Amazon S3



Practice Exam Two: Bonus!The NABCEP Entry Level Exam is a timed test, which you will be given 2 hours to complete.Note: This second practice exam may be harder than the NABCEP Associate Exam. There is no way to tell exactly what will be on the exam, and there have been surprises. Studying this material may get you a higher score than required to pass. Additionally, I have added 5 extra questions on this exam; since you are studying in your comfortable zone, if you can do well on this exam in 2 hours, you should be set for the real thing!A common question I get about the NABCEP exams is, “what is the passing score?” NABCEP does scaled scoring, which means that they use top-secret scientific scoring methods, and nobody ever knows what the passing score is. Scores are not based on a percentage.Answers and explanations follow this exam.Set your clock for 2 hours, put batteries in your calculator, sharpen your pens and go!If an array is facing south at equinox at noon, what must the tilt angle be in order for the array to face directly at the sun at latitude 30?a. 33 degreesb. 48 degreesc. 18 degreesd. 30 degreesThe temperature rating of the insulation of a conductor when designing a PV system affects thea. ability of the wire to withstand fireb. ability of the wire to withstand smokec. ability of the wire to carry currentd. ability of the wire to withstand physical damageWhen 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?a. Currentb. Voltagec. Ohmsd. Amp hoursGiven a PV module with the following characteristics, what would be the expected output at Standard Test Conditions if the inverter and PV were working perfectly and sending power to the grid?20 in series1 PV source circuitVoc = 44VVmp = 35.2VPower = 305WIsc = 9.27Aa. 704V and 8.66Ab. 600V and 8Ac. 1000V and 8.2Ad. 700V and 9.27AWhich is the best and safest way to determine current in a PV output circuit?a. Megohmmeterb. Insulation testerc. Clamp on ammeterd. Through a digital multimeterA remote cabin uses the loads below per day, how much total energy is used per day?1000W toaster for 6 minutes1.2kW hot water heating element for 3 hours per dayThree 17W LED lights for 3 hours per dayiPhone 100 charger at 20W for 3 hours per daya. 0.13 cWhb. 39 kWhc. 3.9 kWhd. 3900mWhWhat is “blocking” used for?a. Bypass diodesb. Attaching to a roof in a place where there is no rafterc. Leveling off a parapetd. Inserting reverse current into a circuit to prevent forward bias currentIf 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 roofb. Removing the GFCI fuse before going on the roofc. Leaving the disconnect in the on positiond. Lockout TagoutWho makes requirements for electrical safety for employees?a. Employerb. Employeec. OSHAd. NECTypical utility interactive systems in the US willa. Sell to the utility with a feed in tariff (FIT)b. Export to the utility extra power for creditc. Use batteriesd. Send energy to diversion loadsA PV system that would produce 7kWac under STC conditions, which is not clipping power is installed in a location with an average of 6PSH (peak sun hours, aka kWh/square meter per day average) would produce how much energy in one year?a. 14,008 kWhb. 1,503 kWhc. 3,307 kWhd. 15,330 kWhWhen PV modules are tested by CSA to the UL 1703 standard, they are tested among other things fora. Power production over long periods of timeb. Fire safetyc. For maximum performance in cloudy conditionsd. For temperatures down to -60CIf an inverter indicates that there has been a ground fault, what is the first thing that an O & M technician should do?a. Close all the disconnectsb. Open all the disconnectsc. Turn on the systemd. Replace the GFDI (ground fault detection and interruption) fuseIf doing an energy audit, which device is the best to replace to conserve energy?a. New resistance heaterb. New geothermal heat pump systemc. New refrigeratord. New air conditionerWhen 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 modulesb. Test voltage every 5 minutesc. Make sure that connectors are opend. Keep tape over the glass and around the corners of the framesWhich of the following is the worst design flaw when an inexperienced person designs a PV system?a. Multiple orientations within a PV source circuitb. Multiple orientations for different PV source circuitsc. Occasional shading on a module that is in a PV source circuit that has its own MPPd. Microinverters used on a commercial jobPart of the process of turning silicon into a solar cell is called?a. Anodizationb. Oxidationc. Dopingd. DumpingHow do residential rooftop mounting systems typically attach to a rooftop, so that they do not fly away when the wind blows?a. Lag screws into rafters or purlinsb. Screws into sheathingc. Flashingsd. BallastsWhat is the shape of a typical monocrystalline solar wafer?a. Circularb. Squarec. Rectangulard. Square with rounded cornersWhat is the largest array size of the following if you are using a 24V battery bank and a 20A charge controller?a. 500Wb. 2kWc. 1000Wd. 280WWhich of the following is able to change dc power into ac power with a predetermined specific frequency and voltage?a. Inverterb. Power converting utilityc. Step up transformerd. Step down transformerWhat color wires can be used for equipment grounding (earthing is international term) wires in the US?a. Green, bare or green with yellow stripeb. White or bluec. Yellow or blued. Any colorWhat does MPPT stand for?a. Maximum payback period timeb. Maximum power performance trackc. Maximum power point trackingd. Minimum peak performance timeWhich is the best solution of the following for multiple orientations when designing a PV system?a. Battery backup string inverter with secure power supplyb. Microinverterc. Charge controllerd. Hybrid inverterIf you want to use modules that are dissimilar and in multiple orientations, what is the best type of system to use?a. 2 channel MPPT inverterb. Small 12V battery systemc. Dc-to-dc converter (power optimizer) systemd. Central inverterIn the western part of the USA and Canada, what direction does the north arrow of a magnetic compass point?a. South of westb. West of northc. East of northd. West of eastYou are rebuilding an old battery system for a PV museum and everything is in amps and amp hours. You are told that the system needs to have 33% more PV production on average than what the loads require. The loads will require 20Ah per day and the insolation will be 5PSH. If the module current at STC is 8A at Imp and 9A at Isc, how many PV source circuits would be needed to meet the minimum requirements stated here?a. 1b. 2c. 3d. 4Which tilt angle from horizontal would get the best annual production from a location in Toronto at 43 degrees north?a. 42 degreesb. 58 degreesc. 15 degreesd. 20 degreesA multimodal inverter that has an internal automatic transfer switch would have to monitor what in order to transfer to backup power?a. Current and voltage from PV arrayb. Primary power source voltagec. Primary power source currentd. Backup power source viabilityWhich of the following will have the highest voltage setting for charging flooded lead acidbatteries?a. Bulk chargeb. Absorption chargec. Float charged. Equalization chargeBesides calculations, where can we find out what would be the maximum series fuse rating of a PV module?a. On the back of the moduleb. On the PV wire instructionsc. By multiplying Imp x 1.56 and rounding up to the next common fuse sized. By multiplying Isc x 1.25 and rounding up to the next common fuse sizeIs there a difference between solar noon and noon as most people know it and if so, what is the difference?a. Solar noon is the same as noon as most people know it.b. Solar noon is not dependent on time zonesc. Solar noon is dependent on time zones, but does not incorporate daylight savings timed. Solar noon is noon at GMTWhat contributes to determining the ampacity or the temperature rating of a conductor?a. Insulationb. Insolationc. Fill factord. Sealing racewaysThe definitions of the difference of a PV output circuit and inverter input circuit for a grid-tied system are very similar and some believe overlap. In many diagrams, what is the point where the PV output circuit becomes an inverter input circuit?a. Combiner boxb. Inverter terminalsc. DC disconnectd. AC disconnectWhat kind of PV system is used so that people have power if the utility ceases to exist, but can still work with the utility?a. Stand-aloneb. Direct-coupledc. Multimodald. Grid-tied hybridIf someone had a snow lodge with a wall facing south, what would be the best argument for increasing tilt to very steep or even vertical on the wall?a. To decrease reflection from solar modules onto people walking towards the lodgeb. To increase production from reflection off the snowc. To prevent heat buildup