Powering a 1.5-Ton Inverter AC with Solar panels and Batteries

Introduction

With rising electricity costs and an increasing focus on sustainability or having erratic grid supply, more homeowners are looking to go off-grid. A 1.5-ton inverter air conditioner (AC) can be one of the most energy-hungry appliances in a home, especially in hot climates where it operates for long hours cooling the rooms. In this blog, we’ll break down the process of designing an off-grid solar system specifically to power a 1.5-ton inverter AC for a master bedroom. Our goal? Achieving 100% independence from the grid for the peak cooling months (April through October).

Understanding the Room’s Cooling Needs

Our system is designed for a 250 sq. ft. master bedroom with west-facing windows. Such a setup receives significant afternoon and evening heat, leading to increased AC demand during the late afternoon, evening, and nighttime. Using actual hourly consumption data for each month, we observed peak AC usage between 7 PM and 5 AM, along with the need for an additional buffer to handle varying demands.

Step 1: Analyzing Monthly Energy Requirements

By examining hourly consumption patterns, we found that June had the highest energy requirement during nighttime hours, with approximately 9.8 kWh required between 7 PM and 5 AM. This peak value is critical for sizing our battery storage, as we’ll need a buffer to ensure reliable cooling throughout the night.

Here’s a summary of the AC’s estimated energy requirements from April to October based on actual usage data:

Month	Nighttime Consumption (7 PM - 5 AM)
April	6.8 kWh
May	9.4 kWh
June	9.8 kWh
July	8.7 kWh
August	7.9 kWh
September	6.7 kWh
October	5.2 kWh

Step 2: Calculating Battery Storage with a 1.5x Buffer

To ensure uninterrupted cooling throughout the night and to handle unexpected surges, we chose to provide 1.5 times the battery capacity needed for the highest demand month (June). This approach adds a substantial buffer, making the system more reliable.

Battery Storage Calculation

• Highest Nighttime Requirement: June, with 9.8 kWh.

• 1.5x Buffer Requirement:9.8 kWh×1.5=14.7 kWh9.8 kWh×1.5=14.7 kWh

• Recommended Battery Capacity: 15 kWh (rounded up for ease and reliability).

With this 15 kWh battery, the system will be able to cover the AC’s nighttime operation, including any demand fluctuations, ensuring reliable cooling throughout the summer months.

Step 3: Sizing the Solar Array

Next, we calculate the solar panel capacity required to both power the AC during daylight hours and fully recharge the 15 kWh battery daily. We assessed daily AC consumption for each month (April through October) and determined the maximum daily requirement.

Solar Array Calculation

• Daily Requirement: The peak daily usage occurs in May, with an estimated 21.2 kWh required.

• Solar Array Size: To consistently generate 21.2 kWh/day, we need a 5.5 kW solar PV system based on average daily solar production data.

This 5.5 kW solar array will generate sufficient energy to power the AC throughout the day and recharge the battery for nighttime use.

Final System Design

Based on the calculations above, here’s the recommended 100% off-grid system configuration:

1. Solar Array: 5.5 kW – to generate sufficient power daily for AC operation and battery charging.

2. Battery Storage: 15 kWh lithium-ion – to cover nighttime needs with a 1.5x buffer.

3. Inverter: 3 kW – sized to handle the AC’s load efficiently, with surge capacity for startup demands.

Benefits of the Off-Grid Solution

1. Energy Independence: This system provides complete independence from the grid, especially during high-demand summer months.

2. Cost Savings: By relying solely on solar power, you avoid substantial summer electricity bills.

3. Environmental Impact: A solar-powered AC significantly reduces carbon emissions, contributing to a greener and more sustainable home.

Tips for Maximizing Efficiency

To further improve efficiency and reduce demand on the battery and solar system, consider these practical steps:

1. Enhance Insulation: West-facing rooms often receive intense heat, which increases cooling needs. Using thermal curtains, external shades, or reflective window films can reduce heat gain, lowering the AC’s workload.

2. Smart Thermostat Settings: Set the AC between 26°C - 27°C to maintain a comfortable temperature without excessive energy consumption.

3. Pre-Cooling Strategy: Cool the room before peak sunlight hours to reduce the load during the hottest parts of the day.

Conclusion: A Sustainable Off-Grid Cooling Solution

By designing a 100% off-grid solar system with a 5.5 kW solar array and 15 kWh battery, you can meet the cooling demands of a 1.5-ton inverter AC in a west-facing master bedroom, ensuring comfortable indoor temperatures from April through October. This system combines energy independence, cost savings, and environmental benefits, making it an ideal solution for sustainable home cooling.