Section 5: PV Module Fundamentals Flashcards

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1
Q

Tell me about the silicon used for solar pv

A

Silicon has 4 electrons in the outer shell, just like carbon

It is a semi-conductor (not an insulator, not a conductor)

99.99999% pure silicon (&N for 7 Nines pure). Silicon for solar is 6N and higher

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2
Q

What’s the difference between monocrystalline and polycrystalline silicon?

A

Monocrystalline:

This is the oldest and most developed of the three technologies. Monocrystalline panels as the name suggests are created from a single continuous crystal structure. A Monocrystalline panel can be identified from the solar cells which all appear as a single flat color.

Construction
They are made through the Czochralski method where a silicon crystal ‘seed’ is placed in a vat of molten silicon. The seed is then slowly drawn up with the molten silicon forming a solid crystal structure around the seed known as an ingot. The ingot of solid crystal silicon that is formed is then finely sliced ingot what is known as a silicon wafer. This is then made into a cell.

The Czochralski process results in large cylindrical ingots. Four sides are cut out of the ingots to make silicon wafers. A significant amount of the original silicon ends up as waste.

Polycrystalline:

Polycrystalline also start as a silicon crystal ‘seed’ placed in a vat of molten silicon. However, rather than draw the silicon crystal seed up as with Monocrystalline the vat of silicon is simply allowed to cool. This is what forms the distinctive edges and grains in the solar cell.

Because of lower silicon purity, polycrystalline solar panels are not quite as efficient as monocrystalline solar panels. Lower space-efficiency. You generally need to cover a larger surface to output the same electrical power as you would with a solar panel made of monocrystalline silicon.

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3
Q

What is Swanson’s Law?

A

As the number of installations increases, cost of those installations decreases

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4
Q

What is Voc

A

Voc - voltage open circuit. This is the maximum amount of voltage that the module will produce with no load. This is a point on the IV curve that does not produce power.

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5
Q

What is Vmp?

A

Vmp - Maximum of power in a power producing situation

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6
Q

What is Isc?

A

ISC - Current short circuit - maximum of current a module will produce when voltage across the circuit is zero.

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7
Q

What is Imp?

A

Current max power - maximum amount of current a module can produce when under load.

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8
Q

What is max series fuse rating?

A

maximum amount of current a module can produce when under load.

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9
Q

What is the temperature coefficient?

A

a de-rate factor that reduces or increases the amount of voltage, current, and power based on temperature changes.

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10
Q

How does temperature affect pv efficiency?

A

has an inverse relationship with efficiency. Manufacturers will provide voltage correction factors to calculate voltage under different temperatures.

Higher temperature = lower voltage

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11
Q

What is string sizing?

A

Refers to the max and min number of modules that can be configured in a series string with an inverter without exceeding its capabilities.

String sizing is usually done at the manufacturer’s website. Still good to know how to do this manually.

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12
Q

What is the IV curve?

A

The IV Curve is a graphical representation of all the possible current and voltage combinations - in sense, power points for a pv device.

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13
Q

How does irradiance affect current?

A

Current goes up as irradiance goes up? More sunshine = more current

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14
Q

What is Maximum Power Point Tracking?

A

Devices inside inverters that monitor levels of current and voltage and keep power at the intersection of Vmp and Imp by applying the appropriate amount of resistance at any given time

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15
Q

What are Bypass diodes?

A

These are found on solar panels, or the junction box on the back of inverters or on pv source circuits. They pass current around, rather than through, a string of pv cells that are shaded in order to prevent over heating in a particular string.

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16
Q

What is nominal voltage?

A

Nominal means “in name”

Before MPPT inverters and charge controllers were invented, the voltage of the PC would be matched up with the voltage of a battery.

Nominal voltages are different from Vmp and Voc. Typical voltages for 12V nominal are:

  • Voc 22V solar
  • Vmp 17V solar
  • Battery resting 12.6 V
  • Battery charging 14.5 V

Solar voltage nees to be higher than battery voltage so that when they are connected, the energy will go from the solar to the battery.

17
Q

What happens in a series string?

A

Current remains the same, voltage is cumulative

18
Q

What happens in a parallel string?

A

Current is cumulative, voltage remains the same

19
Q

What happens when dissimilar modules are wired on the same string?

A

Don’t put dissimilar modules in series.

No cell within a string can outperform the weakest link. So if there are 4 modules (4A, 5A, 8A, and 3A respectively) then the current flow on the string is 3A

20
Q

Should you ever put modules in the same string in different orientation?

A

No. A series can’t outperform the weakest link, so you limit the whole string because of different shading levels

21
Q

What is thin film pv?

A

Mostly used in large utility scale projects.

First Solar is the main thin film manufacturer.

It has very thin layers deposited on glass or other substrate. Typically less efficient.

Better performance when it is hot and when it is cloudy relative to crystalline PV watt for watt. Also ideal for shaping into various building components.

22
Q

How do you calculate module efficiency?

A

1) Determine watts of module, i.e. 250 watt module
2) Determine area of module, i.e. length times width
3) Divide module watts by panel area, i.e. 250 watts/1.68m^2 = 149 watts per square mater.
4) Compare to STC (1000) and get percentage. 149 watts/meter squared is 14.9% efficiency

23
Q

What is UL 1703?

A

UL 1703 is the standards test for plat plate solar pv modules. Testing includes hailstone, fire, salt spray, corrosion resistance etc