have to travel from source to consumer.
• Reduce system maintenance cost (no transmission and distribution wires)
• Increased flexibility in system design, expansion and growth
• Reduction in customers' outage costs and experiences
• Increased response to changing loads
• Cogeneration benefits (heat capture)
• Reduction in time to respond to customers needs - fuel cell construction is quicker than central station units and large transmission improvements, making it easier to match incremental capacity additions to load growth. This reduces opportunity cost and risk relative to investing in large central station units.
• Customers are spending money installing power quality devices to alleviate power fluctuations, or bargaining for damage payments from generators. Fuel cell installations may mitigate or eliminate these situations.
From a global perspective, system reliability (availability) is extremely important for DP penetration in rural energy development. Remote locations need systems that will not breakdown and can be left unattended.
4) Challenges
A) Cost Reduction B) Fuel Flexibility
C) Endurance and Reliability
D) Infrastructure
E) Non-Technical Barriers
F) Innovative Technical Development
G) Other Issues: Government Regulation, Insurance, etc.
A) Cost Reduction
The high capital cost for fuel cells is by far the largest factor contributing to the limited market penetration of fuel cell technology. In order for fuel cells to compete realistically with contemporary power generation technology, they must become more competitive from the standpoint of both capital and installed cost (the cost per kilowatt required to purchase and install a power system).
In the stationary power market, fuel cells could become competitive if they reach an installed cost of $1,500 or less per kilowatt. Currently, the cost is in the $4,000+ range per kilowatt. In the automobile sector, a competitive cost is on the order of $60 - $100 per kilowatt, a much more stringent criterion.
The high capital cost (on a $/kW basis) today has lead to a significant effort focused cost reduction. Specific areas in which cost reductions are being investigated include:
1. Material reduction and exploration of lower-cost material alternatives
2. Reducing the complexity of an integrated system
3. Minimizing temperature constraints (which add complexity and cost to the system)
4. Streamlining manufacturing processes
5. Increasing power density (footprint reduction)
6. Scaling up production to gain the benefit of economies of scale (volume) through increased market penetration.
B) Fuel Flexibility
Fuel cells must be developed to use widely available fossil fuels, handle variations in fuel composition, and operate without detrimental impact to the environment or the fuel cell. The capability of running on renewable and waste fuels is essential to capturing market opportunities for fuel cells.
The primary fuel used in a fuel cell is hydrogen, which can be obtained from natural gas, gasoline, coal-gas, methanol, propane, landfill gas, biomass, anerobic digester, gas and other fuels containing hydrocarbons. Increasing the fuel flexibility of fuel cells implies that power generation can be assured even when a primary fuel source is unavailable. This will increase the initial market opportunities for fuel cells and enhance market penetration.
C) Endurance and Reliability
Fuel cells could be great sources of premium power if demonstrated to have superior reliability, power quality, and if they could be shown to provide power for long continuous periods of time. The high-quality power of fuel cells alone could provide the most important marketing factor in some applications. Coupled with longevity and reliability this could greatly advance fuel cell technology.
Although fuel cells have been shown to be able to provide electricity at high efficiencies and with exceptional environmental sensitivity, the long-term performance and reliability of certain fuel cell systems has not been significantly demonstrated to the market. Research, development and demonstration of fuel cell systems that will enhance the endurance and reliability of fuel cells are currently underway.
D) Infrastructure
There are many issues related to infrastructure. Some cross markets and some are market specific (e.g. fuel):
• Fuel Infrastructure
o Many of initial vehicles are hydrogen-based. Consequently, an infrastructure for producing, distributing, storing, delivering and maintaining hydrogen fuel is important.
o In the case of portable applications, the most likely fuel is methanol-based and will be sold in a cartridge-like format. An infrastructure for producing, distributing, storing, delivering and maintaining such a device is imperative to support such a market.
• Human Resource Infrastructure
o Service: This is a brand new technology crossing a diverse number of industries. Qualified service and maintenance personnel will be needed.
o Development: A critical need today is for qualified technical personnel to assist in the development and commercialization of these products.
E) Non-Technical Barriers
Over the next several years, RD&D will enable the widespread utilization of fuel cells for distributed power generation. However, there are other (non-technical) issues and barriers that must be addressed to enable this widespread use of fuel cells (as well as other distributed generation technologies). These issues include, but are not limited to:
• How will codes and standards for permitting be determined and ultimately enforced?
• Will unmanned operation be generally permitted?
• What siting requirements and processes will be required for fuel cells?
• What emissions regulations (if any) will fuel cells be subject to comply with?
• How will competition transition charges (CTC) be assessed?
• How will distribution charges be assessed?
• Can insurance for these installations be adequately supported and obtained?
• What interconnect standards will be set for distributed resources in various utility service territories?
• What depreciation schedules will be allowed?
The answers to these questions and others will dramatically impact the market penetration of fuel cell systems and other distributed generation technologies.
F) Innovative Technical Development
Fuel cells need to experience a few breakthroughs in technology development to become competitive with other advanced power generation technologies. These technological breakthroughs will likely occur either directly through support of innovative concepts, or as spin-offs to the thought process and work entailed in innovative concepts. These innovative concepts must be well grounded in science, but can differ from the traditional fuel cell RD&D in that they investigate the balance of plant, controls, materials, and other aspects of fuel cell technology that have not been previously investigated. Innovative and fruitful concepts might be found in these areas:
1. New fuel cell types
2. Contaminant tolerance (CO, sulfur)
3. New fuel cell materials (electrolyte, catalyst, anode and cathode)
4. New balance of plant (BOP) concepts (reformers, gas clean-up, water handling, etc.).
G) Other Issues: Government Regulation, Insurance, etc.
Other issues affecting fuel cell commercialization include yet-to-be-determined governmental rules and regulations regarding siting, insuring, and certifying fuel cell products.
Also, business issues such as the depreciation rate for fuel cell products and the manner banks lend money for purchasing fuel cells will affect the market introduction of products. In addition, regulatory issues concerning criteria pollutants could become more restrictive in the future, thereby facilitating the compulsory installation and use of fuel cells. Another significant boost for fuel cells' entry into the marketplace could be government subsidized credits and financial reward for the aversion or reduction of gases contributing to global climate change, such as carbon dioxide.
