Off-grid by design — sun in, batteries through the night, generator only when the desert won't cooperate.
Key
Active — In service now
Planned — Designed, not yet built
Backup — Standby / secondary
Conveys — Included with the property
There is no utility connection
Nothing arrives on a wire. Every watt the house uses is made here, stored here and spent here, which makes the sizing question a different one than it is on the grid — there is no meter to lean on in February and nothing to sell back in June.
Cooling sets the size
Two mini-splits are the load the whole design answers to. A place with only lights and a fridge would need a fraction of this. The array and the bank are sized for the worst week rather than the average day, because an average-day system fails on exactly the days you need it.
Heat is the constraint, not sunlight
Sun is the easy part out here. Heat is what narrows the choices: batteries stop accepting charge above a ceiling, inverters step down their output, and a closed power room sits about six degrees above the air outside. Nearly every part was picked for how it behaves at 110 °F, not how it rates at 77 °F.
Designed, not built
The design is finished and has been audited three times. Nothing is installed and nothing is ordered. So this page is a system on paper — the reasoning, the constraints and the open questions are the parts worth publishing while the building is still ahead.
Solar PV (existing)
Active
Array2,500 W
System24 V
TypeOff-grid
OwnershipOwned · conveys
Conveys with the property
The system that's already on the ground and runs the place today.
Solar array
Planned
Array15.84 kW
Modules36 × 440 W bifacial
Strings2 / 1 / 1 across 3 trackers
System48 V
Thirty-six bifacial modules split across three trackers. Bifacial earns its keep on a desert ground mount — pale ground throws light back at the underside of the panel. The split isn't arbitrary: two strings share the first tracker and have to match each other, while the other two take one string each and can face wherever the ground allows.
Battery bank
Planned
Modules6 × EG4 LL-S 48 V 100 Ah
ChemistryLiFePO₄
System48 V
Total30.72 kWh · ~23 usable
Cycle life7,000 cycles
EnclosureSix-slot welded rack
Six modules in a floor-standing rack, anchored to the wall. The choice between these and a cheaper wall-mounted pair came down to nine degrees: these accept charge to 122 °F, the cheaper line stops at 113 °F. A power room that reaches about 111 °F on a 105 °F afternoon leaves eleven degrees of headroom instead of two — and a battery that stops charging on the hottest afternoon of the year quits on exactly the day the array is making the most power.
Inverter / charger
Planned
ModelEG4 18kPV (hybrid)
Output12 kW continuous
System48 V
PhaseSplit-phase 120/240 V
Trackers3 MPPT · 4 string inputs
PV window120–500 V · 600 V ceiling
One box doing four jobs — solar charge controller, battery charger, inverter, and the switch that brings the generator in. It makes full power from 230 V up, so the strings are sized to sit inside that window on a cold clear morning, when panel voltage runs highest.
A second-hand panelboard that came out of a restaurant. Free, and not yet proven — on a used board the neutral assembly and the listed bonding means have to be confirmed present before anything is trusted to it, and the breakers it already holds decide whether it gets used at all or replaced outright. That inventory is the first job on the list.
Generator
Backup
ModelHonda EU7000iS
Output7,000 W · 120/240 V
EngineHonda GX390 · EFI
Noise52–60 dBA
Runtime6–18 hr / tank
RoleBackup only
Conveys with the property
Honda EU7000iS inverter generator — fuel-injected with Eco-Throttle and CO-MINDER, quiet enough for overnight runs. On hand for long cloudy stretches, not the daily driver.
Load shedding
Planned
Trips at25% state of charge
ShedsOuter pedestal + front cooling zone
ControlInverter dry contacts → contactor
The part that decides what the house gives up before it gives up entirely. Two circuits run out through a contactor instead of straight off the panel; when the bank falls to a quarter charge the inverter drops them and everything else keeps running. Deciding that order in advance beats discovering it at two in the morning.