Appliances
Add everything your cabin runs on solar. Tap a preset or add a custom item.
System Settings
Battery Chemistry
System Voltage
Days Without Sun
Cloudy day backup your batteries should cover
Location & Panels
Auto-fills NREL sun hours.
Override after selecting a state.
The Math
How It Works
Every number in your results comes from standard electrical engineering. Here are the four calculations that drive each output, and why they matter for off-grid cabin design.
Peak Sun Hours & Panel Array
Peak sun hours are not the same as daylight hours. One peak sun hour represents 1,000 W/m² of solar irradiance sustained for a full hour — it's how meteorologists normalize a day's total solar energy into a single usable number for system design.
A cabin in Colorado at 5.5 peak sun hours doesn't see 5.5 hours of perfect midday sun — it receives the energy equivalent spread across the whole day. We divide your daily Wh load by sun hours and a 0.8 real-world efficiency factor to get required panel wattage. Select your state and the calculator fills this from NREL PVWatts data automatically.
Panel array (W) = daily Wh ÷ (peak sun hours × 0.8 efficiency)
Battery Bank & Depth of Discharge
Battery capacity is not fully usable. Discharging a lead-acid battery (AGM or Gel) below 50% of its rated capacity accelerates sulfation — plates degrade, capacity shrinks permanently, and lifespan shortens. Lithium iron phosphate (LiFePO4) safely supports 80% discharge without measurable cycle loss.
For a cabin needing multiple days of backup, the battery bank is usually the single largest cost driver. A 10 kWh lithium bank stores 8 kWh usable. To get the same usable storage from AGM, you need twice the rated capacity at nearly twice the weight — and the cabin floor has to hold it.
Battery bank (Ah) = (daily Wh × backup days) ÷ (DoD × system voltage)
Inverter Sizing
Your inverter converts DC battery power to 120V AC for standard outlets. It needs to handle your peak simultaneous load — not your daily total consumption. The calculator sums all appliance wattages, applies a 1.25× safety factor, then rounds up to the nearest standard inverter size.
Motor loads — well pumps, chest freezers, washing machines — draw 3–5× their rated wattage for a fraction of a second at startup. This surge can trip an undersized inverter even when continuous power is within spec. When buying, check the inverter's surge rating alongside its continuous rating. Most quality units handle 2× continuous for several seconds.
Inverter size = total peak load (W) × 1.25, rounded to next standard size
Cost Estimation
The cost estimate covers the four major hardware components: solar panels, battery bank, inverter, and charge controller. Panel pricing uses $0.70–$1.40/W (wholesale to retail). Lithium batteries are priced at $300–$450/kWh; AGM/Gel at $130–$220/kWh. Inverter cost scales with rated output from $350 to $6,000+.
The range reflects DIY component pricing — the low end assumes budget brands and bulk panel pricing, the high end assumes name-brand inverters and premium LiFePO4. It does not include mounting hardware, wiring, conduit, breakers, fusing, a transfer switch, generator backup, permits, or professional labor — typically another $1,000–$5,000+ depending on your setup. Budget at least 30% above the hardware estimate for balance-of-system costs.
Est. cost = panels + batteries + inverter + controller (hardware only)
FAQ
Common Questions About Off-Grid Cabin Solar
How much solar power does an off-grid cabin need?
Most off-grid cabins need between 1.5 kW and 6 kW of solar panels depending on daily energy use and location. A minimal weekend retreat with lights, a fan, and a laptop might run on 1–2 kW. A full-time cabin with a chest freezer, well pump, and washing machine typically needs 3–6 kW.
Add your appliances in the calculator above for a precise number. The key driver is your daily watt-hour consumption — not the number of rooms or square footage.
What system voltage is best for an off-grid cabin?
48V is the right choice for most off-grid cabin systems above 2 kW. Higher voltage means lower current for the same power, which allows thinner wire over long cable runs and reduces resistive heat loss.
12V is practical only under 600W. 24V works from 600W to 2 kW. Above 2 kW, 48V is the clear winner — nearly all quality off-grid inverter-chargers are 48V, and the battery wiring is far more manageable.
How do I size an inverter for an off-grid cabin?
Your inverter needs to handle your peak simultaneous load — not your daily total consumption. Add up the watts of every appliance that might run at the same time, then multiply by 1.25 for a safety margin.
Pay attention to motor surge: well pumps, chest freezers, and washing machines draw 3–5× their rated wattage for a split second at startup. Check the inverter's surge rating — most quality units handle 2× continuous for a few seconds. If your well pump is 500W continuous, look for an inverter with at least 2,000W surge capacity.
Can I run a well pump and AC unit on solar?
Yes, but both require careful sizing. A ½ HP well pump draws about 500W continuous but can surge to 2,000W at startup — your inverter must handle that surge rating, not just the continuous watts.
A window AC at 1,000W for 8 hours adds 8 kWh to your daily load, which can roughly double panel and battery requirements for a small cabin. Add these appliances one at a time in the calculator to see the exact impact on system size and cost.
How much does an off-grid cabin solar system cost?
Hardware alone — panels, batteries, inverter, charge controller — typically runs $3,000–$15,000 for a DIY cabin system. The battery bank is usually 40–50% of total hardware cost. LiFePO4 batteries cost $300–$450 per kWh but last 10–15 years with minimal maintenance.
Add 30% above the hardware estimate for balance-of-system costs: mounting, wiring, conduit, breakers, fusing, a transfer switch, permits, and any professional labor. The cost estimate above shows hardware only.
How accurate are these off-grid solar estimates?
The electrical formulas are standard engineering — the same ones professional solar designers use. The 0.8 efficiency factor accounts for panel temperature derating, MPPT losses, and wiring resistance. Accuracy depends on your inputs: use label wattages and honest daily usage hours.
Cost ranges are based on 2024 component pricing for DIY procurement and do not include structural, electrical, or labor costs. Size panel and battery capacity 20% above the calculated minimum when buying equipment to account for real-world variation and future load growth.
Related Tools
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Size your panel array, battery bank, and charge controller for van life or RV travel.
↳ 500 Wh/day, 5 sun hrs → 125W panels
Battery Bank Sizing
Usable and gross capacity needed for any backup duration, chemistry, and load.
↳ 10 kWh, 24 hr backup → 12.5 kWh gross
Solar Payback & ROI
Simple payback, IRR, NPV, and 25-year savings chart — with federal and state incentives.
↳ $18K system, 30% ITC → 8.4 yr payback