Should I go 12V or 24V in a van build?

Under about 2,000 Wh/day and a 1,000 W inverter, 12V keeps everything simple and compatible with automotive gear. Above that, 24V halves your currents — thinner cables, smaller controller, less heat.

Do I need a battery-to-battery (DC-DC) charger?

Almost certainly yes if the vehicle drives regularly — 30–60 A of charging while driving often matters more than an extra solar panel in winter. It depends on your alternator.

Why does an induction hob dominate the system size?

Cooking on electricity is the single biggest driver of van system cost. Thirty minutes of induction (~750 Wh) needs about 250 W of extra solar just to replace it daily. Many builds keep gas for cooking and halve their electrical budget.

WattNeeded / Van & RV electrical sizer

Size your van or RV electrical system

Build your real daily usage from the appliances below and get four honest numbers: battery bank, solar array, inverter, and charge controller — with every step of the math shown.

1 · Your system

Battery voltage Chemistry Days of autonomy Peak sun hours/day

Days of autonomy = cloudy days your battery must cover without solar input. Peak sun hours: ~3 (UK/northern Europe average), 4 (US temperate average), 5–6 (sunny south). The default follows your region setting (top right).

2 · What runs each day?

	Appliance	Qty	Hours/day

Add your own

AC items run through your inverter (≈15% conversion loss, and they set the inverter size). DC items run straight off the battery. Wattages are typical — check your gear's labels.

Your system

0 Wh/day

DC loads0 Wh

AC loads (incl. ÷0.85 inverter loss)0 Wh

🔋 Battery bank: 0 Wh (0 Ah @ 12 V)

☀ Solar array: 0 W

⚡ Inverter: —

🎛 MPPT controller: 0 A

[Affiliate recommendations slot — batteries, panels and inverters matching the computed sizes, populated once affiliate programs are joined.]

How this calculator works (the honest math)

Daily energy: Wh = watts × hours × quantity, summed. AC appliances are divided by 0.85 for inverter conversion loss before they hit the battery.

Battery bank: daily Wh × days of autonomy ÷ usable fraction. LiFePO4 can safely use ~90% of rated capacity; AGM only ~50% before you damage it. Amp-hours are just Wh ÷ system voltage — the number battery listings use.

Solar array: daily Wh ÷ (peak sun hours × 0.75). The 0.75 covers real-world losses: panel heat, dust, imperfect angles, controller efficiency. Flat-mounted van panels rarely beat this.

Inverter: the sum of your AC appliances' running watts plus 20% headroom, rounded up to a standard size. If you'll never run two big AC loads at once, you can size to the largest one instead — that's a lifestyle promise, not an engineering one.

MPPT charge controller: rated amps ≥ solar watts ÷ battery voltage × 1.1. Going 24 V or 48 V cuts controller amps (and cost, and cable thickness) — the main reason bigger builds leave 12 V behind.

Should I go 12 V or 24 V?: Under ~2,000 Wh/day and a 1,000 W inverter, 12 V keeps everything simple and compatible with automotive gear. Above that, 24 V halves your currents — thinner cables, smaller controller, less heat.
Do I need a battery-to-battery (DC-DC) charger?: Almost certainly yes if the vehicle drives regularly — 30–60 A of charging while driving often matters more than an extra solar panel in winter. It's not sized here because it depends on your alternator.
Why is my induction hob dominating everything?: Cooking on electricity is the single biggest driver of van system cost. Thirty minutes of induction (~750 Wh) needs ~250 W of extra solar just to replace it daily. Many builds keep gas for cooking and halve their electrical budget.