Understanding Your Utility Company’s PTO kW Calculation (Con Edison / PSEG)

Clarifying How Total System kW Is Calculated

When reviewing your Permission to Operate (PTO) letter from your utility company, you may notice a difference between the system size listed on your permit and approved plans, and the size reflected in the utility’s documentation. This post explains why that discrepancy occurs and how utility companies calculate total system kilowatts (kW).

DC vs. AC Power: Why the Numbers Differ

Solar panels generate DC (direct current) electricity, but most homes and businesses use AC (alternating current) power. To make solar energy usable, inverters are installed to convert DC to AC. Some energy is lost during this conversion due to heat, wiring resistance, and other electrical factors.

As a result, the DC system size shown in your approved plans is typically larger than the AC system size reported in your utility company’s PTO documentation (usually listed as “Final As-Built kW – Solar”)

Example System Overview

• Modules: SPR-440W
• Quantity: 25
• Total DC System Size: 11.00 kW (as shown on approved plans)

• Inverter: SPR-A-IQ7HS-0.369 
• Quantity: 25
• Total AC System Size: 9.23 kW (as reported by Utility Company)

How Is the Total DC kW Calculated?

We calculate your DC system size by multiplying the power rating of a single solar panel (in kilowatts) by the total number of panels: 0.440 kW × 25 panels = 11.00 kW (DC)

How Is the Total AC kW Calculated?

Your utility company calculates AC system size by multiplying the output of a single inverter by the total number of inverters: 0.369 kW × 25 inverters = 9.225 kW

This value is then rounded to the nearest hundredth: 9.23 kW (AC)

Need More Help?

If you have any questions or need further assistance, please contact our service team at service@empower-solar.com or call us at 516-837-3459.

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About the Author

EmPower Solar develops, engineers, installs, and services solar and battery systems for residential and commercial clients. Since 2003, EmPower Solar has empowered thousands of New York homeowners and businesses with 35 megawatts of distributed solar. Its vision is to create a new energy paradigm powered by clean, renewable energy for a more prosperous, healthy, and civil world. The company culture is defined by the EmPowering Way, which results in consistent 5-star customer service reviews. For more information visit empower-solar.com.