If “Power My House” means to reach net-zero electrical utility bill, the necessary number of panels can be calculated based on yearly usage. A generic number of panels can be determined for an “average” home in the U.S., or a more specific answer can be determined for your home. Another approach is to determine how much solar energy you can produce. The later is a simple question to answer based on your home’s available sun facing roof space.
Solar Panels
The commercial solar cells available today probably represent the state of the art for years to come. Good solar panels composed of monocrystalline silicon cells generate about 100 milliwatts per square inch (6.45 square cm). Commercial panels come in a variety of sizes, 100 watts and up; however, the power generated per square inch remains about 100 milliwatts. Number of panels required can decrease, but not the area.
“Average” Home
How much electricity does an average 2-story 3-bedroom house use per day, per month or per year. The US Energy Information Agency has estimated that the average U.S. home uses 8,900 Kwh (kilowatt hours) per year or about 24 Kwh per day. If this average home is in a climate that will produce an average of 6 hours of sunlight for maximum power generation, each square inch of optimally oriented panels can produce 600 milliwatts per day.
Consequently, about 40,000 square inches (24000 watts per day / 0.6 watt hours per inch per day) or 278 square feet of solar paneling would meet household need. If purchasing a 100-watt panel measuring about 6 square feet, an average home would require 46 panels.
Your Home
These calculations are for a fictional system but serve as a guideline. Your energy requirements may be substantially more, or less, than the average value used above. If your goal is to reduce your electricity bill to zero, you simply need to know your homes normal needs to tell you if it is possible and practical.
Electrical company invoices often show not only current months usage, but previous months as well. On request, the company may be able to provide a 12-month total. Alternatively, one can take meter readings each day over a week or even a month to include a few weekends when power use is typically higher.
Since usage typically is seasonable, this should be taken into account. For most of the U.S., winter usually represents the highest period of usage; however, in some areas of the country summers that require maximum use of AC may represent peak usage.
For example, if your energy bills or meter readings show that your yearly usage is 12000 Kwh per year, a solar power system would require a 63-panel array (47 x 12000 / 8900 = 63) of 100-watt panels. Roof space required would be 375 square feet.
