How to Calculate How Many Solar Power Panels Are Needed for a Whole House

Solar power is the way to the future in energy development. Completely renewable, sustainable and fairly reliable, solar energy is becoming more of a reasonable energy source and less of a craze. If you are thinking of getting in on this sustainable resource for energy, you first will have to do some significant planning. You need to know exactly how much equipment you will need to buy to maintain your current state of living, and that has to do with calculating the number of solar panels you will require. There are numerous calculators available on the Internet regarding solar panel calculations; however, you can follow these simple steps to calculate by hand today.

Things You'll Need

• Pencil
• Paper
• Calculator

Instructions

1. Determine the number of kilowatt hours or kWh your household uses on a typical day. This can be done by examining your electric bill and dividing your monthly kWh measured by the number of days in the billing cycle. For a more accurate estimate, look at your year-end kWh usage and divide by 365.

2. Calculate the amount of energy that can be stored in your battery bank. Determine the size of battery bank required with this formula: (total load in watts X days of backup storage) / (system voltage X efficiency after system losses). As an example, the average household uses 29 kWh per day, and let's say you want two days of backup storage with 24-volt batteries: (29,000 X 2) / (24 X 0.80) = 3,020.83 amp hours at 24 volts. Most 24-volt batteries will sustain around 5 amp hours, and since you will also be charging your system constantly with the solar panels, you can assume that there will only be a 5 percent draw on your batteries. Thus, 3,020.83 / 5 = 604 X .05 = 30.2 or a bank of 31 24-volt batteries.

3. Calculate the number of solar panels needed for your battery bank. Divide the total amp hours per day (3,020 in our example) by the average sun hours per day (based on the solar insolation chart, 4.2 in our example) to get the total array amps needed. Determine the peak amps produced by the solar module you are looking at purchasing (divide the module's wattage by the peak power point voltage, 17 in our example). Divide the total array amps by the peak mps and round to the highest whole number (43 in our example). This gives you the total solar panels needed for your home application based on your energy requirements and the solar panels you are looking at purchasing.

Tips & Warnings

• Use the link in Resources for an automatic online solar panel calculator.

Resources

• Read this Article in Spanish
• This website provides both "on-grid" and "off-grid" solar panel calculators