Source: http://www.nfcrc.uci.edu
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Hybrid cars
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1 - Gasoline Power vs. Electric Power
The gasoline-electric hybrid car is just what it sounds like -- a cross between a gasoline-powered car and an electric car. Let's start with a few diagrams to explain the differences between a gasoline-powered car and a typical electric car.
A gas-powered car has a fuel tank, which supplies gasoline to the engine. The engine then turns a transmission, which turns the wheels.
An electric car, on the other hand, has a set of batteries that provides electricity to an electric motor. The motor turns a transmission, and the transmission turns the wheels.
The hybrid is a compromise. It attempts to significantly increase the mileage and reduce the emissions of a gas-powered car while overcoming the shortcomings of an electric car. To be useful to you or me, a car must meet certain minimum requirements. The car should be able to:
· Drive at least 300 miles (482 km) before re-fueling
· Be refueled quickly and easily
· Keep up with the other traffic on the road
A gasoline car meets these requirements but produces a relatively large amount of pollution and generally gets poor gas mileage. An electric car, however, produces almost no pollution, but it can only go 50 to 100 miles (80 to 161 km) between charges. And the problem has been that the electric car is very slow and inconvenient to recharge. A gasoline-electric car combines these two setups into one system that leverages both gas power and electric power.
2 - Gasoline-electric Hybrid Structure
Gasoline-electric hybrid cars contain the following parts:
· Gasoline engine - The hybrid car has a gasoline engine much like the one you will find on most cars. However, the engine on a hybrid is smaller and uses advanced technologies to reduce emissions and increase efficiency.
· Fuel tank - The fuel tank in a hybrid is the energy storage device for the gasoline engine. Gasoline has a much higher energy density than batteries do. For example, it takes about 1,000 pounds of batteries to store as much energy as 1 gallon (7 pounds) of gasoline.
· Electric motor - The electric motor on a hybrid car is very sophisticated. Advanced electronics allow it to act as a motor as well as a generator. For example, when it needs to, it can draw energy from the batteries to accelerate the car. But acting as a generator, it can slow the car down and return energy to the batteries.
· Generator - The generator is similar to an electric motor, but it acts only to produce electrical power. It is used mostly on series hybrids (see below).
· Batteries - The batteries in a hybrid car are the energy storage device for the electric motor. Unlike the gasoline in the fuel tank, which can only power the gasoline engine, the electric motor on a hybrid car can put energy into the batteries as well as draw energy from them.
· Transmission - The transmission on a hybrid car performs the same basic function as the transmission on a conventional car. Some hybrids, like the Honda Insight, have conventional transmissions. Others, like the Toyota Prius, have radically different ones
The Mercedes-Benz M-Class HyPer -- a hybrid concept vehicle
You can combine the two power sources found in a hybrid car in different ways. One way, known as a parallel hybrid, has a fuel tank that supplies gasoline to the engine and a set of batteries that supplies power to the electric motor. Both the engine and the electric motor can turn the transmission at the same time, and the transmission then turns the wheels. The animation below shows a typical parallel hybrid. You'll notice that the fuel tank and gas engine connect to the transmission. The batteries and electric motor also connect to the transmission independently. As a result, in a parallel hybrid, both the electric motor and the gas engine can provide propulsion power.
By contrast, in a series hybrid, the gasoline engine turns a generator, and the generator can either charge the batteries or power an electric motor that drives the transmission. Thus, the gasoline engine never directly powers the vehicle. Take a look at the diagram of the series hybrid, starting with the fuel tank, and you'll see that all of the components form a line that eventually connects with the transmission.
The structure of a hybrid car harnesses two sources of power to increase efficiency and provide the kind of performance most of us are looking for in a vehicle.
3 - Hybrid-car Performance
The key to a hybrid car is that the gasoline engine can be much smaller than the one in a conventional car and therefore more efficient. Most cars require a relatively big engine to produce enough power to accelerate the car quickly. In a small engine, however, the efficiency can be improved by using smaller, lighter parts, by reducing the number of cylinders and by operating the engine closer to its maximum load.
There are several reasons why smaller engines are more efficient than bigger ones:
· The big engine is heavier than the small engine, so the car uses extra energy every time it accelerates or drives up a hill.
· The pistons and other internal components are heavier, requiring more energy each time they go up and down in the cylinder.
· The displacement of the cylinders is larger, so more fuel is required by each cylinder.
· Bigger engines usually have more cylinders, and each cylinder uses fuel every time the engine fires, even if the car isn't moving.
This explains why two of the same model cars with different engines can get different mileage. If both cars are driving along the freeway at the same speed, the one with the smaller engine uses less energy. Both engines have to output the same amount of power to drive the car, but the small engine uses less power to drive itself. But how can this smaller engine provide the power your car needs to keep up with the more powerful cars on the road?
Let's compare a car like the Chevy Camaro, with its big V-8 engine, to our hybrid car with its small gas engine and electric motor. The engine in the Camaro has more than enough power to handle any driving situation. The engine in the hybrid car is powerful enough to move the car along on the freeway, but when it needs to get the car moving in a hurry, or go up a steep hill, it needs help. That "help" comes from the electric motor and battery -- this system steps in to provide the necessary extra power.
The gas engine on a conventional car is sized for the peak power requirement (those few times when you floor the accelerator pedal). In fact, most drivers use the peak power of their engines less than one percent of the time. The hybrid car uses a much smaller engine, one that is sized closer to the average power requirement than to the peak power.
4 - Improving Fuel Economy
Besides a smaller, more efficient engine, today's hybrids use many other tricks to increase fuel efficiency. Some of those tricks will help any type of car get better mileage, and some only apply to a hybrid. To squeeze every last mile out of a gallon of gasoline, a hybrid car can:
· Recover energy and store it in the battery - Whenever you step on the brake pedal in your car, you are removing energy from the car. The faster a car is going, the more kinetic energy it has. The brakes of a car remove this energy and dissipate it in the form of heat. A hybrid car can capture some of this energy and store it in the battery to use later. It does this by using "regenerative braking." That is, instead of just using the brakes to stop the car, the electric motor that drives the hybrid can also slow the car. In this mode, the electric motor acts as a generator and charges the batteries while the car is slowing down.
