Off-grid solar system design is fundamentally different from grid-tied solar. Without the utility grid as a backup, every component must be sized correctly to ensure reliable power 365 days a year. A mistake in battery bank sizing means dark nights. An undersized solar array means the batteries never fully recharge. This guide walks through the complete design process with real-world numbers.
Whether you are powering a remote cabin, a home in a rural area, or an off-grid workshop, the same five-step design process applies: load analysis, solar array sizing, battery bank sizing, charge controller selection, and inverter sizing. Each step builds on the previous one, so follow them in order.
Step 1: Perform a Detailed Load Analysis
Every off-grid design starts with understanding how much energy you use per day. Create a table of every AC and DC load, its wattage, and the hours per day it runs. The goal is total daily energy consumption in watt-hours (Wh).
| Appliance | Watts (W) | Hours/Day | Wh/Day |
|---|---|---|---|
| LED lights (10 × 10W) | 100 | 5 | 500 |
| Refrigerator (Energy Star) | 150 | 8 | 1,200 |
| Laptop + charger | 60 | 4 | 240 |
| LED TV (32") | 50 | 4 | 200 |
| Ceiling fan | 75 | 8 | 600 |
| Washing machine | 500 | 1 | 500 |
| Router + modem | 20 | 24 | 480 |
| Water pump | 200 | 1 | 200 |
| Total Daily Load | 3,920 Wh |
For a full-time home, include larger loads like well pumps, freezers, microwaves, and power tools. Always add a 15-25% safety margin for unexpected loads and system inefficiencies. In this example, 3,920 Wh rounds to 4,000 Wh/day with margin included.
Step 2: Size the Solar Array
The solar array must generate enough energy to replace what you use each day, accounting for system losses. The key metric is peak sun hours (PSH) for your location — the equivalent number of hours per day at 1,000 W/m² irradiance.
Example (4,000 Wh/day at 4.5 PSH):
Example (12,000 Wh/day at 3.5 PSH, northern climate):
The 1.20 loss factor accounts for inverter efficiency (92-96%), wire losses (2-3%), charge controller losses, dust, and temperature derating. In colder climates (below 25°C) panels perform better, but winter has fewer sun hours — design for December/January PSH, not the annual average.
| Climate | Winter PSH | Summer PSH | Design PSH |
|---|---|---|---|
| Southwest US (Arizona) | 5.0 | 7.5 | 5.0 |
| Southeast US (Florida) | 4.0 | 5.5 | 4.0 |
| Northern US / Canada | 2.5 | 5.5 | 2.5 |
| Central Europe | 1.5 | 5.0 | 1.5 |
| South Asia (Pakistan/India) | 4.0 | 6.0 | 4.0 |
| Australia (most regions) | 4.5 | 6.5 | 4.5 |
Use the PSH for your latitude from our Baseline Generation Profile tool in the sidebar. Enter your coordinates and it calculates site-specific irradiance data automatically.
Panel Selection
For off-grid systems, 550W panels are the sweet spot in 2026, offering the best balance of $/W and manageable string sizing for 48V battery banks. For a 1,100 W array, you would use 2 panels (achieving 1,100W exactly) wired in series to keep voltage high for MPPT charging.
See Solar Panel Wattage Explained for a full comparison of 400W to 700W panel options and how they affect string configuration at different battery voltages.
Step 3: Size the Battery Bank
The battery bank provides power when the sun is not shining. The key parameters are battery voltage, depth of discharge (DoD), and days of autonomy (how many days you want to run on battery alone).
Example (4,000 Wh/day, 48V system, 2 days autonomy, 80% DoD for lithium):
Example (4,000 Wh/day, 48V system, 2 days autonomy, 50% DoD for lead-acid):
| Battery Type | Usable DoD | Cycle Life | Cost Factor | Best For |
|---|---|---|---|---|
| Lithium (LiFePO4) | 80-90% | 4,000-6,000 | 2-3x lead-acid | Full-time living, long lifespan |
| AGM / Gel (Lead-Acid) | 50% | 800-1,200 | 1x baseline | Cabins, seasonal use, budget builds |
| Flooded Lead-Acid | 50% | 1,000-1,500 | 0.7x AGM | Large off-grid, requires maintenance |
| Nickel-Iron (NiFe) | 60-80% | 10,000+ | 4-5x lithium | Extreme longevity, harsh environments |
Days of autonomy should be 2-3 for most climates. In areas with extended cloudy periods (Pacific Northwest, UK), consider 4-5 days. Each extra day of autonomy roughly doubles the battery cost.
See Battery Bank Voltage Guide for help choosing between 12V, 24V, and 48V architectures. For designs over 2,000 Wh/day, 48V is strongly recommended for higher inverter efficiency and lower wire costs.
Step 4: Select the Charge Controller
The charge controller regulates the solar array output to safely charge the battery bank. Two types exist: MPPT (maximum power point tracking) and PWM (pulse width modulation). For any off-grid system over 500W, choose MPPT — it extracts 20-30% more energy from the array.
