Off-Grid Solar System Calculator
Size your off-grid solar system by calculating required solar panels, battery bank, and inverter capacity. Essential for cabins, RVs, or remote installations without grid access.
About this calculator
An off-grid solar system must meet your daily energy demand without any utility backup. The total system requirement combines two components: the solar array size and the battery bank capacity. Solar array size (W) = (dailyLoad × 1.3 / (peakSunHours × systemEfficiency)) × 1000, where 1.3 accounts for a 30% system loss buffer. Battery bank size (Wh) = (dailyLoad × autonomyDays / (batteryType / 100)) × 1000, where batteryType represents the usable depth-of-discharge percentage (e.g., 50 for lead-acid, 80 for lithium). Peak sun hours reflect the average daily solar irradiance at your location. System efficiency captures inverter and wiring losses, typically 0.75–0.85. Together these ensure your system can generate enough power daily and store enough energy to survive cloudy days.
How to use
Suppose your cabin uses 3 kWh/day, you want 2 days of autonomy, your location gets 5 peak sun hours, you use lithium batteries (80% DoD), and system efficiency is 0.80. Solar array = (3 × 1.3 / (5 × 0.80)) × 1000 = (3.9 / 4) × 1000 = 975 W. Battery bank = (3 × 2 / (80 / 100)) × 1000 = (6 / 0.8) × 1000 = 7,500 Wh. So you need approximately 975 W of solar panels and a 7.5 kWh battery bank to reliably power your cabin off-grid.
Frequently asked questions
How many solar panels do I need for an off-grid home using 5 kWh per day?
With 5 kWh/day, 5 peak sun hours, and 0.80 system efficiency, your required array is (5 × 1.3 / (5 × 0.80)) × 1000 = 1,625 W. At 400 W per panel, that means roughly 4–5 panels. Always round up and account for seasonal variation in sun hours, which can drop significantly in winter months.
What is the difference between lead-acid and lithium batteries for off-grid solar systems?
Lead-acid batteries typically allow only 50% depth of discharge (DoD) to maintain their lifespan, while lithium iron phosphate (LiFePO4) batteries can safely discharge to 80% or more. This means a lithium bank needs to be physically smaller to deliver the same usable energy. Lithium batteries also charge faster, last longer (2,000–5,000 cycles vs. 300–700), and perform better in temperature extremes, though they cost more upfront.
How many days of autonomy should I plan for in an off-grid solar system?
Most off-grid designers recommend 2–5 days of battery autonomy depending on your climate and risk tolerance. In sunny climates with predictable weather, 2–3 days is common. In cloudy or high-latitude regions, 4–5 days provides a safety buffer against extended low-generation periods. More autonomy days dramatically increase battery bank size and cost, so balancing this against a backup generator can be a cost-effective compromise.