· Sometimes shut off the engine - A hybrid car does not need to rely on the gasoline engine all of the time because it has an alternate power source -- the electric motor and batteries. So the hybrid car can sometimes turn off the gasoline engine, for example when the vehicle is stopped at a red light.
· Use advanced aerodynamics to reduce drag - When you are driving on the freeway, most of the work your engine does goes into pushing the car through the air. This force is known as aerodynamic drag. This drag force can be reduced in a variety of ways. One sure way is to reduce the frontal area of the car. Think of how a big SUV has to push a much greater area through the air than a tiny sports car. Reducing disturbances around objects that stick out from the car or eliminating them altogether can also help to improve the aerodynamics. For example, covers over the wheel housings smooth the airflow and reduce drag. And sometimes, mirrors are replaced with small cameras.
· Use low-rolling resistance tires - The tires on most cars are optimized to give a smooth ride, minimize noise, and provide good traction in a variety of weather conditions. But they are rarely optimized for efficiency. In fact, the tires cause a surprising amount of drag while you are driving. Hybrid cars use special tires that are both stiffer and inflated to a higher pressure than conventional tires. The result is that they cause about half the drag of regular tires.
· Use lightweight materials - Reducing the overall weight of a car is one easy way to increase the mileage. A lighter vehicle uses less energy each time you accelerate or drive up a hill. Composite materials like carbon fiber or lightweight metals like aluminum and magnesium can be used to reduce weight. All of the hybrid cars on the market utilize some or all of these efficiency tricks. We will be looking closely at the technology of the Honda Insight and the Toyota Prius.
The 2006 Honda Insight (left) and 2006 Toyota Prius
Although both of these cars are modified parallel hybrids, they are actually quite different in character. The Honda Insight and the Toyota Prius both have a gasoline engine, an electric motor and batteries, but that is where the similarities end.
2007 Hybrid Car Reviews
These 2007 hybrid car reviews cover every gas-electric hybrid vehicle on sale today. Prices and fuel economy -- both EPA ratings and our real-world results -- are included, along with a critique by the auto editors of Consumer Guide.
5 - List of 2007 hybrid cars
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Base Price Range
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EPA mpg Estimates
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CG Observed mpg
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2007 Honda hybrid cars
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2007 Honda Accord Hybrid
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$31,090 - $33,090
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28-35
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27.5
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2007 Honda Civic Hybrid
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$22,600 - $24,350
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49-51
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37.8-38.0
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2007 Lexus hybrid cars
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2007 Lexus GS 450h
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$54,000
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25-28
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22.7
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2007 Nissan hybrid cars
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2007 Nissan Altima Hybrid
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$24,400
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36-42
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n/a
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2007 Saturn hybrid cars
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2007 Saturn Aura Green Line
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$23,000 (estimated)
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29-35 (est)
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n/a
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2007 Saturn Vue Green Line
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$22,370
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27-32
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25.8-28.4
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2007 Toyota hybrid cars
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2007 Toyota Camry Hybrid
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$26,000
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38-40
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28.6-31.2
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2007 Toyota Highlander Hybrid
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$32,490 - $36,550
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27-31
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22.8-26.4
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2007 Toyota Prius
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$22,175 - $23,070
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51-60
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41.7-45.2
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Source: http://auto.howstuffworks.com/
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Geothermal energy
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The word geothermal has its roots in two Greek words, geo (earth) and therme (heat) and means Earth's heat and in accordance to that Earth's thermal energy is also called geothermal energy. Inner Earth's heat is the result of forming planets from dust and gases that happened more than 4 billions years ago, and since radioactive decompose of elements in rocks continuously regenerates this heat, geothermal energy is renewable energy resource. Basic medium that is transferring heat from inner to surface is water or steam, and this component is renewing itself on a way in which water from rains is bursting deep on fissures heating itself and circulates back to surface where it appears in shapes of geysers and hot springs.
Earth's Crust is from five to 50 kilometers deep and is composed of rocks. Substances from Inner Core are constantly getting on surface through volcanic vents and through leaks on ocean's bottom. Under Crust is a Mantle that is reaching to a deep of 2900 kilometers and is made of stuff rich with iron and magnesium. Underneath it all are two layers of core-liquid layer and solid layer, located precisely in planet's core. Radius of the Earth is about 6378 kilometers and nobody knows exactly how Earth's inner looks like, all that was said before are nothing but scientific presumptions of how the inner of the planet looks. These presumptions are based on experiments taken in conditions of high pressure and huge temperatures.
Earth has couple of layers. Main layers are outer hard core (Crust), liquid wrapper-mantle (Mantle), outer liquid core (Outer Core) and inner hard core (Inner core).
By dropping deeper through the Crust temperature rises approximately about 17 °C to 30 °C by every kilometer deeper (50 – 87 °F every one mile deeper). Under the crust there is Mantle that is composed of partly melted rocks and temperature of this layer is between 650 and 1250 °C (1200 – 2280 °F). In Earth's core temperatures could be according to some estimations between 4000 and 7000 °C (7200 – 12600 °F). Since heat is always transferring from hotter to colder parts, heat from inner Earth gets transferred to surface and this heat transfer is the major mover of tectonic plates. On places where tectonic plates are connected, leaking of magma to upper layers is possible and this magma then gets cooled creating in process new layer of the Earth's crust. When magma gets to surface it can create volcanoes, but in most cases stays beyond surface making huge reservoirs and here it's cooled in the process that lasts from 5000 to one million years. Areas underneath which these magma pools can be found have high temperature gradient which means that temperature rises very fast as the depth increases and these areas are therefore highly favorable for exploit of the geothermal energy.
