Photovoltaic Tutorial:

Step-By-Step Guide to Going Solar

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3. Perform an energy audit and load analysis.

Energy audits serve three basic objectives:

Performing an energy audit sounds like a Herculean task the way some people describe it. On a few websites, you'll find a long set of instructions on how to calculate the electrical loads in your home. You may also be encouraged to buy a "Kill-a-watt" meter or other device that measures the power that each appliance is using while plugged in.

It may be an interesting experiment to see how watts are measured, but for a grid-tied PV system, it's generally not necessary. A more direct approach is to gather your monthly electric bills for the past 12 months. Make a list of the months and write down the kilowatt hours you were charged for. Then add up the numbers. This annual usage figure becomes the 100% offset around which your solar electric system will be sized. Most homeowners eventually buy an array that offsets between 30 or 75 percent of kilowatt hours.

If you have MS Excel on your computer (or Apache OpenOffice), you can download a utility audit form from our worksheets page and try it out.

If you're interested in rebates for old appliances, or plan to apply for low-interest FHA loan, a more detailed energy audit is required. Even if it's not mandatory, a top-down audit will help you use conservation as a revenue-generating activity (via rebates and avoided kWh charges and rebates). That, in turn, translates to an earlier payback on your PV investment.

A detailed energy audit incorporates the following steps:

If you're considering an off-grid solar electric system, you'll also need to perform a load analysis. That kilowatt meter mentioned earlier now comes in handy in measuring appliances, electronics and tools around the house . Besides exposing energy-hog appliances that must be replaced, this task fulfills two other objectives:

Among its other benefits, a load analysis will ideally produce a graph like the one above, illustrating the average on/off usage of various electric loads. This data will help you size your array an inverter so that when maximum demand is placed on an offgrid PV system, you'll have enough juice for every load.

You only need to perform a load analysis for a grid-tied PV system if you plan to include battery back-up. In this case, you'll need to make a list of circuits and/or appliances and lights that will be hooked up to a subpanel (i.e. secondary load center) in the event of a grid power outage.

For more info, has published a 12-page article on how to perform both an energy audit and load analysis.

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Continued on Page 4... (How to Perform a Site Survey)

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