Example (1,100W array, 48V battery):
Example (4,200W array, 48V battery):
Always oversize the charge controller. A 40A controller running at 29A stays cool and operates at peak efficiency. Running a controller at 95% of capacity causes thermal stress and reduced lifespan. Most MPPT controllers also need the array voltage to be significantly higher than battery voltage — typically at least 5V above battery voltage for 12V systems and 10V+ for 48V systems.
| Array Size | Battery Voltage | Max Current | Recommended MPPT |
|---|---|---|---|
| 500-1,200W | 48V | 10-25A | 30-40A |
| 1,200-2,400W | 48V | 25-50A | 60A |
| 2,400-4,000W | 48V | 50-83A | 80-100A |
| 4,000-6,000W | 48V | 83-125A | 2 × 60-80A |
Modern MPPT controllers from Victron, OutBack, MidNite Solar, and EPEVER support PV array voltages up to 150V, 250V, or even 600V. Higher array voltage means thinner copper wire from the roof to the controller, reducing installation cost significantly on long cable runs.
Step 5: Size the Off-Grid Inverter
Off-grid inverters must handle both continuous loads and surge loads. Surge loads (motor starting currents, compressor inrush) can be 3-7x the running wattage for 1-5 seconds. This is the most common cause of inverter undersizing.
Surge Capacity = Must exceed largest motor + all other running loads
Example cabin loads: Refrigerator (150W running, 800W surge), washing machine (500W running, 2,500W surge), lights (100W), laptop (60W), fan (75W). Total continuous = 885W × 1.25 = 1,106W. Largest surge (washing machine at 2,500W) plus other running loads (385W) = 2,885W.
Example full-time home: Well pump (1,000W running, 5,000W surge), refrigerator (150W, 800W), freezer (200W, 1,000W), washing machine, microwave (1,200W), lights (200W), electronics (200W). Total continuous = 2,950W × 1.25 = 3,688W. Largest surge (well pump at 5,000W) + others (1,750W) = 6,750W.
| Inverter Size | Typical Surge Rating | Suitable For |
|---|---|---|
| 1,000-1,500W | 2,000-3,000W | Tiny cabin, phone charging, lights only |
| 2,000-3,000W | 4,000-6,000W | Small cabin with fridge, laptop, lights |
| 3,000-5,000W | 6,000-10,000W | Medium cabin, washing machine, power tools |
| 5,000-8,000W | 10,000-16,000W | Full-time home, well pump, kitchen appliances |
| 8,000-12,000W+ | 16,000-24,000W+ | Large home, workshop, heavy machinery |
Complete System Sizing Reference Table
| Daily Load | PSH | Solar Array | Battery (48V LiFePO4) | MPPT | Inverter |
|---|---|---|---|---|---|
| 2,000 Wh | 4.0 | 600W (1 × 550W) | 48V 100Ah | 30A | 1,500W |
| 4,000 Wh | 4.5 | 1,100W (2 × 550W) | 48V 200Ah | 40A | 3,000W |
| 6,000 Wh | 4.0 | 1,800W (4 × 450W) | 48V 300Ah | 60A | 4,000W |
| 8,000 Wh | 3.5 | 2,750W (5 × 550W) | 48V 400Ah | 80A | 5,000W |
| 12,000 Wh | 3.5 | 4,200W (8 × 550W) | 48V 600Ah | 2 × 60A | 6,000W |
| 20,000 Wh | 4.0 | 6,000W (11 × 550W) | 48V 1,000Ah | 2 × 80A | 8,000W |
Wiring and Safety Considerations
Off-grid systems require careful attention to wire sizing to prevent voltage drop and fire hazards. Key rules:
- PV-to-controller: Keep voltage drop under 3%. Use the highest array voltage your MPPT allows (150V-600V) to reduce current and wire size.
- Controller-to-battery: This is the highest-current path. For a 40A controller at 48V, use at least 6 AWG copper for runs under 2 metres; upgrade to 4 AWG for longer runs.
- Battery-to-inverter: For a 3,000W inverter at 48V (62.5A continuous), minimum 4 AWG, but 2 AWG or 1/0 AWG is recommended for surge handling and minimal voltage drop.
- Overcurrent protection: Every circuit must have a fuse or breaker rated at 1.25x the expected current. DC-rated breakers are essential — AC breakers will not interrupt DC arcs safely.
- Grounding: All off-grid systems need a single-point earth ground. Bond the negative busbar to ground at one location only to prevent ground loops.
Use the Pro Suite for Automated Off-Grid Design
The Solar Metrix Pro Baseline Generation Profile module in the sidebar automates the entire sizing process. Enter your daily load, select your location (or enter latitude/longitude), and choose your preferences:
- Solar array size in kWp with panel count and string configuration
- Battery bank capacity in Ah at 12V, 24V, or 48V, with lithium vs lead-acid comparison
- MPPT charge controller amperage with model recommendations
- Inverter size with surge capacity check against your loads
- Auto-saved data flows into the full Pro Suite for detailed energy modelling
Share your design with installers or use it to source components. The system also generates a one-line wiring diagram showing all component interconnections with wire gauge recommendations.
Design your off-grid solar system now
Open the Off-Grid Design Tool →Data sources: NREL PVWatts v8, SolarPro Magazine design guidelines, Victron Energy wiring handbook, Canadian Electrical Code Part I, US NEC Article 690. All system sizing examples are for educational purposes. Always work with a licensed electrical contractor for final design and installation.
Last updated: July 2026 | Browse all guides