Off-Grid Solar System Design Guide | PES Supply
Off-Grid Solar System Design Guide
Complete guide to designing and sizing off-grid solar with battery backup
Off-Grid System Components
- Solar panels: Generate DC power from sunlight
- Charge controller: MPPT preferred (30% more efficient than PWM)
- Battery bank: Stores energy for nights and cloudy days
- Off-grid inverter: Converts DC to AC (pure sine wave required)
- Backup generator: For extended cloudy periods
- Transfer switch: Automatic or manual switch between inverter and generator
Step 1: Calculate Your Daily Energy Needs
List all appliances, their wattage, and daily run hours:
| Appliance | Watts | Hours/Day | Daily Wh |
|---|---|---|---|
| Refrigerator | 150 | 24 | 3,600 |
| LED Lights (8) | 80 | 5 | 400 |
| TV | 150 | 4 | 600 |
| Well Pump | 1,000 | 1 | 1,000 |
| Phone/Laptop | 100 | 6 | 600 |
| Microwave | 1,000 | 0.5 | 500 |
| Total | 6,700 Wh (6.7 kWh/day) |
Step 2: Size the Battery Bank
Battery Bank Size = Daily Wh × Days of Autonomy / (DoD × Inverter Efficiency × Battery Voltage)
Example: 6,700 Wh × 3 days / (0.9 × 0.9 × 48V) = 519 Ah @ 48V = ~24.9 kWh
| Daily Usage | 2-Day Battery | 3-Day Battery | Recommended |
|---|---|---|---|
| 3 kWh/day | 7 kWh | 10.5 kWh | 2× EG4 5kWh |
| 5 kWh/day | 12 kWh | 17.5 kWh | MidNite PowerFlo16 |
| 10 kWh/day | 25 kWh | 35 kWh | Fortress eVault + EG4 |
| 15 kWh/day | 37 kWh | 52 kWh | 2× Fortress eVault |
Step 3: Size the Solar Array
Solar Array kW = Daily Wh / (Peak Sun Hours × System Efficiency)
Example: 6,700 Wh / (5 sun hours × 0.7) = 1.9 kW array (oversize 25% for charging + usage = 2.4 kW)
Step 4: Choose the Inverter
| Peak Load | Inverter | Battery Compatible | Price |
|---|---|---|---|
| 3,000W | EG4 3000EHV | 48V LiFePO4 | $1,500-$2,000 |
| 6,500W | EG4 6500EX | 48V LiFePO4 | $2,500-$3,500 |
| 10,000W | Growatt SPH 10000TL3 | 48V / HV | $3,000-$4,000 |
| 12,000W | Schneider XW Pro | 48V | $4,000-$5,500 |
Step 5: Choose Charge Controller
For systems under 2kW, a single MPPT charge controller (60A) is sufficient. For larger systems, use multiple controllers or a high-voltage hybrid inverter with built-in MPPT.
| Controller | Max Current | Max Voltage | Price |
|---|---|---|---|
| MidNite Classic 200 | 96A | 200V | $700 |
| Victron MPPT 150/100 | 100A | 150V | $800-$1,000 |
| EG4 6500EX (built-in) | 120A | 500V | Included |
Complete Off-Grid System Examples
Cabin System (3-5 kWh/day)
- 6× 450W solar panels (2.7 kW array)
- EG4 3000EHV inverter/charger (3 kW)
- 2× EG4 LifePower4 5kWh batteries (10 kWh)
- MidNite Classic 200 charge controller
- Backup: Honda EU2200i generator
- Estimated cost: $8,000-$12,000
Whole Home Off-Grid (10-15 kWh/day)
- 20× 450W solar panels (9 kW array)
- EG4 6500EX inverter (6.5 kW) × 2 in parallel
- 4× EG4 LifePower4 5kWh batteries (20 kWh)
- DuroMax XP15000HX backup generator
- Automatic transfer switch
- Estimated cost: $20,000-$30,000