When off-grid solar makes sense
An off-grid system has no connection to the utility, so it has to produce and store all the power the property uses: panels, a battery bank, a charge controller, an inverter that runs without the grid and usually a backup generator.
Going off-grid makes sense mainly where connecting to the grid is expensive: remote cabins, farms and rural lots where bringing in a utility line would cost tens of thousands of dollars. Ask the utility for a line-extension quote first; it is the number an off-grid system has to beat. You stop paying an electric bill and grid blackouts no longer affect you, but you pay for a battery bank and usually a generator instead, and the system has to be sized for your worst winter week rather than an average day. That takes a clear picture of your own energy use and a willingness to use less of it in winter.
A worked sizing example
The math starts with how much energy you use per day, not with panels. Say a cabin uses 10 kWh a day, about a third of a typical US home.
- Panels: one kilowatt of panels produces about 3.5 kWh a day on average in New York and about 4.8 kWh in Phoenix (PVWatts, National Laboratory of the Rockies). Covering 10 kWh a day on average takes roughly 2.1 kW in Phoenix and 2.9 kW in New York, but winter days produce far less than the average, so off-grid designers size for the worst month, often doubling the panel count in northern states or relying on a generator in winter.
- Batteries: three days without sun at 10 kWh a day means 30 kWh of usable storage, the capacity of more than two typical home batteries. For comparison, the median battery installed with grid-tied home solar in 2023–2025 stored 13.5 kWh (Tracking the Sun), and three-quarters stored about 19 kWh or less.
- Inverter: sized for the largest load that runs at once, such as a well pump starting while the fridge runs, not for daily energy.
This is why off-grid systems cost much more than grid-tied ones for the same home: the battery bank and the oversizing for winter, not the panels, drive the price.
How the system is designed and built
- Load list: every appliance, its wattage and its daily hours of use, plus the surge when motors such as well pumps start.
- Sizing: the array is sized for the worst month and the batteries for the days without sun you choose, as in the example above.
- Equipment: an off-grid or hybrid inverter, an MPPT charge controller and, today, usually lithium iron phosphate (LFP) batteries.
- Installation: panels often go on a ground mount so they can be tilted steeply for winter sun, and batteries go in a space that stays within the manufacturer’s temperature range.
- Generator: wired to start automatically when the batteries fall below a set charge.
- Commissioning: the installer tests the system under load and sets the charge limits and generator start points.
Cost factors
| Factor | Impact on cost |
|---|---|
| Battery bank size | Usually the biggest cost. Five days of storage costs more than twice as much as two. |
| Battery chemistry | Lithium batteries cost more upfront than lead-acid but last more cycles and need no watering. |
| Winter oversizing | In northern states, covering winter use can take roughly twice the panels an average day needs. |
| Peak loads | Running a well pump, air conditioner or shop tools at once requires a larger inverter. |
| Generator | An automatic standby generator, transfer wiring and a fuel tank add thousands of dollars. |
Who it suits
- Properties far from the grid, where a line extension costs more than the system.
- Cabins and seasonal homes with small, predictable loads.
- Owners willing to manage their use in winter and to maintain a generator.
If the grid is available but unreliable, grid-tied solar with a battery is usually the better choice: it keeps the power on during outages and still uses the grid the rest of the time.
Questions to ask your installer
- Is the design based on a load list of my actual appliances, including winter use?
- How many days without sun does the battery bank cover, and at what depth of discharge?
- Can the inverter handle the surge when the well pump or refrigerator starts?
- What battery chemistry are you proposing, and what are its warranty years and cycles?
- How does the generator start, and how many hours a year do you expect it to run?
- How do I monitor the batteries, and what maintenance do they need?
What to watch out for
- Sizing from an average day. A system designed for average production runs short every winter and leans on the generator far more than planned.
- Batteries in an unheated space. Most lithium batteries can’t be charged below freezing unless they have built-in heating, and every battery has a temperature range in its warranty.
- Grid-tied equipment. Inverters made for grid-tied systems may not run without the grid. Check that the inverter is rated for off-grid use.
- No service plan. You may be far from the installer. Ask who will respond if the inverter fails and how long parts take to arrive.