Geothermal energy has huge potential because its quantity is 50000 times bigger from all energy that can be gained from oil and coal across the world. Geothermal resources are located from shallow surface all the way to couple of kilometers deep reservoirs of hot water and steam which could be brought to surface and there exploited. In nature geothermal energy is mostly in the form of volcanoes, hot water springs or wells and geysers. In some countries geothermal energy is being used for millenniums in form of baths and recreational-sanative bathing. However, progress in science didn't stop only in exploring healing effects of geothermal energy and has pushed use of geothermal energy in many different ways of which two take special place, namely its use in producing the electricity and its use in heating the households and industrial installments. Uses of geothermal energy for central heating of the buildings and for generating electricity are the main ways of its exploration, but not the only ones. Geothermal energy can be also used in many other ways and it's used for pasteurizing milk, paper manufacturing, in swimming pools, drying timber and wool, animal husbandry etc.
Main disadvantage when exploiting geothermal energy is the fact that there aren't many places on the Earth highly suitable for exploit. Best areas are on the edges of the tectonic plates, namely areas of high volcanic and tectonic activity. Next picture presents tectonic map of the world and areas suitable for exploiting geothermal energy.
Earth is divided to tectonic plates which are moving and colliding all the time, creating in process places suitable for exploit of the geothermal energy. Most suitable areas for exploiting this energy are located on so called Ring of Fire.
Electrical energy production
One of the most interesting forms of exploiting geothermal energy is production of electrical energy. Hot water and steam from Earth is used for initiation of generators and in this process there's no combustion of fossil fuels and as a result there's no harmful emissions of gases to the atmosphere, only water steam gets released. Additional advantage is that these power stations can be implemented in variety of different surroundings from farms, sensitive desert areas all the way to recreational-forest areas.
Beginnings of exploiting the Earth's heat for generating electrical energy are connected with small Italian place Landarello and the year 1904. This year marks beginning of experiments with this form of electricity production after steam was used for propulsion of the small turbine, which charged five light bulbs, and this experiment is considered to be first use of geothermal energy for electrical energy consumption. There in year 1911 building of first geothermal power station begun with power of 250 KW. That was the only geothermal power station in the world for almost half a century. Working principle is simple, cold water gets pumped on hot granite rocks near the surface and out comes hot steam to 200+ °C and under high pressure that steam then starts generators. All Landarello's installments had been destroyed in Second World War, then rebuilt and expanded and even today in use. This installment even today produces electricity for about million of households, namely almost 5000 GWh yearly gets produced, which is about 10 % of the world's electricity production from geothermal resources. Although geothermal energy is renewable energy resource, pressure of the steam in Landarello decreased for 30 % from year 1950.
Momentarily are in use three basic types of geothermal power stations:
Dry steam – extremely hot steam is used here, typically above 235 °C (445 °F). This steam is used for direct running of generators. This is the most simple and oldest principle and it's still in use because it's the far cheapest principle of generating electrical energy from geothermal resources. Earlier mentioned first geothermal power station in Landarello worked on this principle. The largest power station that is using this principle is at this moment located in northern California and it's called The Geysers and is producing electrical energy since 1960. Amount of produced electrical energy from this power station is still enough to supply city of the size like San Francisco.
Flash steam – here's used hot water from geothermal reservoirs that is under great pressure and on temperatures above 182 °C (360 °F). By pumping the water from these reservoirs towards power stations pressure gets decreased and hot water gets transformed to steam which then starts turbines. Water that wasn't transformed to steam is returning back to reservoir for purpose of another use. Majority of modern geothermal power stations are using this principle.
Binary cycle – Water used in binary cycle is colder than the water used by other principles of generating electrical energy from geothermal resources. In binary cycle hot water is used for heating the liquid that has significantly lower boiling temperature, and this liquid is then exhausted on temperature of the hot water, afterwards starting generators' turbines. Advantage of this principle is higher efficiency of the procedure and there's also much bigger availability of the necessary geothermal reservoirs than it is when using other procedures. Additional advantage is complete closeness of the system since used water is returning back to reservoir and with this loss of the heat is decreased and there's also almost any loss of water. Majority of newly planned geothermal power stations will use this principle.
Principle that will be used when building new power stations depends of type of geothermal energy resource, namely of temperature, depth and quality of water and steam in chosen region. In all cases condensed steam and geothermal liquid's remains are returning back to well increasing the endurance of geothermal resource.
This picture presents simplified principle of generating electrical energy from geothermal resources. Hot steam and water are used for moving the turbine's generators and used water and condensed steam are returning back to well.
Use of geothermal energy for other purposes
Another interesting form of exploiting geothermal energy is heating. The largest geothermal system used for heating is located on Iceland, in its capital Reykyavik and 89 % percent of households in Iceland are heated on this way. Although Iceland is by far largest exploiter of geothermal energy per capita with earlier mentioned number of 89 % of all household on Iceland heated on this way, Iceland is not alone in exploiting geothermal energy. Geothermal energy is also widely exploited in some areas of New Zealand, Japan, Italy, Philippines and some parts of the USA like San Bernardino in California and in capital of Idaho, Boise. Geothermal energy is also used in agriculture for increase of the crop. Water from geothermal reservoirs is used for heating greenhouses for production of flowers and vegetables. When heating greenhouses it's not only air that's heated, but also the soil on which plants grow. This is used for centuries in central Italy and Hungary and is momentarily covering 80% of energetic needs of greenhouses with exploit of geothermal energy. Heat pumps are another form of using the geothermal energy. Heat pumps are spending geothermal energy for circulation of geothermal liquid that is later used for heating, cooling, cooking and preparation of hot water and on this way need for electrical energy gets significantly decreased. There is another wide specter of geothermal energy's use but there's no need to explaining it all on detailed way. Some other exploits are for instance fish breeding, different types of industrial use, balneology - use for recreation and healing (hot springs bathing), etc.
 One of wells of hot water on Iceland suitable for exploit of geothermal energy. Iceland is the state that uses by far its natural location for exploit of the geothermal energy.
