general Flashcards
(155 cards)
1
Q
During the summer solstice, the solar altitude at solar noon will be _____
A
69.5 degrees (due to 90-44 = 46, 46 + 23.5 = 69.5) this example uses Lat = 44
2
Q
All inverters used in PV systems must be listed to what standard?
A
UL 1741 standard
3
Q
What is the power performance ratio?
A
ratio of what the system is actually producing divided by what it should be producing with the given environmental conditions
4
Q
Ohm’s law
A
V = A x R
5
Q
What can function as both a load-break disconnecting means and overcurrent protection?
A
circuit breaker
6
Q
what do overcurrent protection devices do?
A
protect a conductor from current exceeding its ampacity
7
Q
What is the best option when structural members are not located in the area required to install a roof attachment?
A
install wood blocking between the rafters/trusses
8
Q
The point of connection may be located
where?
A
supply side or the load side
9
Q
The 2017 NEC states a ___ degree C adder for conduit less than 7/8” off roof top
A
33
10
Q
List other wire options
A
- RHW-2
- USE-2
- PV wire
11
Q
IFR and IRC requirements for roof access pathways
A
36” upslope and 18” ridge
12
Q
Measured voltage will differ from the nameplate value based on _______?
A
cell temp
13
Q
stand alone inverters convert DC from ______ to AC power
A
Batteries
14
Q
Describe pitch
A
rise over run, for every x” horizontal, you move x” vertical
15
Q
when is a rapid shutdown device required?
A
If the PV system has circuits on or in a house or building
16
Q
What has a strong effect on average and peak operating temperature of all equipment in array set up/
A
Mounting system design
17
Q
What is the primary purpose of Solar Pathfinder or Solmetric Suneye
A
evaluate shading
18
Q
what must a PV source circuit fuse have?
A
- properly sized
- rated for max system V
- DC rated
- UL listed (or equivalent)
19
Q
Pre-operational tests include
A
- Continuity of grounding and bonding.
- AC circuit voltage and phasing.
- Insulation resistance for PV array source and output circuits.
- PV circuit open-circuit voltage and polarity.
- PV source circuit short circuit current.
(Other tests for systems with energy storage) - Voltage and polarity between solar controller and battery banks.
- Voltage and polarity between battery bank and inverters.
- Battery voltage (individual cells and battery banks).
- Specific gravity of flooded lead acid batteries.
20
Q
dual axis tracker
A
daily movement (E to W) AND seasonal variation (azimuth, sun’s altitude change)
21
Q
What conduit should be used in dessert environments?
A
Steel (EMT or IMC), due to high temp difference and low corrosion requirements
22
Q
List some types of DC divisionary loads
A
- resistive water heating elements
- dc water pumps
- other loads that can utilize or store the energy in some other form
23
Q
What can cause a hotspot?
A
When cells that are unshaded attempt to pass current through cells in the same series string that are shaded
24
Q
Calculation for system performance
A
ac kWh / (dc kWp x PSH) = 0.7 to 0.85
25
What are requirements for load side connections?
```
1. Dedicated Overcurrent
and Disconnect. The
interconnection of one or
more inverters in a system
must have a dedicated
disconnecting means and
overcurrent protection
[705.12(B)(1)]
2. Bus or Conductor Ampere Rating
(3) Marking
(4) Suitable for Backfeed.
(5) Fastening
(6) Wire Harness and Exposed Cable Arc-Fault Protection
```
26
List advantages for larger systems using multiple inverters
1. Distributed at different subarray locations (avoids long DC circuits)
2. Provides redundancy (multiple options in case of failure and more tracking)
3. Aids in finding faults
4. Aids in optimizig the output of individual subarrays which have different size, type, orientation and partially shaded
27
What factors are used to calculate the expected AC energy production?
1. wiring losses
2. module mismatch
3. module soiling
4. inverter efficiency
5. orientation
6. tilt angle
28
Voltage drop _____ as wire length / current increases
increases
29
When is max. solar irradiation?
solar noon
30
What is used to measure Voc?
Voltmeter
31
what can temperature compensation help with?
to fully charge a battery during colder conditions, and helps protect it from overcharge and excessive electrolyte loss during warmer conditions
32
VRLA battery characteristics
1. Immobilized electrolyte ( gel or absorbed in fiber glass separator mats between plates)
2. Spill proof
3. No electrolyte main.
4. $$$
5. Less tolerant of over charging and operating temps
6. Do not release gases under normal operating conditions/charging
7. Lower ventilation requirements
33
Autonomy
the number of days that a fully charged battery can meet system loads without any charging
- CAL: 400 Ah battery (nom. Battery cap) has desired allowable depth of discharge of 75% => 300 Ah, if the load is 100 Ah per day, then you would have 3 days of autonomy
34
What is the switch used in inverters to convert DC to AC?
