Renewable Energy Systems Flashcards
What are the five main types of renewable energy systems
Solar (photovoltaic, thermal), wind (small, large), hydro (micro, kinetic), geothermal, fuel cell
What are some pros of the HAWT
Most efficient, can produce more energy because of higher wind speeds
What are some pros of the VAWT?
Simpler construction so less expensive, doesn’t have to be oriented to the wind, low down on the ground
What are the four main points that determine amount of power produced in a wind turbine?
Wind speed, height of tower, diameter and shape of rotor blades, blade pitch
Which components are found in the Nacelle?
Blades, hub assembly, low speed shaft, gearbox, high speed shaft, generator, yaw assembly, brakes
Where is the pitch control assembly housed?
In the hub assembly
What is yaw control?
Where the Nacelle rotates on the top of the tower shaft
Which brake system is fail safe?
Rotor brake
Which brake system is hydraulically applied, mechanically released?
Yaw brake
Which brake system is mechanically applied and hydraulically released?
Rotor brake
What is the purpose of a SCADA?
Essential to large wind farms, they monitor things like wind speed, humidity, air pressure, pitch, and they tell how much power is being produced. They show if there are any problems with the wind power system.
What are the three main types of generators found in wind turbines?
Induction, Synchronous (SFIG)
Doubly fed induction (DFIG)
What is the most common type of motor used in a DFIG?
Wound rotor motor with ac input from the grid
What is the most common type of motor for a SFiG?
Asynchronous or Induction motor with DC input
What is the main component of a DFIG that makes it different from an SFIG?
The controller. The controller uses generated voltage and input voltage from the grid.
Controller changes frequency of the stator field to provide a more constant nominal output voltage. Reactive power of the stator can be varied to maintain PF at unity.
Which electrical component is a check valve similar to?
A diode. Allows flow in one direction only.
Which electrical component is a PRV similar to?
A Zener diode
What is mechanical restriction?
A physical point in tubing where size is reduced
What is electrical restriction?
Something that reduces/opposes flow of electrons.
Inductor, reactor, or choke.
What is a wind vein or weather vein?
Senses wind direction
What is an anemometer?
Senses wind speed
What is an encoder?
Measures the distance in degrees that the yaw has travelled/twisted
Which electrical component is an accumulator similar to?
A capacitor
What is the purpose of a shunt trip circuit breaker?
To remotely and quickly turn off a circuit breaker.
What are the steps of one entire CPU cycle?
Operation status, yaw control, blade pitch control, power generation circuit, monitoring
What is cut out speed?
The maximum speed which can produce power before it shuts down to prevent damage
What is the average cut in speed?
6m/s
What is the average cut out speed?
22-25m/s
What is the MPP?
Maximum Power Point. The point in which optimum speed and torque are reached and produce the most power.
How does a double acting cylinder work?
Alternates cycles of pressurized fluid to both sides of the piston
How does a single acting cylinder work?
There is a small air port in the cylinder that lets in clean air for compression
What does the accumulator do?
Stores energy in the form of fluid under pressure. Potential energy may be converted into working energy to assist the pump (acts as a capacitor)
Can be filled with a gas ex) nitrogen
How is the flow of refrigerant reversed in a hydraulic power circuit?
Four way valve. Acts as a four way switch.
What are the three contributing factors to power in the wind?
Air density, cross sectional area of blades, wind speed.
Define solar power
Conversion of sunlight into electrical energy
What is the most available renewable energy source?
Solar power
What is Concentrating Solar Power (CSP)?
Systems that focus sunlight energy into a small concept tested beam that is used to boil a liquid, producing steam energy
What is a PV cell made of?
Crystalline silicon
What is the short circuit current of a solar cell?
Max current that can flow through a solar cell when generated voltage is at zero (when its terminals are shorted together for transportation)
What is open circuit voltage in a solar cell?
Max voltage that the solar panel can produce with no load on it
How does connected many cells in series affect the current and voltage of a solar panel?
The current will stay the same and the voltage and power will directly multiply.
