Medium Voltage and Solar Energy Systems: A Comprehensive Guide, Exams of Electrical and Electronics Engineering

Download Medium Voltage and Solar Energy Systems: A Comprehensive Guide and more Exams Electrical and Electronics Engineering in PDF only on Docsity! NABCEP PV ASSOCIATE EXAM QUESTIONS WITH VERIFIED SOLUTIONS. An off-grid installation has a 1HP pump that is on 10% of the time and a 20W light that is on 100% of the time. What is the monthly energy use? - ANS 68KWh 1HP = 746W 746W * 0.1 * 24hours * 30days = 53712Wh 20W * 24hrs * 30days = 14400Wh 14400 + 53712 = 68112Wh 68kWh What kind of ground faults do most inverters detect? - ANS DC Inverters detect dc ground faults. AC ground faults are detected on the AC side of the inverter at the distribution paned (MSP, load center). Most inverters are not connected to high or medium voltage. Medium voltage is thousands of volts, large utility scale inverters are connected to medium voltage via a transformer Current carrying ability of a conductor (wire) is called - ANS Opacity According to ohms law and voltage drop, the relationship between voltage drop and current is - ANS Proportional. Ohms law: V = I*R More current makes more voltage drop. This is a reason why we need a larger wire with more current, so the wire resistance is less with a larger wire and there will be less voltage drop. An array in a hot and dry place is not producing as expected in summer time. Which of the following is NOT a likely problem: a) Decreased ac wire size and voltage loss b) String size too short C) String size too long D) Soiling - ANS C) String size too short. When it is hot, voltage can be low. Too long of a string would be a problem when it is too cold not too hot. When using a digital millimeter, what is the first thing you should do? - ANS Inspect the meter. Always inspect first, look before you touch Is the worst design error? A) BIPV on a commercial job B) A fast-growing tree to the north of an array in Idaho C) PV at 5-degree tilt at 40 degrees latitude D) Different tilt angles in a PV source circuit - ANS D) Different tilt or azimuth operation within a source circuit is bad. Series connections should not have different orientations MPPT is for - ANS MPPT is maximum power point tracking and will optimize the energy harnessed from PV. Some inverters have multiple MPPTs. Charge controllers often, but don't always, have MPPTs Concentrated PV: A) Only works with direct sunlight B) Usually has a single axis tracker C) Will get 30% power during cloudy conditions D) Is using heat to make electricity - ANS A) Only works in direct sunlight. Usually works with 2-axis trackers to always point at the sun and will not work at all in cloudy conditions. Concentrated PV =! Concentrating Solar thermal Fall protection should be used at heights over - ANS 6 feet Parallel PV circuit connections increase - ANS Parallel increase current. Series increase voltage Optimal tilt for off-grid PV system in the winter - ANS Latitude + 15 degrees is optimal tilt to maximize winter production. The sun is lower in the winter, requiring a higher tilt angle What is the most acceptable rating of an enclosure for exposed circuit conductors mounted on an outside wall? - ANS NEMA 3R Bypass diodes are located in the A) Combiner box B) Inverter C) Wiring harness D) PV Module - ANS Bypass diodes are in PV module junction box. Diverts current around a group of cells if one is shaded. Usually 3 diodes/PV module PV array at higher elevation would tend to produce more - ANS Current. Higher elevation, less atmosphere, more irradiance, more current. High elevation can also be cooler meaning more voltage from cold temps. How much 14% efficient PV fits on 25 Square Meters A) 3000W B) 4.5kW C) 4000W D) 3.5kW - ANS D) 3.5kW. 14% efficient = 0.14*1000W/M^2 = 140 W/m^2 140 * 25 = 3500W = 3.5kW Which is the smallest conductor? - ANS 18 AWG 18 AWG, 10 AWG, 0 AWG, 3/0 AWG What is the simplest type of PV system - ANS Direct coupled is the simplest with just PV and a load that only works when the sun is out Sun path charts differ based on - ANS Latitude Series connections increase - ANS Voltage. Parallel increases current The longest shadow at 2PM would be on - ANS the winter solstice (12/21) somewhere between 14 and 15V. If a 12V lead-acid battery is at 50% depth of discharge, it will measure about 12V Unit for resistance - ANS Ohms Wind uplift forces in the construction industry in the US are measured in... - ANS Pounds per square foot (past) Direction on a compass is - ANS Azimuth Hydraulic analogy for voltage is - ANS Pressure. Current is flow Which room cannot have a PV dc disconnect? A) Kitchen B) Attic