What size system do I need?

Your system size depends on your monthly energy use, as well as site factors like shading, sun hours, panel facing, etc. Our solar calculator is a great way to get an estimate based on your personal usage and location in just a few minutes.

If you would like to learn more about the factors that go into the system design process, check out these guides: Calculate Your kWh Usage Gather the kilowatt-hours (kWh) usage from your electric bill. You’ll want to have full 12 months of usage to be able to look at peaks and valleys in usage over a year. Energy consumption spikes in the summer and winter with heavy use of your A/C and heating units.

Determine your average monthly kWh usage. Add up your kWh usage for 12 months and divide by 12 to figure out your average monthly consumption. Your grid-tied system will tend to overproduce in the summer with peak sun exposure. Figure your daily kWh usage. Divide by 30 to determine your daily kWh usage. To determine your home’s energy usage more accurately, use our home appliances power consumption table to find out how many kWh your appliances would use per month. If your utility provides a favorable net metering policy, the energy your system generates can be banked with the utility as a credit that can be used later.

Not all utility companies give you credit; check with your local provider. 2. Look Up Your Peak Sun Hours Average peak sun hours vary greatly depending on your location and local climate. You’ll want to determine how may peak hours of sunlight you’ll get so you can make the most of the solar power: Look up your peak sun hours, through a sun hours chart to determine the number of hours per day the sun produces peak sunlight. Find the nearest city to you and write down the daily average of peak sun hours. 3. Calculate the Size of Your Solar System To figure out how to size your solar system, take your daily kWh energy requirement and divide it by your peak sun hours to get the kW output. Then divide the kW output by your panel’s efficiency to get the estimated number of solar panels you’ll need for your system.

(Daily kWh ÷ average sun hours) x 1.15 efficiency factor = DC solar system size For example, if you live in New Mexico, you average six peak sunlight hours per day. You’ll need 6.2 kW DC according to the formula: (33 kWh ÷ 6.1 sun hours) x 1.15 efficiency factor = 6.2 kW DC solar system size required Using the example above with a 6.2 kW DC system, you can multiply this number by 1,000 to confirm that you need 6,200 watts of solar panels. 6.2 kW x 1000 (convert to watts) = 6200 watts solar panel required Fine-Tuning the Estimated System Design To make the solar system sizing estimate as accurate as possible, you’ll also want to take into account the type of roof mount you’ll need, the direction your panels will face, and the appropriate size panels to fit your design.

1. Select Your Mount Type A roof mount is the simplest and most cost-effective solution since it costs less than other racks. To determine if you can use a roof mount: Pull up the address on Google Maps. Check to see if you have any viable south-facing options for a roof mount. If the solar array cannot face south, on the preferred angle, you’ll need to adjust the system by adding more solar.Your solar system should point toward the equator, so if you live in the Southern Hemisphere, look for north-facing options instead. Often the slope of the roof is already set up for solar gain, and it keeps the solar panels close to the inverter and service panel. This results in greater efficiency and costs less in conduit and wire.

2. If a roof mount is not an option, look into a ground mount or pole-mounted solution. On the flat ground, you can position solar panels in any direction you want to maximize sun exposure, unlike on a slanted roof. Even if you don’t live in your home long enough to break even on energy costs, the premium that home buyers are willing to pay to move into your solar-ready home will be more than enough to cover the investment.

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