solar!

NABCEP Prep

1000 Kilowatts

1 megawatt

1000 megawatts

1 gigawatt

In a solar cell the phosphorous layer is on the Top/Bottom_ and has a Positive/Negative_ charge

Top, Negative (boron, bottom, positive)

The P-N Junction

in the cell, where the light excites the electrons and causes them to flow

Explain the relationship between current and voltage

Current (I, intensity) * Voltage (V, pressure) = Power

What type of energy does a PV cell generate?

DC, this is also the type stored in batteries

Typical AC cycles in the US

60 hertz or cycles per second

the function of an electric service panel

allows for the distribution of power through branch circuits protected by circuit breakers . connected to the utility with the service entrance conductors

function of the electric meter

typically next to ESP, sometimes outside, counts amount of kwh flowing to or from a building

Main Circuit Breaker

allows shutoff of utility and provides over current protection

Branch circuits

run to loads/circuits like lights or outlets

Charge Controller

regulates battery charging to prevent over charging

In a grid direct system, the AC service panel is important because

it serves as the point of interconnection

Electrical pressure or potential. Also a unit of electromotive force

Voltage (V, E). Electricity won't flow without the potential difference, will push current to lower voltage source

Rate/Intensity of electrical current flow

Current, Amperage (I or A). Electricity won't flow without the potential difference, will push current to lower voltage source

explain resistance and what it is measured in

Ohms

Resistance is the opposition to electrical current or "friction" in a circuit

What factors affect resistance?

Material: Aluminum more resistant than copper

Area: cross sectional, greater means less R

Length: longer means more R

Temperature: higher means more R

Power Rating of an array tells you

just size of power, not number of mods or energy

Relationship between W V and A

W=V*A

amp hours are used for

battery capacity, Ah*V= Wh

A point on the I-V curve represents

the available power of a module

what utility bill charges can solar usually offset?

cost of energy per kwh, not fixed charges like service/connection fees, minimums or taxes

In a net meter scenario, what connects an AC service panel to the grid?

a bi-directional meter

what is the setup of a dual meter system?

there is one meter for production and one meter for consumption

what is a downside of capacity based incentives for solar?

there is no accountability for performance

How does lease financing work for solar?

building owner leases system for no up front cost, flat monthly fee

PV component in order of size: module, panel, cell, array?

cell --> module --> panel, --> array

What is the common semi conductor material for cells?

silicon

what cell technology dominates the market?

crystalline silicon

what is thin film cell technology?

deposite a thin layer of PV material on the substrate

Monocrystalline silicon wafer manufacturing

Efficient but expensive, ingot is squared off into a wafer, chemical and heat treatment to absorb more light, blueish from anti-reflective, metal contact grid is printed so electrons have short distance to travel, lines called busbars, white diamond shape is the backsheet

Polycrystalline silicon

silicon pieces melted down to ingot to bricks and wire saws wafer, shard look called grain boundaries, can pack more closely

Thin film cell technology

cost/efficiency vary by manufacturer, no crystalline structure, layers sprayed onto substrate, transparent conducting oxide (no grid) lasers mark the cells

How do you calculate module efficiency?

Power in / power out given physical size, watts per square foot or meter. higher output does not necessarily mean higher density.

No voltage all current point on IV curve

I(sc) short circuit

All voltage no current point on IV curve

V(oc) open circuit

What is the function of a junction box?

where wires meet outside world, typically 3 bypass diodes per box. Purpose: prevent overheating when shaded. help with safety and performance. DC:DC converter AKA power optimizer

If a wire lead and connector click together does that mean they are compatible?

NO. most mods have pre-wired leads with quick connnects

Module power warranties operate under what conditions?

STC: 1,000 watts per meter squared, 25 degrees C 77 F, 1.5 air mass

Assumes all manufacturer instructions followed

What is the rating of a module on an IV curve?

MPP

On a module spec sheet, what does TkVoc represent?

the temperature coefficient at open circuit voltage --> for every degree C above 25 module will lose a certain percentage of V

How are cell temperature and Voltage related?

as cell temperature increases, V decreases

voltage window needs to operate within the boundaries of the inverter T/F

True

How are irradiance and current related?

Irradiance and current are proportional

What does a pyranometer do?

Digital reading of the sunlight's intensity

Calculate the expected output given these conditions- Measured irradiance: 750 w/m sq. Current at STC: 24 A

18 A

Convert STC (1000) with actual and apply to array

Are shade and power loss of a module proportional?

No- that is why bypass diodes are important. shade stops current flow but BD makes a path so power not lost for whole mod

Functions of a Digital Multi-meter?

Digital screen with a dial to switch the function —> DC/AC Voltage, resistance, continuity, current, The current testing is limited to the internal fuse rating. Do NOT test current with a meter probe- you will pull an arc

Clamp-on ammeter

Basic functions of DMM plus a clamp on current clamp for a safe non contact tester. The jaws go around the conductor to measure the amperage with inductance.