underneath the modulesd. To increase summer production for net-metering situationsOn a southeast facing residential rooftop, what is the most common type of mounting system?a. BIPVb. Flush mounted rack mountc. Tilt up rack mountd. BallastedWhy do we need to know the lowest expected temperature?a. Prevent under currentb. Prevent under voltagec. Prevent over currentd. Prevent over voltageWhat is the maximum number of modules in series given that Voc = 44V, Vmp = 38V, cold temperature = -22C, Temperature coefficient Voc = -0.3%/C, Inverter maximum input voltage = 550V?a. 8b. 9c. 11d. 10If you are sizing a PV system on a building for a location with net-metering, what is the best way of the following to size the system?a. Multiply load factor by power factor by energy usageb. Size the system based on energy usage, budget and available spacec. Size the system based on offsetting the entire electric bill alwaysd. Size the system based on how much will fit on the roofIf magnetic declination is 5 degrees east, then where is true south?a. Where the compass reads 0 degreesb. Where the compass reads 180 degreesc. Where the compass reads 185 degreesd. Where the compass reads 175 degreesWhat is the recommended way that roofers make structural attachments to protect against water intrusion?a. Caulking around the screwb. Extrusionsc. Flashingd. SyzygyWhat is the main use of PV wire?a. Intermodule connectionsb. Inverter ac connectionsc. Must be used on grounded systemsd. PV output circuitsIf we wanted to calculate an average power over time, what would we do mathematically?a. Take demand charges and divide by timeb. Divide energy by timec. Divide Ah by timed. Divide resistance by powerWhich types of wires can be used for connecting modules beneath arrays with exposed conductors?a. THWN-2 and THHNb. XRS and FTPc. PV wire and USE-2d. NMC and RTTWWhat information is needed in order to perform inter-row spacing calculations?a. Solar constant and currentb. Solar zenith angle and power of modulesc. Shading derating factor and azimuthd. Solar elevation angle and solar azimuth angleIn dry places, what would typically be the most common type of maintenance on a PV system?a. Removing leavesb. Washingc. Shade analysisd. MoisturizingWhich characteristics of a wire would lead to more voltage drop?a. Long and wideb. Short and widec. Long and thind. Short and thinWhich type of system is best for seasonally tilting the PV modules?a. Flush mountb. Reverse tiltc. Pole mountd. BallastWhat is the minimum number of modules that you can put in series for proper performance with a high solar cell temperature of 65 degrees, a Vmp of 31V, a temperature coefficient of Vmp of -0.45%/C and in inverter low MPPT voltage of 215V?a. 5b. 9c. 7d. 8When working on a battery bank with a hydrometer, what is the most important personal protective equipment?a. Fall protectionb. Apronc. Eye protectiond. Equalizer What causes the skin to be more conductive and dangerous when working with electricity?a. Moistureb. Densityc. Sized. CapacityWhich device is used to determine that series wiring has been done correctly?a. Clamp on ammeterb. Digital multimeterc. Meggerd. PyranometerWho approves the interconnection of a PV system?a. Local contractor boardb. State Public Utility Commission (PUC)c. Utilityd. Authority Having JurisprudenceWho will typically be required to approve the plans of a PV system?a. Local contractor boardb. State Public Utility Commission (PUC)c. Utilityd. Authority Having Jurisdiction (AHJ)A 16A interactive inverter output circuit will require a circuit breaker of how many amps?a. 16Ab. 20Ac. Less than 16Ad. 30AIn North American homes, typical voltages are:a. 110/208 Vacb. 277/480 Vacc. 100 Vacd. 120/240 VacGround fault detection on a typical interactive inverter is most often due to a ground fault:a. at the PV arrayb. at the utility meterc. at the earthd. at the loadsOf the following, which is worst for stand-alone lead-acid batteries?a. Undersized PV arrayb. Temperatures between 20C and 30Cc. Fine stranded conductorsd. Anti-islandingA 16A interactive inverter that operates at a 240V utility nominal voltage will produce howmuch power when clipping?a. 38kWb. 3840Wc. 15kWd. 0.038MWWhat does a hydrometer measure?a. Water temperatureb. Specific gravity of battery acidc. Lithium densityd. Surfactant levelsA 50kW interactive PV system has 15% system losses in a location getting 5.4 peak sunhours per day average throughout the year. What would be the expected annual energy output?a. 2 MWhb. 44 kWhc. 8.3 kWhd. 83,768 kWhA typical interactive PV system will NOT:a. Reduce greenhouse gassesb. Reduce use of fossil fuelsc. Power a remote cabin isolated from the gridd. Reduce air pollutionWhat is the highest angle which the sun can be anywhere in the world?a. 23.5 degreesb. 45 degreesc. 90 degreesd. 180 degreesWhen sizing a stand-alone PV system, we often have to consider the critical design month,which would have the:a. Best insolation and most load usageb. Worst insolation and most load usagec. Worst insolation and least load usaged. Best insolation and least load usageIf a PV module produces 265W at Standard Testing Conditions and the dimensions of the PVmodule are 998mm wide and 1681mm long, what would be the efficiency of the PV module?a. 14.1%b. 22%c. 26.5%d. 15.8%Of the following, which is the most subject to damage during an installation?a. The frames due to bendingb. The glass due to corrosionc. The backsheet due to contact with sharp edges and module cornersd. The conductors due to water damageWhat instrument can best test the insulation resistance of a conductor?a. Insulometerb. Megohmmeterc. Digital multimeterd. Caloric wire testerWhat is the solar altitude angle?a. The angle between straight overhead and the sunb. The angle between 45 degrees above the ground and the sunc. The angle between the horizon and the sund. The angle between sunrise and sunsetWhat is the solar window?a. Any place the sun can be in the sky in a particular location throughout the yearb. A transparent device used to determine sun pathsc. The location in the sky where the sun will never be, such as northd. A window that faces south in the northern hemisphere or a window that faces north in the southern hemisphere.What is the main function of the Authority Having Jurisdiction?a. To check Code complianceb. To approve utility interconnectionsc. To ensure worker safetyd. To make sure that the employer does not discriminateThe maximum power rating of the largest load of an off-grid system is limited by:a. the size of the batteryb. the size of the arrayc. the size of the inverterd. the size of the charge controllerWhich type of inverter will provide maximum power point tracking on a module per modulebasis.a. Central inverterb. String inverterc. Bipolar inverterd. MicroinverterWhat type of PV racking system is often seen on a commercial low-slope roof withoutpenetrations and with concrete pavers or blocks to keep it from blowing away?a. Ballastedb. Aerodynamicc. Hyperstationedd. Epoxy stationedIn what order is performance from best to worst of the different types of PV systems?a. Roof, Pole, Ground, BIPV (building integrated PV)b. Pole, Ground, BIPV, Roofc. Pole, Ground, Roof, BIPVd. BIPV, Pole, Roof, GroundAnswersIf an array is facing south at equinox at noon, what must the tilt angle be in order for thearray to face directly at the sun at latitude 30?a. 33 degreesb. 48 degreesc. 18 degreesd. 30 degreesDiscussion: If you were on the equator, you would be at zero latitude and the sun with be right over your head at solar noon at equinox. That would be zero latitude with a zero-degree tilt. If you were 1 degree latitude north, then you would have to tilt the module a 1 degree tilt to the south to compensate for being 1 degree from where you first were. If you are 30 degrees north and the sun is in line with the equator (equinox), then you would have to tilt your PV module 30 degrees to line up with the sun at solar noon at equinox. If you were at 90 degrees latitude on the north pole, you would have the sun on the horizon and would have to tilt your PV at a 90-degree tilt to directly point at the sun.The temperature rating of the insulation of a conductor when designing a PV system affectsthea. ability of the wire to withstand fireb. ability of the wire to withstand smokec. ability of the wire to carry currentd. ability of the wire to withstand physical damageDiscussion: Different conductors (wires) have different types of insulation and one thing that makes a conductor more valuable is if it has an insulation that can handle more heat. When a wire has more current going through it, it will heat up. As that wire heats up, it can get to a point where it will damage that insulation. If we have insulation that can handle