Section 5: PV Module Fundamentals Flashcards
Tell me about the silicon used for solar pv
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
What’s the difference between monocrystalline and polycrystalline silicon?
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.
What is Swanson’s Law?
As the number of installations increases, cost of those installations decreases
What is Voc
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.
What is Vmp?
Vmp - Maximum of power in a power producing situation
What is Isc?
ISC - Current short circuit - maximum of current a module will produce when voltage across the circuit is zero.
What is Imp?
Current max power - maximum amount of current a module can produce when under load.
What is max series fuse rating?
maximum amount of current a module can produce when under load.
What is the temperature coefficient?
a de-rate factor that reduces or increases the amount of voltage, current, and power based on temperature changes.
How does temperature affect pv efficiency?
has an inverse relationship with efficiency. Manufacturers will provide voltage correction factors to calculate voltage under different temperatures.
Higher temperature = lower voltage
What is string sizing?
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.
What is the IV curve?
The IV Curve is a graphical representation of all the possible current and voltage combinations - in sense, power points for a pv device.
How does irradiance affect current?
Current goes up as irradiance goes up? More sunshine = more current
What is Maximum Power Point Tracking?
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
What are Bypass diodes?
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.
