Looking to add air conditioning to an off-grid solar power system? Wondering how many solar panels it takes to run a typical 1.5 horsepower (HP) window unit or portable AC unit? You’ve come to the right place.
Buying an efficient 1.5 HP AC unit and calculating the right amount of solar capacity is key to keeping cool without overloading your system or draining your batteries faster than they can recharge. In this article, we’ll cover solar panel requirements to run a 1.5 HP air conditioner, plus tips for sizing your system correctly.
What Size Air Conditioner Uses 1.5 HP?
Air conditioner power consumption is measured in watts or horsepower:
- 1 horsepower (HP) = 746 watts
- A typical 1.5 HP air conditioner draws about 1,119 watts
Many common portable or window AC units designed to cool 300-500 square feet of space have capacity around 1.5 HP or 12,000 BTU (British Thermal Units per hour). More examples:
- LG 10,000 BTU (1.3 HP) portable air conditioner
- Honeywell 14,000 BTU (1.8 HP) portable AC unit
- GE 1.4 HP (10,500 BTU) window air conditioner
So if you see an AC unit advertised as 1.5 HP or in the 10,000-15,000 BTU range, plan for around 1,100-1,500 watts for sizing your solar system. Peak power draw may be even higher during hot weather or starting up.
How Many Solar Panels to Run a 1.5 HP AC Unit?
Figuring out the number of solar panels needed comes down to your AC unit’s power demands plus efficiency losses during the conversion and storage process from solar energy to usable 120V AC power.
Here’s a simplified overview of sizing solar panels for air conditioning:
- Air conditioner wattage x Hours used per day This gives you the Watthours (Wh) per day to run your AC.
- Watthours / Inverter & wire efficiency Convert solar panel production into usable AC output by accounting for 10-20% conversion losses.
- Watthours needed / Average sun hours Divide by your location’s average peak sun exposure hours to get the solar panel Watthour capacity required each day.
- Total Watts / Panel watt rating Determines the minimum number of panels based on dividing total AC Watthour needs by the individual solar panel output.
Let’s walk through an example calculation…
- 1.5 HP (1,100 watt) portable AC unit
- Running AC 5 hours per day
- Inverter/wiring 85% efficient
- 6 peak sun hours per day
- 320 watt solar panels
- 1,100 watts x 5 hours = 5,500 Watthours (Wh)
- 5,500 Wh / 0.85 efficiency = 6,470 Wh
- 6,470 Wh / 6 sun hours = 1,078 panel Watthours
- 1,078 Wh / 320 watts per panel = 3.4 panels
Rounding up, you would need at least 4 x 320 watt solar panels in this example, or a 1,280 watt solar array.
Keep in mind that solar panel output is lower than rated during real-world conditions like high temperatures and cloudy weather. It’s smart to oversize your solar array by at least 20% relative to theoretical needs to maintain stable power.
Tips for Sizing Your Solar AC System
Here are a few key tips for powering an efficient 1.5 HP air conditioner with solar panels:
- Choose the highest efficiency ENERGY STAR AC unit available in your required BTU range. More efficient units have lower starting and running power demands.
- Calculate peak summer solar panel output based on sun conditions in your area, not just yearly averages. Use lower efficiency ratings for solar panels and system components during hot weather.
- Factor in increased air conditioning runtime and higher electricity usage on the hottest summer days when sizing your system.
- Oversizing your solar array capacity relative to estimated AC power needs will minimize voltage drops and provide a battery power buffer on cloudy, rainy weather days.
What About Batteries for Solar AC?
Pairing your solar panels with an appropriately-sized battery bank evens out the system’s power delivery and provides stored energy to run the AC unit even when the sun isn’t actively shining.
As a guideline, you’ll want at least 3-5 days of battery capacity relative to the AC unit’s usage needs. This allows for multiple cloudy days while maintaining reliable air conditioning runtime each day without draining the batteries too low.
For this example 1.5 HP AC unit running 5 hours per day, you would want a battery bank with at least 15-25 KWh of usable capacity:
- 1.5 HP x 5 hours x 3-5 days = 22.5 to 37.5 KWh
A set of high quality lithium batteries provides enough storage capacity while maximizing cycle life for repeated air conditioning duty.
I hope this overview gives you a better understanding of how to calculate the number of solar panels needed to run a typical 1,500 watt window or portable air conditioner. With a properly sized solar array and battery bank, you can stay cool off-grid even during a power outage!