ADU Knowledge
June 11, 2024

Do I HAVE to install solar panels on my ADU?

Argi Avetisyan
Argi Avetisyan
Gather ADU expert
Do I HAVE to install solar panels on my ADU?
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Navigating the ins and outs of home improvement can be daunting, especially when it involves understanding changing regulations. If you're considering building an accessory dwelling unit (ADU) in California, you might be wondering whether you need to install solar panels. This question is more relevant than ever as many states, including California, push for sustainability and renewable energy in new construction projects. In this article, we’ll break down everything you need to know about the requirements for solar panels on your ADU.

The Rise of Sustainable Living

As more people become eco-conscious, the demand for sustainable living solutions has grown. Solar energy is now a popular choice for homeowners wanting to reduce their carbon footprint. California has been a leader in this movement, championing renewable energy sources, especially in new construction projects. The state mandates solar installations on new builds, but how do these requirements affect your ADU?

Understanding ADUs and Solar Requirements

ADUs are secondary housing units on the same property as a primary residence. They can serve multiple purposes—guest houses, rental units, or even home offices. In California, laws around ADU construction have been changing to promote sustainability. But do these laws mean you have to install solar panels on your ADU?

Breaking Down the Regulations

State law generally requires solar panel installations on new constructions, including ADUs. However, exemptions exist based on factors like the size of the ADU and the climate zone. For instance, ADUs smaller than 620 square feet may be exempt from the solar mandate in specific regions. Conversely, units above 1,125 square feet generally need solar installations, regardless of location.

Local Jurisdictions and Their Role

Different local jurisdictions can interpret and apply building codes differently. Some areas may have stricter regulations than others. It's vital to consult with local authorities or a knowledgeable contractor to understand the specific requirements for your project.

Calculating Your Solar Needs

Your contractor will typically assess whether your ADU needs solar panels by considering factors like the unit's size and the local climate zone. These calculations help determine the minimum photovoltaic (PV) system size required for compliance. The installation can either be on the ADU itself or the primary residence, expanding an existing solar system if necessary.

Costs and Incentives

Installing solar panels can increase your ADU project costs by $12,000 to $18,000 on average. However, various incentives, such as the federal residential solar energy tax credit, can offset these expenses. Homeowners can claim a 30% tax credit on the total installed cost, making the investment more manageable.

The Installation Process

Once it's determined that your ADU requires solar panels, your contractor will guide you through the necessary steps. This includes design, permitting, and installation phases. Most ADU plans are designed to accommodate solar panels, making the integration smoother. However, unique roof structures may need adjustments.

The Benefits of Solar Panels

Why consider solar panels for your ADU? Here are some compelling reasons:

Environmental Impact

Solar energy reduces the reliance on fossil fuels, cutting down greenhouse gas emissions. By installing solar panels, you're contributing to a cleaner environment and a more sustainable future.

Financial Savings

While the initial investment might be steep, solar panels can significantly reduce your electricity bills. Over time, the savings can offset the installation costs, providing long-term financial benefits.

Property Value

Homes with solar panels often have higher property values. Potential buyers see the advantages of lower utility bills and the environmental benefits, making your property more attractive.

Factors to Consider

Before deciding on solar panels for your ADU, consider these factors:

Upfront Costs

The initial investment for solar panels can be substantial. However, it's essential to consider the long-term savings on your utility bills. Additionally, there are various financing options and incentives available to help offset these costs.

Available Incentives

Many states, including California, offer incentives and rebates for installing solar panels. These incentives can significantly reduce the overall cost of your solar energy system. Always check for the latest programs and eligibility criteria.

Energy Needs

Assessing your energy consumption is crucial when deciding on solar panels. The size and design of your ADU, as well as your energy usage patterns, will determine the number and type of panels you need.

Solar Panel Requirements for ADUs in California

California has been a leader in promoting renewable energy, and this extends to ADUs. Understanding the regulations can help you make an informed decision about solar panels for your accessory dwelling unit.

Title 24 Building and Energy Efficiency Standards

According to California's Title 24 standards, new ADUs are generally required to include solar panels. These regulations aim to make new buildings more energy-efficient and environmentally friendly.

Net Energy Metering (NEM) Programs

If you already have a solar system under the NEM 2.0 program, adding an ADU won't affect your current status. However, any new installation for the ADU will fall under the NEM 3.0 regulations, which offer lower compensation rates for excess energy.

Exemptions and Special Cases

There are specific scenarios where ADUs might be exempt from the solar panel requirement. For example, if you're converting an existing structure or if your ADU's roof is too small or shaded, you might qualify for an exemption.

ADU with solar panel

Real-life Examples

Let's look at some homeowners who have successfully installed solar panels on their ADUs:

Case Study 1: Los Angeles

A homeowner decided to build an ADU for rental income. She installed solar panels on her ADU, benefiting from the federal tax credit and local incentives. Within a few years, she saw a significant reduction in her electricity bills and a boost in her property value.

Case Study 2: San Diego

Another homeowner built an ADU as a home office. Initially hesitant about the solar installation cost, he took advantage of financing options. Today, his electricity bills are minimal, and he's proud of his contribution to a sustainable future.

