Four architectures
| Type | Best for | Trade-off |
|---|---|---|
| String | Clean unshaded roof, one or two planes | Whole string tracks together. Cheapest per watt. |
| Micro | Complex roofs, heavy shade, many planes | Per-module MPPT. More failure points on the roof. |
| Optimizer + string | Middle ground | Module-level tracking, one box on the wall. |
| Hybrid | Solar + battery + backup | One box does PV, charging, and grid-forming. |
The MPPT window
Every inverter has a DC input range: an absolute maximum voltage it will survive, and a minimum voltage below which the MPPT stops tracking. Your string has to live between those two numbers on the coldest morning and the hottest afternoon of the year. That is what the string sizing calculator does.
Do not do thisExceeding the max DC input voltage — even once, for a few seconds, on a cold clear morning — destroys the inverter and voids the warranty. The manufacturer can read the fault log. Size to the record low, not the average low.
Clipping and DC/AC ratio
Oversizing the array relative to the inverter (a DC/AC ratio above 1.0) is normal and usually correct. The array almost never hits nameplate, so a 1.2:1 ratio flattens the production curve and fills the shoulders of the day. Above about 1.3:1 you start throwing away real energy at noon.
Grid-forming vs grid-following
- Grid-following — needs an AC reference to sync to. Grid goes down, it shuts off. Anti-islanding, UL 1741.
- Grid-forming — creates its own 60 Hz reference. Required for any backup or off-grid function. This is the difference between "I have solar" and "I have power when the grid is down."
A solar array with a plain grid-tied inverter and no battery gives the homeowner nothing in an outage. Say that out loud before the sale, not after.
Efficiency numbers that matter
- CEC weighted efficiency — the honest one. Weighted across the load profile.
- Peak efficiency — the marketing one. Hit at exactly one operating point.
- Tare / standby loss — 20–60 W burning 24/7. On an off-grid system that is 0.5–1.4 kWh a day gone before you turn anything on.