Conclusion
Since estimated total amount of geothermal energy that could be used is significantly bigger than the total quantity of energy resources based on oil, coal and natural gas all together, geothermal energy should be having more significant impact. Especially since it's cheap, renewable energy resource that is also ecologically acceptable. But since geothermal energy isn't easily available on all areas, at least areas where this energy is easy available should be exploited (edges of tectonic plates) because this could soften the pressure on fossil fuels helping Earth to recover from dangerous greenhouse gases.
Source: http://www.our-energy.com
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Tankless Water Heater
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What is a Tankless Water Heater?
Tankless Water Heaters, also called Instantaneous or Demand Water Heaters, provide hot water only as it is needed. Traditional storage water heaters produce standby energy losses that cost you money. We do not leave our homes heated while vacationing. We only heat our homes when there is a demand for heat. In the same way, a Tankless Water Heater is used only when there is a demand for hot water.
How do Tankless Water Heaters work?
Tankless Water Heaters heat water directly without the use of a storage tank. Therefore, they avoid the standby heat losses associated with storage water heaters. When a hot water tap is turned on, cold water travels through a pipe into the unit. In an electric Tankless Water Heater an electric element heats the water. In a gas-fired Tankless Water Heater a gas burner heats the water. As a result, Tankless Water Heaters deliver a constant supply of hot water. You don't need to wait for a storage tank to fill up with enough hot water. Typically, Tankless Water Heaters provide hot water at a rate of 2 – 5 gallons (7.6 – 15.2 liters) per minute. Typically, gas-fired Tankless Water Heaters will produce higher flow rates than electric Tankless Water Heaters. Some smaller Tankless Water Heaters, however, cannot supply enough hot water for simultaneous, multiple uses in large households. For example, taking a shower and running the dishwasher at the same time can stretch a Tankless Water Heater to its limit. To overcome this problem, you can install a “whole house” type Tankless Water Heater or install two or more Tankless Water Heaters, connected in parallel for simultaneous demands of hot water. You can also install separate Tankless Water Heaters for appliances—such as a clothes washer or dishwater—that use a lot of hot water in your home.
Other applications for Tankless Water Heaters include the following:
- Remote BBQ or outdoor sink
- Poolhouse or pool shower
- Remote bathrooms or hot tubs
- To serve as a booster, eliminating long pipe runs, for solar water heating systems, dishwashers and sanitation
For homes that use 41 gallons or less of hot water daily, Tankless Water Heaters can be 24% – 34% more energy efficient than conventional storage tank water heaters. They can be 8% – 14% more energy efficient for homes that use a lot of hot water, around 86 gallons per day. You can achieve an even greater energy savings of 27% – 50% if you install a Tankless Water Heater at each hot water outlet.
Selecting a Tankless Water Heater
Before buying a Tankless Water Heater, consider the following:
- Fuel Type
- Location, Size and Demand
- Application
1. Fuel Type
The first thing that you'll need to decide when selecting a Tankless Water Heater is the fuel type. You will need to select between an Electric Tankless Water Heater (like Eemax Tankless Water Heaters or Stiebel Eltron Tankless Water Heaters) or a Gas-Fired Tankless Water Heater (like Rheem Tankless Water Heaters).
If you plan to purchase an Electric Tankless Water Heater, consider the Electrical Requirements:
- Voltage
- Amperage
- Circuit Breaker
Voltage:
Many retailers sell units that will accommodate 110V, 120V, 208V, 220V, 240V, and 277V.
Amperage
Different Electric Tankless Water Heaters will have various requirements in amp draw. You will want to ensure that you can support the electrical demands of your Electric Tankless Water Heater.
Circuit Breaker
You must ensure that you have a circuit or circuits that will support your Electric Tankless Water Heater. It may be necessary to put your Electric Tankless Water Heater on its own circuit or circuits.
You should consult with a qualified, licensed electrician for more information.
If you plan to purchase a Gas-Fired Tankless Water Heater, consider the Gas-Type and Venting Requirements: You will first need to identify whether your gas type is Natural Gas or Propane. It is imperitive that you examine your current gas line to ensure that it will meet the requirments of your new Gas-Fired Tankless Water Heater. The requirements of the Tankless Water Heater may exceed that of your existing tank-style water heater. Next, you will need to consider venting requirements for your specific installation scenario. There are a few important things to keep in mind when purchasing the gas venting accessories for your Gas-Fired Tankless Water Heater. Be sure that you purchase Category III stainless steel (UL1738 certified) venting for your Gas-Fired Tankless Water Heater. "Type B" venting accessories are not acceptable. Also, be sure to check local building code to ensure that your specific needs will be completely met. Additionally, many Tankless Water Heater manufacturers offer gas venting "kits". It is recommended that customers evaluate the needs of their specific installation to ensure that they will be getting all of the necessary gas venting accessories. Depending on where you will be installing the Tankless Water Heater, a pre-made kit will probably not meet your needs. Ensure that you measure out the vent route and consider where the discharge will go through the wall or ceiling, consider the necessary clearances, and consider ample access to air for combustion, then buy the appropriate gas venting pieces. *Note: Gas-Fired Tankless Water Heaters may still require a minimal electrical connection. Be sure to review installation requirements for the units you are considering for purchase.
2. Location, Size, and Demand
When deciding which Tankless Water Heater to purchase, you will also need to consider where you will need hot water. Are you looking for a unit that will heat the water at one bathroom sink (single point application), an entire bathroom (multipoint application), or an entire house, apartment, or condo (whole house application)? It is important to recognize the number of fixtures that will require hot water. Each fixture will have its own demands. The chart below illustrates the typical flow rates (demand) for some standard fixtures:
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Typical Flow Rates in Gallons per Minute (gpm)
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Fixture Type
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Lavatory
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Bathtub
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Shower
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Kitchen Sink
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Pastry Sink
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Laundry Sink
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Dish-washer
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Flow Rates
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0.5
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2.0 – 4.0
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1.5 – 3.0
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1.0 – 1.5
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1.5 – 2.5
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2.5 – 3.0
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1.0 – 3.0
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The flow rate is especially important, since Tankless Water Heaters will generate a temperature rise based on the flow rate demanded.
