Complete Off-Grid Solar Guide 2025
Everything you need to know about sizing and building an off-grid solar system—from weekend cabins to full-time homes. Covers panels, batteries, inverters, real costs, and common mistakes to avoid.
Understanding Off-Grid Solar
Off-grid solar systems generate and store their own electricity without any connection to the utility grid. Unlike grid-tied systems, they require battery storage to provide power when the sun isn't shining.
Off-grid makes sense when grid connection costs are prohibitive (often $15,000-50,000+ for remote properties), when you want true energy independence, or for mobile applications like RVs and vans. Before designing your system, use our Battery Runtime Calculator to understand how long your batteries will power your essential loads.
System Voltage: 12V vs 24V vs 48V
Higher voltage = lower current = smaller wire sizes and less power loss. Calculate your exact wire requirements with our Wire Gauge Calculator and check for voltage drop using our Voltage Drop Calculator.
Small systems under 1kW. RV lighting, fans, basic loads.
Medium systems 1-3kW. Full-time vans, small cabins.
Large systems 3kW+. Homes, large cabins. Recommended for stationary.
Core Components
Solar Panels
Monocrystalline panels dominate the off-grid market for their efficiency and durability. Current pricing (2025):
Commodity Rigid
300-450W panels
$0.40-0.65/W
Brand-Name RV
100-200W panels
$0.80-1.20/W
Premium Flexible
Thin-film
$2.50+/W
Batteries
LiFePO4 (Lithium Iron Phosphate) has become the standard for off-grid systems. It offers 10+ year lifespan, 100% depth of discharge, and no maintenance—replacing lead-acid in most applications. Estimate your charging times with our Solar Charge Time Calculator.
12V LiFePO4 Options
Battle Born 100Ah
$800-900
SOK 100-280Ah
$400-999
LiTime 100Ah
$250-400
48V Rack Batteries (Homes/Cabins)
EG4 LiFePower4 V2
5.12kWh
$1,400-1,700
Rich Solar Alpha 5 Pro
5kWh
$1,300-1,500
Charge Controllers
Top MPPT Picks
Victron SmartSolar
100/30 to 150/60
Renogy Rover 40A
Budget pick
Inverters
For off-grid, you need a pure sine wave inverter. All-in-one inverter/chargers bundle inverter + MPPT + charger in one unit.
Renogy PUH, GoWISE 1500W
Weekend cabin, CPAP, lights, small fridge
EG4 3000EHV-48
Small cabin, full-time RV. "Little yellow Pikachu" - Will Prowse
EG4 6000XP, Victron MultiPlus II
Whole-home off-grid
System Sizing Methodology
Step 1: Calculate Daily Load (Wh/day)
List every device, its wattage, and hours of daily use:
Daily Wh = Watts × Hours per day
Add 20% for inverter inefficiency and system losses: 1,540 × 1.2 = 1,848 Wh/day. Use our Battery Runtime Calculator to determine how long your battery bank will power these loads.
Step 2: Size Your Battery Bank
Determine days of autonomy (backup without sun). Our Battery Bank Sizing Calculator makes this easy:
- Weekend cabin: 1-2 days
- Full-time off-grid with generator: 2-3 days
- No generator backup: 3-5 days
Battery Capacity = Daily Wh × Days of Autonomy ÷ Depth of Discharge
Step 3: Size Your Solar Array
Solar sizing depends heavily on your location's peak sun hours (PSH). Use our Panel Output Calculator to estimate production based on your location:
Array Size (W) = Daily Wh ÷ Peak Sun Hours ÷ System Efficiency
Step 4: Size Your Inverter
Add up the wattage of all devices you might run simultaneously. Add 25% headroom for surge loads (motors, compressors). Use our Inverter Size Calculator to determine the right inverter for your needs.
