The Cost of Powering (and backing up) Central Air

Central air conditioning is a significant contributor to home energy consumption, especially during the hot summer months. This article will break down the costs associated with running a central air conditioning unit, including electricity costs, potential savings, and the costs of various backup solutions like solar panels, battery storage, and generators.

Understanding the Electricity Usage of Central Air Conditioning

Q: How much electricity does a central air conditioning unit use?

• Average Power Consumption: A typical central AC unit consumes about 3.5 kW (kilowatts) per hour.
• Usage Duration: For this example, let’s assume the AC runs for 6 hours a day during the summer months.

Daily Electricity Consumption:

• Calculation: 3.5 kW × 6 hours = 21 kWh (kilowatt-hours) per day

Monthly Electricity Consumption:

• Calculation: 21 kWh/day × 30 days = 630 kWh

Q: What is the average cost of running a central air conditioning unit?

• Average Electricity Rate: $0.13 per kWh (U.S. average residential electricity rate)

Daily Cost:

• Calculation: 21 kWh × $0.13/kWh = $2.73 per day

Monthly Cost:

• Calculation: 630 kWh × $0.13/kWh = $81.90 per month

Seasonal Cost Breakdown

Assuming the air conditioning runs for three months during the summer:

Total Summer Electricity Usage:

• Calculation: 630 kWh/month × 3 months = 1,890 kWh

Total Summer Cost:

• Calculation: $81.90/month × 3 months = $245.70

Backup Solutions for Central Air Conditioning

During a power outage, maintaining a comfortable indoor temperature becomes a priority. Here, we will explore the costs of different backup solutions.

Solar Panels

Q: How many solar panels are needed to power a central AC unit?

• Average Solar Panel Output: 300 watts (0.3 kW) per panel, with 4 peak sunlight hours per day.

Daily Output per Panel:

• Calculation: 0.3 kW × 4 hours = 1.2 kWh/day

Panels Needed:

• Calculation: 21 kWh/day / 1.2 kWh/day = 17.5 panels

Rounding Up:

• Total Panels: 18 panels

Cost of Solar Panel Setup:

• Average Cost: $3,000 – $5,000 per kW installed
• Total Cost: 18 panels × $1,000/panel (average) = $18,000

Is it practical to think that an average array of solar panels could power a central AC? Given the high energy load required to run a central AC unit, a typical residential solar array might struggle to meet these demands, especially during peak cooling times. While 18 panels could theoretically provide the necessary power, this assumes optimal conditions, continuous sunlight, and no other household energy needs. Therefore, relying solely on solar panels for a central AC might not be practical for most homeowners.

Battery Storage

While battery storage provides a reliable backup solution, the cost can be prohibitive. For an average homeowner, investing in a 21 kWh battery solely for air conditioning might be too expensive, especially when considering the need for additional capacity for other essential appliances.

Q: What size battery is needed to power a central AC unit for one day?

• Total Energy Needed for 6 Hours: 3.5 kW × 6 hours = 21 kWh

Battery Size Needed:

• Calculation: 21 kWh (considering efficiency losses and Depth of Discharge (DoD))

Cost of Battery Storage:

• Average Cost: $500 – $700 per kWh
• Total Cost: 21 kWh × $600/kWh (average) = $12,600

Home Generators

Powering central air conditioning with a home generator.

Q: What size generator is needed to power a central AC unit?

• Average Power Output: 5 kW generator

Fuel Consumption:

• Approximate Consumption: 0.5 gallons of fuel per hour

Total Fuel for 6 Hours:

• Calculation: 0.5 gallons/hour × 6 hours = 3 gallons of fuel per day

Cost of Generator Setup:

• Average Cost: $500 – $1,500
• Fuel Cost: Varies by fuel price, approximately $3/gallon
• Total Fuel Cost for 3 Months: 3 gallons/day × 30 days/month × 3 months = 270 gallons
• Total Fuel Cost: 270 gallons × $3/gallon = $810

Generators can be a more affordable and practical solution for short-term power outages. However, they rely on a continuous fuel supply, which can become costly and inconvenient over long periods.