Off-Grid Solar for Beginners — What Size System Do You Actually Need?
Source: Dev.to
Sizing a Real Off‑Grid System
Calculate Daily Power Consumption
Before buying anything, determine your daily load in watt‑hours (Wh). Below is an example load list for a typical off‑grid cabin.
| Item | Watts | Hours/day | Wh/day |
|---|---|---|---|
| LED lighting (10 bulbs) | 50 | 5 | 250 |
| Laptop | 45 | 6 | 270 |
| Phone charging | 10 | 3 | 30 |
| Small chest freezer | 30 | 24 | 720 |
| Water pump (DC) | 150 | 1 | 150 |
| Fans (2×) | 60 | 8 | 480 |
| Total | 1,900 Wh/day |
A modest off‑grid container home in Missouri typically uses 1,500 – 2,500 Wh/day (excluding electric cooking or air conditioning).
Panel Sizing
Missouri receives 4.5 – 5.5 peak sun hours per day on average.
[ \text{Panel watts needed} = \frac{\text{Daily load (Wh)}}{\text{Peak sun hours} \times \text{System efficiency}} ]
Using a 0.8 (80 %) system efficiency and 5 peak sun hours:
[ \frac{1,900\ \text{Wh}}{5\ \text{h} \times 0.8} \approx 475\ \text{W} ]
Add a 25 %–50 % margin for cloudy days and winter, resulting in a 750 W – 1,000 W array.
Real‑World Panel Options (2026)
- 2 × 400 W panels – $240‑$400 (used) or $400‑$600 (new)
400 W is the sweet spot for value‑to‑output ratio in 2026.
Battery Sizing
Aim for 2 – 3 days of autonomy without sun.
[ 1,900\ \text{Wh} \times 3\ \text{days} = 5,700\ \text{Wh} ]
Assuming a 25 % depth‑of‑discharge (DoD) limit, the required nameplate capacity is about 7,125 Wh, which translates to:
- ≈ 200 Ah at 48 V
- ≈ 600 Ah at 12 V
Most beginners start with 100 Ah at 48 V (4,800 Wh) and add a second bank within a year. LiFePO₄ banks are modular and well‑suited for this approach.
Battery Options (2026)
| Capacity | Type | Approx. Cost |
|---|---|---|
| 100 Ah 48 V LiFePO₄ | Chinese brands, reliable | $600 – $900 |
| 200 Ah 48 V LiFePO₄ | – | $1,100 – $1,500 |
| DIY from 280 Ah cells | – | $400 – $600 (equivalent capacity) |
Charge Controller & Inverter
- MPPT charge controller – matches panel voltage to battery voltage efficiently. Do not use PWM.
- 40 A MPPT for a ~1 kW system: $80 – $150
- Hybrid inverter (inverter + MPPT combined) – simplifies wiring.
- 3 kW hybrid inverter: $250 – $500
Example Bill of Materials
| Item | Cost |
|---|---|
| 3 × 400 W panels | $600 |
| 200 Ah 48 V LiFePO₄ battery | $1,200 |
| 3 kW hybrid inverter/MPPT | $400 |
| Wiring, connectors, breakers | $200 |
| Mounting structure (ground mount) | $300 |
| Total | $2,700 |
This configuration handles the example load with margin and can be expanded by adding more panels or batteries as budget permits.
Practical Considerations
- High‑draw appliances (electric stove, central AC, electric water heater, dryer) are impractical off‑grid without a massive system. Propane is a cheaper, simpler alternative for cooking and hot water.
- Seasonal Sun Hours
- Winter (Dec‑Jan): ~3.5 peak sun hours – size for winter, not summer.
- Summer (Jun‑Aug): 6 + hours – expect surplus power.
- Storm Protection – In Missouri, severe weather is common. Ground‑mount panels and anchor them to concrete. Roof‑mounted panels on a container can leak at penetrations.
- Battery Longevity – LiFePO₄ batteries last 3,000 – 5,000 cycles (8 – 15 years) with almost zero maintenance.
- Panel Maintenance – Clean 2 – 4 times per year; panels last 25 – 30 years. Warranty matters.
- Inverter Maintenance – Fan filters need cleaning; replace the inverter every 10 – 15 years.
- Annual Maintenance Cost – Roughly $50 for cleaning supplies and a few hours of attention.
Hood Homestead Phase 1 Solar System (Case Study)
- Panels: 4 × 400 W (1,600 W array)
- Battery: 200 Ah 48 V LiFePO₄ (9,600 Wh)
- Inverter: 3 kW hybrid inverter
- Mounting: Ground mount with concrete anchors
Installed cost: ≈ $2,700
This system powers the container indefinitely with 2 – 3 days of sun per week.
Follow the build log at thehoodhomestead on Dev.to.