more heat, then that same size piece of copper wire can handle more current, since it can handle the heat. In solar we often use wire that is rated for 90C, rather than wire that is rated for 75C, which is also a common rating for wire. A 90C rated wire can carry more current than a 75C rated wire.When a bypass diode kicks in from a leaf on a solar cell, which parameter would you seereduced on a single string with string level MPPT?a. Currentb. Voltagec. Ohmsd. Amp hoursDiscussion: Bypass diodes are connected in parallel to groups of solar cells. A 60-cell module has 3 groups of 20 cells and a 72-cell solar module has 3 groups of 24 cells. Each group when it has a solar cell that is shaded, will have that particular group of solar cells bypassed (under normal operating conditions). When a group of solar cells are bypassed, then the voltage contribution from those cells is not used, so the voltage would be less. When a bypass diode kicks in, it sacrifices voltage for current.Given a PV module with the following characteristics, what would be the expected output at Standard Test Conditions if the inverter and PV were working perfectly and sending power to the grid?20 in series1 PV source circuitVoc = 44VVmp = 35.2VPower = 305WIsc = 9.27Aa. 704V and 8.66Ab. 600V and 8Ac. 1000V and 8.2Ad. 700V and 9.27ADiscussion: STC conditions when a PV system is operating, means that the array will be working at Imp and Vmp, so then we just need to know how many are in series and how many parallel. In this case we know that there are 20 in series and with a single 1 PV source circuit (string), so the current would be that of a single solar module (same as a single cell).The tricky part about this question is that Imp is not given and the best way to solve for Imp is to use the formula:Volts x Amps = PowerVmp x Imp = PowerImp = Power / VmpImp = 305W / 35.2V = 8.66A20 in series x 35.2Vmp = 704V (limit for voltage on 1 and 2 family dwellings is 600V)1 PV source circuit x 8.66A = 8.66AWhich is the best and safest way to determine current in a PV output circuit?a. Megohmmeterb. Insulation testerc. Clamp on ammeterd. Through a digital multimeterDiscussion: The best and safest way to determine current in this situation is without even touching any wires. A clamp on ammeter can measure current by putting a clamp around a wire. Make sure to only put the clamp around a single wire, because if you put it over 2 wires in a circuit, the currents will cancel each other out and you would get a reading of zero amps when there is current.A remote cabin uses the loads below per day, how much total energy is used per day?1000W toaster for 6 minutes1.2kW hot water heating element for 3 hours per dayThree 17W LED lights for 3 hours per dayiPhone 100 charger at 20W for 3 hours per daya. 0.13 cWhb. 39 kWhc. 3.9 kWhd. 3900mWhDiscussion: Let’s do the calculations:Power x Time = Energy, just make sure to get your units right.I am going to convert to kW and hours first to get an answer that is in kWh.Toaster = 1000W = 1kW for 6 min = 6min / 60min/hr = 0.1 hrHot water heating element = 1.2kW for 3 hrLED lights 3 lights x 0.017kW = 0.051kW for 3hriPhone 100 = 0.020kW for 3hrToaster = 1kW x 0.1hr = 0.1kWhHot water heating element = 1.2kW x 3hr = 3.6kWhLED Lights = 0.051kW x 3hr = 0.153kWhIPhone 100 = 0.02kW x 3 hr = 0.06kWhSum it all up:0.1kWh + 3.6kWh + 0.153kWh + 0.06kWh = 3.9kWhWhat is “blocking” used for?a. Bypass diodesb. Attaching to a roof in a place where there is no rafterc. Leveling off a parapetd. Inserting reverse current into a circuit to prevent forward bias currentDiscussion: Blocking is done by roofers when they need to add a block to get the strength of a rafter when making an attachment. There are cases where a solar installer wants to make an attachment in a place on a roof where there is no rafter, so they can take a block of wood and fasten it to adjacent rafters to get a strong connection. Wooden roofs are often made with rafters and on top of the rafters is a roof deck, which is often made of plywood or oriented strand board (OSB). The roof deck itself is considered by most to not be strong enough to fasten a solar system to, so the connection will be made to the rafters. Rafter roofs have the rafters on a sloped roof go from up to down. Other types of roofs use purlins instead of rafters and purlins will go from side to side on the roof. Most metal roofs are purlin roofs.There is a diode called a blocking diode, which 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 roofb. Removing the GFCI fuse before going on the roofc. Leaving the disconnect in the on positiond. Lockout TagoutDiscussion: LOTO (lockout tagout) is a system of turning something off and then locking it in the off position, so that nobody comes by and tries to turn the system on while you are working on it. Fall protection should also be used in this situation, since the troubleshooter is on the roof.Who makes requirements for electrical safety for employees?a. Employerb. Employeec. OSHAd. NECDiscussion: OSHA = Occupational Health and Safety Administration and this is the name of the agency responsible for making worker safety rules in the US and many countries.Typical utility interactive systems in the US will:a. Sell to the utility with a feed in tariff (FIT)b. Export to the utility extra power for creditc. Use batteriesd. Send energy to diversion loadsDiscussion: In the US and in many other places, PV systems on buildings usually can export power to the grid for credit if they are producing more than they are using. This type of arrangement is called net-metering. As PV saturates the grid more on some places, there can be changes to this system and in some other places people are not allowed to export. When people connect to the grid and do not export to the grid, they often add batteries to their PV systems and we call these grid-connected battery systems that cannot export “self-consumption” systems. A FIT is a system where people have a PV system and there is a rate that they get credit for producing and selling to the utility that is unrelated to if or how much they pay for electricity. A FIT is usually based on a 20-year contract.A diversion load is a load that is turned on a times when we are making extra electricity that we do not have any other reason to use, such as when batteries are fully charged and the sun is still up.A PV system that would produce 7kWac under STC conditions, which is not clipping power is installed in a location with an average of 6PSH (peak sun hours, aka kWh/square meter per day average) would produce how much energy in one year?a. 14,008 kWhb. 1,503 kWhc. 3,307 kWhd. 15,330 kWhDiscussion: With these types of questions, we should just use all of the relevant information that we are given. It is doubtful that we would be expected to come up with derating factors ourselves.Here are the relevant numbers:7kWac output under STC6 kWh/square meter per day insolation (PSH)365 days per year (we do have to come up with this number7kW x 6PSH x 365 days = 15,330kWh per yearThe reason we mentioned no clipping here, is in some cases, a PV array will be oversized relative to an inverter and the inverter can be putting out full power for up to 6 hours at a time. The numbers we are working with are not adjusted for clipping. Adjusting for clipping is advanced and would require software simulations. In this case, the inverter is not assumed to be a 7kW inverter, it could be an 8kW inverter, we just know that it is putting out 7kWac at STC.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 timeb. Fire safetyc. For maximum performance in cloudy conditionsd. For temperatures down to -60CDiscussion: The best answer here is fire safety. One thing we know for sure is that they test things for fire safety. The other answers are not correct.If and inverter indicates that there has been a ground fault, what is the first thing that an O&M technician should do?a. Close all the disconnectsb. Open all the disconnectsc. Turn on the systemd. Replace the GFDI (ground fault detection and interruption) fuseDiscussion: The best thing is the safest thing and the safest thing to do here is to turn everything off. Turning off electrically means opening disconnects. If we do something that leaves the inverter on, that is not safer. If we replace the fuse, that does not take care of the problem. Often a fuse is replaced, and the system may work for a while until there is higher irradiance and then the fuse will open again, because the problem has not been corrected. Replacing a fuse when the ground fault has not been corrected can be a fire hazard. Most inverters installed today do not have ground fault fuses. Most inverters installed in 2010 in the US do have ground fault fuses.If doing an energy audit, which device is the best to replace to conserve energy?a. New resistance heaterb. New geothermal heat pump systemc. New refrigeratord. New air conditionerDiscussion: In 2010 and earlier most people in the solar industry would tell you that you should not heat with resistance heating using PV, since PV was more expensive than it is now. There are other technologies that are more effective at saving energy than resistance heating, such as heat pumps, which often work with geothermal systems. Resistance heating elements can be very close to 100% efficient at turning electricity into heat, but it can be a better proposition to take heat out of the earth and bring it into your house.