For example, a Stiebel Eltron Tempra 12, running on 240 Volt power, will raise the water temperature by 54°F at 1.5 gpm, 36°F at 2.25 gpm, and 27°F at 3.0 gpm, above the ambient incoming water temperature, up to 125°F.
A larger unit, like the Stiebel Eltron Tempra 36, running on 240 Volt power, will raise the water temperature by 92°F at 1.5 gpm, 92°F at 2.25 gpm, and 82°F at 3.0 gpm, above the ambient incoming water temperature, up to 125°F.
Temperature Rise Based on Flow Rate, Up to 125°F
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Flow Rate
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1.5 gpm
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2.25 gpm
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3.0 gpm
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Tempra 12
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54°F
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36°F
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27°F
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Tempra 36
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92°F
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92°F
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82°F
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This means that if you are using a 1.5 gpm shower and a 1.5 gpm kitchen sink simultaneously, a total demand of 3.0 gpm, the Stiebel Eltron Tempra 12 will raise the temperature 27°F, whereas the Stiebel Eltron Tempra 36 will raise the temperature 82°F.
Next, you should look at your ambient incoming water temperature. If you live in a cold climate, like New York, your incoming water temperature will likely be much lower than if you live in a warm climate, like Florida. Your best bet is to find out how much temperature rise you will need in order for your hot water to reach the desired heat. If the ambient incoming water temperature for your shower is 65°F, you are using a 2.0 gpm shower, and you want to raise that temperature to 115°F, you will want to look for a Tankless Water Heater that will provide at least a 50°F temperature rise at 2.0 gpm (115°F - 65°F = 50°F). However, if you anticipate additional simultaneous demand, such as the hot water from a sink being used while someone is showering, you will need to add the sink's gpm to the shower's gpm in order to determine your overall gpm demand and then find the temperature rise necessary to meet your overall needs.
3. Application
You may have a specific application in mind for your Tankless Water Heater. Here are a few examples of the different models and their functionality for a specific application:
Single Point Application
A single point application is one where only one fixture will require an Electric Tankless Water Heater.
Eemax Flow Controlled
The "Flow Controlled" range of water heaters from Eemax are ideally suited to serve two points, like two sinks, in close proximity.
Thermostatic
The Thermostatic Tankless Water Heater serves as a booster for temperature loss from long pipe runs, dishwashers and sanitation. Thermostatic units are good for applications where precise temperature control is essential; such as schools, hospitals and laboratories.
Eemax Series Two
Eemax Series Two units are ideally suited for residential showers, entire bathrooms, smaller houses, condos, summer cabins and apartments. They will also accommodate industrial boosters, higher flow rate applications such as wash down stations and higher flow rate accurate temperature control applications such as photo labs.
Whole House Indoor Use
Larger Whole House units are designed to serve an entire house, apartment, condo, or cabin, where multiple points of use will exist.
Whole House Outdoor Use
Larger Whole House units are designed to serve an entire house, apartment, condo, or cabin, where multiple points of use will exist.
Tankless Water Heater Installation and Maintenance
Proper installation and maintenance of your Tankless Water Heater can optimize its energy efficiency.
Proper installation depends on many factors. These factors include climate and local building code requirements. You should have a qualified, licensed plumbing and heating contractor install your Tankless Water Heater.
Do the following when selecting a contractor:
- Request cost estimates in writing
- Ask for references
- Check the company with your local Better Business Bureau
- Confirm the company will obtain a local permit, if necessary, and understands local building codes
Be sure you contractor first consults the manufacturer’s installation and instruction materials. Manufacturers usually provide the necessary installation and instruction manuals with the product. Your contractor should also contact your municipality for information about obtaining a permit, if necessary, and about local water heater installation codes.
Many Tankless Water Heaters have a life expectancy of more than 20 years. They also have easily replaceable parts that extend their life by many more years. In contrast, storage water heaters last 10 – 15 years.
You should consult the manufacturer's website or literature, such as the manual, for detailed warranty information.
Periodic water heater maintenance can significantly extend your water heater's life and minimize loss of efficiency. Read your owner's manual for specific maintenance recommendations.
Source: http://www.tanklesswaterheaterguide.com/
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Compact fluorescent light bulbs
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Compact fluorescent light bulbs save consumers money — and their use can help slow global warming. So why haven't they come into widespread use yet?
A compact fluorescent light bulb (CFL) is a tiny version of the long overhead lights in your office. It's twisted into a spiral. The CFL fits into the same fixtures where you use regular incandescent bulbs. The CFLs cost more, but they use about one-third of the electricity of the incandescent bulbs.
Utilities and local governments have tried giving them away to promote switching over to CFLs.
Wal-Mart hopes to more than double its sales of them in 2007. |
"We are committed to selling 100 million CFL bulbs this year," said Andy Rubin, Wal-Mart vice president for sustainability.
He said one CFL should last five years, and the customer's electric bills should be 50 cents to 75 cents lower each month as a result of switching from one standard bulb to one compact fluorescent bulb.
If the nation's largest retailer were to meet its goal of selling 100 million CFL bulbs, the aggregate electric bill savings would be $3 billion, according to Rubin.
When Wal-Mart itself switched to CFLs in its ceiling-fan-lights displays, it saved $8 million a year.
"There is a real desire right now for action," Rubin said. By buying CFLs, customers know they are helping curb greenhouse gases. "Everyone can do this."
Brian Huyser, creator of onebillionbulbs.com, believes in that message so much that he started a Web site preaching the gospel of CFLs.
The inspiration was a Discovery Channel documentary on global warming. The narrator said, "If each family switched out one bulb, it would be the equivalent of taking one million cars off the road."
"I went to bed that night intrigued," Huyser said. The next morning, he decided to start onebillionbulbs.com. "After all, what could be easier than changing a light bulb?"
But Randall Stross's experience with CFLs may demonstrate one of the hurdles. Stross, author of The Wizard of Menlo Park, writes about how Americans clung to their gas lights at first, even though they were impressed with the quality of Thomas Edison's electric lights.
