IMM-Glossary
1. AC
Alternating current electricity. AC current varies over time, creating a sine-wave waveform.
2. Air mass
A measure of how far light travels through the Earth's atmosphere. One air mass, or AM1, is the thickness of the Earth's atmosphere. Air mass zero (AM0) describes solar irradiance in space, where it is unaffected by the atmosphere.
3. Airfoil
The cross section profile of the leeward side of a wind generator blade. Designed to give low drag and good lift. Also found on an airplane wing.
4. Alternator
A device that produces alternating current (AC) electricity from the rotation of a shaft. Used in wind and water turbines to generate electricity.
5. Amps
The volume of electricity flowing through a conductor. Can be compared to the gallons per minute (gpm) of water flowing through a pipe.
6. Anemometer
A device that measures wind speed. Important in designing a properly sized wind power system.
7. Angle of attack
The angle of relative air flow to the blade chord.
8. Angle of incidence
The angle between a ray of sunlight striking a surface and a line perpendicular to that surface. Rays perpendicular to a surface have a zero angle of incidence.
9. Array
A number of photovoltaic modules electrically connected to produce a single electrical output.
10. Azimuth
The angular measure between due south and the point on the horizon directly below the sun.
11. Balancing
With wind turbine blades, adjusting their weight and weight distribution through 2 axes so that all blades are the same. Unbalanced blades create damaging vibration.
12. Blade
The part of a wind generator rotor that catches the wind.
13. Braking system
A device to slow a wind turbine's shaft speed down to safe levels electrically or mechanically.
14. Brushes
Devices for transferring power to or from a rotating object. Usually made of carbon-graphite. Found in electric motors, alternators and generators.
15. Buckets
In an impulse hydro turbine, the buckets are attached to the turbine near the runner, and used to 'catch' the water. The force of the water hitting the buckets turns the runner, which turns the alternator drive shaft, causing the alternator to generate power.
16. Cavitation
Air bubbles in a closed water system. Greatly reduces efficiency in a hydro turbine generator system, and can damage water pumps and pipes in a home water supply system.
17. cf/s
A unit of measurement for water flow. Flow equals the volume of water (cubic feet) passing through an area in a given time period (per second). 1 cf/s = 7.48 gallons per second.
18. Chord
The width of a wind turbine blade at a given location along the length.
19. Concentrator array
A PV array which uses concentrating devices (reflectors, lenses) to increase the intensity of the sunlight striking the array.
20. Cowling
The protective covering over a generator or motor.
21. Cut-In
The rotational speed at which an alternator or generator starts pushing electricity hard enough (has a high enough voltage) to make electricity flow in a circuit.
22. DC
Direct current electricity. DC current does not vary with time, creating a flat waveform.
23. Diffuse radiation
The sunlight received indirectly, as a result of scattering due to clouds, fog, dust, moisture vapor or other substances in the atmosphere.
24. Diode
A solid-state device that allows electricity to flow in only one direction.
25. Direct radiation
Sunlight received directly, which has traveled in a straight path from the sun, also referred to as beam radiation.
26. Diversion
A water diversion redirects a flow of water from its natural course. Diversions can either be open like a canal or ditch, or a closed like a pipeline.
27. Diversion Load
Water and wind turbines require diversion loads to use the excess power they generate after the battery bank is fully charged. Ventilation fans and heating elements are popular choices.
28. Downwind
Refers to a Horizontal Axis Wind Turbine in which the hub and blades point away from the wind direction, the opposite of an Upwind turbine.
29. Drag
In a wind generator, the force exerted on an object by moving air. Also refers to a type of wind generator or anemometer design that uses cups instead of a blades with airfoils.
30. Draught tube
The flared tube bridging the gap between a reaction-style water turbine and the tail water. A draught tube maintains the sealed system necessary for creating 'suction head' which dramatically increases turbine power output.
31. Dynamic pressure
The water pressure in a pipeline while the water is flowing. It is equal to the static pressure (measured in a closed pipline) minus pressure loss from friction, turbulence and cavitation in the pipeline and fittings.
32. Elevation
The sun's angle above the horizon.
33. Flat-plate array
A PV array which does not use concentration.
34. Flow
Flow is the volume of water passing through an area in a given time period. It is most often measured in cubic feet per second (cf/s) or gallons per minute (GPM).
35. Flume
Open and closed flumes serve to channel water into a reaction-type water turbine.
36. Forebay
A closed tank at the top end of a hydro power diversion pipeline. It allows the water to settle before entering the penstock. Usually where the primary filter/trash-rack is installed.
37. Francis turbine
A type of reaction turbine. Francis turbines have nine or more fixed vanes on the runner. Water enters the runner from the side (through the vertical vanes), and exits out the bottom of the turbine (a 90 degree change in direction). Francis turbines operate with 4 to 2000 feet of head, and can be as large as 800 megawatts of output.