If you add 60 cells the voltage and power will multiply 60 times. The short circuit current will stay the exact same.
How does connecting many panels in parallel affect current and voltage?
The voltage will stay the same across both panels as they’re connected in parallel, the current will double therefore the power output would also double.
What is the MPP of a solar panel?
The bias potential at which solar cell outputs are at maximum power.
MPP current and MPP voltage will be lower than short circuit current and open circuit voltage.
Define solar irradiance
Input power. How much sunlight is striking the panel.
What are the three standard points of testing a solar panel?
Cell temp of 25°, irradiance of 1000w/m2, air mass of 1.5
What is the average generated voltage of one cell?
600mV
How does irradiance affect power?
The amount of irradiance affects the amount of current produced, and then current affects voltage
How does array coverage affect generated power output?
For 10% coverage there will be a 90% power output reduction. Cells are connected in series so only the beginning of the series will generate.
What are the two sensors that measure sunlight?
Pyranometer, pyrheliometer
What is a pyranometer?
Detects sunlight in a 360° view
What is a pyrheliometer?
Detects sunlight in one direction only
What is the purpose of a bypass diode?
Allows current to bypass a damaged or shaded cell, preventing power output loss
What is the purpose of a blocking diode?
Used to prevent charged batteries to discharge at night. Allows current to flow in only one direction.
How are diodes connected, in series or parallel?
Bypass diodes in parallel, blocking diodes in series after the string
What is a stand alone PV system?
Operated independently from utility (cabin), common for smaller electrical loads
What is a stand alone DC PV system?
Have an output that is directly connected to DC loads, sometimes DC-DC converters and/or MPPTs are used
What is a stand alone AC PV system?
Has an output that is directly connected to an inverter for AC loads
What are the components of a SAPS?
PV array, charge controller, storage battery, DC/AC inverter
What is an inverter?
Changes DC to AC
What is a rectifier?
Converts AC to DC
What is a stand alone hybrid PV system?
Uses both PV and other sources of electrical power to supply electrical loads. Ex) generator (still not grid connected)
Most reliable source of system.
What is a utility interactive PV system?
A utility PV system operates in parallel with the grid and can deliver electrical power directly to the grid.
Does not require a battery bank.
Inverter must meet bc hydro requirements (over voltage, under voltage, over frequency, under frequency, anti islanding)
What is net metering?
Net metering is where excess energy produced from your utility interactive system offsets your utility bill for grid power used.
Produce/sell energy in the day and use energy at night, your bill will be offset/credited
What is dual metering?
Similar to net metering but it uses two different meters. One meter for power consumed from the grid, another for power produced from solar fed to the grid
What is a utility interface PV system?
Uses either utility or PV system for source of loads by use of a transfer switch.
Can exist in stand alone or utility interactive modes.
What are the four charging methods for batteries?
Bulk charging, absorption charging, float charging, equalization charging
What is bulk charging?
Used in lead acid batteries, these allowable current is delivered to batteries to charge them to approx 80%
What is absorption charging?
Once bulk charging is at 80%, absorption charging takes place to slowly charge the remainder of the battery by reducing the current.
What is float charging?
Takes place after absorption charging. Battery maintains a full charge from a small amount of constant current. (Trickle charging)
What is equalization charging?
Applied periodically to batteries to maintain specific needs among individual battery cells
What are the four types of inverters for solar?
Stand alone, grid tied, grid dependant, grid interactive
What are the three types of inverter outputs?
Square wave, modified square wave, true sine wave
What is a solar tracker?
A genetic term for a device that orients towards the sun. Ex) panels, reflectors, lenses
What is the azimuth angle?
The angle between suns position and due north or south on a horizontal plane
What is surge capacity?
The max amount of power a solar inverter can supply for a short period of time.
What is MPPT?
Maximum power point tracking. Devices used to track voltage and current inputs and outputs, to find maximum power point.
What are the three factors to determine PV module power output?
Load impedance, solar irradiance, cell temperature.
