What is the difference between a Main Panel Upgrade(MPU) and Derating a Main Panel?

As a homeowner considering a rooftop solar installation, understanding the intricacies of your home’s electrical system is crucial. Two terms you may encounter during the planning process are “derating a main panel” and “main panel upgrade.” These distinct processes impact your home’s electrical capacity and safety, and their differences must be understood. In this comprehensive guide, we’ll delve into the specifics of derating a main panel and performing a main panel upgrade, explain why they may be required for a rooftop solar installation, and discuss the pros and cons of each. Our goal is to provide you with a clear understanding of these options so you can make an informed decision about your solar project.

Part 1: Derating a Main Panel

1.1 What Is Derating a Main Panel?

Derating a main panel involves lowering the maximum current capacity of a breaker or panel to safely manage the extra electrical load from a solar system. This adjustment ensures that the panel does not become overloaded and can handle the added power from solar energy. By derating, homeowners can maintain their electrical system’s safety and efficiency while integrating solar power.

1.2 Why Is Derating Required for Solar Installation?

The National Electrical Code (NEC) requires that the total output current of your solar system should not exceed a certain percentage of your main panel’s busbar rating, commonly set at 120%. By derating your main panel, you ensure that your solar system operates safely and efficiently, avoiding potential hazards such as overloaded circuits or fires.

1.3 How Does Derating a Main Panel Work?

To derate your main panel, you’ll need to determine the maximum current output allowed for your solar system based on your panel’s rating. For example, if you have a 100 amp main panel, the maximum combined current from the utility and solar system should not exceed 120 amps (100 amps x 120%). This means that the solar system should be designed to generate a maximum of 20 amps of output current.

1.4 Pros and Cons of Derating a Main Panel


  1. Cost-effective: Derating your main panel is typically more affordable than upgrading since it doesn’t require purchasing and installing a new panel or subpanel.
  2. Safety: Derating ensures that your solar system complies with NEC guidelines, reducing the risk of overloaded circuits or fires.
  3. Simplicity: Derating a main panel is generally less complex than performing a full panel upgrade, making it easier for homeowners and installers alike.


  1. Limited Solar Capacity: Derating may result in a reduced solar system capacity, limiting the amount of solar energy you can generate and potentially affecting your return on investment.
  2. Not Always Feasible: In some cases, derating may not be possible due to the limitations of your existing main panel, requiring you to consider a panel upgrade instead.
  3. If you derate your main panel and then add additional loads in the future like a hot tub or pool pump that draws a significant amount of electricity you may be required to do a main panel to support these additional loads. If you do not, your main panel may not be able to support these additional loads. 

Part 2: Main Panel Upgrade

2.1 What Is a Main Panel Upgrade?

A main panel upgrade involves replacing your existing main panel with a higher-capacity one or adding a subpanel to accommodate the extra current generated by your solar system. This option is generally required when your current main panel cannot be derated to meet the NEC requirements or when the added solar capacity would exceed the panel’s safe limits.

2.2 Why Is a Main Panel Upgrade Required for Solar Installation?

When your home’s electrical capacity isn’t sufficient to support a solar system or when derating isn’t feasible, a main panel upgrade becomes necessary. Upgrading your main panel allows for a larger solar system, helping you achieve greater energy savings and environmental benefits. Additionally, a main panel upgrade ensures that your solar installation adheres to the NEC guidelines, promoting safety and avoiding potential legal issues or penalties.

A main panel upgrade might be required if your existing panel is outdated, has reached its maximum capacity, or if the added solar energy would push the panel beyond its safe operating limits. Moreover, if your home has plans for future electrical needs, such as an electric vehicle charging station or additional appliances, an upgrade will provide the necessary capacity to accommodate these demands.

2.3 How Does a Main Panel Upgrade Work?

A main panel upgrade involves the following steps:

  1. Assess the existing main panel’s capacity, age, and condition.
  2. Determine the necessary electrical capacity to accommodate the solar system and any potential future electrical loads (such as electric vehicle charging or home additions).
  3. Choose an appropriately sized new main panel or subpanel based on the assessment and calculations.
  4. Safely remove the existing main panel or install a subpanel, following all local codes and regulations.
  5. Connect the solar system to the upgraded main panel or subpanel, ensuring all components are properly installed and integrated.

