LiFePO4 Solar System Calculator

How do you want to power your off-grid setup?

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1. Daily consumption

Select your use case and add appliances

What are you building?
ApplianceWattsHrsWh/day

2. System voltage

Choose 12V, 24V or 48V for your setup

Add appliances above to get a voltage recommendation

3. Powerpack selection

All-in-one portable power stations

Add appliances above to see matching powerpacks.

3. Battery selection

Find the right LiFePO4 battery for your net energy need

4. Inverter

Size your inverter based on peak load

Add appliances to the energy calculator to receive an inverter recommendation.

5. Solar generation

Choose your solar array and location

☀️ Include solar in this build?
Solar yield will be subtracted from your daily consumption to size the battery bank.
☀️ Solar array designer
TOTAL WP
400 Wp
STRING VOC
45.0 V
cold: 51.7 V
ARRAY ISC
11.5 A
MPPT NEEDED
75/15
min 55V / 15A
2 panels total (2S × 1P).
📍 Location:52.37°N, 4.89°E
Loading map...
Click anywhere on the map to calculate solar yield for that location.

5. Solar analysis

Yield from your chosen panel at this location

Pick a powerpack in step 3 to see the solar analysis.

6. Wiring diagram

Auto-calculated cable sizes and fuse ratings

1S1P(1×)
Cables & Fuses
SegmentCurrentLengthmm²AWGLoss%Sized byFuseStatus

7. Final check

System fit verdicts on your selected components

Add appliances in step 1 to run the final check.

8. Procurement list

Your complete bill of materials with purchase links

Select a battery and inverter to generate your procurement list.
📚 Learn the fundamentals Quick rules of thumb — Already built? Skip straight to the result. Want to learn the engineering? Start here.

Quick rules of thumb

Six formulas that get you to a usable system size in five minutes. Open the calculator below for the precise version with NASA POWER data and live wiring diagram.

⚡ System voltage
<500 Wh/day → 12V · 500–2000 → 24V · >2000 → 48V
24V halves cable thickness vs 12V at the same power. 48V halves it again.
more: system voltage →
🛡 Fuse rating
Fuse A ≈ 1.25 × continuous current · Class T at the battery
2000W inverter at 12V draws 167A → fuse 200A. Class T (200 kA) directly on the bank.
more: Class T fuses →
📅 Autonomy days
1–2 days sunny climate · 3–5 days winter or cloudy
Cabin in Alps for winter use → plan 4 days of zero-solar buffer.
more: autonomy days →
❓ Frequently asked questions FAQ — 6 common off-grid sizing questions

Frequently asked questions

Quick answers to the most common off-grid sizing questions.

How many solar panels do I need for an off-grid system?
Divide your daily Wh consumption by the local peak sun hours and the system efficiency (~78%). For example, 1500 Wh/day in a region with 4 peak sun hours needs 1500 / (4 × 0.78) ≈ 480 Wp of solar. Round up and add 20–30% for cloudy days. The calculator does this automatically using NASA POWER data for your exact coordinates.
What size battery do I need for my off-grid setup?
Multiply daily consumption by your desired autonomy days (typically 1–3), then divide by the usable depth of discharge. LiFePO4 supports 80–100% DoD, so 2000 Wh/day × 2 days ÷ 0.9 ≈ 4444 Wh of battery. At 12V that is one 400Ah bank; at 24V two 100Ah in series, and so on.
Should I choose 12V, 24V or 48V for my system?
As a rule of thumb: under 500 Wh/day pick 12V, between 500 and 2000 Wh/day pick 24V, above 2000 Wh/day pick 48V. Higher system voltage halves cable thickness and lets you use cheaper inverters at the same power. The calculator pre-selects a recommended system voltage from your consumption.
Why LiFePO4 instead of lead-acid or lithium-ion?
LiFePO4 (lithium iron phosphate) offers 3000–6000 cycles versus 200–500 for lead-acid, supports 80–100% depth of discharge versus 50%, weighs about a third, and has the safest thermal profile of any lithium chemistry. The upfront cost is higher but the cost per kWh delivered over the lifetime is dramatically lower.
Do I need an MPPT charge controller or is PWM enough?
Use MPPT for any panel array above 100 W or whenever the panel voltage is much higher than the battery voltage. MPPT extracts 20–30% more energy than PWM and is required if you want to wire panels in series. PWM only makes sense for very small 12V systems with a single 12V-nominal panel.
How do I calculate cable size and fuse rating?
Cable cross-section is determined by current draw and acceptable voltage drop (target under 3% on critical runs). Fuses are sized just above continuous current (typically 1.25× the maximum) and must have a high DC interrupt rating — Class T fuses (200 kA) are required directly at any lithium battery terminal. The wiring diagram in the calculator computes both for every segment automatically.