• Large Thyristors (semiconductive switch) are used in high power apps
Connected in parallel to increase current and power capability of an inverter
35
Calculated max continuous current, used to size min. overcurrent devices in DC PV circuits
Isc x 1.25 x 1.25
36
DC to DC converters?
1. boost or stabilizes the DC output of module (raise or lower voltage)
2. they DO NOT convert DC to AC => still need string inverter
37
Can irradiance be used to verify Isc?
YES, If irradiance measurements are made simultaneously with short-circuit current measurements, the measured Isc can be compared to the STC Isc adjusted for
irradiance [Measured Isc ≈ STC Isc x (Measured Irradiance / 1000)].
38
List 3 common, trusted wire management devices?
1. metal clips
2. nylon 6 wire ties (good for aluminum)
3. nylon 12 wire ties (good for galvanized steel)
39
Describe float charging
The charger now just holds the battery at a lower specified voltage - trickling the lowest number of Amps in to the battery that it can- to maintain the float Voltage
40
Characteristics of metal-oxide semiconductor field effect transistors (MOSFETs)
- lower voltage operation, high efficiency, low resistance
- Very high speed switch rate
- Used in low to medium-power apps (1 -10 kW)
41
How to determine the daily energy consumption
all loads power use (DC and AC) x average daily time of operation
42
If your latitude is 44 degrees north, the solar altitude at solar noon during an equinox will be _____
```
46 degrees
(90-44=46)
```
43
What is the distance between the bottom of the PV module and surface they are attached to maximize passive cooling gains?
2 to 6 inches
44
Wire rated for 90 C but not "W" for wet
THHN
45
when battery temperature decreases, what happens to the Voltage?
It increases
46
Calculate the min overcurrent device for an inverter output circuit (AC)
max. circuit current x 1.25
47
What ratio is required for ladder height and contact to building?
4:1 (every 4 ft of height, 1 ft out)
48
It is wise to keep 1" space between conduit and roof, why?
1. help prevent smaller debris from being trapped under the conduit
2. reducing conduit temperature
3. eliminating the need for a temp adder
49
List common pitches
(1/12) =5 degrees
(2/12) = 10 degrees
(5/12) = 23 degrees
50
what is considered a low slope roof?
pitch of less than 2:12
51
Insulation resistance testing is used to identify what?
1. damage or insulation faults in PV modules and
interconnect wiring
2. to locate ground faults
3. to assess the degradation of array wiring, PV
modules, and other system components.
52
what is the purpose of an overcurrent device?
to prevent conductors from overheating and possibly causing a fire
53
Best tilt of 1. winter 2. summer 3. overall average production or spring/ fall
1. + 15 degree Lat
2. - 15 degree Lat
3. Latitude
54
What is the PVWatts calculator used for?
calculate the performance and provide an energy estimate for grid-direct PV systems
55
system grounding
connects a current-carrying conductor
| in an electrical system to ground, or earth potential
56
During the winter solstice, the solar altitude at solar noon will be ______
22.5 degrees (due to 90 - 44 = 46, 46 - 23.5 = 22.5) this example uses lat = 44
57
Manufacturer testing includes
* Wind or snow loading of module.
| * Structural strength testing for array structure components.
58
Define magnetic declination
the angular difference, measured in degrees, between true N/S and magnetic N/S
59
Describe Bulk charging (generally)
The charger throws amps in to the battery - as many as it can (while being limited by any specific limits set in the charger). As loads of amps pile in to the battery - the battery voltage rises. When the battery voltage reaches the specified absorption V - bulk stops - and absorption starts. This phase will simply go on as long as it takes - to get to the battery V to the set absorption V
60
Solidly grounded conductor must be ______
white or grey
61
what is the acceptable voltage drop?
2% - 5% overall
62
List the key indicators for system performance in grid-tied PV systems?
ac power output (kW) and energy production (kWh
63
Rate of charge/ discharge
▪ Ratio of the nominal battery capaciity ( C ) to the charge or dischagre time period in hours
▪ EX: 100 Ah battery discharged at 5 amps for 20 hours
▪ C/20 or 20 hour discharge rate
▪ The higher the discharge rate and lower temp, the less C that can be withdrawn
64
What does altitude refer to?
the angle of the sun relative to the Earth's horizon
65
Does aluminum or copper have lower resistance?
copper
66
Give examples of an overcurrent device?
breakers and fuses
67
Capacity
a measure of battery energy storage, amphere-hours (Ah) or kilowatt-hours (kWh
68
Determining wire size
of strings x Isc x 1.25 x 1.25 = A
69
Characteristics of insulated gate bi-polar transistors (IGBTs)
- High current and voltage
- Lower switch speeds
- More common for high-voltage, larger power apps (> 100 kW)
70
What is the calculation to determine the inverter output circuit
1.25 x continuous current
71
Maintenance plans for PV systems include?