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 modulesb. Test voltage every 5 minutesc. Make sure that connectors are opend. Keep tape over the glass and around the corners of the framesDiscussion: When handling PV modules, installers will start by moving the modules around when they are not electrically connected to anything. It could be safe to cover the modules before moving them around, but you never see anyone doing that, since it would be very time consuming to install a system that way. It would also be time consuming to repeatedly test the voltage. Putting tape over all of the glass would be very hard to remove when the modules are sitting in the hot sun.Which of the following is the worst design flaw when an inexperienced person designs a PV system?a. Multiple orientations within a PV source circuitb. Multiple orientations for different PV source circuitsc. Occasional shading on a module that is in a PV source circuit that has its own MPPd. Microinverters used on a commercial jobDiscussion: It is a solar sin to have multiple orientations within a single PV source circuit (string). With multiple orientations, there will always be modules that are not facing the sun as much as other modules and those modules getting the least amount of light would limit the amount of current to flow through the PV source circuit, because of the series effects of current flowing through a system acting like water flowing through pipes of different diameters. If there are different source circuits that are paralleled together, but the individual circuits have different orientations, the currents will just add, so it is not so bad when the different orientations are in different PV source circuits. Occasional shading of a module that is in a single string with a single MPPT will not be a big problem, since the bypass diode will bypass the shaded module and the rest of the modules can still work at their optimal voltage. Microinverters can be used on commercial jobs. The inverter cost may be more, but there can also be other benefits.Part of the process of turning silicon into a solar cell is called?a. Anodizationb. Oxidationc. Dopingd. DumpingDiscussion: Doping silicon to make a solar cell (or a computer chip) involves adding trace elements that will make the solar cell work properly. These elements are often boron (P doping, P for positive) and phosphorous (N doping, N for negative). Anodization is the process of coating metal (usually aluminum) and oxidation is when oxygen reacts with another element, such as aluminum to create aluminum oxide, which is not conductive for electricity. Dumping is a trade term and is what manufacturers in the US and Europe complain about when they say that China is selling PV at a loss in order to gain market share and put other PV manufacturers out of business.How do residential rooftop mounting systems typically attach to a rooftop, so that they do not fly away when the wind blows?a. Lag screws into rafters or purlinsb. Screws into sheathingc. Flashingsd. BallastsDiscussion: Fastening to a structural portion of a roof is the best way to fasten PV, so that it does not blow away. Screwing into sheathing, which is the plywood or OSB that is attached to the rafters is not recommended by roofing professional organizations, such as the National Roofing Contractors Association (NRCA). Flashing is recommended for waterproofing, it is just not what holds the roof down. Ballasted PV systems are held down by something heavy onto a flat (low-slope) roof. Typical residential systems are not ballasted and are often on sloped roofs.What is the shape of a typical monocrystalline solar wafer?a. Circularb. Squarec. Rectangulard. Square with rounded cornersDiscussion: Monocrystalline solar is made with a process, sort of like candle making, so we have a part of the process where the monocrystalline silicon is cylindrical. This cylindrical shape is then sliced as thin as possible and we have a round piece of silicon. The round piece of silicon is typically trimmed, so that we can fit more into a given space. If we made it perfectly square, it would work very well, but the cost of trimming so much off, is not worth it to a point. We can also call this shape a squircle, look it up! Polycrystalline (multicrystalline) solar cells are square.What is the largest array size of the following if you are using a 24V battery bank and a 20A charge controller?a. 500Wb. 2kWc. 1000Wd. 280WDiscussion: We do not want to exceed voltage and current. Since we are saying the voltage is 24V and the current can’t exceed 20A, then doing math:Volts x Amps = Power24V x 20A = 480WThe best answer is: 280W Looking at this in an advanced perspective, the 20A controller calculation would be calculated from 156% of Isc and Imp, which determines power is about 7% less than Isc.480V/1.56 = 308W308W x 0.93 = 286WDo not be overwhelmed by this or another advanced question. There is always an advanced question on this exam that most people cannot answer.Which of the following is able to change dc power into ac power with a predetermined specific frequency and voltage?a. Inverterb. Power converting utilityc. Step up transformerd. Step down transformerDiscussion: An inverter converts dc to ac power. A transformer can convert ac to ac of different voltages. A charger or rectifier can convert ac to dc.What color wires can be used for equipment grounding (earthing is international term) wires in the US?a. Green, bare or green with yellow stripeb. White or bluec. Yellow or blued. Any colorDiscussion: Equipment grounding conductors (EGC) can be green, bare or green with a yellow stripe. If it has the word grounding with g at the end, it may be one of these colors. If it is a grounded conductor, it would be white in North America or blue in much of the rest of the world. Grounded does not end with the letter g.What does MPPT stand for?a. Maximum payback period timeb. Maximum power performance trackc. Maximum power point trackingd. Minimum peak performance timeDiscussion: All interactive inverters that are connected to PV have MPPT. MPPT is maximum power point tracking, where the inverter can work at the appropriate voltage, so that the inverter is working at the sweet spot on the IV curve to maximize power production. This sweet spot of maximum production will change depending on temperature and irradiance. Cold temperatures increase voltage and move the IV curve to the right, while bright irradiance will increase current and move the IV curve up. Maximum power point tracking will optimize production differently under different situations. Charge controllers and dc-to-dc converters can also have maximum power point tracking.Which is the best solution of the following for multiple orientations when designing a PV system?a. Battery backup string inverter with secure power supplyb. Microinverterc. Charge controllerd. Hybrid inverterDiscussion: A Microinverter will do maximum power point tracking on a PV module level, so that the PV source circuit is one module. Every module will work independently. Dc-to-dc converters (power optimizers) can also have maximum power point tracking on a PV module level.If you want to use modules that are dissimilar and in multiple orientations, what is the best type of system to use?a. 2 channel MPPT inverterb. Small 12V battery systemc. Dc-to-dc converter (power optimizer) systemd. Central inverterDiscussion: Dc-to-dc converters will optimize each module with module level maximum power point tracking, so we can have modules that are dissimilar and in different orientations. On the other hand, with a standard string inverter, we have to have all of the modules on a single PV source circuit to be similar (same brand and characteristics), since one module that is different can affect the entire string negatively.In the western part of the USA and Canada, what direction does the north arrow of a magnetic compass point?a. South of westb. West of northc. East of northd. West of eastDiscussion: Solar people like to line up their PV with true azimuth rather than magnetic