What is a geothermal open loop system?
Water or refrigerant is directly exchanged
What is a geothermal closed loop system?
Water or refrigerant is contained or sealed
How long can geothermal systems be online for?
90-100%, very little maintenance or downtime
How long can coal be online for?
75%
How long can nuclear be online for?
65%
What length are vertical heat pumps in the ground?
60-120m
What length are horizontal heat pump loops?
> 2m
Define conduction
Transfer based on physical contact.
Temp difference, thickness of material, surface area
Define convection
Transfer based on a circulating liquid or gas.
Can be natural or forced (fan or pump)
Define thermal radiation
Transfer through a vacuum
Define sensible heat
Heat that causes a change in temp
Define latent heat
Heat that causes a change in state
What is the most common use of geothermal energy?
Industrial use for flash steam plants.
What is the heat capacity of water?
4200 j/kg
What is the melting point of the heat pump system?
When all ice meets the melting stage of ice and water
What is the boiling point of the heat pump system?
When water meets the water and steam “wet steam” mixture
What is superheat?
When the wet water and steam mixture continues to heat and creates a dry steam
What are the three types of compressors?
Piston, scroll, and rotary
What is the basic refrigeration cycle?
Evaporator, condenser, compressor, metering device, expansion device
When will the evaporator be outside and the condenser inside?
When heating the home
When will the evaporator be inside and condenser outside?
When cooling the home.
What is an evaporator?
A heat exchanger that uses refrigerant
What is a condenser?
A coil that removes heat from the refrigerant, changes from liquid to a gas
What is a compressor?
Circulates and pressurizes refrigerant.
What is an expansion device?
Controls the flow and pressure of refrigerant
What are the different types of heat transfer?
Conduction, convection, thermal radiation
Define geothermal energy
Energy that the earth has stored in its mass
What are the four industrial application of geothermal electricity?
Dry steam (high temp steam), flash steam (high temp steam and water), binary power plant (low temp reservoir), hybrid (flash and binary)
How much less carbon dioxide do geothermal power plants emit than other fossil fuels?
1000-2000 times less
What is a ground source heat pump?
A heat pump that transfers heat to/from earth
What is a ground loop?
A system that allows movement of a fluid to transfer the heat to/from ground.
What are the materials used for piping of a geothermal system?
Usually pex or pex-A
Flexible, corrosion resistance, durable
What is the purpose of a reinforced ubend?
Structural integrity and load bearing capacity
What is thermal resistance?
Insulating valve, made of a material that resists or blocks heat transfer
Define emissivity
The amount of heat a surface can emit/absorb compared to theoretical “blackbody”
Is the amount of energy required greater in latent or sensible heat?
Latent heat. Greater energy is required to change state.
Define dew point
Once superheated Vapor releases its energy, its temperature decreases until condensation begins. Dew point. Temp does not change again until ever trace of Vapor has returned to liquid.
Which renewable energy system is the most cost effective way to heat water?
Solar thermal
Define solar collector
Device that gathers and transfer solar energy to be medium
Define an active system
Use one or more pumps to circulate fluid
Define a passive system
Use pressure or convection, there are no pumps
Define direct system
Contains no recirculation, one or more pumps is used, considered an open loop system
Define indirect system
Non potable fluid is recirculated as a medium for heat transfer. Classified as closed loop system.
What is the most efficient solar collector?
Evacuated tube
What is an active indirect system?
Water is being circulated in a closed loop system, water is being used to heat another water source but not being directly consumed
What is a passive direct system?
The water that is being heated is also being consumed.
Define a differential temperature controller
Electronic device usually containing at least two temp sensors to control temperature between two or more points
What is an expansion tank in a solar thermal system?
A safety device that absorbs increased volume of water when the pre heat system is engaged and heating.
What is a heat exchanger in a solar thermal system?
A coil of tubing in the water storage tank, the coil stores the energy and transfers the heat to the liquid.
Define a rotameter
A device that measures the rate at which liquid or gas flows through a pipe (flow meter)
What are some pros of hydrogen fuel cells?