1. Inspections of components and wiring systems
2. Evaluation of structural attachments and weathersealing
3. Cleaning and removing debris around arrays
4. Performing battery maintenance
5. Conducting electrical tests and verifying performance
6. Replacement of damaged or failed system components
72
What should be included in the as-built or record drawings?
1. The physical location and installation method of electrical equipment and wiring.
2. The rating of electrical equipment and wiring.
3. The functional location of electrical equipment (i.e. between specific components, in series or parallel, etc.).
73
List test equipment used in commissioning the solar system
1. Digital multimeter
2. Clamp-on ammeter
3. Irradiation (sunlight intensity) meter
4. Infrared temperature sensor / gun or thermocouple
5. Torque tools (wrench(es) and screwdriver)
6. Insulation resistance tester (megohmmeter)
7. Thermal imaging (IR) camera or scanner
8. I-V curve tracer
9. Hydrometer (for flooded lead acid batteries)
10. toruque wrench/ screwdriver
74
define peak sun hours
the equivalent number of hours per day when solar irradiance averages 1000 W/sq m
75
What conduit should be used in tropical and underground?
PVC, due to small temp difference and high corrosion requirements
76
Polarity can be verified while measuring Voc, how can this be verfied?
If conductor polarity is reversed in a multi-circuit combiner, circuits end up connected in series rather
than parallel and this will result in excessive voltages that may exceed the rating of connected
equipment.
77
What does PVWatts account for in system losses?
1. soiling
2. shading
3. snow
4. mismatch
5. wiring
6. connections
7. light-induced degradation
8. nameplate rating
9. age
10. availability
78
What tools can be used to test Isc?
digital multi-meters and clamp-on ammeters
79
Temperature effects what more?
Voltage
80
What should be used to properly secure clamps to PV module?
Torque screwdriver or wrench
81
what do you need to calculate the expected voltage?
```
use an infrared temperature gun and calculate an expected voltage based on the module STC
Voc, the number of modules in series, the module temperature coefficient of Voc, and the
measured temperature at the time of the test.
```
82
Single axis tracker
daily movement, E to W
83
Testing ac circuits
1. continuity
2. phasing
3. voltage.
4. voltage drop
84
Steel requirements for fittings
- Requires fittings for runs over 100 ft
| - Requires 4" fitting every 375 ft
85
What is the AC output minimum for Large-Scale Photovoltaic (PV) Electric Power Production Facility?
5,000 kW
86
What estimation do we use for PV system cost?
$2 - $5 per Watt
87
List advantages for module level inverters
1. Individual mod MPPT
2. Better energy harvest of shaded and multi-directional arrays
3. Min field installed DC wiring and DC source circuit issues
4. Safer due to max DC volts on a module level ( dealing with much smaller levels than a string series)
88
Testing for mechanical integrity via pulling/shaking is allowed for verifying what?
1. all sections of the array structure are securely connected
2. all modules are firmly mounted on the array structures.
3. all balance-of-system equipment is securely mounted.
89
What is the acceptable variation in Voc from expected value?
+ or - 5%
90
which batteries are temperature compensation features recommened for?
all types of sealed batteries, which are much more sensitive to overcharging than flooded types.
91
How much power should a 4,800 Watt (STC) crystalline silicon array produce when the array
temperature is 45°C and the irradiance is 840 W/m2? The inverter efficiency is 95%; module
mismatch and the dc and ac wiring losses are 2% and 3% respectively, and soiling is minimal.
System Adjustment Factors:
1. Temperature: [1 - (45°C–25°C) x (–0.005/°C)] = 0.90
2. Irradiance: (IRR ÷ 1000W/m2) = 840 ÷ 1000 = 0.84
3. Inverter Efficiency: 0.95
4. Mismatch and dc and ac wire losses: 5% total = 0.95
5. Soiling: 0% = 1.0
Inverter Output Power = 4800 x (0.9) x (0.84) x (0.95) x (0.95) x (1.0) = 3275 W
92
One effective method for electrically connecting two aluminum structure pieces is...
have stainless fasteners with serrations. Stainless star washers can also be used to break through the non-conductive coatings and establish effective bonding.
