The number of solar panels you need to collect adequate energy to power your household system depends on several factors. Your typical electrical usage, the average amount of sun you can collect in a day, the voltage of your batteries, and the amp capacity of the solar panels you choose are the figures you need to calculate an answer, according to Advanced Energy Group's Solar4Power web site.

Calculate your energy usage

There are different ways to calculate your home's typical energy usage. You can list every electrical appliance or device in your household that requires power. Include lights, kitchen appliances, computers, televisions, personal care appliances, stereos, and anything else you intend to power with your solar energy system. Check device labels to see how much wattage each requires. Multiply the wattage by the hours per day of usage for each appliance. Then, total all amounts and multiply by 7 for the average weekly wattage requirement to run your household. Another option, if you are currently a power-grid customer, is to average the kWh (kilowatt hours) detailed in your summer low and winter high electrical bills. Or, for a general idea of your energy consumption, you can use a national average. According to Mother Earth News, "most systems installed in the United States are in the range of 2 to 5 kW" per day. If you consider your household typical, you can take a guess on your consumption using this guideline, although it does not yield very accurate results.

Location determines energy collection

The amount of solar energy your system can soak up in a day is directly dependent on where you live. You could check available resources to find your average hours of sunlight for a given year. Weather services may provide this information; check your local meteorology statistics. For a general idea of your average sun hours which takes into account the earth's tilt at your latitude, the Solar4Power web site provides a chart listing major US cities with high, average and low solar hour figures.

Know your battery capacity

In order to accurately calculate the number of solar panels in a system, you need to know the voltage of the batteries which will store the energy your panels collect. Your battery capacity will be 12, 24 or 48 volts, depending on such considerations as the distance between your solar panels and batteries, according to Solar4Power.

Calculate your amps capacity

Take your average weekly usage (in watts) and multiply it by 1.25 to allow for energy loss within your power system. Let's say you will use 7 kW of energy per week, so 7,000 watts times 1.25 equals 8,750 watts. Divide this number by the voltage of your batteries. If you have 24 volt batteries, dividing 8,750 watts by 24 equals 365. Divide 365 by 7 to get your daily requirement: 52. Divide 52 by your average sun hours per day. If your average is 4, your answer will be 13. This number represents the total amps capacity of your solar array. The number of modules you will need depends on the capacity of the panels you select. For example, if you choose solar panels with a 4 amp capacity, you will need 4.

Source:

Solar4Power

"Mother Earth News;" Calculating Solar Power Costs; Alicia Reich; December 2009-January 2010

Resource:

Solar Insolation for U.S. Major Cities