Case Study: Determining kWh Usage, Needs, and Costs for Essential Always-On Appliances
Introduction
For homeowners looking to understand their energy consumption, focusing on essential always-on appliances like refrigerators, freezers, and internet routers is a great starting point. This case study will guide you through calculating the total kWh usage, determining the costs, and evaluating the size of solar panels, battery storage, and generators needed to power these appliances during a power outage.
What is a Kilowatt-Hour (kWh)?
A kilowatt-hour (kWh) is a unit of energy that measures the amount of electricity used over time. It is calculated by multiplying power (in kilowatts) by time (in hours). For example, if you run a 1-kilowatt appliance for 1 hour, you consume 1 kWh of electricity. To learn more about the language of energy, check out our home energy glossary or review our guide to the kWh.
Step 1: Calculate the Total kWh Usage of Essential Appliances
Appliances Considered: There’s certainly many appliances that could be on this list of essentials, but for this article we’re going to keep it simple with the very basics to understand the economics of your home’s energy. Most of us can’t live without internet and most of us can’t live with rotting food. Lets start with…
- Refrigerator
- Freezer
- Internet Router
Assumptions:
- Average power consumption for each appliance
- Appliances run continuously (24/7)
- Average electricity rate: $0.13 per kWh (U.S. national average)
Table: Power Consumption and Daily kWh Usage
| Appliance | Power Consumption (Watts) | Daily kWh Usage (kWh) | Monthly kWh Usage (kWh) | Annual kWh Usage (kWh) |
|---|---|---|---|---|
| Refrigerator | 150 | 3.6 | 108 | 1314 |
| Freezer | 200 | 4.8 | 144 | 1752 |
| Internet Router | 15 | 0.36 | 10.8 | 131.4 |
| Total | – | 8.76 | 262.8 | 3197.4 |
Step 2: Determine the Monthly and Annual Costs
Monthly and Annual Costs of essential appliances
| Appliance | Monthly kWh Usage (kWh) | Monthly Cost ($) | Annual kWh Usage (kWh) | Annual Cost ($) |
|---|---|---|---|---|
| Refrigerator | 108 | 14.04 | 1314 | 170.82 |
| Freezer | 144 | 18.72 | 1752 | 227.76 |
| Internet Router | 10.8 | 1.40 | 131.4 | 17.08 |
| Total | 262.8 | 34.16 | 3197.4 | 415.66 |
Step 3: Evaluating Options for Powering Essential Appliances
In the case of a power outage, homeowners need reliable backup power solutions. We’ll explore the requirements for solar panels, battery storage, and generators.
Introduction to Backup Power Options To ensure continuous power during outages, it’s essential to evaluate various backup power options. This includes calculating the size and capacity of solar panels, batteries, and generators needed to sustain essential appliances like refrigerators, freezers, and internet routers.
Solar Panels
Daily kWh per Panel:
Assume each solar panel produces 300 watts and gets 5 hours of sunlight per day.
Daily kWh per Panel Calculation:
300 watts×5 hours÷1000=1.5 kWh/day300 \text{ watts} \times 5 \text{ hours} \div 1000 = 1.5 \text{ kWh/day}
Number of Panels Needed:
8.76 kWh/day÷1.5 kWh/day/panel≈5.84 panels8.76 \text{ kWh/day} \div 1.5 \text{ kWh/day/panel} \approx 5.84 \text{ panels}
Total Panels Required:
To cover the energy needs, round up to 6 panels.
Estimated Cost:
- Solar Panels: $2,000 per panel
- Total Cost for 6 Panels: $2,000 x 6 = $12,000
Battery Storage
Total kWh for 3 Days:
8.76 kWh/day×3 days=26.28 kWh8.76 \text{ kWh/day} \times 3 \text{ days} = 26.28 \text{ kWh}
Battery Storage Calculation:
A typical home battery like the Tesla Powerwall has a capacity of 13.5 kWh.
Number of Batteries Needed:
26.28 kWh÷13.5 kWh/battery≈1.95 batteries26.28 \text{ kWh} \div 13.5 \text{ kWh/battery} \approx 1.95 \text{ batteries}
Total Batteries Required:
To ensure adequate power for 3 days, round up to 2 batteries.
Estimated Cost:
- Battery Storage: $10,000 per battery
- Total Cost for 2 Batteries: $10,000 x 2 = $20,000
Generators
Generator Output in kWh:
- Power Requirement: Total of 8.76 kWh per day.
- Generator Size Needed: A generator rated at least 2 kW (2000 watts) running for approximately 12 hours would meet this need.
Fuel Consumption:
- Average Fuel Consumption: Portable generators consume about 0.5 gallons of gasoline per hour at 50% load.
Daily Fuel Consumption:
0.5 gallons/hour×12 hours=6 gallons/day0.5 \text{ gallons/hour} \times 12 \text{ hours} = 6 \text{ gallons/day}
Fuel Consumption for 3 Days:
6 gallons/day×3 days=18 gallons6 \text{ gallons/day} \times 3 \text{ days} = 18 \text{ gallons}
Estimated Cost:
- Generator Cost: $1,500 for a 2 kW generator
- Fuel Cost: $3 per gallon
- Total Fuel Cost for 3 Days: 18 gallons x $3 = $54
- Total Cost: $1,500 + $54 = $1,554
In Conclusion…
Okay that was a lot of math! Hope we didn’t lose you. In summary…
Here’s a detailed breakdown of what it costs annually to run these appliances, as well as what it would cost to keep them running during a power outage.
Annual Cost of Running Essential Appliances:
- Total Annual kWh Usage: 3197.4 kWh
- Total Annual Cost: $415.66
Backup Power Options:
- Solar Panels:
- Number of Panels Needed: 6
- Estimated Cost: $12,000
- Battery Storage:
- Number of Batteries Needed: 2 (26.28 kWh capacity)
- Estimated Cost: $20,000
- Generators:
- Generator Size Needed: 2 kW
- Fuel Needed for 3 Days: 18 gallons
- Estimated Cost (Generator + Fuel): $1,554
By understanding these costs and requirements, we hope we can help you make informed decisions about the best backup power solutions to maintain essential services during outages, optimize their energy use, and reduce costs. Whether investing in home solar panels, battery storage, or a home backup generator, having a clear understanding of kWh usage and costs is crucial for effective energy management.
