- Количество слайдов: 105
Renewable Energy #1 Electricity Definitions
Everything made of Atoms
Electrons flow when the electrical balance is upset Current- movement of electrons between atoms.
Current n n Flow of electrons can be measured in units called AMPERES “Amps” 6. 28 x 1018 electrons per second = 1 Amp What is always produced when current flows? HEAT
Conductors n n n Materials that allow easy electron shifting. Examples include: gold, platinum, aluminum, copper, silver. What’s most common in homes?
Resistance n n Even best conductors have some resistance. Examples are lights, motors, heaters Measured in ohms Like water flowing through a pipe
n n n Longer, smaller diameter wires have more resistance than bigger diameter ones. Heat and or light builds up. Incandescent bulbs work this way
Insulators n n n Items from which the electrons are not easily “freed” Examples: glass, rubber, wood, porcelain, plastic Opposite of a conductor
Voltage Measurement of a potential difference between two points along a conductor. (It is the pressure that makes current flow).
Voltage supplied by generator or battery
Power n n n Measurement of work an electric current can perform in a given time. Measurement of the rate at which it can be converted into some other form of energy such as light, heat, or mechanical force. Measured in watts or k. W (1000 watts)
Higher watts requires more electricity n n n More watts don’t mean higher output though. Appliances rated in watts. Home usage measured in k. W and power plants in m. W megawatts output
Horsepower In motors, 1 Hp = 746 watts Watts = voltage x amperage
Energy n n The work done over a period of time. Example of usage: Blow dryer used 2 hours each week and rated at 1500 watts. 1500 x 2 = 3000 watts. 3000 / 1000 (conversion to k. W) = 3 k. W used
Energy Use Calculations n n Need this information 1 the rated power of the appliance, usually given in watts; 2 the length of operating time, 3 the cost of electricity.
Example n n A tool has a power rating of 1500 watts and is used for 6 hours at an electricity cost of. 08 per kwh. How much does it cost to run the tool? 1500 / 1000 = 1. 5 (conversion to k. W) 1. 5 x 6 hrs = 9 kwh 9 x. 08 =. 72 to run the equipment
You try this example n n n n A refrigerator is rated at 1200 watts. It runs about 20% of the time during the day. Cost is 7 cents per k. What is the annual cost to run the appliance? Answer: 1200/1000 = 1. 2 k. Wh 24 hrs x 20% = 4. 8 hours 1. 2 x 4. 8 = 5. 76 kilowatt hours 576 x 365 = 2100 k. Wh 2100 x. 07 = $147. 00
Reading hand-style gauges 1 - record the number on the far right dial that was just passed (7) then the same with the next to the left (3) 2 - If the hand is directly on a number- If the hand on the right has passed zero, write down the number the hand on the left is pointing to, in this case, the 7. If the hand on the right is not past zero, then write down the next lowest number on the dial you're reading. THIS METER IS 8737 KWH
More on electricity n n Appendix A The New Solar Electric Home textbook http: //lansing. apogee. net
END This material is based upon work supported by the National Science Foundation under award DUE-0434405
Renewable Energy #2 AC, DC, Safety
Alternating Current (AC) More economical to produce. n Typical in households and business n George Westinghouse first distributed it commercially in 1886. n Voltage can be easily stepped up or down depending on needs. Results in high versatility. n
n Oscillation of voltage and current evident in sine waves of 60 cycles per second in N. America and 50 cycles per second in Europe
Five characteristics of AC Amplitude n Frequency n RMS n Cycles n Peak to peak n
Amplitude n The first characteristic of AC power is its "amplitude". Amplitude is the maximum value of current or voltage. It is represented by either of the two peaks of the sine wave. This voltage level is also referred to as the peak voltage, and can be either positive or negative. Positive and negative refer only to the direction of current flow. A negative number does not mean that the voltage or current flow are less than zero, only that the current flows in the opposite direction.
Cycle A cycle is one complete repetition of the sine wave pattern. It is produced by one complete revolution (360 degrees) of the AC generator. n Since the sine wave begins at zero, goes positive through the positive peak, then negative through zero and reaches the negative peak, and to zero, we say a full cycle has been completed. n
Frequency (Hertz) n The number of times the sine wave pattern cycle occurs in a second is called the frequency. Frequency was originally measured in cycles per second, or CPS. Today, the unit of measurement for frequency is called Hertz, in honor of the scientist George Hertz.
