What does the maximum power point tracking (MPPT) function of an inverter do?
- Adjusts the array's operating voltage to get the most power
- Turns the array mechanically so that it faces the sun
- Limits the array voltage on cold days to a safe value
- Shuts the inverter down whenever the grid voltage has been lost
Show the answer
A. Adjusts the array's operating voltage to get the most power
MPPT electronics continuously shift the array's operating point to the knee of the IV curve, which moves as irradiance and temperature change. Physically following the sun is done by a tracker, which is a mounting system rather than an inverter function.
Reference: Inverters: maximum power point tracking
Which conductor types are permitted for exposed single-conductor PV source circuit wiring run within the array outdoors?
- THHN or THWN
- NM cable or UF cable
- XHHW or TW
- PV wire or USE-2
Show the answer
D. PV wire or USE-2
Exposed array wiring must stand up to sunlight, heat and moisture, so listed PV wire (PV cable) or sunlight-resistant USE-2 is used. THHN is a building wire meant for raceways and is not rated for exposed use on a roof.
Reference: NEC 2023, 690.31(C)(1)
A 24 V battery is connected to a 6 ohm resistive load. How much current flows?
- 144 A
- 4 A
- 0.25 A
- 30 A
Show the answer
B. 4 A
Ohm's law gives current as voltage divided by resistance: 24 V ÷ 6 Ω = 4 A. Multiplying the two (144) is the common slip, and 0.25 comes from dividing resistance by voltage.
Reference: Ohm's law: I = E / R