How Solar Power Systems Are Sized

Solar power systems are designed to produce a set average amount of energy on a daily or yearly basis. Switch to Solar calculates how much energy your home or business will need based on your utility bills, designing our system to provide you with the maximum amount of electricity your available space and budget will allow.

If your solar energy system includes a battery backup, we will size your solar panel array and battery bank to meet all of your average daily needs under the worst case insolation scenario (insolation describers the amount of sunlight your solar panels will receive).

Switch to Solar typically oversizes your solar panel array by a certain percentage relative to the inverter capacity to account for seasonal variations in temperature and system degradation over time. The range is typically 10% to 25% depending on local climate conditions.

Basic Sizing Steps for Grid-Tied Solar Energy Systems

Grid-tied solar energy systems are typically sized to provide a specific percentage of total annual electricity consumption. Limiting factors often include available space and budget. Switch to Solar’s process to sizing a grid-tied solar power system includes these steps:

  1. Determine the amount of kilowatts you’ll require, given the tilt and azimuth of the site, to generate an annual output close to your target. In Maryland, DC and Virginia, one kW of solar panel capacity oriented within 150 of the optimal tilt and azimuth, with no shading, produces roughly 1,359 kilowatt-hours per year.
  2. Adjust your initial estimate based on available space. To produce one kilowatt, we’ll require about 67 square feet of roof space for the solar panels.
  3. Make any additional adjustments to account for the electrical characteristics of the system, such as whether you plan to use string inverters, DC optimizers with string inverters, or microinverters.

How Are Off-Grid Photovoltaic Systems Sized?

Standalone solar power systems are sized differently than a grid-tied system. Because there is no standby supply from the grid for these systems, it is common to size the system to meet the average monthly load in winter, which typically has the lowest average daily insolation, plus the inefficiencies caused by charging and discharging a battery. The battery storage capacity is sized to handle the electrical loads when insolation is unavailable.

Switch to Solar sizes our off-grid solar systems using these steps:

  1. First, we determine the size and duration of all your electrical loads to calculate your average daily energy use.
  2. Then we size your battery storage capacity based on average daily energy use, depth of discharge limit, and desired days of autonomy.
  3. Third, we size your solar panel array to handle the period with the highest load and lowest solar insolation.
  4. Finally, we determine the size of the charge controller and electrical balance of system (BOS) components.

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