azimuth. True azimuth is determined by the axis of rotation of the spin of the earth and magnetic azimuth is determined by a slowly moving magnetic north pole. In this era, the magnetic north pole is south of the true north pole above the middle of Canada. This means that when we are on the west coast of the US and Canada, that the north needle of a compass will be pointing slightly east of true north. On the other hand, if you were on the east coast of the US or Canada, you would find that the north needle of a magnetic compass would point slightly west of true north. In the past this was more important for solar installers, but these days we often use a device, such as our phones or google earth, that will show us true azimuth and no need for a correction with 21st century technology. Navigation with boats and planes is often done with magnetic azimuth.You are rebuilding an old battery system for a PV museum and everything is in amps and amp hours. You are told that the system needs to have 33% more PV production on average than what the loads require. The loads will require 20Ah per day and the insolation will be 5PSH. If the module current at STC is 8A at Imp and 9A at Isc, how many PV source circuits would be needed to meet the minimum requirements stated here?a. 1b. 2c. 3d. 4Discussion: First let us determine the requirements in Ah, since this question is using those units:Required 20Ah per day with 33% extra required20Ah x 1.33 = 26.6Ah requiredSince Ah are Amps x hours, then to solve for Amps:Ah = A x hrA = Ah/hrWe have a location with the equivalent of 5 hours of peak sun per day, then, we can use 5 hours for our time:A = 26.6Ah / 5PSH = 5.32AWe can optimistically infer that each PV module would operate at Imp when producing power (would be less without MPPT).Since the Imp of the module is 8A, which is significantly greater than the 5.32A required, we can be comfortable that 1 single PV source circuit would be adequate for this design.Which tilt angle from horizontal would get the best annual production from a location in Toronto at 43 degrees north?a. 42 degreesb. 58 degreesc. 15 degreesd. 20 degreesDiscussion: In most locations in the world outside of the tropics, it is reasonably safe to assume that a tilt angle that is slightly less than latitude is optimal. In the early days of solar, latitude was considered optimal for annual production. The only answer that is slightly less than 43-latitude is 42-latitude. If something between 30 degrees and 42 degrees was another option to choose from, it would be a tough choice and it is doubtful that a good test maker would give you two good answers on a multiple-choice exam.A multimodal inverter that has an internal automatic transfer switch would have to monitor what in order to transfer to backup power?a. Current and voltage from PV arrayb. Primary power source voltagec. Primary power source currentd. Backup power source viabilityDiscussion: A multimode inverter is usually an inverter that will have an output of the inverter that is interactive and connects to the grid and another output that can operate in stand-alone mode when the grid is down. These inverters will power only the loads that are connected to the stand-alone mode output when the grid goes down. Internally to the multimode inverter, there is an automatic transfer switch (ATS) that will cause the interactive portion of the inverter to shut off and then the inverter will operate the stand-alone output of the inverter. This inverter will monitor the frequency and voltage of the utility grid (primary power source), so that it will know when to switch to stand-alone mode.Which of the following will have the highest voltage setting for charging flooded lead acid batteries?a. Bulk chargeb. Absorption chargec. Float charged. Equalization chargeDiscussion: Of the different charging settings, the equalization charge is the highest voltage. An equalization charge is a timed, controlled overcharge of a battery that will cause the battery to make bubbles of hydrogen and oxygen as water molecules are electrolyzed. This would ruin the batteries if done often, but if done on a maintenance schedule and if water is added to the batteries to replace the molecules that gassed off, then it can be good for the system. Only batteries that you can add distilled water to can be equalized.Besides calculations, where can we find out what would be the maximum series fuse rating of a PV module?a. On the back of the moduleb. On the PV wire instructionsc. By multiplying Imp x 1.56 and rounding up to the next common fuse sized. By multiplying Isc x 1.25 and rounding up to the next common fuse sizeDiscussion: Maximum series fuse rating of a PV module can be calculated by multiplying Isc x 1.56 and then rounding up to the next common fuse size, which is often 15A or 20A. The answer c was almost right, except it used Imp rather than Isc. Maximum series fuse rating is required and always printed on the label on the back of the PV module. Fuses are not always required, when there are 1 or 2 strings, but when the fuse is required with 3 or more strings on a single MPPT, then the fuse size cannot exceed the maximum series fuse rating.Is there a difference between solar noon and noon as most people know it and if so, what is the difference?a. Solar noon is the same as noon as most people know it.b. Solar noon is not dependent on time zonesc. Solar noon is dependent on time zones, but does not incorporate daylight savings timed. Solar noon is noon at GMTDiscussion: Solar noon is different at every location that is east or west of another location, even if it is 5 miles different. Solar noon is when the sun is as high in the sky as it will get, and this is determined by the relationship of the earth and sun as the earth spins. In the old days before time zones as travel became faster with trains, there was a lot of confusion about what time it was, because it was solar noon a few minutes different from town to town as someone went east to west or west to east. Time zones were invented by train companies trying to get everyone on schedule.What contributes to determining the ampacity or the temperature rating of a conductor?a. Insulationb. Insolationc. Fill factord. Sealing racewaysDiscussion: The insulation around the wire is different for different situations. Some insulation can be exposed to UV light in wet places and other insulation can only be used inside of conduit inside a building. There are different temperature ratings of insulation and if we have a copper wire with a thickness of copper measured as 10AWG, if that same piece of copper had insulation that could handle 90C temperatures rather than 75C temperatures, then all else being the same, the 90C would have a greater ampacity and could carry more current. Ampacity is the ability to carry current. Insolation sounds like insulation, but insolation is “incident solar radiation”, which is a measure of solar energy over time, typically expressed in peak sun hours (PSH) per day.The definitions of the difference of a PV output circuit and inverter input circuit for a grid-tied system are very similar and some believe overlap. In many diagrams, what is the point where the PV output circuit becomes an inverter input circuit?a. Combiner boxb. Inverter terminalsc. DC disconnectd. AC disconnectDiscussion: Often on diagrams, a PV output circuit goes from a dc combiner to a dc disconnect and then from the dc disconnect to the inverter it is labeled as an inverter input circuit. Both of these circuits will carry the same current.What kind of PV system is used so that people have power if the utility ceases to exist, but can still work with the utility?a. Stand-aloneb. Direct-coupledc. Multimodald. Grid-tied hybridDiscussion: A multimodal inverter can operate in different modes, such as interactive (grid-tied) and stand-alone mode. Many times, a bimodal inverter is incorrectly called a hybrid inverter. Hybrid is defined as a system that has more than one source of power (not including utility or batteries), so we could have a hybrid PV and wind system that may or may not have battery backup.If someone had a snow lodge with a wall facing south, what would be the best argument for increasing tilt to very steep or even vertical on the wall?a. To decrease reflection from solar modules onto people walking towards the lodgeb. To increase production from reflection off the snowc. To prevent heat buildup underneath the modulesd. To increase summer production for net-metering situationsDiscussion: When the sun is low in the winter or at very high latitudes, some installers will factor in reflection to increase light on the PV. This can also be done with other reflective surfaces, such as a white roof, white gravel or