93
Microinverters are typically wired in ________
parallel
94
What type of screws are recommended to use to simplify the pilot hole drilling process?
fully threaded lag screws
95
Calculation for weighted average operating time
(Wh/day of load 1 x hr running of load 1) + (wh/day of load 2 x hr running of load 2) / (wh/day of load 1 + wh/day of load 2)
96
Where are bypass diodes located and what is there purpose?
1. in module's junction box
| 2. to prevent hotspots in a cell or module
97
How do you find the max. overcurrent device for PV source circuit?
It will be manufacturer specific, listed on the module
98
How do you approx cost of PV system?
take the approx or known PV size in kW and multiply ($2.00-5.00/watt)
99
Modules in series are connected ______
Positive to negative
100
The Earth has a ____ degree tilt
23.5
101
Flooded battery
- Liquid electrolyte solution
- Open-vent flooded types have removable vet caps ( permit electrolyte main. And water additions)
- Release hydrogen and oxygen gases ( due to electrolysis and results in H2O loss)
102
The overcurrent protection device should have a rating ________ that of the conductor
equal to or less than
103
When dealing with ballasted systems, what is something to consider?
Water pooling which can lead to excess load weight on roof
104
For mounting systems that use adhesive attachment of the PV module to the mounting surface, what 3 things are important to consider?
1. compatible with roof material
2. thermal expansion/contraction
3. moisture
105
The ampacity of a conductor depends on what?
1. material
2. temp rating of its insulation
3. operating conditions
106
What is considered a rapid shutdown initiation device?
1. a PV disconnect
2. service disconnect means
3. readily accessible switch that clearly states "ON" or "OFF"
107
What are two functions of a microinverter?
track individual MPPT and convert DC to AC
108
Transformer-based and Transformerlesss inverters are functionally or solidly grounded?
Functionally grounded
109
solar irradiance effect what more?
Current
110
List a few recent requirement updates in 690
• New labeling requirements to warn operators, fire fighters and maintenance
personnel of the hazards.
• rapid shutdown provisions for emergency response.
• Specific wiring methods and wire management practices to improve safety and
system durability.
• calculating voltages and currents.
• use of listed PV-rated overcurrent protective devices.
• Revised requirements for PV system disconnects and equipment isolation.
• Clarifying the options and requirements for system grounding and equipment bonding.
• Clarifying the options and requirements for ac connections within building
electrical systems.
• New exception to arc fault detection for certain PV output circuits not on buildings.
111
what is the difference between the 2014 and 2017 NEC on grounding systtems?
2017 requires that both positive and negative conductors be disconnected to equipment
-disconnect both conductors to equipment so the inverter or other equipment can be properly
isolated and worked on safely during daylight hours.
112
What is considered a steep slope roof?
pitch of 2:12 or greater
113
Calculation to find maximum number of
| modules per source circuit
1. Voc x (correction factor found on table 690.7(A) for the low cold temp) = corrected Voltage "CV"
2. max V for inverter / "CV" = max # of mods
114
The equipment grounding conductor must be ______?
bare wire, green, or green with yellow stripes
115
equipment grounding
connects a current-carrying conductor
in an electrical system to ground, or earth potential, examples include: PV module frames, racks, enclosures, junction boxes, conduit and other metallic components that are likely to become energized
in a fault
116
Functionally grounded conductors need to be _______
any color EXCEPT white, gray, or green
117
functionally grounded
AKA ungrounded; has a reference to
| earth that is other than a solidly grounded system.
118
What tool measures irradiance?
pyranometer
119
What is the current leading battery type?
Lithium-ion, installer will not directly interact with battery, that is done in the factory
120
What operating voltage do crystalline silicon PV cells typically have?
0.5 V
121
PVC requirements for fittings
- Requires exspansion fittings for straight runs over 20 ft
| - Requires one 4" fitting for run over 75 ft
122
When working on energized equipment and circuits what PPE is required?
1. eye protection
2. appropriate footwear
3. hard-hats
4. safety vests
5. insulated gloves
6. face-shields
7. ear plugs
8. arc-rated clothing
123
Typically, the PV array
is configured at _____ voltages than the battery, and dc to dc power conversion circuits
in the MPPT controller automatically provides a lower voltage and higher current output to the
battery.
higher
124
List advantages of multi-mode inverters
1. Operates as either interactive (grid tied) or standalone (battery) ! (NOT simultaneously) !
2. Interface and control auxiliary sources (generator)
3. Used in places where back up power supply (battery or generator) is needed for critical loads
125
What do the use of conduit provide?
