What battery type is best for off-grid solar?

LiFePO4 (lithium iron phosphate) is the best choice for new off-grid installations: 90% depth of discharge (vs 50% for lead-acid), 3,000–6,000 cycle life (vs 400–1,200), no maintenance, no off-gassing, and faster charging. Despite higher upfront cost, the 10–15 year lifespan makes lifetime cost lower than lead-acid batteries.

How many days of battery autonomy do I need for off-grid?

Two to three days of autonomy is typical for most climates. Add 1–2 days for climates with frequent extended cloudy periods (UK, Pacific Northwest). Each additional day of autonomy adds the same amount of battery capacity, so it's the biggest cost lever in system design.

Off-Grid System Sizing Calculator

Enter your daily energy needs and system preferences — get a complete bill of materials with panels, batteries, controller, inverter, and cost estimates.

Energy requirements

Daily energy need?

kWh/day

Days of autonomy?

days

System configuration

Battery type?

Peak sun hours?

Panel wattage?

System voltage?

Complete off-grid system BOM

6 panels × 400W = 2.40 kW solar

Solar panels

6 × 400W = 2.40 kW

~$840

Battery bank (LiFePO4)

26.7 kWh usable / 556 Ah at 48V

~$10,667

MPPT charge controller

80A, 48V rated

~$240

Inverter (pure sine wave)

2,000W

~$700

Wiring, fuses, mounting

Estimate

~$1,726

Estimated total~$14,173

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How to Use This Calculator

Start with daily energy consumption

Enter your total daily energy need in kWh. If you have a utility bill, divide your monthly kWh by 30 for an average daily figure. For a new off-grid design, list every appliance with its wattage and daily hours of use, then sum: kWh = (watts × hours) / 1000. Common daily totals: cabin (1–3 kWh), small off-grid home (5–10 kWh), full-size home (10–20 kWh).

Set days of autonomy

Autonomy is how many consecutive cloudy days your battery bank covers with no solar input. Two days suits most climates; harsh northern or rainy climates may need 3–5 days. More autonomy means a larger (more expensive) battery bank but more energy security. Many off-grid homeowners compromise with 2 days of autonomy plus a backup generator for extended cloudy stretches.

Choose battery type wisely

LiFePO4 (lithium iron phosphate) is now the clear choice for new off-grid installations: 90% depth of discharge, 3,000–6,000 cycle life, no maintenance, no off-gassing. The upfront cost is higher but the 10–15 year lifespan means lower lifetime cost than lead-acid, which needs replacement every 3–5 years. The calculator accounts for each battery type's usable depth of discharge automatically.

The result is a full bill of materials

The BOM includes panel count, battery bank sizing, MPPT controller, inverter, and estimated costs for each component. Use it as a starting point for supplier quotes — actual prices vary by brand, quality, and region.

The Formula

Battery bank (kWh) = Daily kWh × Autonomy days / Battery DoD Battery bank (Ah) = Battery kWh × 1000 / System voltage Solar array (kW) = Daily kWh / (Sun hours × 0.86 system efficiency) Panel count = ceil(Solar kW × 1000 / Panel watts) MPPT controller (A) = Array kW × 1000 / System voltage × 1.25 Inverter size = Average hourly load × 2 (safety factor)

The depth of discharge (DoD) multiplier is critical: LiFePO4 at 90% DoD means if you need 10 kWh of usable energy, you only need 10/0.9 = 11.1 kWh of rated capacity. Lead-acid at 50% DoD means you need 10/0.5 = 20 kWh of rated capacity for the same usable storage. This is the core reason LiFePO4 is economically competitive despite higher per-kWh cost.

System efficiency of 86% (0.86) accounts for: MPPT tracking efficiency (~95%), wiring losses (~97%), battery round-trip efficiency (~LiFePO4: 97%, Lead-acid: 80–85%), and temperature derating. Using 86% overall is a conservative default that works well across system types.

Example

Off-grid family home — Mountain Southwest, USA

A family wants to go off-grid in New Mexico. Daily consumption: 8 kWh. They want 3 days autonomy. LiFePO4 batteries, 400W panels, 48V system, 5.5 peak sun hours.

Battery bank needed8 kWh × 3 days / 0.90 = 26.7 kWh

Battery bank at 48V26.7 kWh / 48V × 1000 = 556 Ah

Solar array needed8 / (5.5 × 0.86) = 1.69 kW

Panel countceil(1.69 × 1000 / 400) = 5 panels

Actual solar array5 × 400W = 2,000W (2 kW)

BOM Summary

Solar panels5 × 400W ≈ $700

Battery bank27 kWh LiFePO4 ≈ $10,800

50A MPPT controller≈ $150

3,000W inverter≈ $1,050

Wiring, fuses, mounting≈ $1,730

Total estimate~$14,430

The battery bank dominates the off-grid system cost — typically 50–60% of total BOM. This is why autonomy days is the single most powerful cost lever. Reducing from 3 days to 2 days autonomy would save about $3,600 on batteries in this example.

FAQ

How much does a complete off-grid solar system cost? ▼

Typical ranges in 2026: small cabin system (2 kWh/day, LiFePO4): $4,000–8,000; medium off-grid home (8 kWh/day): $12,000–20,000; large homestead (15 kWh/day): $25,000–45,000. Battery type dramatically affects cost — LiFePO4 costs $300–500/kWh vs. flooded lead-acid at $100–150/kWh (but lead-acid has 1/4 the lifespan, making lifetime cost similar or higher). DIY installation can reduce costs by 30–50% vs. professional installation, but requires electrical knowledge and permits.

LiFePO4 vs AGM — which is better for off-grid? ▼

LiFePO4 wins on every technical metric: 3,000–6,000 cycles vs 400–1,200 for AGM; 90% DoD vs 50%; 97% efficiency vs 80–85%; no maintenance, no off-gassing, works in a wider temperature range, and charges 3× faster. The upfront cost premium (2–3×) is offset by the longer lifespan — a LiFePO4 bank lasting 10–15 years vs AGM at 3–5 years. For permanent off-grid installations, LiFePO4 is almost always the economically superior choice when the full lifecycle cost is considered. AGM makes sense for temporary setups or very tight upfront budgets.

Do I need a generator for off-grid living? ▼

A generator is strongly recommended as a backup for off-grid systems, even with adequate battery autonomy. Reasons: extended cloudy periods can exceed even a 5-day battery bank, heavy power tools and welders may need more power than the inverter can sustain, seasonal consumption changes (winter heating, summer AC) can temporarily exceed system capacity, and generator charging is much faster than solar for emergency replenishment. A properly sized hybrid inverter can seamlessly switch between solar, battery, and generator. Size the generator to your peak load, not average load.

Why is 48V the recommended system voltage for off-grid homes? ▼

At 48V, the same power requires 4× less current than at 12V. Lower current means: thinner (cheaper) wire throughout the system, smaller MPPT controller (amps-based pricing), less heat in connections, and larger inverters are available at 48V. The battery bank is also more practical — a 20 kWh, 48V LiFePO4 bank uses readily available 100Ah cells in a 4S configuration, while a 12V bank for the same storage would require 1,666 Ah — impractical and very expensive. Every experienced off-grid designer recommends 48V for any system above 2–3 kWh storage.