Photovoltaic Tutorial:
Step-By-Step Guide to Going Solar
return to previous page3. Perform an energy audit and load analysis.
Energy audits serve three basic objectives:
- To find out how much solar power you need
- To fulfill a key requirement of some tax credits, rebates and loans
- To lower your monthly utility bill by eliminating wasteful consumption
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:
- Make a list of aging appliances, then check for buyback offers from your utility company or state public utilities commission. Also sniff out any product rebates available before purchasing new energy-saving models. (For federal offers, check here. For California state offers, check here, or check the DSIRE website if you' live in another state.)
- Check to see what electronics in your home remain on or in standby mode 24/7/365 when not being used, and start turning some of them off. One way to simplify this taks is to install power strip where where multiple devices are plugged in. (This includes entertainment centers desktop computers and cordless tool battery banks.) A strip allows you to flip one easy-to-reach switch to turn off everything at once.
- If you haven't already, replace incandescent bulbs with CFL bulbs. The latter may cost three times the price, but will last five times as long and use a fraction of the wattage. (Read more about CFL's on the federal Energy Saver website.) Outside lights left on all night should be replaced with motion detectors.
- If you live in a location with extreme temperatures, or own an old house, do an insulation check (or hire someone to do it). Easy DIY fixes include installing rolls of fiberglass insulation in the attic and basement, if needed. (Insulating exterior walls are a much tougher assignment.) Windows should be caulked or replaced if they're thin-paned or allow cold air to penetrate through their frames. Likewise, exterior doors should be lined with weatherizing strips inside the jambs. For more advice, see the D-I-Y Home Audit Checklist postedat EnergySolution.com
- Blinds or heavy curtains should be used on windows to block cold outdoor temperatures from radiating into the house. Awnings above windows along southern exposures will diminish the effect of radiating heat in the summer.
- Passive solar heating building design (in winter) and cooling (in summer) are other options consider. To learn more about how to use the sun to naturally warm your home and provide indoor light, (or how to use shade to block the sun's heat), here's an overview from Alternative Energy News.
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:
- To identify the heaviest amount of current draw (aka load) you'll ever need your solar electric system to cover at any one time. For instance, your refrigerator, dryer, televison, nine overhead lights, microwave and two computers may all routinely be up and running at once, so you'll need a big enough solar array, battery bank and supplemental energy sources (wind turbine, AC generator, etc.) to supply the juice.
- To identify how many kilowatt hours the system must generate each month to cover your electricity consumption. This information is used to determine what designers refer to as the critical design month, when the ratio between usage and available sun hours is the most extreme. An offgrid system is sized based on the data for this month.
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, HomePower.com 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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