Figuring out off-grid solar system cost before you commit to a design can save you thousands of dollars and weeks of frustration. Get the math wrong and you'll either run out of power on a cold January night or pay for twice the capacity you'll ever need. Here's how to size your system, estimate real costs, and make confident decisions.
Start With Your Energy Load
Before any calculator is useful, you need to know how much electricity you actually consume. Walk through your cabin or home and list every appliance, its wattage, and how many hours per day you run it.
Common loads to include:
- Lighting: LED fixtures, 5–15W each, 4–6 hours/night
- Refrigerator: 100–400W, running roughly 8 hours equivalent per day
- Water pump: 300–700W, 1–2 hours/day
- Laptop or devices: 45–100W, 4–8 hours/day
- Electric heating or AC: 1,000–5,000W (often avoided off-grid due to cost)
- Power tools or workshop equipment: 1,000–2,000W, intermittent
Add up the watt-hours (W × hours = Wh) for everything. A modest cabin typically lands between 1,500–4,000 Wh per day. A full-time off-grid home can easily exceed 10,000 Wh daily.
Size Your Solar Array
Your solar panels need to generate enough power to cover daily consumption and charge your battery bank, accounting for system inefficiencies (typically 20–25% losses).
Basic formula: Daily Wh ÷ peak sun hours ÷ 0.75 efficiency factor = required solar wattage
For a location receiving 4.5 peak sun hours per day with a 3,000 Wh daily load:
3,000 ÷ 4.5 ÷ 0.75 = ~889W of solar panels
Most designers round up and add a safety buffer. Expect to install 1,200–1,500W for that scenario. Panel costs range from $0.30–$0.60 per watt for hardware alone, though installed prices including racking and wiring run $1.00–$2.00 per watt.
Calculate Battery Bank Size
Your battery bank covers nighttime use and cloudy days. A common rule is sizing for 2–3 days of autonomy without sun.
- Lithium iron phosphate (LiFePO4): Most popular choice now. Usable depth of discharge is ~90–95%. Expect $400–$800 per kWh of usable capacity.
- Lead-acid (AGM or flooded): Cheaper upfront at $150–$300 per kWh, but only 50% usable capacity and shorter lifespan (3–7 years vs. 10+ for lithium).
For the 3,000 Wh/day cabin needing 2 days autonomy: 6,000 Wh usable. In lithium that's roughly a 6–8 kWh battery bank costing $2,400–$6,400 depending on brand and installation.
Factor In Inverter, Charge Controller, and Balance of System
The panels and batteries get the attention, but these components add up fast:
- Inverter/charger: Converts DC power to AC. Sized to handle peak loads. A quality 3,000W unit runs $800–$2,500.
- MPPT charge controller: Manages solar input. Budget $200–$600 for a properly sized unit.
- Wiring, conduit, breakers, disconnects: Add $500–$2,000 depending on system complexity.
- Mounting hardware: Ground mounts cost more than roof mounts—budget $300–$1,500.
Real-World Off-Grid Solar System Cost Ranges
Putting it all together, here's what complete installed systems typically cost:
| System Size | Use Case | Installed Cost Range | |---|---|---| | 1–2 kW solar / 5 kWh battery | Small cabin, basic loads | $8,000–$14,000 | | 3–5 kW solar / 10–15 kWh battery | Full-time small home | $18,000–$32,000 | | 6–10 kW solar / 20–30 kWh battery | Larger home, well pump, shop | $35,000–$65,000 |
DIY installations can cut labor costs by 30–50%, but permitting, electrical work, and equipment sourcing still require serious time and skill.
Generator Backup
Most off-grid systems include a propane or gasoline generator for winter backup or high-demand periods. A quality 6,000–10,000W propane unit runs $2,000–$5,000. Factor this into your budget from day one rather than treating it as an afterthought.
Getting Accurate Quotes
Online calculators give you a solid starting estimate, but real quotes require a site assessment—roof or ground conditions, local sun data, utility interconnection rules (even off-grid properties have permit requirements), and load details only you know.
Mercoly makes it easy to compare and find trusted off-grid and cabin power system providers in one place, so you're not cold-calling random contractors hoping someone specializes in remote solar installations.
Work through your load numbers first, then use this framework to pressure-test any quote you receive—if a proposal seems dramatically under or over these ranges, now you know what questions to ask.
Start building your load list today and reach out to a vetted installer to get an accurate quote for your specific site.