1. Physical protection
2. Sunlight resistance
3. Temp extremes
4. Corrosion resistance
126
What loss factors do PV Watts estimate?
1. soiling,
2. shading
3. snow
4. mismatch
5. wiring
6. connections
7. light-induced degradation
8. nameplate rating
9. age
10. availability
127
At what value of resistance is sufficiently low to prevent hazardous voltage before a fault clears?
50 V, For example, if the overcurrent device on a circuit is 30 A, the measured resistance for the bonding of that circuit should be less than 1.67 Ohm
(50 V / 30 A = 1.67 Ω).
128
State of charge
% of available C compared to the fully charge state
129
List commissioning protocol outline
1. Ensuring a safe workplace and documenting personal protective equipment (PPE)
requirements.
2. Verifying final installation details.
118 • System Commissioning Copyright © 2019 NABCEP v.8 NABCEP PV Certification Study Guide
3. Completing a system checkout and visual inspection of mechanical and electrical systems.
4. Verifying proper termination torque of mechanical and electrical connections.
5. Performing electrical and mechanical tests on the system.
6. Performing initial start-up and operational tests.
7. Verifying expected output and performance.
8. Demonstrating and verifying shutdown and emergency procedures.
9. Completing system documentation, including an as-built planset.
10. Conducting user training and orientation.
130
General guidance for circuits from the inverter to the service entrance is to keep the voltage drop below what?
1%
131
Define altitude angle
the vertical angle above the horizon, measured in degrees from the horizon to the sun's position
132
Wire rated "W" for wet but not 90 C
1. THWN
| 2. XHHW
133
How do you approx PV system size with roof area?
square feet x 10Watts per sq ft
134
What affects solar power (irradiance)?
1. clouds
2. rain
3. sun's changing position in the sky
4. what's in the atmosphere (reflecting light)
135
What method can be used to perform an insulation resistance test?
Between the positive dc conductor and ground, and between the negative dc conductor
and ground.
136
Typically where do the smaller AND larger PV systems have their point of connection?
While many smaller PV systems can
meet the requirements for load side connections, larger systems commonly use supply side
connections when the requirements for load side connections cannot be feasibly met
137
What inverter is rated for 1000 VDC (input) to 1500 VDC?
central inverter
138
What does a pyranometer measure?
Irradiance (W/m^2) AKA sunlight intensity
139
List 3 primary considerations to PV system size
1. available space
2. budget
3. annual consumption
140
Is flashing required for standing seam metal roofs?
No
141
What reduces or enhances solar irradiation?
1. ozone
2. earth's position in relation to the sun
3. altitude
142
Field mechanical tests include
1. Soil testing for arrays using screwed or driven piles.
2. Concrete slump test for any foundations.
3. Torque testing to the manufacturer’s specification for mounting structures and module
attachments, wire terminations, and battery terminals.
143
Roof pitch is equivalent to ?
the slope of the roof
144
Dc-to-DC converters (optimizers) are typically wired in ______
series
145
Will the sun be higher or lower in the middle of the day closer to the equator?
higher
146
Where should insulation resistance testing be performed on the system?
1. PV source circuit combiner boxes
2. PV output
3. inverter output circuit conductors
147
What affects voltage drop?
1. wire size/gauge
2. circuit current
3. circuit voltage
4. circuit length
148
What is used as a OCPD and why
fuses/ circuit breaker, prevents the backflow of current to PV mods
149
During visual inspection it is important that all ________ are correctly installed and within code
signs, labels, and directories
150
What is tested verify proper array configuration and that the circuits are clear from major faults?
Isc
151
Describe absorption charging (generally)
the charger continues to throw amps at the battery - but in this phase it doesn't allow the voltage to go above the specified absorption V. So, as time goes on, in this phase, the number of Amps drop off, as the battery gets fuller, the charger requires less amps to maintain the battery at the specified V. Eventually the number of Amps being thrown at the battery drops to almost nothing - to hold the battery at the specified absorption V. At this stage, or, when hitting the time limit set for absorption, the charge stops absorption and switches to float. This phase will go on for as long as it takes, or, for a specified time if time limited in settings of any given charger.
152
Irradiance
instantaneous intensity (POWER) of sunlight; W/m^2
153
Irradiation
ENERGY; Power/time
154
Parallel connections are made by?
Connecting a positive to positive or negative to negative
155
depth-of-discharge
% of C that has been removed from a battery compared to a fully charged state; for deep cycle batteries (75%-80%)
