Skoolie Electrical Basics: Sizing Solar, Lithium Batteries and Inverters
Written by Kyle at Getboatparts. I design electrical systems for skoolie, van and bus conversions, and the method below is the same one I use on consultations. Send me your build details for free system design help.
Skoolies have the same problems as boats: off-grid, vibrating, 12/24 V DC, and expensive to get wrong. Marine-grade parts work well here.
Step 1: Energy budget (Wh/day)
List every load: watts × hours per day. A 12 V fridge (~45 W average × 24 h = 1,080 Wh), LED lights (60 W × 5 h = 300 Wh), a MaxxAir fan (30 W × 10 h = 300 Wh), laptops (150 W × 6 h = 900 Wh). Add 20% for losses. Most full-timers land at 2–4 kWh/day. Induction cooking, electric water heating and rooftop AC push it far higher.
Step 2: Battery bank
Size for 1.5–2 days of autonomy at 80% usable. 3 kWh/day × 2 ÷ 0.8 = 7.5 kWh, which is ~600 Ah at 12 V or ~300 Ah at 24 V of LiFePO4. Don't use lead-acid on a full-time build: the weight and the 50% depth-of-discharge limit work against you.
- Victron Lithium Battery Superpack 12V/200AH NG $1,808.62
- Victron Lithium Battery Superpack 24V/100AH NG $1,808.62
- Victron Lithium Battery 24VDC 300AH NG Smart LIFEPO4 $3,985.86
Step 3: Solar
Daily Wh ÷ peak sun hours (~4 averaged across a year, ~2.5 in northern winters) ÷ 0.75 derate. That gives 3,000 ÷ 4 ÷ 0.75 ≈ 1,000 W. A bus roof fits 6–8 residential-size panels. Wire them in series-parallel to keep the voltage under the MPPT's limit.
- Victron Smartsolar MPPT 100/50 UL Approved $196.36
- Victron MC4 Solar Connect Pair 1X Male 1X Female $14.00
Step 4: Inverter/charger
Size for the biggest simultaneous AC load plus surge. That's usually 2,000–3,000 VA. An inverter/charger also gives you a shore-power charger and automatic transfer in one box.
- Victron Multiplus-II 12/3000 120-50 2X 120V UL Approved $1,102.40
- Victron Multiplus-II 24/3000 70-50 120V UL Approved $1,010.25
- Victron Multiplus-II 48/3000 35-50 120V $949.96
Step 5: Alternator charging
- Victron Orion XS 12/12-50A DC-DC Battery Charger $332.44
- Victron Orion-Tr 12/24-5A 120W Isolated DC-DC Conveter $72.34
Step 6: Distribution, fusing and wire
Put a Class T fuse at the battery positive, a main disconnect, bus bars and a fused DC distribution block. Size cable for 3% drop. On a 3,000 VA 12 V inverter, that's often 4/0. See our wire gauge guide.
- Blue Sea 5502 Class T Fuse Block 225-400 AMP $58.69
- Blue Sea 5119 300A Class T Fuse A3T $90.17
- Blue Sea 3000 Battery Switch HD ON/OFF $104.47
- Blue Sea 2307 Busbar 4 X 1/4 Stud with Cover $37.48
- Blue Sea 5026 Fuse Block Screw Term Blade $62.94
- Ancor Red 2/0 AWG Battery Cable Sold by the Foot $13.99
Not sure about your numbers? Free system design help: send your loads, roof space and budget, and I'll spec a complete parts list you can order here.
FAQ
How much solar does a skoolie need?
Work from your daily Wh. A typical full-time skoolie with a 12 V fridge, lights, fans, laptops and a vent fan uses 2–4 kWh/day. Plan 800–1,500 W of roof solar, more if you run induction cooking or AC.
12V, 24V or 48V for a bus?
12 V is simplest for under ~2,000 W inverters. 24 V or 48 V halves or quarters the current, which means thinner cable and cooler connections, so it's preferred for 3,000 W+ inverters and big solar arrays.
Can I charge from the bus alternator?
Yes. Use a DC-DC charger (e.g., Victron Orion XS) so the lithium bank doesn't overload the alternator. Bus alternators are often 24 V or high-output 12 V, so check before you buy.