Peak to Peak n There are two values of voltage that we must be familiar with. The first is "peak-topeak" voltage. This is the voltage measured between the maximum positive and negative amplitudes on the sine wave. It is twice the amplitude. This value is the maximum voltage available, but is not all useable in practical applications.
n n The second value of voltage is the actual useful voltage that is available and is called RMS. This stands for Root Mean Square and it is the standard way of measuring and reporting alternating current and voltage. It is not the peak; it is the average. The RMS is found by multiplying the peak amplitude by the square root of 2 (approximately 0. 707). This yields the actual, useable voltage. It is typically represented by a dotted line drawn across each peak near the 70 percent point.
The Power Grid n n Series of electricity distribution lines Electricity produced at low voltages then stepped up to 69, 000 – 765, 000 volts and sent long distances. Large voltages are split and redistributed at substations near big cities. More reductions at residential transformers
Transmission Voltages 69 and 138 k. V common n Also in operation are 44, 115, 169, and 230 k. V n The largest systems may have 345, 500, 765 k. V with experiments done using 1100 k. V (1, 100, 000 volts!) n
Why are high voltages needed? Loss of power due to long distances. n Can remedy problem with larger diameter wires or higher voltage (more push). Higher voltage is cheaper than larger diameter. n
Direct Current (DC) Low amperage, high voltage n Straight alignment of electrons flowing in one direction n Thomas Edison’s first systems were DC n
DC Generator n A single loop of wire in a magnetic field can be used as a DC generator. When the loop is stationery, it is not cutting any magnetic lines of force and the current and voltage are zero. As the loop of wire is rotated through the magnetic field, it starts to break the magnetic lines of force and current and voltage are induced in the wire loop.
DC continued n Voltage and current remain steady unlike AC which oscillates.
Static Electricity Build up of electrons in an object like a person. Eventually, they are discharged to a cathode (more positively charged object) n Can damage sensitive electrical equipment and ignite petroleum n
What’s a thermocouple? Two dissimilar metals joined and heated at junction will cause small current to flow. n This current flow can be linked to valves on furnace allowing fuel to flow as long as flame is present but shut-off if fire goes out as safety device. n
A small amount of electricity can be generated from heat by connecting two dissimilar metals and heating the spot where they are joined. Metals such as copper and constantan, a copper/nickel alloy, or iron and nickel are typical pairs.
Video Electric Motors
Risk of Shock Depends on n internal and external moisture of skin exposed subepidermal tissue and skin thickness
Safety People can detect 1/100 Amp (1 milliamp) Tongue most sensitive. n At 15+ milliamps, muscles contract and you can’t let go of an electrified object. Pain is felt at this level. n Electrical burns occur both inside and outside the body at 50 milliamps. Flesh is cooked. n
n 1/10 Amp (100 milliamps), heart stops (fibrillation). Do CPR
Safety cont. Resistance ranges from 10, 000 ohms when dry to 1000 ohms when wet n Example: A dry person touches 120 V household power. 120 V / 10, 000 ohms = 0. 012 amps or 12 milliamps. Can still let go but electricity is definitely felt. n
Safety cont. n Example if person is wet. 120 volts / 1000 ohms = 0. 12 amps or 120 milliamps. This is enough to kill you!
Electricity Trivia n n How many volts and amps are required to operate an Electric Chair? Answer: 2000 – 2200 volts at 7 -12 amps
Websites *http: //lansing. apogee. net *http: //people. howstuffworks. com/po wer 1. htm
END This material is based upon work supported by the National Science Foundation under award DUE-0434405
Renewable Energy #3 Electrical Power Phases, Grounding, and Fuses
Grounding z 3 rd prong is ground z Provides easier pathway than user for electrical short-circuit to return to breaker box rather than through person’s body back to the earth.
Ground vs grounding z Black insulated- carries electricity, called “hot”. z White or grey insulated- “neutral or ground” energized z Grounding wire is bare and is for safety. Sometimes green painted.
What about adapters? z Old homes have only 2 prong outlets and adapters are used. z Can ground to outlet if outlet is grounded. Attach adapter to center plate screw.
Double-Insulated Items z. Some drills, coffee makers, blow dryers, blenders etc. are manufactured with nonconductive surfaces and two insulative layers making third grounding prong unnecessary. z. Industrial equipment will often have third prong and use more durable metallic cases and shielding.