white paint. There are companies that sell bifacial PV, which can collect light from the front and the back of the module. This is another way of collecting extra light from a reflective surface.On a southeast facing residential rooftop, what is the most common type of mounting system?a. BIPVb. Flush mounted rack mountc. Tilt up rack mountd. BallastedDiscussion: Sloped residential roofs that face anywhere from the directions east through south to west are commonly installed with flush mounted solar. Flush mounted means mounted close to the roof with the slope of the roof. Many residential roofs are sloped and have flush mounted PV systems. My roof has flush mounted PV facing all directions.Why do we need to know the lowest expected temperature?a. Prevent under currentb. Prevent under voltagec. Prevent over currentd. Prevent over voltageDiscussion: Lower temperatures cause higher PV voltages. If the location gets very cold, we will not be able to connect as many modules in series as if we were in a location that never was cold.What is the maximum number of modules in series given that Voc = 44V, Vmp = 38V, cold temperature = -22C, Temperature coefficient Voc = -0.3%/C, Inverter maximum input voltage = 550V?a. 8b. 9c. 11d. 10The Math the fast way:25C + 22C = 47C47C x .003 = 0.1410.141 + 1 = 1.1411.141 x 44V = 50.204Voc cold550V / 50.2V = 10.96Max in series = 10To see what could happen with 11 in series:50.2V x 11 = 552V, which is over 550V and could void inverter warranty.Remember to round down for cold temperature string sizing (round up for hot).If you are sizing a PV system on a building for a location with net-metering, what is the best way of the following to size the system?a. Multiply load factor by power factor by energy usageb. Size the system based on energy usage, budget and available spacec. Size the system based on offsetting the entire electric bill alwaysd. Size the system based on how much will fit on the roofDiscussion: Basing a PV system size on a building usually has many factors, such as energy usage, budget and available space. Basing on offsetting the entire bill is not usually done, but often newbies in the industry try unsuccessfully to sell every system to offset the entire load. Filling up the roof is at times the limiting factor, but often there are other factors.If magnetic declination is 5 degrees east, then where is true south?a. Where the compass reads 0 degreesb. Where the compass reads 180 degreesc. Where the compass reads 185 degreesd. Where the compass reads 175 degreesDiscussion: If magnetic declination is 5 degrees east, then the compass needs a 5-degree correction. The north needle rather than pointing true north would be pointing 5 degrees and 5 degrees would be magnetic north and would indicate zero degrees on a magnetic compass. In order to correct, we would have to add 5 degrees when going from magnetic to true with east declination. An example of magnetic declination to the east is in California. In San Francisco with 15 degrees east magnetic declination, if a magnetic compass reads 180 degrees, then we would add 15 degrees and have 195 degrees true azimuth. To solve our problem, for true south with 5 degrees east declination, with a magnetic compass heading of 175 degrees, we would add 5 for east declination and get a reading of 180 degrees, which is true south. True south in this case is 175 magnetic.What is the recommended way that roofers make structural attachments to protect against water intrusion?a. Caulking around the screwb. Extrusionsc. Flashingd. SyzygyDiscussion: Flashing is a thin piece of impervious material (usually metal) installed to prevent passage of water. Roofing best practices recommend flashing to seal penetrations, especially on shingle roofs. Flashing is typically overlapping roofing material, so that with gravity water will go over the flashing, rather than under.What is the main use of PV wire?a. Intermodule connectionsb. Inverter ac connectionsc. Must be used on grounded systemsd. PV output circuitsDiscussion: Prior to implementation of the 2017 NEC, PV wire was required on ungrounded systems. After the 2017 NEC, there was no special requirement for PV wire in the NEC. PV wire is often used for the connections between modules (intermodule connections) and for what are often called home runs, where the end of a PV circuit is connected to a junction box or an inverter on a roof.If we wanted to calculate an average power over time, what would we do mathematically?a. Take demand charges and divide by timeb. Divide energy by timec. Divide Ah by timed. Divide resistance by powerThe Math:Power x Time = EnergyPower = Energy / TimeSince power often goes up and down, this calculation will only find the average power used.Which types of wires can be used for connecting modules beneath arrays with exposed conductors?a. THWN-2 and THHNb. XRS and FTPc. PV wire and USE-2d. NMC and RTTWDiscussion: The types of wire often used to connect modules beneath the arrays is PV wire and USE-2 wire. Both of these types of conductors can withstand heavy outdoor use, such as UF light, rain, wind and snow.What information is needed in order to perform inter-row spacing calculations?a. Solar constant and currentb. Solar zenith angle and power of modulesc. Shading derating factor and azimuthd. Solar elevation angle and solar azimuth angleDiscussion: Inter-row spacing calculations are advanced PV and you will not be required to perform these calculations for the NABCEP Associate exam. To give you a head start on the topic, it is good to understand the concepts to a degree. At a higher latitude, farther away from the equator, the sun will be lower in the sky, so the rows will have to be farther apart than if the system was closer to the equator (lower latitude). Another reason that the rows will have to be farther apart is because at higher latitudes, the sun rises later in the day in the winter. If we want to have production, say at 9am at a higher latitude, we will also have to use the angles to calculate for an azimuth correction, in order to get sunlight in the morning during winter. Once again, this question is advanced for this class, so do not worry about this unless you are sure you understand everything else. This will not be the type of question that will be the difference of a pass or fail. It will keep geniuses from getting bored. Another interesting fact is the solar constant is the irradiance at the earths distance from the sun (this is not irradiance on earth, since earth has an atmosphere to filter light). The earth is about 93 million miles (on average) from the sun and the irradiance at this distance is 1366 watts per square meter. 1366 watts per square meter is the solar constant. This will also not be on your exam, so make sure not to remember thisRemember that the solar elevation is the angle over the horizon at which the sun is and that the solar azimuth angle is going to be the azimuth at which the sun is. The solar azimuth angle is always going to be 180 degrees or zero degrees at solar noon. It will be 180 degrees at solar noon for those of us north of the tropic of cancer, which is 23.5 degrees latitude.In dry places, what would typically be the most common type of maintenance on a PV system?a. Removing leavesb. Washingc. Shade analysisd. MoisturizingDiscussion: In dry places, the common maintenance problem is washing PV modules. In some places, such as the Arabian desert, there are frequent dust storms and a lack of water. There are robotic waterless systems that can be used to dust off modules every day. In many places like California modules will get washed once per year, depending on who is making the decision. Rain is the most common and cost-effective method used. Many people never wash modules. Removing leaves is usually not a huge problem, since we tray and install PV not under trees.Which characteristics of a wire would lead to more voltage drop?a. Long and wideb. Short and widec. Long and thind. Short and thinDiscussion: Voltage drop is the loss of voltage over a wire and to be avoided. There is going to be more voltage at the source of power and less at end of the conductor where power is going. A wire is a good conductor with low resistance, but a thinner wire has more resistance. Also, a longer wire has more resistance. A short and thick wire will have the least amount of voltage drop and a long and thin wire will have the most voltage drop. This is common sense, since if a thin wire worked better, we would only have thin wires and if a long wire worked better, we would be always trying to run wires longer.Which type of system is best for seasonally tilting the PV modules?a. Flush mountb. Reverse tiltc. Pole mountd. BallastDiscussion: A pole mounted system is usually