An inverter turns the DC your panels and batteries make into the AC your house runs on, and every inverter you will ever shop belongs to one of four families. The families differ on two questions: where does the DC-to-AC conversion happen (on the roof, or in one box on the wall), and what is the machine's relationship with the grid (exports, runs beside it without exporting, or ignores it). Answer those two and you know the family before you know the model.
The four families
A string inverter is the classic grid-tied box. Panels wired in series (strings) feed high-voltage DC down to one wall-mounted unit that converts and pushes AC into your panel and, when production beats consumption, out through the meter. No battery, no backup. Grid-tied string inverters shut down in an outage because they are required to stop energizing a dead utility line, a rule that protects the crew fixing it. We rarely sell a plain one; the family matters because the next two are built on it.
A microinverter puts the conversion on the roof: one small inverter bolted under each panel, so every panel is its own tiny AC power plant. A real example from a build at one of our own houses: 22 Canadian Solar 395W panels, each on an Enphase IQ8+, wired as two branches of 11 into a combiner, 8.69kW of DC making 6.6kVA of AC. Panel-level conversion means shade on one panel does not drag a whole string, and there is no high-voltage DC run. The trade: you bought 22 inverters, and service means going on the roof.
A hybrid is a string inverter that also manages a battery and can island the house. Grid up, it can power loads, charge the battery, and export. Grid down, it disconnects and runs the house from PV and battery. This family is the heart of the systems we design and project-manage: the EG4 18kPV, FlexBOSS18, and FlexBOSS21.
An off-grid inverter runs loads from PV and battery and never exports. Several will accept grid or generator power as an input for charging and pass-through, and power only flows one way: in. No interconnection agreement, no net metering, no utility conversation. That is the EG4 XP family (6000XP, 12000XP) and the little 3000EHV.
The EG4 lineup by the numbers
Every number here comes from the spec sheet named in Sources.
| Unit | Family | Continuous output | Max PV | MPPTs | Max PV voltage |
|---|---|---|---|---|---|
| 3000EHV | Off-grid, 120V | 3,000W | 5,000W rated solar input | 1 | 500 VDC (array Voc) |
| 6000XP | Off-grid | 6,000W | 8,000W utilized | 2 | 100 to 480 VDC input range |
| 12000XP | Off-grid | 12,000W (15,000W with PV on the newer model) | 24,000W utilized | 2 | 500 VDC absolute max |
| 18kPV | Hybrid | 12,000W at 240V | 18,000W utilized | 3 | 600 VDC absolute max |
| FlexBOSS18 | Hybrid | 13,000W with PV, 10,000W battery-only | 18,000W recommended max | 2 | 600 VDC absolute max |
| FlexBOSS21 | Hybrid | 16,000W with PV, 12,000W battery-only | 21,000W recommended max | 3 | 600 VDC absolute max |
Three reading lessons hide in that table.
The with-PV and battery-only numbers are different machines. A FlexBOSS21 is a 16kW inverter at noon and a 12kW inverter at 9 PM. Size your after-dark loads against the battery-only number, because that is the one holding the house when the AC kicks on at night.
The PV ceiling is your growth budget. The 12000XP's 24,000W of usable PV is the standout, and it is why that unit anchors serious off-grid builds.
Max PV voltage is a warranty line, never a suggestion. The 12000XP spec sheet gives a DC input range of 100 to 480 VDC and a max PV input voltage of 500 VDC, with a footnote that damage above 500 VDC is not covered under warranty. Design to the 480V range; 500V is the cliff edge. This is the spec people misremember as 600V because the hybrids are 600V machines. Never carry a voltage limit from one model to another. Pull it from that model's own datasheet, every time.
Which family for which house
Grid or no grid does most of the sorting. Want export credits or whole-home backup beside the utility? Hybrid. Past the last pole, or done with the utility on purpose? XP. A shaded, complicated roof on a plain grid-tied budget, or an AC-coupled addition to an existing system? Micros. A single 120V load like a well house or a shed office? The 3000EHV is a 3kW inverter and charger with one MPPT and a 5,000W rated solar input, and at 18 pounds it is the smallest unit in the lineup.
One flag on the 3000EHV for permitted work: its spec sheet lists CE for safety certification and an IP21 indoor rating, with no UL1741 line. The XPs and hybrids all list UL1741. For anything an inspector will look at, that line matters, and where your local inspector lands on it is a field-verify question before you buy.
The XPs never export, so if you are dreaming about the meter spinning backward, you are in the wrong family no matter how good the XP price looks. And micros plus a battery is possible through AC coupling, and that becomes a hybrid-family conversation anyway, because something still has to manage the battery.
Two families, one property
A customer's EV-charging build shows a clean family choice: twelve 585W panels, one EG4 wallmount battery, and a 6000XP or 12000XP (sized per the loads). No grid tie at all; the whole system exists to move sunlight into a truck. An off-grid inverter was the right call, and the reason was never that the site lacked grid power. Nothing needed to flow back out.
One of our own houses is the opposite corner: a FlexBOSS21 hybrid runs the place, and a 22-panel microinverter array AC-couples into the same system. Two families, one roof, each doing the job it is shaped for.
Not sure which family your house is? Answer four questions in the builder and it sorts you, or start with the ten-minute estimate.
Sources
- EG4 12000XP Spec Sheet, v1.2.6
- EG4 6000XP Spec Sheet, v1.4.4
- EG4 18kPV Spec Sheet, v1.4.3
- EG4 FlexBOSS21 Spec Sheet, v1.2.9
- EG4 FlexBOSS18 Spec Sheet, v1.0.7
- EG4 3000EHV Spec Sheet, v1.1.2