Meter safety check

Inspect for damage, oil, compromised probe wire insulation, loose tips, proper ratings

To test a meter, procedures include:

Proper PPE, calculate expected values before testing, test V and polarity before installing fuses/closing the disconnect, confirm there is no current before operating a non load break rated device

Testing voltage and polarity

Red probe from meter goes positive, black to negative, Operating voltage (Vmp) requires gloves and PPE, Reverse probes to test polarity (should be negative), Operating current only clamp on amnmeter

Why do you test for continuity

Determine whether an electrical path exists, verify if the fuse is good, most have Audible indication

What does the pyranometer measure?

Irradiance in W/m squared

Describe a series connection

Negative lead or home run from one module connected to positive of other

IV curves of PV cells in series

Long across the voltage because it is additive

Parallel connection IV curve

Taller because the current is additive

On the AC side are there series connections?

No,m loads are connected in parallel because circuits have the same voltage

In a series connection, voltage is additive/constant

Additive

In a series connection, current is additive/constant

Constant throughout the circuit

Microinverters are connected with series//parallel connections

Parallel —> the current is additive to increase power

What factor limits the number of modules wired in series or parallel?

The inverter size

With four batteries wired in series (the negative is connected to the positive) each being 1.5 Volts and 4Ah, what are the total volts and amps of the circuit?

Series- volts additive so 6 V, current same so 4ah

On the DC side, you have to be aware of the circuit voltage because of what piece of equipment? Module, inverter, conductor

Inverter

What are important factors for sizing a system?

Customer motivation, utility, consumption, finances, space

Why are on site visits important for solar?

Remote tools are not 100% accurate for structural and electrical info, need accuracy for permitting

What unit is an electrical meter measured in?

Rating in amps

The solar azimuth angle represents:

The sun's position in degrees east or west of true S/N top view

Altitude angle

Sun's position in degrees above the horizon

On a sun chart the path through the sky is shown (N = 360, E = 90). The X-axis represents the azimuth angle or altitude?

X-axis is azimuth

On a sun chart the center of the graph faces the equator, meaning S is in the the northern hemisphere. What changes the sun's altitude angle- longitude or latitude?

Latitude, each location has one

Why do sun charts matter?

Inter row shading calculations

If an area gets 6000 wh/m squared of sun a day, how many peak sun hours is that?

6

What loss factors need to be considered for peak sun hour adjustments?

Tiles and orientation, soiling, shading, snow

An array told angle shows the degrees off the horizon. A more shallow tilt (flatter panel compared to horizon) will have more production in the winter or summer?

Summer because the sun is higher

What is the degree threshold for a steep roof price increase?

30 degrees, 7/12

What explains why a compass will not necessarily align with true north or south

Magnetic declination

Typical module to rail connection with a mounting foot are what shape?

L. Foot to structural membrane

Distance between mounting feet is called:

Rail span

What does cantilever mean?

The amount of module overhang beyond the last attachmentd

Advantage of ballasted vs driven pile mounting for a ground mount?

There is no penetration into the ground

What is the OSHA safety threshold for roof mounted systems?

4/12 or 18 degrees, the PV / fire code says 9.5 degrees or 2/12

Explain the importance of flashing

A component is installed to reduce leak potential between the mounting foot and shingle

On a corrugated metal roof mount do you penetrate the peak or vertical seam?

Peak to avoid water pooling. Standing seam does not have penetration

Why is grounding important?

Because it protects against electrical shock and forces the V to zero

In the tree for equipment grounding, what represents equipment grounding conductors?

Branches: smaller wires to connect system parts

What represents grounding electrodes in the tree analogy?

Roots: plate/rod/pipe physically in the earth

What part of the tree is the grounding electrode conductor

The trunk- wire, connection

Equipment grounding is required in all systems T/F

True

Terms bonded and grounded are interchangeable T/F

False

Equipment Grounding Conductor

The conductive path that provides a ground-fault current path and connects normally non-current-carrying metal parts of equipment together and to the system grounded conductor or to the grounding electrode conductor, or both.

UL 2703

Rack integrated equipment grounding: manufacturer has done the development/testing to make mechanic installation a bond

Ways to bond module frames

Equipment grounding washers, grounding electrodes, grounding electrode conductors

The NEC requires a grounding electrode conductor to be no smaller than: 4Awg, 6Awg, 8Awg

8Awg, typically 6 or more

What is between the Grounding electrode and AC service panel?

Grounding electrode conductorw

What is between the AC service panel and inverter/AC/DC disconnect/ DC combiner box?

Equipment grounding conductors

Ungrounded conductors

AC side: hot wires, line 1 and 2, 120V each

DC since maybe +/- or both depending on inverter

Grounded conductors

AC side: neutral conductor, white wire ensures 0 V

DC: most PVs do not have a solidly grounded DC conductor

AC System grounding happens at one point? T/F

True: grounding solidly connected to grounded

Transformerless inverter

Ungrounded on DC side. Invs monitor faults through connection to EGC