C) Bathroom D) Bedroom - ANS Bathroom. PV dc disconnect not allowed in bathroom (think wet feet) Stand-alone inverter output goes to: - ANS Loads. Off-grid inverter output goes to loads. Loads are what use electricity Best sealant for residential rooftop - ANS Polyurethane and silicone are the best. Silicone is a sealant, silicon is what solar cells are made of 500W/m^2 for 4 hours is - ANS 2kWh For a supply side connection, the output of the inverter is limited by - ANS Service entrance conductor capacity. The loads are already protected from the utility by the main service disconnect (main breaker) Which is the smallest installable part of a PV system? A) Solar panel B) Solar module C) Solar array D) PV source circuit - ANS Solar module. A solar module is the smallest unit that you can install. A solar panel is made up of solar modules. You cannot install a single solar cell, a number of solar cells are put together to make a module. 60 or 72 What is the most typical hazard with PV systems of the following? A) Shock B) Arc Flash C) Lightning D) Earthquake - ANS Shock. Solar installers are always concerned about shocks and falls. Arc flashes can be very dangerous but are less common A 4kW PV system with 15% losses in a location with 4.5 sun hours per day, what would be the annual output? - ANS 5585kWh. 4kW * .85 * 4.5 sun hours * 365 days If available roof area is 12m^2 and the PV is 15% efficient, then how much PV will fit? - ANS 1.8kW 0.15 * 1000W/m^2 150W/m^2 * 12 m^2 = 1800W Which of the following is a typical direct PM system application? A) Lighting B) Batteries C) Pumping water D) Fire alarm - ANS Pumping water is a common direct-coupled PV application. Current is affected mostly by A) The number of solar cells in series B) The size of the solar cell C) The back sheet of the solar module D) The temperature of the cell - ANS The size of the solar cell determines the current of a PV module. A larger solar cell will capture more photons and convert them to electron flow. The number of cells in series determines the voltage In California (east of the zero-degree isogonic line) the north needle of the compass will point: - ANS Slightly East of true North. In California, magnetic declination is to the east Maintenance of sealed valve regulated lead-acid batteries includes: A) Checking fluid levels B) Equalization charge C) Scrubbing lead plates D) Cleaning terminals - ANS Cleaning terminals. On a SEALED lead-acid battery (also known as maintenance free), one does not have access to the electrolyte fluids. Equalization is not done on sealed batteries, since equalization requires distilled water to be added to the battery. All batteries can have their terminals cleaned. Given that Vic is 19V and the temperature correction factor for voltage is 1.2. What would be the maximum system voltage if there were 16 modules in series - ANS 346V. 18V * 1.2 correction factor * 16 in series = 346V STC watts can be calculated by - ANS Vamp * Imp = STC watts. At Vic there is no current and power is zero. At Sic there is no voltage and power is zero PV Module - ANS turns light into electricity. A group of solar cells in a sealed unit. Interactive inverter - ANS Often called a grid tied inverter. An inverter that reads the voltage of the grid or micro-grid and produces as much power and current as it can, regardless of loads. Interactive inverters are sold according to maximum power output power. They also have dc and ac operating voltage ranges Micro inverter - ANS A small inverter that is mounted behind a PV module String inverter - ANS An inverter that has PV source circuits (modules connected in series) connected to the inverter Central inverter - ANS A large inverter, usually in the MW range without PV source circuits connected directly to the inverter. The PV source circuits come out of the combiners to the inverter. AC module - ANS A module with AC output listed for such use. Can be a micro- inverter mounted on a module if it was tested together Dc-to-dc converter - ANS Power optimizer. Often mounted behind modules and convert voltage and current. Can often perform other tasks such as monitoring and turning of PV modules. Transformers do for ac what optimizers do for dc Loads - ANS Devices that use energy. A light bulb is a load Conductors - ANS Wires Conductor sizes - ANS From small to large 18AWG, 16AWG, 14AWG, 12AWG, 10AWG, 8AWG, 6AWG, 4AWG, 2AWG, 1AWG, 0AWG, 2/0AWG, 3/0AWG, 4/0AWG AWG - ANS American Wire Gauge Grounded conductor - ANS A conductor that is intentionally referenced to ground but carries current. The color of the grounded conductor is white. In ac wiring the grounded conductor is also