Overload Protection z. Fuses and breakers that y 1 Protect the equipment from being subjected to loads in excess of their rating (overloads, too hot, shorts) y 2 Protects device from overloads entering through power source (power surges)
Prevent overloads z Use correct size fuses z Don’t overload circuits with too many “splitters” or extension cords z Repair worn wiring
Start-up Loads z. Fuse or breaker at circuit box protects the wiring but sometimes another fuse is used on the device as additional protection. z. Motors may draw 5 times more amps at start-up as when running.
z. Example: A motor runs at 3 amps after start-up but requires 15 amps to get going. A rock jams the impeller and locks it up so 17 amps are generated. The 20 amp breaker at circuit box won’t trip but the motor will burn out. A special slow-blow fuse capable of withstanding initial starting load should be used to protect motor.
Slow Blow (time delay) fuse z Capable of withstanding higher than rated loads for short duration before solder in cup melts and spring retracts link and opens circuit.
Ground Fault Circuit Interrupters GFCI z. Devices that sense a drop of current and opens the circuit before damage occurs. Senses difference between Hot and Neutral wire of 0. 005 v before tripping. z. Hit reset to restore power and look for reason.
Circuit Breakers z A circuit breaker is essentially a combination of a thermostat and a switch. The circuit breaker has a bimetal strip which heats and bends during a circuit overload. This bending action trips the breaker and opens the switch, thus breaking the circuit. z As soon as the metal strip cools (about two minutes or so) the breaker can be manually reset completing the circuit again. Most units reset either by flipping a switch or by pushing on the breaker. Since there is no easily removed part like a fuse, they are less likely to be replaced with the wrong size if frequent tripping occurs in a circuit.
Fuses z. Cartridge type- Arm trips to open circuit z. Screw in or plug type- piece of metal melts at certain amperage. Can be replaced with wrong size more easily.
Single Phase z. Common for residential use z. Voltages in 115 or 230 z. Suitable for lower loads, motors up to 7. 5 horse power. z. Many motors can operate on either 115 or 230 volts with only minor adjustments.
Three phase power z. Used in industrial applications for heavier loads. z. More easily accommodates heavy start-up loads without lights dimming elsewhere on power grid. z. Phase converters can convert single phase to three phase but are very expensive
Inverters z Devices that convert DC to AC or AC to DC
Review z. Global Warming- Increase in Earth’s temperature caused by gasses associated with fossil fuel combustion and manufacturing z. Carbon Sequestration- Binding atmospheric carbon in organic matter
z. Current- movement of electrons between atoms z“flow” of electrons measured in amps z. Heat generated z. Conductors allow electron flow z. Insulators resist electron flow z. Ohms- measurement of resistance
z. Voltage- pressure z. Current (amps)- how much is flowing z. Watts- rate of use z. Voltage x Amps = Watts z 746 watts = 1 Hp
z 1 k. W = 1000 watts z. AC- alternating current z. DC- direct alignment of electrons z. AC voltage easily stepped up or down with transformers z. In U. S. we use 60 hertz or cycles z 15 milliamps causes muscle contraction and pain, 100 milliamps causes death
Websites zhttp: //auto. howstuffworks. com/wfc. htm
z. This material is based upon work supported by the National Science Foundation under award DUE-0434405
Renewable Energy #4 Batteries
What’s a battery? • DC electricity storage device, not electricity producer.
Battery History • 2200 B. C. Parthian Empire may have created a battery from a clay jar into which a copper tube was inserted through which an iron rod was suspended. When filled with an acid like vinegar, about 2 v could be generated
History of batteries • 1800 Allesandro Volta discovered the galvanic battery. It was a series of alternating zinc and copper plates separated by acid dampened cloth or card. Column supported by glass rods. More plates = more volts! • 1859 Gaston Plante made first lead-acid battery
• 1927 Silver zinc- rechargeable, stores lots of energy, but very expensive • 1930 Nickel Zinc- Rechargeable and environmentally safer than Ni-Cd • 1945 Mercury Batteries- highest volumetric energy density, buttons, used in calculators, watches, reliable over wide range of temperatures.
Terms • Some are one-time use (called primary batteries) • Reusable or rechargeable can be used may times (secondary batteries).
Cycling • Cycling means filling then discharging with electricity. • Automobile batteries are not designed to be deep cycled. Short burst of energy for starting are needed then the alternator immediately recharges the cell. • Can only tolerate 10% depth of discharge for about 200 cycles
• Batteries can be the weakest link in an electrical system if not taken care of.
