Is a 12V or 24V system better for off-grid?

12V works well up to about 2,000W of solar. Above that, 24V or 48V is more efficient — the same power at higher voltage requires much smaller cables. Vans and boats typically stay at 12V because most accessories are natively 12V.

12V Solar Calculator

Enter your 12V loads, panel size, and battery — get panels needed, charge controller size, and battery autonomy instantly.

12V loads — enter watts & hours per day

Load name

Watts

Hrs/day

System parameters

Panel wattage?

Battery bank?

Ah @ 12V

Peak sun hours?

hrs/day

Your 12V solar system needs

2 × 200W = 400 W total

Daily load1,515 Wh

Daily production1,600 Wh

Charge controller42A MPPT

Battery autonomy0.8 days

Array fuse42A

Your 200 Ah battery provides less than 1 day of backup. Consider upgrading to at least 253 Ah for 1-day autonomy.

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How to Use This Calculator

Enter your 12V loads

List every DC appliance you run at 12V. For each one, enter the wattage (from the label, manual, or a watt-meter measurement) and the hours per day it runs. The fridge should be entered at 24 hours with its average draw (not peak). Add or remove rows to match your actual loads.

Set panel wattage, battery, and sun hours

Enter the wattage of each individual panel you plan to use. 100W panels are popular for boats and vans where space is tight. 200W is common for medium-sized off-grid setups. Enter your battery bank in Ah at 12V — the calculator checks whether your existing or planned battery provides enough autonomy. Peak sun hours for your location determines daily production.

Read the output

You'll see the panel count needed, total watts, daily production estimate, MPPT charge controller size, battery autonomy in days, and the recommended fuse for the array. If the battery autonomy is under 1 day, the calculator flags it with a suggestion to upgrade.

The Formula

Daily Wh = Sum of (Load Watts × Hours/day) Solar Watts needed = Daily Wh ÷ Peak Sun Hours ÷ 0.80 (efficiency) Panels needed = Solar Watts needed ÷ Panel Wattage (round up) Charge controller Amps = Total panel Watts ÷ 12V × 1.25 Battery autonomy (days) = Battery Ah × 12V × 0.50 DoD ÷ Daily Wh Array fuse (A) = Total panel Watts ÷ 12V × 1.25

The 0.50 DoD for battery autonomy assumes AGM batteries. If you're using LiFePO4, your actual autonomy is higher — use 0.80 instead of 0.50 in your own calculations. The 0.80 system efficiency accounts for MPPT losses, wire resistance, and temperature derating typical for 12V systems in warm conditions.

Example

Morgan — 12V van setup, Pacific Northwest

Morgan's van has LED lights (15W, 5 hrs), a roof fan (35W, 8 hrs), phone charging (20W, 4 hrs), and a 12V compressor fridge (45W, 24 hrs). They're in the Pacific Northwest (4.5 peak sun hours) with 200W panels and a 200Ah battery bank.

LED Lights75 Wh/day

Roof Fan280 Wh/day

Phone Charging80 Wh/day

12V Fridge1,080 Wh/day

Total daily load1,515 Wh/day

Result

Solar needed422W (3 × 200W panels)

Charge controller79A MPPT

Battery autonomy0.8 days (needs upgrade)

Array fuse79A

The 200Ah battery only provides 0.8 days of backup — Morgan should upgrade to 300Ah for a comfortable 1.2 days. Three 200W panels fit a high-roof Sprinter roof and produce about 1,700 Wh/day on a sunny Pacific NW day, comfortably covering the 1,515 Wh load. A 60A MPPT controller handles the 600W array (use a 40A if staying at 400W, upgrade when adding a third panel).

FAQ

What can I run on a 12V solar system? ▼

A 12V solar system powers everything that runs natively at 12V: LED lights, fans, 12V fridges, USB chargers, water pumps, navigation electronics, and 12V laptops. For AC appliances (microwave, coffee maker, hair dryer), you'll need an inverter to convert 12V DC to 120V AC. Most van and boat builds run primarily on 12V to maximize efficiency, since every DC-to-AC conversion loses 10-15% of energy.

Is a 12V or 24V system better for an off-grid setup? ▼

12V works well up to about 2,000W of solar and modest daily loads. Above that, wire size and heat become problematic at 12V — the same 2,000W at 12V draws 167A, requiring very heavy cables, while at 24V it draws only 83A. For larger systems (3,000W+ solar, whole-house off-grid, buses), 24V or 48V is more efficient and practical. Vans and boats typically stay at 12V because most marine and vehicle accessories are natively 12V.

What MPPT charge controller do I need for a 12V system? ▼

Size by dividing total panel watts by 12V and multiplying by 1.25. For 400W of panels: 400 ÷ 12 × 1.25 = 41.7A — use a 40A or 60A controller. Common sizes: 20A (up to 260W), 30A (390W), 40A (520W), 60A (780W). Always buy one size up if you plan to expand. Victron SmartSolar, Renogy Wanderer, and EPever MPPT are reliable choices at different price points.

How do I measure my actual 12V load? ▼

The most accurate method is a battery monitor (like Victron BMV-712 or Renogy 500A shunt monitor). It tracks amp-hours in and out over time, giving you real daily consumption. For a quick estimate, plug each appliance into a Kill-A-Watt meter (for AC) or use a DC clamp meter on the 12V circuit. Label appliance plates often list wattage, but actual draw is often 10-20% less than rated.

Why does my 12V fridge use so much power? ▼

Compressor fridges (BougeRV, ARB, Iceco) run 24/7, making them the #1 consumer in most van and boat setups. A 12V fridge rated at 45W might only run its compressor 50-60% of the time at moderate ambient temperature, giving an average draw of 22-27W — but in a hot van or in summer, it runs 80-90% of the time, pushing average draw closer to 40W. Measure your fridge over 24 hours with a battery monitor for the most accurate reading.