the easiest to seasonally tilt. Some installers will setup systems so that during the shorter times of the year, they will tilt up the PV to catch the low sun and closer to summer solstice they will tilt the PV up to catch the higher sun more effectively. Often seasonal tilt systems are set up with good intentions and then after a few seasons, people will get busy and forget to tilt the system. Seasonal tilting was more popular when PV was more expensive. Now in the age of cheap PV, it can be a better investment to buy more PV rather than paying someone to tilt the system a few times per year.A reverse tilt for example is when someone installs PV on a north facing roof and tilts the PV to the south. This is less common than it used to be for aesthetic and other reasons.What is the minimum number of modules that you can put in series for proper performance with a high solar cell temperature of 65 degrees, a Vmp of 31V, a temperature coefficient of Vmp of -0.45%/C and in inverter low MPPT voltage of 215V?a. 5b. 9c. 7d. 8Discussion: This is a hot temperature string sizing question where we want to make sure that the voltage does not go below a certain point. The differences with the cold temperature string sizing are:1- Use the hot solar cell temperature, which is often about 30C over ambient2- Use Vmp not Voc (Vmp is operating and lower)3-Use temperature coefficient for Vmp not Voc4-Use the inverter low end operating voltage (often low range MPPT)5-Round up for number in series, to keep your voltage high enoughHere is the calculation:65C – 25C = 40C40C x 0.0045 = 0.18 (corresponds to 18% loss of voltage)1 – 0.18 = 0.82 (corresponds to keeping 82% of Vmp)0.82 x 31Vmp = 25.42Vmp hot temperature215V / 25.42V = 8.46 in seriesRound up to 9 in order to keep voltage over 215V at all timesAlways round up with this calculation.If we only had 8 in series, then:8 in series x 25.42V = 203V on a hot dayThe system would not MPPT on a hot day in this case, so we need at least 9 to keep it working efficiently.When working on a battery bank with a hydrometer, what is the most important personal protective equipment?a. Fall protectionb. Apronc. Eye protectiond. Equalizer Discussion: A hydrometer is something that is used to check the specific gravity of the battery electrolyte. The electrolyte is a mixture of acid and water. Sulfuric acid is heavier than water and the hydrometer can test the acid content this way. Checking the acid can lead to splashes and the last place you want acid is on your eyes, so eye protection (goggles) is more important that protecting your clothes with an apron, unless you have a fashion disease. Batteries are usually heavy and not at a height where fall protection is required.What causes the skin to be more conductive and dangerous when working with electricity?a. Moistureb. Densityc. Sized. CapacityDiscussion: Moisture causes the skin to be more conductive and electricians are trained to be careful when it is wet. Sweating can also cause someone to be more conductive to electricity. Wet earth is more conductive, and it is easier to ground systems to earth in wet places, rather than dry deserts. One of the reasons the NEC does not allow us to install a PV dc disconnect in the bathroom, is because of the moisture shock hazard situation.Which device is used to determine that series wiring has been done correctly?a. Clamp on ammeterb. Digital multimeterc. Meggerd. PyranometerDiscussion: Series connections increase voltage with a PV system. We typically will test the open circuit voltage of a PV source circuit once our wiring is in place, in order to check that the wiring is correct, so a digital multimeter can measure voltage among other things.Here are what the other instruments (wrong answers) measure:Clamp on ammeter: Measures current with a clamp around a conductorMegger: Measures conductor’s insulation resistance, also called an insulation tester. We want the insulation around a wire to have a very high resistance and the wire itself (usually copper) to have a very low resistance).Pyranometer: Irradiance meter, measures the brightness of sunshine.Who approves the interconnection of a PV system?a. Local contractor boardb. State Public Utility Commission (PUC)c. Utilityd. Authority Having JurisprudenceDiscussion: An interconnection agreement is an agreement between the solar energy producer and the utility. The utility needs to approve of someone connecting solar energy to their grid.Who will typically be required to approve the plans of a PV system?a. Local contractor boardb. State Public Utility Commission (PUC)c. Utilityd. Authority Having Jurisdiction (AHJ)Discussion: The Authority Having Jurisdiction that approves plans for a PV system is often the governmental agency’s permitting department. Often it is a city, or a county, but in some cases can be a state, a province or a country.A 16A interactive inverter output circuit will require a circuit breaker of how many amps?a. 16Ab. 20Ac. Less than 16Ad. 30ADiscussion: There is always a correction factor for PV systems in determining the size of the circuit breaker, where the current coming out of the inverter is multiplied by 1.25 to determine the size of the breaker (overcurrent protection device). For breakers under 800A, we will round up to the next common overcurrent device size. In the case of this question, we do not need to round up because 16A x 1.25 = 20A exactly, which is a common overcurrent protection device size. Wires and other equipment also need to be able to handle this 125% of the current among other things. This question is probably more advanced than most questions you will see on the NABCEP Associate exam, but you never know for sure.In North American homes, typical voltages are:a. 110/208 Vacb. 277/480 Vacc. 100 Vacd. 120/240 VacDiscussion: Typically, residential voltages in North America are what is called split phase 120/240Vac. In much of the rest of the world, the voltage in a house is between 220V and 240V and not split phase. In a North American house, the outlets are 120V, but some permanent loads are 240V. Non-North American electricians always find it fascinating how we have two different circuits sharing a neutral in North America in our houses.Ground fault detection on a typical interactive inverter is most often due to a ground faulta. at the PV arrayb. at the utility meterc. at the earthd. at the loadsDiscussion: Inverters detect dc ground faults and the most common place for these faults to occur is at the solar array. Ground faults on the ac side of a system are dealt with like ground faults in buildings are already dealt with, using circuit breakers and other special equipment.Of the following, which is worst for stand-alone lead-acid batteries?a. Undersized PV arrayb. Temperatures between 20C and 30Cc. Fine stranded conductorsd. Anti-islandingDiscussion: It is not healthy for batteries to be left without a full charge. This is especially true for lead-acid batteries, but also important for other battery technologies. I let my computer go really dead too many times and had to replace my mac, which was expensive. Letting a lead acid battery not receive a full charge often can lead to lead phosphate crystals building up on the battery plates and causes the battery to go bad. Having a PV array that tops off the batteries every sunny day is a good thing. Many people that depend on off-grid systems will start up a generator to top off batteries on darker days.A 16A interactive inverter that operates at a 240V utility nominal voltage will produce how much power when clipping?a. 38kWb. 3840Wc. 15kWd. 0.038MWThe Math:Volts x Amps = Power240V x 16A = 3840WClipping is when an inverter is making as much as it possibly can. If we put 5kW of PV on a 3840W inverter, on a sunny cool day, we would probably clip a little bit of power, which means that we could have made a little bit more power if we had a 4kW inverter. Many designers design PV systems to clip a little bit once in a while, so they can maximize their inverter and ac wiring investment.For example, on a house with a 100A main breaker and a 100A main service panel, a solar installer can put a maximum of 20% more breaker on that service panel, which comes out to be a 20A breaker. This is called the 120% rule and is part of a technical sales or more advanced PV lesson. A sales person might want to maximize a 20A breaker by installing 5kW of PV on a 3.8kW inverter. There are other ways around this and we will leave that for the next book in this series. What does a hydrometer measure?a. Water temperatureb. Specific gravity of battery acidc. Lithium densityd. Surfactant levelsDiscussion: A hydrometer measures specific gravity of battery acid. The specific gravity of water is defined as 1 and a