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.
System Voltage: 12V vs 24V vs 48V
Higher voltage = lower current = smaller wire sizes and less power loss.
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.
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
Step 2: Size Your Battery Bank
Determine days of autonomy (backup without sun):
- 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):
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).
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.
Grounding & Bonding
- 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.