In the case of CFLs at his own house, Stross finds their light quality a bit lacking — and he's not the only one. As an experiment, he put one in the hall and didn't tell anyone.
After a month, his son asked, "Would you please fix the light in the hall?"
"This seems like an ethereal, intangible quality, and one that can't be weighed in the same balance of the very fate of the planet," Stross said. "But we have always taken the quality of light very seriously."
Source: NPR.org
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Fluorescent Lamps
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How Fluorescent Lamps Work
You see fluorescent lighting everywhere these days -- in offices, stores, warehouses, street corners... You'll even find fluorescent lamps in peoples' homes. But even though they're all around us, these devices are a total mystery to most people. Just what is going on inside those white tubes?
In this article, we'll find out how fluorescent lamps emit such a bright glow without getting scalding hot like an ordinary light bulb. We'll also find out why fluorescent lamps are more efficient than incandescent lighting, and see how this technology is used in other sorts of lamps.
Let There Be Light
To understand fluorescent lamps, it helps to know a little about light itself. Light is a form of energy that can be released by an atom. It is made up of many small particle-like packets that have energy and momentum but no mass. These particles, called light photons, are the most basic units of light.
Atoms release light photons when their electrons become excited. If you've read How Atoms Work, then you know electrons are the negatively charged particles that move around an atom's nucleus (which has a net positive charge). An atom's electrons have different levels of energy, depending on several factors, including their speed and distance from the nucleus. Electrons of different energy levels occupy different orbitals. Generally speaking, electrons with greater energy move in orbitals farther away from the nucleus.
When an atom gains or loses energy, the change is expressed by the movement of electrons. When something passes energy on to an atom -- heat, for example -- an electron may be temporarily boosted to a higher orbital (farther away from the nucleus). The electron only holds this position for a tiny fraction of a second; almost immediately, it is drawn back toward the nucleus, to its original orbital. As it returns to its original orbital, the electron releases the extra energy in the form of a photon, in some cases a light photon.
The wavelength of the emitted light depends on how much energy is released, which depends on the particular position of the electron. Consequently, different sorts of atoms will release different sorts of light photons. In other words, the color of the light is determined by what kind of atom is excited.
This is the basic mechanism at work in nearly all light sources. The main difference between these sources is the process of exciting the atoms. In an incandescent light source, such as an ordinary light bulb or gas lamp, atoms are excited by heat; in a light stick, atoms are excited by a chemical reaction. Fluorescent lamps have one of the most elaborate systems for exciting atoms, as we'll see in the next section.
Down the Tubes
The central element in a fluorescent lamp is a sealed glass tube. The tube contains a small bit of mercury and an inert gas, typically argon, kept under very low pressure. The tube also contains a phosphor powder, coated along the inside of the glass. The tube has two electrodes, one at each end, which are wired to an electrical circuit. The electrical circuit, which we'll examine later, is hooked up to an alternating current (AC) supply.
When you turn the lamp on, the current flows through the electrical circuit to the electrodes. There is a considerable voltage across the electrodes, so electrons will migrate through the gas from one end of the tube to the other. This energy changes some of the mercury in the tube from a liquid to a gas. As electrons and charged atoms move through the tube, some of them will collide with the gaseous mercury atoms. These collisions excite the atoms, bumping electrons up to higher energy levels. When the electrons return to their original energy level, they release light photons.
As we saw in the last section, the wavelength of a photon is determined by the particular electron arrangement in the atom. The electrons in mercury atoms are arranged in such a way that they mostly release light photons in the ultraviolet wavelength range. Our eyes don't register ultraviolet photons, so this sort of light needs to be converted into visible light to illuminate the lamp.
This is where the tube's phosphor powder coating comes in. Phosphors are substances that give off light when they are exposed to light. When a photon hits a phosphor atom, one of the phosphor's electrons jumps to a higher energy level and the atom heats up. When the electron falls back to its normal level, it releases energy in the form of another photon. This photon has less energy than the original photon, because some energy was lost as heat. In a fluorescent lamp, the emitted light is in the visible spectrum -- the phosphor gives off white light we can see. Manufacturers can vary the color of the light by using different combinations of phosphors.
Conventional incandescent light bulbs also emit a good bit of ultraviolet light, but they do not convert any of it to visible light. Consequently, a lot of the energy used to power an incandescent lamp is wasted. A fluorescent lamp puts this invisible light to work, and so is more efficient. Incandescent lamps also lose more energy through heat emission than do fluorescent lamps. Overall, a typical fluorescent lamp is four to six times more efficient than an incandescent lamp. People generally use incandescent lights in the home, however, since they emit a "warmer" light -- a light with more red and less blue.
As we've seen, the entire fluorescent lamp system depends on an electrical current flowing through the gas in the glass tube. In the next section, we'll see what a fluorescent lamp needs to do to establish this current.
Cooking with Gas
In the last section, we saw that mercury atoms in a fluorescent lamp's glass tube are excited by electrons flowing in an electrical current. This electrical current is something like the current in an ordinary wire, but it passes through gas instead of through a solid. Gas conductors differ from solid conductors in a number of ways.
In a solid conductor, electrical charge is carried by free electrons jumping from atom to atom, from a negatively-charged area to a positively-charged area. As we've seen, electrons always have a negative charge, which means they are always drawn toward positive charges. In a gas, electrical charge is carried by free electrons moving independently of atoms. Current is also carried by ions, atoms that have an electrical charge because they have lost or gained an electron. Like electrons, ions are drawn to oppositely charged areas.
To send a current through gas in a tube, then, a fluorescent light needs to have two things:
1. Free electrons and ions
2. A difference in charge between the two ends of the tube (a voltage)
Generally, there are few ions and free electrons in a gas, because all of the atoms naturally maintain a neutral charge. Consequently, it is difficult to conduct an electrical current through most gases. When you turn on a fluorescent lamp, the first thing it needs to do is introduce many new free electrons from both electrodes.
There are several different ways of doing this, as we'll see in the next couple of sections.
Start it Up
The classic fluorescent lamp design, which has fallen mostly by the wayside, used a special starter switch mechanism to light up the tube. You can see how this system works in the diagram below.