Inverter Size = Peak Simultaneous Load × 1.25
Real-World System Examples
Small System: ~1kWh/day
Weekend RV or Tiny Cabin
Loads: LED lights, water pump, phone charging, DC fridge, occasional laptop
Components
- • Solar: 400W (4× 100W panels)
- • Battery: 12V 100Ah LiFePO4 (1.2kWh)
- • Controller: 30A MPPT
- • Inverter: 1000-1500W pure sine
Output
400W × 4 PSH = 1.6kWh/day
Enough to cover 1kWh load with margin
Medium System: ~3kWh/day
Full-Time RV or Small Cabin
Loads: Efficient fridge, lights, laptops, router, TV, small microwave
Components
- • Solar: 1500W (4-5× 300W panels)
- • Battery: 48V 100Ah (5.12kWh) - EG4
- • Inverter: EG4 3000EHV-48 all-in-one
Output
1500W × 4 PSH × 0.8 = 4.8kWh/day
Plenty of headroom for cloudy days
Large System: ~10kWh/day
Off-Grid Home
Loads: Full home with efficient appliances, well pump, washer
Components
- • Solar: 5-8kW (sized for winter)
- • Battery: 15-20kWh (3-4× EG4 racks)
- • Inverter: 6-12kW split-phase
Pro Install
Professional installation typically runs $45,000 - $65,000
Installation Best Practices
Wire Sizing
NEC guidelines: ≤3% voltage drop on branch circuits, ≤5% total. Higher current (lower voltage systems) requires much larger wire. Calculate the exact voltage drop for your installation with our Voltage Drop Calculator.
Grounding & Bonding
Proper fusing is critical for safety—calculate the right size with our Fuse Size Calculator.
- 1Use #8 AWG copper minimum for equipment grounding from array to main system
- 2Bond all ground rods together with at least #6 copper if using multiple rods
- 3One neutral-ground bond only—usually at main panel or inverter
Costs: DIY vs Professional
2025 Market Pricing
DIY Costs
- Small (RV/cabin)$3,000 - $20,000
- Whole-home$15,000 - $35,000
Professional Costs
- Small (RV/cabin)$8,000 - $30,000
- Whole-home$45,000 - $65,000
| Feature | DIY | Professional |
|---|---|---|
| Labor savings | 20-30% | 0% |
| Full system understanding | ||
| Code-compliant design | Your responsibility | |
| Permits handled | ||
| Full warranties | Varies | |
| Time investment | High | Low |
Common Mistakes to Avoid
Undersizing solar for winter
Systems designed on annual averages fail in winter. Design for worst-month irradiance.
Using 12V for large systems
A 3kW inverter at 12V draws 250+ amps—requiring massive, expensive cables. Use 24V or 48V.
Undersized cables
Using 4 AWG where 2/0 is needed causes overheating and fire risk.
Wrong fuse ratings
Using 32V DC fuses on 48V systems, or AC-only breakers on DC circuits.
Multiple neutral-ground bonds
Having bonds at inverter AND generator causes GFCI trips and safety issues.
Mismatched parallel batteries
Unequal cable lengths create imbalance. Use equal-length leads and proper busbars.
Ignoring charge current limits
Oversizing solar beyond what your charger can handle just clips production.
Frequently Asked Questions
How big of a system do I need for my cabin/RV/home?▼
Is 12V, 24V, or 48V better?▼
Do I need a generator even with a large solar system?▼
How long do LiFePO4 batteries last?▼
Are all-in-one power stations good for off-grid?▼
Can I install off-grid solar myself?▼
Related Calculators
Battery Runtime Calculator
How long will your battery power your devices?
Solar Charge Time Calculator
Estimate how long to fully charge your batteries
Battery Bank Sizing Calculator
Calculate the right battery capacity for your needs
Solar Panel Output Calculator
Estimate daily energy production from your panels
Inverter Size Calculator
Size your inverter for your load requirements
Wire Gauge Calculator
Find the right wire size for safe installations
Fuse Size Calculator
Calculate proper fuse ratings for your system
Voltage Drop Calculator
Check voltage drop for your wire runs