fully charged battery has a specific gravity of about 1.265. A hydrometer looks a bit like what is known in some circles as a turkey baster.A 50kW interactive PV system has 15% system losses in a location getting 5.4 peak sun hours per day average throughout the year. What would be the expected annual energy output?a. 2 MWhb. 44 kWhc. 8.3 kWhd. 83,768 kWhDiscussion: We are given some data and need to use it in a logical way. All of the data we are given is relevant. Often, we are given irrelevant data that we have to sift through.The Math:If we lose 15%, then we keep 85%100% - 15% - 85%50kW x 0.85 = 42.5kW after losses42.5kW x 5.4 PSH = 229.5kWh/day229.5kWh/day x 365 days = 83,768 kWh per yearA typical interactive PV system will NOT.a. Reduce greenhouse gassesb. Reduce use of fossil fuelsc. Power a remote cabin isolated from the gridd. Reduce air pollutionDiscussion: When you read a question like this, always pay close attention to a word like NOT. Typical residential interactive systems will:Reduce greenhouse gassesReduce fossil fuel useReduce air pollutionMost interactive inverters do not power grids when the grid is down. Interactive means interactive with the utility, so if there is no utility, you probably will not have an interactive inverter.Note: Ac coupled PV systems do have interactive inverters and battery inverters that can work together without a utility, but this is not your average system.What is the highest angle which the sun can be anywhere in the world?a. 23.5 degreesb. 45 degreesc. 90 degreesd. 180 degreesDiscussion: The highest that the sun could ever be anywhere in the world is 90 degrees. This would only happen in the tropics. The sun cannot get higher than 90 degrees, which is straight overhead.When sizing a stand-alone PV system, we often have to consider the critical design month, which would have the:a. Best insolation and most load usageb. Worst insolation and most load usagec. Worst insolation and least load usaged. Best insolation and least load usageDiscussion: The critical design month is the month out of the year when there is the worst combination of factors. This data is often used to determine the sizing of a PV system. Often in the northern hemisphere of the planet, the critical design month is December.If a PV module produces 265W at Standard Testing Conditions and the dimensions of the PV module are 998mm wide and 1681mm long, what would be the efficiency of the PV module?a. 14.1%b. 22%c. 26.5%d. 15.8%Discussion: Efficiency of a PV module is determined by comparing how much power the module puts out in watts per square meter and comparing that the STC power going into the module during testing, which is 1000W per square meter.The Math:Size of PV module in square meters:Convert mm to m 998mm = 0.998m1681mm = 1.681mLength x Width = Area1.681m x 0.998m = 1.68 square metersPower per area calculation:265W / 1.68 square meters = 158W/square meterCompare to STC irradiance:158W / 1000W = 0.158Turn into percentage:0.158 x 100% = 15.8% efficient PVOf the following, which is the most subject to damage during an installation?a. The frames due to bendingb. The glass due to corrosionc. The backsheet due to contact with sharp edges and module cornersd. The conductors due to water damageDiscussion: Often when solar installers are handling PV modules, the corner of one module will come into contact with the backsheet of another module and tear the backsheet. Backsheets are also often are torn by solar rails. Usually the PV module still works with a torn backsheet, but it is possible that the performance and safety over the years can be affected. PV systems will last for a long time and it is good to install a PV system so that it will last longer than the life of a solar installer with proper PPE (personal protective equipment).What instrument can best test the insulation resistance of a conductor?a. Insulometerb. Megohmmeterc. Digital multimeterd. Caloric wire testerDiscussion: A megohmmeter will provide a fast pulse of voltage and we will see if that pulse will escape the wire into the grounding system. If there is a lot of resistance in the insulation, then the test results are good. If the resistance is less, that means that some electrons are escaping from the wire into the grounding system.What is the solar altitude angle?a. The angle between straight overhead and the sunb. The angle between 45 degrees above the ground and the sunc. The angle between the horizon and the sund. The angle between sunrise and sunsetDiscussion: The solar altitude is the angle over the horizon where the sun is. A zero or one degree altitude is sunset or sunrise. Outside of the tropics, the Arctic or the Antarctic, on the longest day of the year, the solar altitude at noon is 23.5 degrees higher than at equinox. On the shortest day of the year at solar noon, the sun is 23.5 degrees lower than the sun at equinox. This is because of the tilt of the earth. This theory breaks apart for flat earth theories.What is the solar window?a. Any place the sun can be in the sky in a particular location throughout the yearb. A transparent device used to determine sun pathsc. The location in the sky where the sun will never be, such as northd. A window that faces south in the northern hemisphere or a window that faces north in the southern hemisphere.Discussion: The solar window is the places in the sky where the sun will be throughout the year. Winter solstice would be the low side of the window and summer solstice is the high side of the window. The sides of the solar window are the horizons in the east and west. The solar window is not a rectangle and has curved sides.What is the main function of the Authority Having Jurisdiction?a. To check Code complianceb. To approve utility interconnectionsc. To ensure worker safetyd. To make sure that the employer does not discriminateDiscussion: The inspecting and permitting agency, often referred to as the AHJ, will check to make sure that the solar plans and building of the solar system is done so that everything will adhere to the local Codes and standards.The maximum power rating of the largest load of an off-grid system is limited by:a. the size of the batteryb. the size of the arrayc. the size of the inverterd. the size of the charge controllerDiscussion: With a stand-alone PV system, the inverter must be able to power whatever is on at one time. At a minimum, someone would have to have their stand-alone inverter to at least be able to power the largest load. With a grid-connected system, we can always rely upon the utility if we need extra current.Which type of inverter will provide maximum power point tracking on a module per module basis.a. Central inverterb. String inverterc. Bipolar inverterd. MicroinverterDiscussion: A Microinverter system has a single inverter for each solar module. Each one of those inverters will have MPPT. Dc-to-dc converters (power optimizers) also have MPPT on a module level basis.What type of PV racking system is often seen on a commercial low-slope roof withoutpenetrations and with concrete pavers or blocks to keep it from blowing away?a. Ballastedb. Aerodynamicc. Hyperstationedd. Epoxy stationedDiscussion: On a low-slope roof (often called a flat roof) it is very common for PV to be installed with systems that have PV and mounted on a specialized mounting system that is only attached to the roof by gravity. Usually there are concrete blocks called paving stones, which are readily available at large hardware stores. Many people think of a ballast as something that makes a fluorescent light work (electrical ballast) or something that makes a boat more stable. This type of ballasted PV system is more like the boat ballast, since it is made of something rather heavy.In what order is performance from best to worst of the different types of PV systems?a. Roof, Pole, Ground, BIPV (building integrated PV)b. Pole, Ground, BIPV, Roofc. Pole, Ground, Roof, BIPVd. BIPV, Pole, Roof, GroundDiscussion: When comparing systems like this, we have to think of what might be different, and here we are comparing mounting systems. The airflow is different for these different mounting systems.Pole mounts have the best airflow, since they are more exposed to the oncoming wind.Ground mounts have the next best airflow, since they usually have considerable airspace underneath them.Roof mounts usually have at least a few inches of airspace underneath them.Building Integrated PV has the least amount of air flow.Airflow takes heat away, so the correct answer is c!See you around! I am at all of the large solar shows, so make sure to introduce yourself or find me on the internet and say hello!Thank you for reading this book!!Sean White ................
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