When the lamp first turns on, the path of least resistance is through the bypass circuit, and across the starter switch. In this circuit, the current passes through the electrodes on both ends of the tube. These electrodes are simple filaments, like you would find in an incandescent light bulb. When the current runs through the bypass circuit, electricity heats up the filaments. This boils off electrons from the metal surface, sending them into the gas tube, ionizing the gas.
At the same time, the electrical current sets off an interesting sequence of events in the starter switch. The conventional starter switch is a small discharge bulb, containing neon or some other gas. The bulb has two electrodes positioned right next to each other. When electricity is initially passed through the bypass circuit, an electrical arc (essentially, a flow of charged particles) jumps between these electrodes to make a connection. This arc lights the bulb in the same way a larger arc lights a fluorescent bulb.
One of the electrodes is a bimetallic strip that bends when it is heated. The small amount of heat from the lit bulb bends the bimetallic strip so it makes contact with the other electrode. With the two electrodes touching each other, the current doesn't need to jump as an arc anymore. Consequently, there are no charged particles flowing through the gas, and the light goes out. Without the heat from the light, the bimetallic strip cools, bending away from the other electrode. This opens the circuit.
By the time this happens, the filaments have already ionized the gas in the fluorescent tube, creating an electrically conductive medium. The tube just needs a voltage kick across the electrodes to establish an electrical arc. This kick is provided by the lamp's ballast, a special sort of transformer wired into the circuit.
When the current flows through the bypass circuit, it establishes a magnetic field in part of the ballast. The flowing current maintains this magnetic field. When the starter switch is opened, the current is briefly cut off from the ballast. The magnetic field collapses, which creates a sudden jump in current -- the ballast releases its stored energy.
This surge in current helps build the initial voltage needed to establish the electrical arc through the gas. Instead of flowing through the bypass circuit and jumping across the gap in the starter switch, the electrical current flows through the tube. The free electrons collide with the atoms, knocking loose other electrons, which creates ions. The result is a plasma, a gas composed largely of ions and free electrons, all moving freely. This creates a path for an electrical current.
The impact of flying electrons keeps the two filaments warm, so they continue to emit new electrons into the plasma. As long as there is AC current, and the filaments aren't worn out, current will continue to flow through the tube.
The problem with this sort of lamp is it takes a few seconds for it to light up. These days, most fluorescent lamps are designed to light up almost instantly. In the next section, we'll see how these modern designs work.
Light Right Away
Today, the most popular fluorescent lamp design is the rapid start lamp. This design works on the same basic principle as the traditional starter lamp, but it doesn't have a starter switch. Instead, the lamp's ballast constantly channels current through both electrodes. This current flow is configured so that there is a charge difference between the two electrodes, establishing a voltage across the tube.
When the fluorescent light is turned on, both electrode filaments heat up very quickly, boiling off electrons, which ionize the gas in the tube. Once the gas is ionized, the voltage difference between the electrodes establishes an electrical arc. The flowing charged particles (red) excite the mercury atoms (silver), triggering the illumination process.
An alternative method, used in instant-start fluorescent lamps, is to apply a very high initial voltage to the electrodes. This high voltage creates a corona discharge. Essentially, an excess of electrons on the electrode surface forces some electrons into the gas. These free electrons ionize the gas, and almost instantly the voltage difference between the electrodes establishes an electrical arc.
No matter how the starting mechanism is configured, the end result is the same: a flow of electrical current through an ionized gas. This sort of gas discharge has a peculiar and problematic quality: If the current isn't carefully controlled, it will continually increase, and possibly explode the light fixture. In the next section, we'll find out why this is and see how a fluorescent lamp keeps things running smoothly.
Ballast Balance
We saw in the last section that gases don't conduct electricity in the same way as solids. One major difference between solids and gases is their electrical resistance (the opposition to flowing electricity). In a solid metal conductor such as a wire, resistance is a constant at any given temperature, controlled by the size of the conductor and the nature of the material.
In a gas discharge, such as a fluorescent lamp, current causes resistance to decrease. This is because as more electrons and ions flow through a particular area, they bump into more atoms, which frees up electrons, creating more charged particles. In this way, current will climb on its own in a gas discharge, as long as there is adequate voltage (and household AC current has a lot of voltage). If the current in a fluorescent light isn't controlled, it can blow out the various electrical components.
A fluorescent lamp's ballast works to control this. The simplest sort of ballast, generally referred to as a magnetic ballast, works something like an inductor. A basic inductor consists of a coil of wire in a circuit, which may be wound around a piece of metal. If you've read How Electromagnets Work, you know that when you send electrical current through a wire, it generates a magnetic field. Positioning the wire in concentric loops amplifies this field.
This sort of field affects not only objects around the loop, but also the loop itself. Increasing the current in the loop increases the magnetic field, which applies a voltage opposite the flow of current in the wire. In short, a coiled length of wire in a circuit (an inductor) opposes change in the current flowing through it (see How Inductors Work for details). The transformer elements in a magnetic ballast use this principle to regulate the current in a fluorescent lamp.
A ballast can only slow down changes in current -- it can't stop them. But the alternating current powering a fluorescent light is constantly reversing itself, so the ballast only has to inhibit increasing current in a particular direction for a short amount of time. Check out this site for more information on this process.
Magnetic ballasts modulate electrical current at a relatively low cycle rate, which can cause a noticeable flicker. Magnetic ballasts may also vibrate at a low frequency. This is the source of the audible humming sound people associate with fluorescent lamps.
Modern ballast designs use advanced electronics to more precisely regulate the current flowing through the electrical circuit. Since they use a higher cycle rate, you don't generally notice a flicker or humming noise coming from an electronic ballast. Different lamps require specialized ballasts designed to maintain the specific voltage and current levels needed for varying tube designs.
Fluorescent lamps come in all shapes and sizes, but they all work on the same basic principle: An electric current stimulates mercury atoms, which causes them to release ultraviolet photons. These photons in turn stimulate a phosphor, which emits visible light photons. At the most basic level, that's all there is to it!
Source: http://home.howstuffworks.com
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