Grid or no grid. That first question does most of the work. If you have utility service and want to keep it, you belong in the hybrid family: a FlexBOSS18 or FlexBOSS21, usually with a GridBOSS at the service. If you are cutting the cord entirely, you belong in the XP family: the 6000XP for a shed or a cabin, the 12000XP V2 for an off-grid home.
The rest is sizing. These are the same four questions we ask when someone walks into the shop, in the same order.
Question 1: Do you have grid service, and do you want to keep it?
This splits the lineup in half.
The hybrid family is built to live alongside the utility. A FlexBOSS18 or FlexBOSS21 runs your loads on sun and battery, and it interconnects with the grid (both carry a UL1741 listing; the FlexBOSS21 adds the SA and SB certifications). Pair one with a GridBOSS at the meter and the whole house can ride through an outage without you touching anything. The 18kPV is the established alternative here: 12,000W of continuous output at 240V, up to 18,000W of PV, three MPPTs, same UL1741/SA/SB listing.
The XP family is the off-grid side. No utility line, no meter, no monthly bill. The 6000XP and 12000XP V2 are all-in-one units we spec for properties where the grid is either unavailable or unwanted. If you want to sell power back to the utility someday, this is the wrong family. Pick a hybrid.
Question 2: How big are your loads?
Continuous output is the number that matters. It is how much the inverter can carry all day, and it has to cover the biggest combination of things you will actually run at once.
The 6000XP puts out 6,000W continuous. That covers lights, outlets, tools, a fridge, a window unit. A shed, a workshop, or a small cabin lives comfortably inside that number.
The 12000XP V2 puts out 12,000W on battery alone and 15,000W with the sun up. That is a real house: well pump, water heater, central air, the works, sized honestly.
The FlexBOSS18 delivers 10,000W on battery and 13,000W with PV helping. The FlexBOSS21 delivers 12,000W on battery and 16,000W with PV and battery working together. That gap sounds small until a hot August afternoon puts the AC and the dryer on at the same time.
Add up your real loads before you pick. Not the panel rating on every appliance in the house, the ones that genuinely run at the same time.
Question 3: How much solar are you planning?
Every inverter has a ceiling on the PV it can use. Buy panels past that ceiling and the extra watts just sit there.
The 6000XP takes up to 8,000W of PV across two MPPTs, 4,000W each. The 12000XP V2 takes a remarkable 24,000W, which is why it anchors serious off-grid builds where winter production has to carry the house. On the hybrid side, the FlexBOSS18 accepts up to 18,000W of PV on two MPPTs, and the FlexBOSS21 stretches to 21,000W on three.
Think a few years out. If the array you want today is 6kW but you can see an EV or a shop addition coming, the bigger PV ceiling is worth having. If your roof or yard maxes out at a modest array, paying for PV capacity you can never fill is the overbuy we talk people out of every week.
Question 4: Backup for a few circuits, or the whole service?
This is the last fork, and it only applies to the hybrid side.
The critical-loads path uses a FlexBOSS18 feeding a small subpanel that holds the circuits you care about: the fridge, some lights, the outlets that matter. When the grid drops, those circuits stay live. It costs less because the battery and the inverter only have to carry the short list.
The whole-home path pairs a FlexBOSS21 with a GridBOSS. The GridBOSS is a 200A microgrid interconnect that sits at your service entrance, manages the grid connection, and hands the entire house to the inverter when the utility fails. It has four smart load ports for managing big loads and accepts up to three EG4 hybrid inverters, so the system can grow after the first install.
Be honest about which one you need. Plenty of families ride out an outage happily on a critical-loads setup, and the money saved buys more battery.
The routing table
| If this is you | Inverter | Continuous output | Max usable PV | The kit that packages it |
|---|---|---|---|---|
| Shed, workshop, or small cabin | 6000XP | 6,000W | 8,000W | Shed & Cabin Kit |
| Off-grid home | 12000XP V2 | 12,000W on battery, 15,000W with PV | 24,000W | Off-Grid System |
| Grid-tied, back up the essentials | FlexBOSS18 | 10,000W on battery, 13,000W with PV | 18,000W | Critical Load Backup |
| Grid-tied, back up the whole house | FlexBOSS21 + GridBOSS | 12,000W on battery, 16,000W with PV and battery | 21,000W | Whole-Home Backup |
Every spec above comes from the manufacturer datasheets we keep on file for each unit.
Good fit, bad fit
The 6000XP is a good fit for a detached building with modest loads and a bad fit for a full-size home. It will run out of continuous output the first time the water heater and the AC ask at the same moment.
The 12000XP V2 is a good fit for a home that is done with the utility and a bad fit for a shed. If your loads live under 6,000W, the smaller unit is plenty and the difference in price buys panels. We tell people this even when it costs us the bigger sale.
The FlexBOSS18 is a good fit when the backup list is short and the budget matters. It is a bad fit if you already know you want the whole house covered; retrofitting your way there costs more than starting on the FlexBOSS21 path.
The FlexBOSS21 with GridBOSS is a good fit for whole-home backup and big PV plans, and a bad fit for someone who only wants the fridge and the wifi to survive a storm. That customer is buying capacity they will never use.
What Ape Solar would check first
Three things, before we recommend anything. First, your actual usage: a year of power bills tells us more than any conversation about what you think you use. Second, the loads that spike: well pumps, big compressors, and central air decide whether the continuous number on paper survives contact with your house. Third, your expansion plans: the inverter you pick sets the ceiling for the array and the batteries you can add later, so we size for where you are headed. The estimate is a quick way to put real numbers behind the first item.
One safety note. Every unit here connects to batteries and, on the hybrid side, to your electrical service. That work belongs to a licensed electrician working under your local permitting authority, and the utility interconnection has its own approval process. In the Florida panhandle, a licensed partner contractor does the install and we run the project end to end through Pro Install.
FAQ
What about the 18kPV?
Still a strong choice. It delivers 12,000W continuous at 240V, takes up to 18,000W of PV across three MPPTs, and carries the UL1741/SA/SB listing. The FlexBOSS21 edges it on output and PV ceiling, which is why the kits standardized there, but an 18kPV already on your shortlist is nothing to talk you out of.
Can I start with critical loads and go whole-home later?
Yes, and the hardware cooperates. The GridBOSS accepts up to three EG4 hybrid inverters, so a system can grow after year one. Tell us the end goal up front and we will route you to the starting point that wastes the least money getting there.
Can the XP units grow with me?
Both parallel up to 16 units, per their datasheets. A 6000XP powering a cabin today can take a second unit when the cabin becomes a house. Most people are better served buying the right size once, though, and that is the conversation to have before checkout.
Which inverters can sell power back to the utility?
The hybrid family. That said, net metering terms are set by your utility, and they vary by state and by tariff, so check yours before you count on export credits. Florida customers can ask us how their utility handles it.
Do I need a GridBOSS with a FlexBOSS?
For whole-home backup, yes; it is the piece that transfers the full service to the inverter when the grid drops. For a critical-loads setup on a FlexBOSS18, the small subpanel does that job for its own circuits instead.
Ready to see what your version costs? Build a system and see the real numbers.