Why LiFePO4 is the default now
Off-grid battery banks used to mean flooded lead-acid: cheap up front, high maintenance, and intolerant of deep discharge. Lithium iron phosphate replaced it for good reasons, and it is what every one of our published kits ships with — EG4 LL-S 16 kWh LiFePO4 modules.
- Deeper usable discharge. LiFePO4 tolerates far more of its nameplate capacity being used regularly, so a smaller nameplate delivers more real energy than lead-acid did.
- No maintenance ritual. No watering, no equalization charges, no ventilation for hydrogen off-gassing.
- Built-in management. Each module has a battery management system that enforces the manufacturer's voltage, current, and temperature limits instead of trusting the owner to.
- Density and modularity. A lot more energy per square foot of floor space, and banks expand by adding matched modules rather than rebuilding the whole array.
Lead-acid still shows up in low-cost DIY builds and occasionally in seasonal cabins where up-front cost is the only constraint. For a home you intend to live in year-round in New Mexico, we do not recommend it.
The three tiers, and which household each fits
Because banks are built from matched 16 kWh modules, real-world capacity steps rather than slides. Our published kits map the three common steps onto three household types.
| Kit | Battery | Array | Typical household | Price |
|---|---|---|---|---|
| Cabin Ready | 16 kWh (1 module) | 6.6 kW | Cabin, casita, or weekend property — lights, refrigeration, light tools | $12,255 |
| Homestead | 32 kWh (2 modules) | 13.2 kW | Full-time home with a well pump and normal appliances | $22,559 |
| Ranch | 48 kWh (3 modules) | 19.8 kW | Larger home, shop loads, or a household that wants extra reserve | $34,255 |
Notice that battery capacity and array size move together. A big bank behind a small array is a bank that never gets fully recharged; a big array in front of a small bank throws away production every afternoon once the bank is full. If you are working out your own numbers, the off-grid sizing guide walks the load inventory and autonomy-day math that produces both figures.
Cold weather: what actually matters in New Mexico
New Mexico is sunny, but it is not warm everywhere. A mountain property sees hard freezes for months; even high-desert parcels drop well below freezing on the clear winter nights that produce the best solar days. Two real effects follow, and both are handled at install time rather than by shopping for a different chemistry.
Usable capacity drops when a bank is cold
A cold battery temporarily delivers less than its rating. This is reversible — capacity comes back as the pack warms — but it lands on the exact December night you were counting on the reserve. The practical answer is location: put the bank inside conditioned space, in an insulated mechanical room, or in an enclosure designed to hold heat, rather than in an unheated shed on the north side of the building.
Lithium must not be charged below freezing
Charging lithium cells below freezing damages them, which is why every reputable manufacturer publishes a charge-temperature window and why quality packs enforce it internally rather than relying on the owner. Discharging in the cold is a different matter and is generally permitted over a wider range — check the datasheet for the specific pack.
Depth of discharge, lifespan, and how sizing protects both
Battery life is a function of how hard the bank is worked. Every cycle counts against the pack, and deeper cycles generally count for more. Manufacturers state this as a cycle rating at a given depth of discharge, and that pairing is specific to the product — which is why we point people at the datasheet rather than repeating a number that varies by model.
The design lesson is the same regardless of the exact figures: a bank that is sized correctly is worked more gently than one that is sized tight. A system that runs to the floor most winter nights ages faster than the same chemistry in a bank with real headroom. That is one reason we would rather add a module at design time than sell a minimum bank and revisit it in three years.
The other reason is practical: expansion is cheap when the inverter, charge controller, and wiring were specified with headroom, and expensive when they were not. Decide your expansion path before install, not after.
Where the generator fits
A generator is not a replacement for storage. It is the thing that lets you stop buying storage at a sensible point. Our design default is three autonomy days; with a generator on site we normally design to two, because the third day was only ever insurance against the rare multi-day overcast stretch that the generator already covers.
- Monsoon stretches. Late-summer storm patterns are the realistic New Mexico case for several low-production days in a row.
- Construction and guests. Temporary loads that were never in the load inventory.
- Faults. A failed controller, a damaged panel, or a snow-covered array on the one week you cannot get up there.
Generators tie into most of the inverters we install for automatic backup, so the transfer happens without anyone walking outside at 2 a.m. On water systems we build the same redundancy at the pump — the Torrance County solar well system includes a generator auto-switch so the well keeps producing on the days the sun does not.
Next steps
If you know your loads, size the bank yourself with the estimator. If you want the whole system engineered — array, bank, inverter, racking, and the permitting that goes with it — see off-grid solar installation, or compare real pricing in what off-grid solar actually costs in New Mexico.