Doing An Energy Audit

How to determine the exact size of solar system you need to meet all your home's energy needs.

Determining your home's exact energy needs (otherwise known as doing an energy audit or doing and electrical audit) isn't as hard as you may think. That's because it involves simply checking out your current utility bill, observing your environment a little and then doing a few easy calculations.

How To Do An Energy Audit Using Kilowatts

The power company measures your energy usage using kilowatts. The more electricity your home consumes, the higher the kilowatts reading that will be appearing on your electric bill.

By using this reading we can determine exactly how much power we use and thus how much we'll need to make.

Follow the instructions below to determine the size of solar system you need to meets all of your homes energy requirements (doing a home energy audit).

Determining Your Energy Needs (Electricity Audit)

1. First, look at your electric bill and get the kilowatt reading. The kilowatt reading should be right beside the "KWH" abbreviation on your bill. Make sure the reading is for a month with average use.

If an average use month is too hard to select, then add up every month's kwh usage for the entire year and divide by 12 to get the average kilowatts used per month.

2. Next divide your monthly average kilowatt use by 30 to get your daily average use.

3. Then divide this number by the average number of full sun hours that there are per day in your area. Usually 5-7 hours.

4. Next multiply this number by 1.15 just to be sure you make up for any unforeseen inconsistencies in effectiveness. This will give you your total in Kilowatts.

5. Lastly, to convert this to watts so that you can better understand what size solar system is needed, just multiply by 1000.

Home Energy Audit Example:

Let's say the average monthly kilowatt reading on your electric bill was 300 kwh. Divide 300 by 30 (days) = 10 kilowatt hours per day. If you have an average of 6 hrs of full sunlight per day, you would then divide 10 by 6 (hrs of sun per day) = 1.67. Then multiply by 1.5 = 2.5. And finally multiply by 1000 to convert to watts.

2.5 x 1000 = 2500 watts
of power is needed per hour to meets
all of your energy requirements.

Your solar system will need to produce 2500 watts per hour.

Even if you don't plan to create this much energy, you should still use this method (doing an energy audit) to determine how much power (watts) you would need, so that you have a clear idea of what to eventually strive for.

Determining The Roof Space Needed

By using the calculation we came up with in the energy audit example above we can then determine the approximate amount of roof space (in square feet) that we'll need to accommodate the solar panels we require.

To do this you must first find out how many kilowatts per hour your solar system can produce for every 100 square feet of panel, then multiply this number by 100.

To give you some idea of this number. A solar system with high efficiency cells is typically capable of producing 1 kw per hour for every 100 square feet. This is something you may want to remember to consider when doing a home energy audit.

Therefore, since we determined that you need to produce 2.5 kw for every hour of full sun (in our energy audit example above), you will need 2.5 x 100 = 250 square feet of dedicated space and therefore 250 square feet of solar panels.

Now that you know about doing an energy audit, click here to go back to the Solar System Sizing section in the exact spot you left off (or just click your browser's back button).