Step one: inventory the loads, not the square footage
Grid-tied solar gets sized off a power bill. Off-grid has no bill to read, so the design starts with an appliance-by-appliance inventory: what runs, how much it draws, and how many hours a day it actually runs. A 2,400 square-foot house with propane heat, propane cooking, and a gas dryer can use less electricity than a 900 square-foot cabin running a resistance heater and a deep freezer.
Every serious design we build works from the same shape of list — a small always-on base load for standby draw, phone chargers, and the inverter itself, plus a line for each real appliance. The big movers are almost always the same handful of items:
- Heating and cooling. Electric resistance heat, mini-splits, and air conditioning dominate any load list they appear on.
- Water heating. An electric water heater is often the single largest daily consumer in an off-grid home.
- Well pump. Short run time, high surge. It shapes inverter selection more than it shapes daily kilowatt-hours.
- Refrigeration. A fridge and a chest freezer run all day, every day, in every season.
- Everything else. Lighting, laundry, kitchen, tools, Wi-Fi, and computers add up but rarely dominate.
One correction always applies: nothing on that list runs at its full theoretical duty every single day. Our sizing math applies a diversity factor to the appliance total rather than stacking worst cases on top of each other, and it discounts the whole figure for weekend or backup-only use patterns. Sizing to a fantasy day where every appliance runs flat out produces a system nobody needs and nobody wants to pay for.
Step two: pick your autonomy days
Autonomy days are how long the battery bank can carry the house with little or no solar input — the cloudy-stretch reserve. It is the single biggest lever on battery cost, and it is the number most people get wrong in both directions.
New Mexico is one of the sunniest states in the country, and that materially changes the answer here compared to the Pacific Northwest or the Northeast. Multi-day full-overcast events do happen — monsoon season delivers them most reliably — but they are the exception, not the winter baseline. That is why two to three days of autonomy is the normal design target for a New Mexico property.
Our default is three days. We drop it to two when the property has a generator that can cover the rare extended storm, because at that point the last day of battery is buying insurance you already own. Going below two leaves no margin for a fouled panel, a dirty array after a dust storm, or a week where somebody runs the shop welder harder than planned.
Step three: battery sizing and array sizing answer different questions
The battery bank
Battery capacity is daily consumption multiplied by autonomy days, then rounded up to whole modules. Modern lithium banks are built from matched units — the batteries in our published kits are 16 kWh LiFePO4 modules — so real bank sizes step 16, 32, 48 kWh rather than landing on whatever decimal the arithmetic produced. Round up, never down.
The array
The array is not sized to your daily kilowatt-hours alone. It has to refill a depleted bank inside the usable solar window of one good day while simultaneously running the house, and it has to do that with real-world losses included: wiring, controller efficiency, panel temperature, soiling, and imperfect orientation. That is why array nameplate is comfortably larger than what a naive daily-kilowatt-hour division suggests. A bank that only ever gets partway back before sunset never recovers from a bad week.
The inverter is sized separately again — off the largest simultaneous demand and the surge from motor loads like a well pump or a compressor, not off daily energy. Our published kits pair a 12 kW off-grid inverter with every tier for exactly that reason.
What altitude and cold actually change
New Mexico designs get built for a wider environmental range than most states force on you. Mountain parcels and high-desert lots are both normal here, and they sit thousands of feet apart in elevation with winter conditions to match.
- Cold raises panel voltage. String layouts must be designed against the coldest morning the site will ever see, not an average day — otherwise the array can exceed the charge controller or inverter input limit on exactly the clear, freezing morning it is producing best.
- Thin, clear air helps production. High-elevation sites see strong irradiance, and panels run cooler, which improves output relative to a hot valley floor.
- Cold temporarily costs battery capacity. Usable capacity falls as a bank gets cold, which is why battery location, enclosure, and conditioning are part of the design and not an afterthought.
- Winter is the design season. Shortest days, lowest sun angle, highest heating load. A system that works in January works in June.
- Monsoon and dust. Late-summer storm stretches are the realistic case for autonomy days, and blowing dust is the realistic case for keeping the array reachable for cleaning.
Three reference systems
Our DIY kits are useful as calibration points even if you want a full installation. Each is a complete, balanced system — array, battery, inverter, wiring — so the ratios between the three columns show what a coherent design looks like at each scale.
| Kit | Array | Battery | Panels | Price |
|---|---|---|---|---|
| Cabin Ready | 6.6 kW | 16 kWh | 12 | $12,255 |
| Homestead | 13.2 kW | 32 kWh | 24 | $22,559 |
| Ranch | 19.8 kW | 48 kWh | 36 | $34,255 |
Read them as tiers of household, not tiers of house. Cabin Ready fits a cabin, a casita, or a weekend property with lights, refrigeration, and light tools. Homestead fits a full-time home with a well pump and normal appliances. Ranch fits a larger home, a shop, or a household that wants more reserve than the minimum. Full installations are quoted individually — site work, racking, trenching, and permitting vary too much between parcels to publish a single number.
Run your own numbers
The off-grid solar estimator walks the same logic described on this page — appliance inventory, usage pattern, autonomy days, generator or no generator — and returns a system size and price for your property. If your site has a well, a shop, or heavy winter loads, read the companion guides on battery storage in New Mexico and what off-grid solar actually costs before you commit to a size.