Do I Need Solar on my Planned ADU?

Do I Need Solar on my Planned ADU?

As California moves toward sustainability and renewable energy, the state is requiring the addition of solar to newly built residences including accessory dwelling units (ADUs). When you are planning to add an ADU to your property it’s crucial to understand when and why you need to install solar panels. 

Is solar required on my Accessory Dwelling Unit? 

California state law requires that any newly built accessory dwelling unit must have solar panels. The California Energy Commission (CEC) requires solar panels to be installed on either the ADU or the primary residence.  

If you already have solar panels on your primary dwelling, in some cases you may add new panels to the existing system to meet energy code requirements for the ADU. However, the solar must be part of the ADU’s permit application, sized per the Energy Code, and comply with other requirements of the building code. 

If you plan to install solar panels or expand the existing solar panel system on the primary residence to satisfy the energy requirements of the ADU, you may be required to upgrade your existing electrical service. It is imperative that the new solar panels or solar expansion is installed after the service upgrade is complete. Electrical service upgrades should always be performed by the ADU contractor to ensure that all measures are being met to accommodate the needs of the ADU. 

Does solar add to my cost for the ADU? 

The cost of installing solar depends on the size of the system (in kilowatts) that is necessary for the energy consumption of the ADU. The solar panels will help reduce the energy bills, making your ADU more sustainable overall. At OneStop ADU we include solar panels as part of the pricing for our predesigned plans (based on Climate Zone 7 requirements, the most common in San Diego County, and ADU square footage). 

Is there a tax credit for solar in California? 

The investment tax credit (ITC) is a 30% federal tax credit for solar photovoltaic (PV) installations. This means a qualified homeowner can receive a 30% tax credit on their tax returns. The credit is calculated on the total installed cost of the solar system and can be used over a number of years until the full credit has been applied.  

What is the qualification for a solar tax credit? 

To qualify for the tax credit, the homeowner must own (not lease) the solar system and pay federal taxes. The solar system must be placed in service and generate electricity for a home during the tax year. The solar system must be new and not an expansion of an existing system.

Will adding solar affect my ADU timeline? 

No additional time will be added to the timeline of the ADU construction. Solar permitting and installation are carried out in parallel with the rest of the design and build process. The solar is simply another component of its overall construction. The actual installation of the panels can occur once the roof is completed, and the solar application is approved. . Inspections are scheduled at different stages of the installation and upon completion, but do not change the timing of the completion of the ADU. 

How will solar affect my ADU design? 

The addition of solar panels on your ADU will generally not affect the overall design of your ADU. All of our OneStop ADU predesigned plans are solar-friendly, meaning they have a roof that will accommodate panels.  

For ADUs with more custom designs, and/or an irregular roof, the location of the solar panels will need to be configured. Any special considerations, such as obstructions or shade will be taken into account during the planning phase. 

Can my existing solar panels on my residence count towards the solar required for the ADU? 

No, an existing solar array on your primary home – without any additions – will not be counted towards the CEC requirement for adding solar panels for new construction. However, you may be able to expand an existing solar system to cover the energy needs of the ADU, and such expansion may be counted towards the ADU during the permitting process. 

However, be aware that each municipality interprets the solar requirement a bit differently. In some cases (even within the same jurisdiction) a plan checker may allow an existing solar array on the main home to count towards the ADU while another plan checker may not. San Marcos and Escondido will specifically not accept existing solar systems as counting towards the requirement, and we have also seen this happen in San Diego. Because of the differences in interpretation, inspectors are moving towards universally enforcing the CEC requirements for new solar when adding an ADU. 

How does Title 24 effect ADU construction? 

Title 24 requires that all new construction must meet energy consumption thresholds. This includes ADUs. Title 24 of California state law refers to a number of regulations California has put in place to ensure energy conservation, including solar requirements.  

All in all, new California ADUs must have solar panels to reduce the energy consumption of the structure being built. This requirement is carried out under Title 24 of California state law, which seeks to ensure energy is being consumed responsibly and as conservatively as possible.  

 Experienced San Diego builders, OneStop ADU serves the entire county, including San Diego, Chula Vista, Oceanside, Carlsbad, and the surrounding areas.  

Let us help you get started on your backyard home. At OneStop ADU, we are familiar with the energy laws in San Diego and surrounding areas. We include solar in our predesigned plans based on ADU size and solar requirements for Climate Zone 7. Visit our website for more information on relevant regulations. If you would like to schedule an in-person meeting and a complimentary feasibility study of your property, contact us by phone at 858-437-8476, or email at  

Solar Installation on an ADU home.
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