Structure • Consist of series of cells rated 2 v each. (12 v battery has 6 cells) • Bank- Many interconnected batteries • Generally more weight = more capacity • Depth of Discharge (DOD)- How much electricity can be repeatedly removed. – Expl. 100 lb discharged to 80% of its capacity stores more usable power than a 150 lb battery with 50% depth of discharge rating
Size of bank depends on • • Days of storage required Avg daily amount of use Maximum load Temperature Types of loads Portion used at night (particularly with PV) Budget
Buy new or used? • If used, check to see cases are clean and free of cracks • Electrolyte clear and clean? • Plates in good shape and not warped or brownish or white from sulfate • Terminals secure in good shape • Cells test properly with digital voltmeter and hydrometer • How were they previously use • Maintenance logbook available • Buy new batteries no older than 6 mo from mfgr.
Other Considerations • Telephone company batteries are better buy than forklift or golf cart batteries because of more careful maintenance usually. • Batteries will self-discharge 10 -15% annually just sitting on a shelf. • Life cycle depends on depth of discharge.
How do batteries work? • Lead acid batteries made up of series of identical cells consisting of plates of two types of lead. Plates immersed in an electrolyte of sulfuric acid and water. • When battery is charged, chemical composition of plates and acid occurs and reversed when discharged. • Battery stores electrical energy in chemical form
During the discharge of the lead-acid secondary cell, lead at the negative electrode is oxidized to solid lead sulfate by the electrochemical reaction: Pb + HSO 4 - --> Pb. SO 4 + H+ + 2 e. The solid Pb. O 2 at the positive electrode is concurrently reduced also to solid lead sulfate by the electrochemical reaction: Pb. O 2 + 3 H+ + HSO 4 - + 2 e- --> Pb. SO 4 + 2 H 2 O
Chemistry cont. • Positive plates are lead peroxide (PBO 2) and negative are sponge lead strengthened with antimony or calcium to form alloy. • Dilute sulfuric acid is liquid. • Fully charged specific gravity is high. • During discharge some acid separates from electrolyte in pores of plates and combines with active plate material creating lead sulfate leaving behind water.
+ - CHARGING + Electrolyte: sulfuric acid and water Lead sponge Lead peroxide - Lead sponge Lead peroxide DISCHARGING Min. lead sulfate and water Min. lead sponge, lead peroxide, sulfuric acid Max. lead sulfate and water. Low S. G.
• If charging continues beyond point where cells can accept energy from charging current, electrolyte is broken down into H and O in process called electrolysis. This reason water must be sometimes added. • Over time, some sulfate remains on plates creating “hardening of arteries” effect which reduces efficiency
Wet and dry • Wet- electrolyte added at factory – Begin to age when electrolyte is added. Aging is called “local action” • Dry- electrolyte added later – developed during WWI – Tend to last longer but must be serviced for long life
Care and feeding of batteries • • Clean Warm but not too hot (70° F ideal) Dry Check regularly and top off with distilled water as needed • Use properly • Best to replace entire bank at same time at end of useful life (at least 6 years) • Keep charged to minimize sulfate formation
Care cont. • Fill dry batteries only with appropriate electrolyte or acid. Wear safety glasses and gloves and don’t smoke. • After initial fill, never add anything but low mineral water.
• Maintain good venting to prevent build-up of H gas. Concentrations of 4% H gas are explosive. Recommended max. conc. 2%
Care cont. • Keep history of battery bank • Measure temperature of electrolyte. Specific Gravity S. G. is affected by temp. • Measure SG with hydrometer. Add one point (0. 001) for every 3° F above 77 and subtract one point (0. 001) for every 3° F below 77 degrees
Battery Hydrometers Typical SG for fully charged battery is 1. 265 to 1. 280 or higher
Hydrometer Use Guidelines • Check each cell of battery being careful not to cross-contaminate cells. • Withdraw electrolyte from deep within the cell sucking up and discharging hydrometer contents several times to get most accurate reading. • Take readings when batteries have been dormant for a couple of hours or when they are under low load as in early morning. (PV systems) • Voltmeter indicates volts. Touching one lead to battery terminal and other to battery surface may cause reading. If so, battery is shorting out on dirty case. Clean with baking soda and water.
Interesting Links • http: //www. batterystuff. com (see battery tutorial section) • http: //www. howstuffworks. com/battery. htm (a great site with loads of information)
• This material is based upon work supported by the National Science Foundation under award DUE-0434405