Most environmentally friendly
Quiet
Low vibration
Efficient
Fast to refill
Long life
What are some applications of hydrogen fuel cells?
Cars, trucks, boats, spacecraft, weather stations, small batteries
How is a fuel cell constructed?
There is a PEM (proton exchange membrane) between two field plates, one plate is an anode and the other plate is a cathode. The anode contains an electrolyte (platinum)
What is the chemical reaction that takes place in a hydrogen fuel cell?
Hydrogen is supplied to the anode, oxygen is supplied to the cathode. Hydrogen undergoes anode reaction with the electrolyte, separating the hydrogen into positively charged ions and negatively charged ions. Hydrogen ions travel through the electrolyte and electrons travel through external circuit which generates small amount of electricity. Cathod reaction combines electrons, hydrogen ions, and oxygen molecules to produce water.
What is the term for many fuel cells combined together?
Fuel cell stacks
What is the Eoc of one singular fuel cell?
1.1-1.2V
What are the three methods for extracting hydrogen?
Electrolysis or steam, reforming, PEM
What are some characteristics of a PEM?
Used in automobiles, low operating temp of 60-80°, quick warm up time, power output of 50-250kW
What are the properties of an alkaline fuel cell?
60-80° op temp, primary application is spacecraft because byproduct is potable water, power output limited to 300-5kW
What are the properties of direct methanol fuel cells
Methanol is the fuel instead of hydrogen, low efficiency, requires platinum
What are the three parable fuel cells?
PEM, alkaline, direct methanol
What are the three stationary fuel cells?
Solid oxide, molten carbonate, phosphoric acid
What are the properties of a solid oxide fuel cell?
Op temp of 800-1000°, very long start up time, reliable once in continuous operation, output as high as 2MW, byproducts are water and carbon dioxide,
What are the properties of molten carbonate fuel cell?
650° op temp, output up to 3MW, fuel is low quality hydrogen with lots of additives, byproduct is greenhouse gases
What are the properties of phosphoric acid fuel cell?
150-200° op temp, output up to 200kW
Define hydrogen electrolysis
Decomposition of water into oxygen and hydrogen gas by the passage of electrical current
Define steam reforming
Steam reforming produces hydrogen with high temp steam which breaks the bonds between hydrogen and carbon in methane
What is the best method to produce high purity hydrogen?
Electrolysis. Uses dc current to decompose water in hydrogen and oxygen
Which method is reversible for producing/extracting hydrogen?
PEM
What are some safety precautions of hydrogen?
Burns clear, very explosive, requires class D extinguisher
What are the three types of hydro kinetic systems?
Vertical axis, horizontal axis, oscillating foil
What is Canadas tidal current potential?
42,000 MW
What are the three factors of power produced by hydrokinetic turbines?
Water density, rotor blade size, water velocity
What are the three hydrokinetic turbine installation methods
Bottom mounted, like anchored, surface mounted with flotation
What is the advantage of a vertical axis hydrokinetic turbine?
The generator and gearbox is installed above the water
What is the disadvantage of horizontal axis hydrokinetic turbines?
These are bottom mounted, they require divers or cranes for servicing.
What is the rated power output for ocean type hydrokinetic systems?
1MW
What is the rated power output for river type hydrokinetic systems?
400kW
What are the two specs for hydrokinetic systems to generate maximum power?
Water dept greater than 6m
Water flow greater than 2m/s
Where are micro hydro systems usually found?
Run of river, no large dams need to be built
How is amount of power available from a river/stream/creek determined?
Water flow rate, head, efficiency of the system
What is the general efficiency of micro hydro systems?
Below 80%, usually between 50-70%
What are the two main types of micro hydro turbines?
Pelton and turgo
Which micro hydro turbine has lower water requirements?
Pelton
Which micro hydro turbine is smaller and more reliable?
Turgo
Which type of generator is mostly used in microhydro systems?
Asynchronous
What is the formula for finding rpm?
N=fx120/p
