Determining Average Usage

Now that you understand how you are billed and what to look for, the next step is to compile at least a 12 month history of your usage. If you haven't lived in your house that long, you'll need to compile as much usage history as you have available. The more data you have, the more accurate your calculation will be. If you are in Arizona and have APS, a 12 and 24 month usage history is available on-line at http://www.aps.com.

Once you have this information, add up the previous 12 months of kWh usage and divide by 365. If you have a 24 month history, you can add them up and divide by 730. This will provide you an with an average daily kWh usage. For example:

	Jan = 548 kWh Feb = 637 kWh Mar = 515 kWh Apr = 606 kWh May = 808 kWh Jun = 997 kWh Jul = 1,103 kWh Aug = 1,117 kWh Sep = 1,034 kWh Oct = 854 kWh Nov = 678 kWh Dec = 717 kWh Yearly Total = 9,614 kWh
	Daily Average = 9,614 ÷ 365 = 26.3 kWh per day

Now that we have this information, we can determine what size photovoltaic system would be required to meet your electricity needs.

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