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
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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
What is a microinverter?
- A small inverter used only in off-grid cabins
- A small inverter mounted at and serving one module
- A DC-to-DC converter that feeds a central string inverter
- A backup inverter that runs during grid outages
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B. A small inverter mounted at and serving one module
A microinverter sits behind each module (or pair of modules), converts its DC to AC there and tracks that module's own maximum power point. A module-level DC-to-DC converter that still needs a string inverter is a power optimizer.
Reference: Inverters: module-level power electronics
What is the function of a DC combiner box?
- Connecting several modules in series to raise voltage
- Converting the combined string output from DC to AC
- Storing surplus string output until the evening demand peak begins
- Connecting several strings in parallel, usually through fuses
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D. Connecting several strings in parallel, usually through fuses
A combiner brings the positive and negative conductors of several strings together in parallel, normally with an overcurrent device for each string, and sends one larger circuit on to the inverter. Series connections are made module to module on the array.
Reference: System components: combiners; NEC 2023, 690.9