Can I Run My AC on Solar? The Brutal Math Behind Air Conditioning
Can I Run My AC on Solar? The Brutal Math Behind Air Conditioning
The dream of Van Life or Off-Grid living usually stops when the temperature hits 90°F. Air Conditioning is the single heaviest electrical load in a home.
It is not just about the running watts; it is about the “Startup Surge” that can instantly overload a 3000W inverter.
To run AC without a generator, you need to master the math of LRA (Locked Rotor Amps) and invest in Lithium. Use this engineering-grade tool by ShockTrail to see if your wallet can handle the cool air.
The Off-Grid AC Estimator
Calculate the Battery Bank and Solar Array required to run your specific AC unit.
Off-Grid AC Estimator
Solar • Batteries • InverterRecommended Continuous: 0W
*Requires Soft Start for 13.5k+ units on <3000W Inverters.
PART 1: The Startup Surge (The Inverter Killer)
A standard 13,500 BTU RV Air Conditioner might use 1,500 Watts while running. A 2,000 Watt Inverter should handle that, right? Wrong.
Locked Rotor Amps (LRA)
When an AC compressor kicks on, it is stopped dead (Locked Rotor). To get that heavy piston moving, the motor pulls a massive spike of current for about 150 milliseconds.
The Spike: A 13.5k unit can pull 50 to 70 Amps at 120V. That is 6,000 to 8,000 Watts of instantaneous power.
[Image of inrush current waveform graph]If your inverter cannot handle a 6,000W surge, it will trip into “Overload Protection” instantly. This is why you need a Soft Starter (like Micro-Air EasyStart), which gently ramps up the power, reducing the surge by 70%.
PART 2: Real-World Case Studies
Cooling a space with batteries is expensive. Let’s look at the actual hardware requirements.
Case Study 1: The “Lunch Break” Cool Down (2 Hours)
The Setup: A van lifer wants to run a 13.5k BTU roof unit for 2 hours to cool the van for a pet or lunch break.
The Math:
- Running Load: 1,500 Watts.
- Total Energy: 1,500W × 2 hours = 3,000 Watt-Hours.
- Battery Drain (12V): 3,000Wh / 12V = 250 Ah.
- Inverter Efficiency Loss (15%): +37 Ah. Total = 287 Ah.
The Hardware: You need Three 100Ah Lithium Batteries ($900+) just for 2 hours of cooling. Lead Acid cannot handle this high current discharge.
Case Study 2: The High-Efficiency Mini-Split (All Night)
The Setup: A highly insulated shed using a 12,000 BTU Mini-Split (SEER 22) set to “Eco Mode” overnight (8 hours).
The Efficiency Difference: Mini-Splits use inverter compressors that run at low speed. Average draw is only 600 Watts.
The Math:
- Energy: 600W × 8 hours = 4,800 Watt-Hours.
- Battery Drain (48V System): 4,800Wh / 48V = 100 Ah.
The Hardware: A single 48V 100Ah Rack Battery ($1,200) can run this system all night. This is why mini-splits are the king of solar AC.
Case Study 3: The 12V Air Conditioner (Trucker Style)
The Project: Installing a native 12V DC Air Conditioner (like Dometic or Cruise N Comfort). No inverter needed.
The Pros: No inverter loss (15% savings). Designed for batteries.
The Cons: Expensive units ($2,500+). Lower BTU output (usually 6k to 10k).
The Math: Draws ~50 Amps continuous at 12V. 8 hours = 400Ah. Still requires a massive battery bank.
PART 3: Solar Replenishment (The Recovery)
Having enough batteries to run the AC is only half the battle. You have to fill them back up the next day.
If you drain 300Ah (3,600Wh) overnight, and you have 5 hours of “Peak Sun”:
3,600Wh / 5 hours = 720 Watts of Solar Panels.
And that assumes 100% efficiency. In reality, you need 900 to 1,000 Watts of solar on your roof just to break even on last night’s cooling. If you have a small van roof, this is physically impossible.
PART 4: Inverter Sizing
To run a standard roof AC, you generally need:
- With Soft Start: 2,000W to 2,500W Pure Sine Wave Inverter.
- Without Soft Start: 3,000W to 4,000W Inverter (Hybrid types like Victron MultiPlus are best because they can “Power Assist” using battery + grid/generator together).
Frequently Asked Questions (FAQ)
Can I run AC directly from solar panels?
No. A cloud passing overhead would drop the voltage and kill the compressor motor. You must have a battery buffer to stabilize the current.
Does a Soft Start save energy?
No. It only reduces the startup surge. It does not lower the running watts. Its sole purpose is to allow a smaller inverter/generator to start the AC without tripping.
Can I use AGM batteries for AC?
It is not recommended. The high current draw (100A+) causes severe voltage sag in lead-acid batteries due to Peukert’s Law, effectively cutting their capacity in half. Lithium (LiFePO4) maintains voltage under high load.
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