Part of the equation is limited to the amount of panels you can fit on your roof, house orientation and external shading and aesthetics. A good southern exposure is ideal for solar power, however solar panels can be west-facing or on a west-facing slope and angled towards the south. Some homeowners want to completely zero out their energy bills for the whole year. Other homeowners go with smaller systems to zero out just their winter energy bills and a lower summer bill. To calculate the size of photovoltaic’s you will need to accomplish either goal you are going to need your electricity bills for the past 12 months.
The 1.7 factor is an estimate for only a particular type and efficiency of panel, but it will give you a good idea for starters. If you are a visual person, feel free to contact me and I can send you a spreadsheet where you can enter in your monthly kWh usage, and a nice graph will visually show you what you are spending now on energy bills, and what they would like with a 5 or 10 kW solar electricity system.
For more information visit www.dsireusa.org to find current APS/SRP or TEP rebates and federal tax incentives for going solar. Visit APS’s website here, SRP’s website here and TEP’s website here for more tips and information. Michael Blue Jay also has a great efficiency website and solar calculator here. You can also see what we have to say on what you should do before you get solar here. For certain homes, coupling solar with efficiency upgrades will stretch your dollar spent 40-50% compared to solar alone.