2.4 Pros and Cons of a Main Panel Upgrade


  1. Increased Solar Capacity: Upgrading your main panel allows for a larger solar system, enabling you to generate more solar energy and achieve greater energy savings.
  2. Future-proofing: A main panel upgrade can accommodate future electrical needs, such as electric vehicle charging or home additions, making it a more flexible long-term solution.
  3. Enhanced Safety: Replacing an outdated or undersized main panel with an upgraded one can improve the overall safety and reliability of your home’s electrical system.


  1. Higher Cost: Upgrading your main panel or adding a subpanel can be more expensive than derating, as it involves purchasing and installing new equipment.
  2. Complexity: A main panel upgrade is generally more complex than derating, requiring more time and expertise to complete.
  3. Possible Permitting and Inspection Requirements: Depending on local regulations, upgrading your main panel may require additional permitting and inspections, which can add time and cost to your solar installation process.


Understanding the differences between derating a main panel and performing a main panel upgrade is essential for homeowners looking to install a rooftop solar system. While derating can be a cost-effective and straightforward option for accommodating your solar system, it may not always be feasible or sufficient depending on your home’s electrical capacity. In such cases, a main panel upgrade may be necessary to ensure the safe and efficient operation of your solar installation.

By carefully weighing the pros and cons of each option and consulting with your dedicated Customer Experience Specialist at DelphiSun, you can make an informed decision that best suits your home’s needs, budget, and long-term goals. With a clear understanding of these processes, you’ll be better equipped to navigate the solar installation process and ultimately enjoy the benefits of clean, renewable solar energy for years to come.

You can view the different Main Panel upgrades in our Adders section of the website. 

TSP Norfolk
3719 E. Virginia Beach Blvd.
Norfolk, VA 23502

TSP Raleigh
150 Dominion Dr.
Morrisville, NC 27560

TSP Charlotte
1201 Carrier Dr.
Charlotte, NC 28216

TSP Greenville
3130 River Rd.
Piedmont, SC 29673

TSP Charleston
5081 Coosaw Creek North
Charleston, SC 29420

TSP Grayson
2255 Loganville Hwy., Suite A.
Grayson, GA 30017

TSP Miami
10050 NW 116 Way
Miami, FL 33178

TSP Orlando
901 Armstrong Blvd.
Kissimmee, FL 34741

TSP Tampa
13620 49th St.
Clearwater, FL 33762

TSP Jacksonville
4737 Dellwood Ave.
Jacksonville, FL 32205

TSP Pensacola
8124 Opportunity Dr.
Milton, FL 32571

TSP Chicago
2108 McDonough St.
Joliet, IL 60436

TSP Kansas City, MO
10452 Baur Blvd.
Olivette, MO 63132

TSP McAllen
1200 Jasmine Ave.
McAllen, TX 78501

TSP Houston
12511 Taylor Rd.
Houston, TX 77041

TSP San Antonio
4223 Dividend Rd.
San Antonio, TX 78219

TSP Austin
365 Warehouse Dr.
Buda, TX 78610

TSP Dallas
2125 Vanco Dr.
Irving, TX 75061

TSP El Paso
10812 Notus Lane.
El Paso, TX 79935

TSP Albuquerque
8509-8519 Jefferson St.
Albuquerque, NM 87113

TSP Denver
5001 Oakland St
Denver, CO 80239

TSP Tucson
3828 S Evans Blvd.
Tucson, AZ 85714

TSP Mesa (Headquarters)
2505 W. Baseline Rd.
Mesa, AZ 85210

TSP Yuma
4450 E 40th St.
Yuma, AZ 85365

TSP Salt Lake City
722 South 5300 West
Salt Lake City, UT 84104

TSP Las Vegas
3570 W Post Rd
Las Vegas, NV 89118

TSP Ontario
3325 Shelby St
Ontario, CA 91764

TSP Valencia
28318 Constellation Rd
Valencia, CA 91355

TSP Oakland
3032 Market St
Oakland, CA 94608

TSP Saramento
1600 Raley Court, Suites 50 & 60
Sacramento, CA 95691

TSP Reno
96 Glen Carran Cr, Unit #106
Sparks, NV 89431