Case Study 3: San Francisco

A family's ADU serves as a guest house. They opted for a battery storage system to maximize Their solar investment. During peak usage hours, the stored solar energy powers Their ADU, further reducing Their reliance on grid electricity.

Exploring Other Renewable Energy Options

While solar panels are popular, other renewable energy sources might be suitable for your ADU:

Wind Energy

If your property is in a windy area, wind turbines can be an effective alternative. They generate electricity by harnessing wind power and can complement solar systems.

Geothermal Energy

Geothermal systems use the Earth's natural heat to generate energy. While the initial setup can be costly, they offer long-term savings and are highly efficient.


If you have access to a flowing water source, small-scale hydropower systems can generate electricity. These systems are reliable and can produce energy continuously.

FAQ About Solar Panels for ADUs

Can the 30% Solar Tax Credit Be Claimed for ADU Projects?

Absolutely. The Residential Clean Energy Credit, which provides a 30% tax credit on the installed cost of solar energy systems, can be applied to newly constructed accessory dwelling units (ADUs) that require solar panel installations to meet California's building codes.

How Many Solar Panels Are Typically Needed for an ADU?

The number of solar panels required for an ADU installation depends on several factors, such as the unit's size, location, and anticipated energy consumption. While the specific number can vary, a minimum of around 8 panels is often recommended for smaller ADUs, with larger units potentially requiring more panels to meet their energy needs.

What Is the Typical Cost Range for Installing Solar on an ADU?

The cost of integrating solar panel systems into an ADU project can fluctuate based on the project's scale and complexity. On average, homeowners can expect to pay between $12,000 and $18,000 for the solar panel installation component. However, it's essential to consider the long-term energy savings and available tax incentives, which can make the investment worthwhile.

Will Adding Solar Panels Extend the ADU Construction Timeline?

In most cases, incorporating solar panel installations into an ADU project does not significantly impact the overall construction timeline. Experienced contractors can coordinate the solar panel installation alongside other construction activities, ensuring a smooth and timely project completion.

Must Solar Panels Be Installed Directly on the ADU's Roof?

No, there is flexibility in terms of where the solar panels can be installed. While mounting them on the ADU's roof is an option, the panels can also be installed on the main house's roof or another suitable location on the property, as long as they receive adequate sunlight exposure and can be efficiently integrated with the electrical system.

Can I use an outside solar vendor for the ADU solar installation?

Unfortunately, we cannot allow outside vendors to work on any components of the ADU project, including the solar installation, due to liability and logistical concerns. The solar photovoltaic (PV) system design is intricately integrated with the ADU's overall electrical design, making it challenging to separate these elements. For this reason, we work with a dedicated solar vendor who handles the complete design and installation of the solar system.

What are the differences between NEM 2.0 and NEM 3.0, and how can I maximize savings under NEM 3.0?

Under NEM 3.0, utility companies offer lower compensation rates for excess solar power sent back to the grid compared to NEM 2.0. NEM 3.0 also includes premium charges during peak usage hours, typically from 4 PM to 9 PM, which can reduce the effectiveness of your solar system in offsetting electricity costs. To maximize savings under NEM 3.0, consider adding a battery storage system to your solar setup. This allows you to store excess solar power generated during the day and use it during peak hours when electricity rates are higher, resulting in greater cost savings. The cost of adding battery backup typically starts around $8,500, and you can include additional features like outage backup or generator input.

Will my existing solar panels on the main home count towards the ADU's required solar installation?

No, an existing solar array on your primary residence, without any additions or modifications, will generally not be counted towards the California Energy Commission's (CEC) requirement for adding solar panels for new construction, such as an ADU. However, you may be able to expand your existing solar system on the primary house to cover the energy needs of the ADU, and such an expansion could potentially be counted towards the ADU's solar requirements during the permitting process.

How consistently are the CEC's solar requirements for ADUs enforced across different jurisdictions?

While there is some room for interpretation by local authorities, there is a trend towards universally enforcing the CEC's requirements for new solar installations when adding an ADU. Some jurisdictions, like San Marcos and Escondido, specifically do not accept existing solar systems as meeting the ADU solar requirement, and this practice has also been observed in areas like San Diego. As of December 2022, the County of San Diego Building Division provided guidance on expanding existing solar systems for ADUs, stating that the system size will be confirmed during inspection, and no separate designation is required on the permit as long as the system matches the energy compliance forms.


Navigating the regulations and requirements for solar panel installations on ADUs can be challenging. However, staying informed and consulting with experts can make the process smoother. Solar panels offer numerous benefits, from environmental impact to financial savings and increased property value. Whether you decide to install solar panels or explore other renewable energy options, taking steps toward sustainability is always a move in the right direction.

For personalized advice and assistance, consider Getting a quote for your ADU project. They'll help you understand the specific requirements for your ADU and guide you through the process.

By making informed decisions today, you can contribute to a sustainable future and enjoy the benefits of renewable energy.

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Not sure where to start with your ADU project?


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