38. Furling
The act of a wind generator yawing (tilting or rotating) out of the wind either horizontally or vertically to protect itself from high wind speeds.
39. Furling tail
A wind generator protection mechanism where the rotor shaft axis is offset horizontally from the yaw axis, and the tail boom is both offset horizontally and hinged diagonally, thus allowing the tail to fold up and in during high winds. This causes the blades to turn out of the wind, protecting the machine.
40. Generator
A device that produces Direct Current from a rotating shaft.
41. Global radiation
Total solar radiant energy impinging on a surface, equal to the sum of direct and diffuse radiation.
42. Governor
A device that regulates the speed of a rotating shaft, either electrically or mechanically.
43. Grid
(power grid or utility grid) This refers to the public utility power system. If you get a monthly electric bill, you are "on the grid."
44. Guide vanes
Used in reaction turbines to change water flow direction by 90 degrees, causing the water to whirl and enter all turbine runner buckets simultaneously, improving turbine efficiency.
45. Guy anchor
Attaches tower guy wires securely to the earth. Anchor designs vary depending on the type of soil present and size of tower being anchored.
46. Guy radius
The distance between a wind turbine tower and the guy anchors.
47. Guy wire
Attaches a tower to a Guy Anchor and the ground.
48. Head
The total vertical distance between the beginning of a hydro system diversion and the micro hydro turbine. The amount of power a turbine produces is proportional to the total available head.
49. Head loss
Obstructions to the flow of water to a hydro turbine. Anything from the friction on the inside of the pipeline, to water turbulence in the pipe or fittings which change the pipeline direction can slow the water flow down, causing head loss.
50. Hertz
The frequency with which an alternating current waveform rises and falls (as it changes polarity).
51. Hub
The center of a wind generator rotor, which holds the blades in place and attaches to the shaft.
52. I-V curve
A current/voltage curve, which expresses the possible combinations of current and voltage output of a photovoltaic device.
53. Impulse turbine
Impulse turbines produce power when a jet of water from an enclosed diversion pipeline 'shoots' through a small nozzle directly onto the turbine runner. Impulse turbines are best for 'high head' sites (with 20 feet of head or more), but they do not require very high flow rates. Pelton and Turgo turbines are two of the most common impulse turbine families.
54. Insolation
The solar energy received at a place over a given period. May be expressed as sun-hours per day, langleys per hour, watts per square meter per hour, or any number of other units.
55. Intake
The point at which water is diverted from a river or stream to the turbine via a diversion. A trash rack/filter and settling tank are often installed at the intake point to prevent debris and sand or silt from reaching the turbine.
56. Isolation diode
A diode which prevents one segment of a PV array from interacting with another array segment. Usually used to prevent array energy from flowing backwards through a sub-voltage series string. May also serve the function of blocking diode.
57. Kinetic Energy
Energy due to motion. Wind and moving water have kinetic energy, which is converted to electrical energy by a wind or hydro turbine.
58. Leading edge
The edge of a blade that faces toward the direction of rotation.
59. Leeward
Away from the direction from which the wind blows.
60. Lift
The force exerted by moving air on asymmetrically-shaped wind generator blades at right angles to the direction of relative movement. Ideally, wind generator blades should produce high Lift and low Drag.
61. Load
(electrical loads or power loads) Any item that draws electrical power. A full size refrigerator would be a large load, a lightbulb would be a small load.
62. Maximum power
Also referred to as peak power. The point on a device's I-V curve where the product of I and V (Pmax, measured in watts) is maximized. The points on the I and V scales which describe this curve point are named Imp (current @ max power) and Vmp (voltage @ max power.)
63. Micro hydro
Hydro power systems with a power output of less than 100kW.
64. Module
A number of solar cells electrically connected, protected from environmental stresses, self-contained and not subdividable, providing a single electrical output.
65. Nacelle
The protective covering over a generator or motor.
66. Off Grid
Anywhere not connected to the public utility power system.
67. Open Circuit Voltage
The voltage that a alternator or generator produces when it is NOT connected to a Load.
68. Pelton turbine
A type of impulse turbine with one or more jets of water hitting the buckets of a runner. The runner resembles a miniature water wheel. Pelton turbines are used in high head sites (20 - 6000 feet), and can be as large as 200 megawatts.
69. Penstock
A closed pipeline through which the water flows to a hydro turbine.
70. Permanent Magnet Alternator
An Alternator that uses moving permanent magnets instead of Electromagnets to induce current in coils of wire.
71. Pitch
The angle between the blade Chord and the plane of the blade's rotation. Also called "setting angle" or "blade angle". A blade carved with a Twist has a different setting angle at the Tip than at the Root.
72. Potential Energy
Energy in a stored form. Batteries store potential electrical energy. Water behind a dam also had potential energy, because the stored water can be released for future power production.