called neutral EGC - ANS Equipment Grounding Conductor: A conductor that is not meant to carry current and connects (bonds) metal equipment together, so that there are no dangerous voltage differences. Green or bare wire. Even "ungrounded systems" have equipment grounding Load center - ANS A place where loads are connected, such as a panel board, also known as a main service panel (MSP) or a subpanel Branch circuit - ANS A circuit coming from a circuit breaker off of a load center. Inverters have dedicated branch circuits Transformer - ANS a device used for charging one ac voltage to another ac voltage Non-isolated inverter - ANS An inverter without a transformer. Does not have a current carrying conductor that is at the same voltage as ground. Most popular inverter in world, very safe PV source circuits - ANS PV modules connected together in series including the PV modules and the conductors. Voltage increases in series, current does not change in series The temperature rating of the insulation of a conductor when designing a PV system effects the... - ANS Ability of the wire to carry current When a bypass diode kicks in from a leaf on a solar cell, which parameter would you see reduced on a single string with string level MPPT - ANS Voltage Which is the best and safest way to determine current in a PV output circuit - ANS Clamp on ammeter What is blocking used for - ANS attaching to a roof in a place where there is no rafter Blocking Diode - ANS Prevents reverse current If you are going to work on the roof to fix a ground fault and the dc disconnect is on the ground level, which of the following is the best safety procedure A: grounding the ungrounded conductor before going on the roof B: Removing the GFCI fuse before going on the roof C: Leaving the disconnect in the on position D: Lockout tag out - ANS Lockout tag out Who makes requirements for electrical safety for employees? - ANS OSHA Typical utility interactive systems in the US will - ANS Export to the utility extra power for credit A PV system that would produce 7kWac under STC conditions, which is not clipping power is installed in a location with an average of 6 PSH would produce how much energy in one year? - ANS 15,330 kWh 7*6*365 When PV modules are tested by CSA to the UL 1703 standard, they are tested among other things for: A: Power production over long periods of time B: Fire safety C: For maximum performance in cloudy conditions D: For temperatures down to -60C - ANS B: Fire Safety If an inverter indicates that there has been a ground fault, what is the first thing that an O&M technician should do? - ANS Open all the disconnects If doing an energy audit, which is the best to replace to conserve energy? a. New resistance heater b. New geothermal heat pump system c. New refrigerator d. New air conditioner - ANS a. New resistance heater When handling PV modules on a roof in sunlight, what is the most common method of safety of the following? a. Take all connectors off the modules b. Test voltage every 5 minutes C. Make sure that connectors are open d. Keep tape over the glass and around the corners of the frames - ANS c. Make sure that connectors are open Which of the following is the worst design flaw when an inexperienced person designs a PV system? a. Multiple orientations within a PV source circuit b. Multiple orientations for different PV source circuits c. Occasional shading on a module that is in a PV source circuit that has its own MPP d. Micro inverters used on a commercial job - ANS a. multiple orientations within a PV source circuit Part of the process of turning silicon into a solar cell is called? a. Iodization b. Oxidation c. Doping d. Dumping - ANS d. Doping How do residential rooftop mounting systems typically attach to a rooftop, so that they do not fly away when the wind blows? - ANS Lag screws into rafters or purlins What is the shape of a typical monocrystalline solar wafer? - ANS Square with rounded corners What is the largest array size of the following if you are using a 24V battery bank and a 20A charge controller? a. 500W b. 2kW c. 1000W d. 280W - ANS a. 280W Which of the following is able to change dc power into ac power with a predetermined specific frequency and voltage? a. Inverter b. Power converting utility c. Step up transformer d. Step down transformer - ANS a. Inverter What color wires can be used for equipment grounding (earthling is international term) wires in the US? - ANS Green, bare, or green with yellow stripe What does MPPT stand for - ANS Maximum Power Point Tracking Which is the best solution of the following for multiple orientations when designing a PV system? - ANS Micro inverter