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Developing a Sustainable Energy System - Kilowatt Hours and Calculating Your Needs |
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Submitted by Teo Graca
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Electric usage in the United States has increased by more than 250% in the last decade (Source: DOE/EIA), so let's look at what a kilowatt hour really is!
A kilowatt is 1,000 watts, and a kilowatt hour is 1,000 watts of usage in one hour. Think of running a device that uses 250 watts of electric for four hours - that would be 250 watts an hour (0.25 kWh) times 4 hours, which equals 1 kWh. In the same way, you may think of miles per hour (mph). If you are going 60 miles per hour, you will go 60 miles in one hour or if you go 30 mph for 2 hours, you have still traveled 60 miles. Think of the old styled power meters that have the revolving disc that spins faster or slower based on power usage.
Let's take a look at some examples of actual power usage versus the power ratings you can find listed on most devices:
Window-Unit AC's
- Rated 1500 watts: run for one hour uses 1.5 kWh
- Rated 1000 watts: run for one hour uses 1 kWh
- Rated 500 watts: run for one hour uses 0.5 kWh
Ceiling Fan
- Rated 24 watts: run for one hour uses 0.024 kWh
Light Bulbs
- Rated 100 watts: run for 1 hour uses 0.1 kWh
- Rated 100 watts: run 24 hours per day for 30 days uses 72 kWh (0.1 kWh times 24 hours times 30 days)
LED lights (They use much less power and last much longer)
- Rated 6 watts: run for 1 hour uses 0.006 kWh
- Rated 6 watts: run 24 hours per day for 30 days uses 4.32 kWh (0.006 kWh times 24 hours times 30 days)
Simple math lets you easily calculate your needs.
Energy for your entertainment systems
If you are into TV's, think of an LCD TV with a 40 inch screen. The average energy consumption for this sized TV is 168 watts, or 0.168 kWh per hour. The LED TV's we tested were about 35% more efficient than LCD TV's and 160% more efficient than plasma TV's. A tried and true (and inexpensive) LCD TV's connected to DVD players, MP4 players and gaming systems are an essential form of entertainment and requires very little power.
DVD players and gaming systems use only about 10-50 watts - this is just 0.01 to 0.05 kWh when used. Today's visual and audio media systems use such a small amount of energy that it is definitely worth having for education or entertainment.
Music Production Systems
Most small music systems, which can be used in addition to your TV speakers, requires very little power. Most are 20-100 watts and require just 0.02 to 0.1 kWh when used.
Other Conversions: If your device lists amps instead of watts...
Watts is the measure of the rate of electrical use at any moment. For example, a laptop computer uses about 50 watts. If your device lists amps instead of watts, then just multiply the amps times the voltage to get the watts. For example:
2.5 amps x 120 volts = 300 watts
If you're outside North America, your country probably uses 220 to 240 volts instead of 120.
Understand the difference between watts and watt-hours
* Watts is the rate of use of a device when in use.
* Watt-hours is the total energy used over time.
So, once more, a 100 watt light bulb would use 100 watts in an hour, or 0.1 kWh when in use.
Saving on your electric bill
Many companies and home owners can save from 20% to 80% per year in energy costs by simply changing to LED lighting. There are companies out there right now that are entirely in the business of reducing energy costs for businesses, and they always start with making the lighting solutions more cost effective.
Developing a Sustainable Energy System
The main purpose of this article is to provide guidelines for people thinking of creating a sustainable energy system like solar, or to simply reduce costs. You can use this article as a resource for planning a more energy efficient household. The key thing to consider is "what is the maximum amount of kWh I need?" - let's cover peak usage versus monthly average usage.
If you are thinking of setting up a solar energy system, you can only collect your power for part of the day, and you need to store that power for use at night. So, if you use most of your energy during the day and just some at night, you need to average the kWh needed and consider the maximum amount needed (peak usage) during the day. It is essential that you generate more than you use during the day so you can store some for night usage.
Determining Energy Needs
Note that in 2010, the average cost of residential electricity was 11ยข/kWh (Source: DOE/EIA) in the U.S. In 2007, the average household used 936 kWh/mo. (DOE) and would pay about $102 per month for it based on the April 2009 average rate. This does not account for peak usage. In other words, if your average use is 936 kWh/mo., but the maximum use is 3,000 kW at any given moment, you have have a system in place to accommodate 3,000 kW, not 936 kW.
In Conclusion
With a sustainable energy system, you may consider that creating a 1.5 kWh system instead of a 3.0 kWh system is much more reasonable, but you would have to make sure that usage never peaks past 1.5kW at any given time.
Many states also have programs to trade electric on a one-to-one basis so you don't need to invest in a battery back up system. If you produce more electricity at any given time than you are using, your electric meter actually runs backwards. Eliminating the need for a battery back up system significantly reduces cost.
There are basically 3 ways to participate in sustainability when it comes to energy, but each becomes significantly more expense to set up:
- Reducing Energy Consumption - Simply things like changing to fluorescent light bulbs or centralizing your entertainment or educational systems can save you a significant amount of money and costs very little implement.
- Producing Your Own Energy - There are a number of ways to do this besides just solar power to subsidize and reduce your reliance of energy from centralized sources, and although the set up costs can be significant, they can save you money within a few years if you use financing, or immediately if you can cover the costs up front.
- Getting Completely Off The Grid - This requires a significant commitment, but brings you to complete sustainability. If the cost of power goes up significantly, your investment will pay off much sooner, plus you don't have to worry about the centralized energy grid that most of us depend on going down.
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