73. Propeller
The spinning thing that makes an airplane move forward. Often incorrectly used to describe a wind turbine Rotor.
74. Propeller turbine
A type of reaction turbine with a propeller-style runner. Water passes through the runner and drives the propeller blades. Propeller turbines can be used from 2 to 300 feet of head, and can be as large as 100 megawatts.
75. Pulse Width Modulation
A regulation method based on Duty Cycle. At full power, a pulse-width-modulated circuit provides electricity 100 percent of the time. At half power, the PWM is on half the time and off half the time. The speed of this alternation is generally very fast. Used in both solar wind regulators to efficiently provide regulation.
76. Rated power output
Used by wind generator manufacturers to provide a baseline for measuring performance. Rated output may vary by manufacturer. For example, one manufacturer's 1500 watt turbine may produce that amount of power at a 30 mph windspeed, while another brand of 1500 watt turbine may not make 1500 Watts until it gets a 40 mph windspeed. Always read manufacturer's ratings statements very carefully.
77. Reaction turbine
Reaction turbines produce power from the pressure of water 'falling' on the runners after flowing through the guide vanes. Reaction turbines can operate with head as low as two feet, but require much higher flow rates than impulse turbines.
78. Root
The area of a blade nearest to the hub. Generally the thickest and widest part of the blade.
79. Rotor
1) The blade and hub assembly of a wind generator. 2) The disc part of a vehicle disc brake. 3) The armature of a permanent magnet alternator, which spins and contains permanent magnets.
80. Runner
The part of a micro hydro turbine that actually attaches to the alternator drive shaft. The 'buckets' on the runner are what the water pushes against to turn the runner and generate electricity.
81. Scroll case
An enclosure used by some reaction water turbines to channel the water into the turbine guide vanes as the optimal angle to maximize the turbine's efficiency.
82. Sellback
When an alternative energy system is connected to the grid, and excess power is sold back to the local utility.
83. Setting angle
The angle between the blade Chord and the plane of the blade's rotation. Also called Pitch or blade angle. A blade carved with a Twist has a different setting angle at the Tip than at the Root.
84. Shaft
The rotating part in the center of a wind generator or motor that transfers power.
85. Short circuit
1) Parts of a circuit connected together with only the impedance of the leads between them. 2) In wind generators, connecting the output leads directly together so as to heavily load a generator in high winds. This creates a "short" circuit path back to the generator, bypassing all other loads.
86. Shunt
An electrical bypass circuit that proportionally divides current flow between the shunt and the shunted equipment. It also allows high current measurements with low-current equipment.
87. Solar panel
A group of photovoltaic modules mechanically mounted on a single frame.
88. Solar spectrum
The total distribution of electromagnetic radiant energy over the band of wavelengths present in solar radiation. The total energy received on a given surface, and how that energy is distributed among various wavelengths, depends on how much of the Earth's atmosphere light has traversed.
89. Standoff mount
A mounting system which supports a PV array above a roof surface.
90. Start-up
The windspeed at which a wind turbine rotor starts to rotate. It does not necessarily produce any power until it reaches cut-in speed.
91. Static pressure
Pressure produced by an unmoving column of water. (also: static head) There are no friction/head losses when water is not moving, so static pressure is determined only by the vertical height of the water column. The static pressure on a 10ft. tall vertical pipe full of water would be the same as a 1000ft. long pipeline with 10ft. of head over its entire distance.
92. Stationary tower
A tower that does not tilt up and down. The tower must be climbed or accessed with a crane to install or service equipment at the top.
93. Stator
The part of a motor, generator or alternator that does not rotate. In permanent magnet alternators it holds the coils and laminates.
94. Suction head
Additional energy in a reaction turbine hydro system, created by the draught tube channeling outlet water. Inlet pressure, from the water 'pushing' on the turbine runner as it enters, creates ~80% of the energy in a reaction system. Suction head, from the vacuum created by the closed outlet system, 'pulls' on the runner as the water exits the system, adding up to ~20% additional power output to the system.
95. Tail
The proper term is actually Vane, but Tail is commonly used.
96. Tail boom
A strut that holds the tail (Vane) to the wind generator frame.
97. Tail race
The channel or pipe carrying water from a hydro turbine outlet back to the stream/river it was diverted from.
98. Thin film cell
A PV cell formed by depositing thin layers of conductive and semiconductive materials, usually using a chemical vapor deposition (CVD) process. Also referred to as amorphous cells because they have no crystalline structure, such cells use less material than cells sawn from crystalline ingots.
99. Thrust
In a wind generator, wind forces pushing back against the rotor. Wind generator bearings must be designed to handle thrust or else they will fail.
100. Thrust bearing
A bearing that is designed to handle axial forces along the centerline of the shaft. In a wind generator, this is the force of the wind pushing back against the blades.
Date Posted: Friday, January 4th, 2008
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