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Estimating Energy Consumption

Through the examples presented in this handout, you will learn how to calculate electrical energy consumption, and discover how simple changes around the house can help you conserve energy and save money.

Estimating Electrical Energy Consumption:


The amount of electrical energy consumed by different appliances is reported in kilowatt-hours (kWh) and one kilowatt-hour is equal to 1000 watts.

The equation used to calculate the number of kilowatt-hours is:

W to kWh example

Example 1:

Assume a laptop uses 50 Watts per hour. If the laptop is used for 8 hours a day, how many kilowatt-hours of electrical energy will it use each month?


Example 1 Solution

Example 2:

Calculate the energy and money saved resulting from this simple substitution:

The retail price of electricity in North Carolina is about $0.10 per kWh. A 23-watt energy efficient light bulb is equivalent to a 100-watt incandescent light bulb. Replacing an incandescent with a 23-watt energy efficient light bulb can save you energy - and money. Here is how:

This is a 23-watt energy efficient light bulb. You can buy this light bulb for about $3.00. It is estimated to last 9750 hours or approximately 13 times longer than the average light bulb.
This is your average 100-watt light bulb. You can buy this light bulb for about $0.50. It is estimated to last 750 hours. In order to get the same amount of life as the energy-saving bulb, you would need to purchase 13 of these incandescent light bulbs. Incandescent Bulb


Remember: We are comparing the energy consumed over a life of 9750 hours (a little over 1 year).

Energy consumption by incadescent light bulb:

Solution 2.1

Energy consumption by energy saving light bulbs:

Solution 2.2

Activity A:

Imagine a light fixture in your home, which holds five energy-saving light bulbs. In an attempt to conserve energy, you remove one of the bulbs from the fixture and use only four of the bulbs.

Questions: Answer:

a) How much energy do you actually conserve in a given month? Assume each bulb is 23 Watts and you leave the fixture on for 12 hours each day.



b) Assuming you are charged $0.10 per kilowatt-hour of energy consumed, how much is your monthly saving on your energy bill?


$ _____

c) How much is your annual saving?


$ _____

Activity B:

A photovoltaic system captures solar energy and converts it to electricity. Use under "Data Export" to answer the following questions. You may also want to look at the guide on instantaneous data versus cumulative data to help you with the following activity.

House Energy Consumed : Cumulative
PV Energy: Cumulative
Wind Turbine Energy: Cumulative
Questions: Answers:
a) Determine how much electric energy was consumed by the Solar House over an averaging period of a week (House - House Energy Consumed), and how much of this energy was provided by the PV panel (Annex - PV Energy) as well as the wind turbine (Annex - Wind Turbine Energy). Use an averaging period of a day.





b) Assuming that each kilowatt-hour of energy is $0.10, how much money did the Solar House save in the previous week by using electrical energy produced by the PV and wind turbine?


$ _____

c) What percentage of the total energy consumed by the Solar House was supplied through the PV and wind turbine?


_____ %



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