— Dave. Measure twice, buy once.

Air Con Solar Sizing: Off-Grid Aussie Guide

Stop guessing. Get your off-grid air con right. No theory. Just the numbers you need to avoid frying your system.

By Dave Miller · off-grid sparky · 22 years wiring solar, batteries and sheds in central QLD

“After burning a $300 compressor in a Rockhampton heatwave, I learned that a 2kW split needs a 5kW battery bank, not a tiny 2kW setup.”

Air Con Solar Sizing: Off-Grid Aussie Guide

Stop guessing. Get your off-grid air con right. No theory. Just the numbers you need to avoid frying your system.

Air conditioner solar sizing worked example: 0.8kW split running 8 hours needs about 2.1kW of panels and an 8kWh battery bank.

BTU: The Only Number That Matters

Forget "1.5kW" or "2.5kW". Australian off-grid air con runs on BTU. Here's how to size it:

Room size (m²) x 100 BTU = Minimum required BTU
Example: 20m² room = 2,000 BTU (but you'll need 2,500+ for Aussie heat)
Fact: 100 BTU = 0.029 kW. So 2,500 BTU = 0.725 kW.

Don't skimp. 2,500 BTU for a 20m² room? You'll be sweating while the AC runs. Aim for 3,000 BTU minimum.

Real talk: Your AC's "kW" rating is useless for solar. It's the BTU that tells you how much power it needs. Always check the BTU on the spec sheet.

Inverter Requirements: The Hidden Trap

Most people blow it here. Your inverter must handle the AC's startup surge (not just running wattage).

Running wattage: 0.725 kW (for 2,500 BTU)
Startup surge: 2.5x running wattage = 1.8 kW
Example: 2,500 BTU AC needs a 2kW+ inverter minimum

Don't buy a 1.5kW inverter for a 2,500 BTU AC. It'll trip constantly. You'll be yelling at the inverter while it's 40°C outside.

Practical Off-Grid Tips (No Bull)

Size for worst case: Add 20% to your BTU calculation. Aussie heatwaves are brutal.
Run it smart: Set to 24°C. Every 1°C lower = 5-10% more power. 24°C is the sweet spot.
Use a dedicated circuit: Don't share the inverter with fridges or lights. ACs need full power.
Insulate first: Double-glazed windows + ceiling insulation = 30% less AC load. Cheap insurance.
Check your battery: 1.8kW surge needs 3+ hours of battery capacity. 24V 200Ah battery = 4.8kWh. That's 2.6 hours for AC alone.

Australian Suppliers & Pricing (indicative prices)

Don't waste time on cheap Chinese ACs. Get Australian-approved models.

Recommended: Solar Batteries Australia (Sydney-based, no BS)

Model: Daikin FTXS35C (3,500 BTU) - $1,299 (includes installation quote)

Why: Runs on 0.95kW (800W startup), perfect for 1.5kW+ inverters. Certified for Aussie off-grid use.

Alternative: Solar Outback (National)

Model: LG LP1219IVSM (12,000 BTU) - $1,899

Why: 1.3kW running, 3.25kW surge. Needs 3.5kW+ inverter. Good for 30m² rooms.

Price note: $1,200-$2,000 is standard for 2,500-3,500 BTU ACs. Don't pay $3k for a basic unit.

The Bottom Line

BTU = your sizing bible. Inverter = must handle startup surge. Insulate first. Buy from a local supplier who knows off-grid.

Get it wrong? You'll be living in a sauna while your battery dies. Get it right? You'll sleep cool without guilt.

Worth a watch: How many solar panels do you need to run Air Conditioning? · A1 SolarStore

It runs through the actual panel count you need for a typical split‑system AC using real wattage numbers, so you can plug those figures straight into your sizing calc. No fluff, just the quick math on how many panels keep the thing running through a hot Queensland summer. — Dave Miller

When to Call a Professional

While many off-grid projects are achievable as DIY, certain situations require licensed professionals:

Electrical work beyond basic 12V DC additions — requires a licensed electrician
Structural modifications to buildings or load-bearing elements
Gas line installation or modification
Solar array installations above safe voltage thresholds
Any work that affects the structural integrity of your property

Always check local regulations and obtain necessary permits before commencing work.