California NEM 3.0 Net Billing Tariff: Battery Sizing for Optimal Savings

Key Takeaways

• California's Net Billing Tariff (NEM 3.0) significantly reduces export compensation for new solar installations.
• Exported electricity is valued by the Avoided Cost Calculator (ACC), not retail rates.
• Battery storage is essential to maximise self-consumption and discharge during high-value evening hours.
• Optimal battery sizing for NEM 3.0 systems is typically 100-120% of daily energy consumption to capture peak export rates.

Understanding California's Net Billing Tariff (NEM 3.0)

California's Net Billing Tariff (NEM 3.0) is the current solar billing structure for new residential solar interconnection applications submitted after 14 April 2023. This tariff applies to customers of Pacific Gas and Electric (PG&E), Southern California Edison (SCE), and San Diego Gas & Electric (SDG&E). Under NEM 3.0, the way solar electricity exported to the grid is valued has changed significantly compared to previous tariffs.

How Exported Solar Energy is Valued Under NEM 3.0

Under NEM 3.0, export compensation is calculated using the California Public Utilities Commission (CPUC) Avoided Cost Calculator (ACC). This calculator values electricity exported based on avoided wholesale generation and transmission costs. This means that the value of your exported solar energy varies hour-by-hour across 8,760 hours of the year. Daytime solar export rates are significantly lower than retail electricity rates. The average residential solar export compensation under the Avoided Cost Calculator is approximately 75% to 80% lower than under NEM 2.0.

This shift in valuation means that simply exporting excess solar generation during the day is no longer an effective strategy for maximising savings. Instead, the tariff is designed to incentivise paired solar-plus-storage systems to maximise self-consumption and discharge during peak grid hours.

The Importance of Battery Storage for NEM 3.0

The structure of NEM 3.0 makes battery storage a critical component for optimising solar savings. With significantly reduced export rates during the day, storing excess solar energy for later use or export becomes financially advantageous.

The CPUC notes that avoided cost export credits spike dramatically during late summer evening hours, specifically between 18:00 and 21:00 in August and September. These are the hours when grid demand is highest, and thus the value of electricity to the grid is at its peak. By storing solar energy generated during the day and discharging it during these high-value evening hours, homeowners can significantly increase the financial benefits of their solar system.

Residential solar customers under the Net Billing Tariff are required to take service on a highly differentiated Time-of-Use (TOU) rate schedule. This further emphasises the need for battery storage to shift energy usage away from expensive peak demand periods.

Optimal Battery Sizing for NEM 3.0 Systems

To effectively navigate the NEM 3.0 tariff and achieve a favourable payback period, battery storage sizing is crucial. The goal is to store enough energy to cover your home's evening consumption and to discharge any remaining stored energy during the high-value export windows, particularly the 18:00 to 21:00 period in late summer.

While specific sizing depends on individual energy consumption patterns, a general guideline for NEM 3.0 systems suggests sizing battery storage to be 100-120% of your daily energy consumption. This allows for:

• Maximised Self-Consumption: Using your own generated solar power during the evening, reducing reliance on expensive grid electricity.
• Strategic Export: Discharging stored energy to the grid during the highest-value export periods, such as the late summer evening hours when avoided cost credits are highest.
• Energy Resilience: Providing backup power during grid outages.

An appropriately sized battery system helps to mitigate the impact of lower daytime export rates by enabling you to use or sell your energy when it is most valuable.

What you can check yourself, and what you cannot

As a homeowner, you can review your past electricity bills to understand your daily energy consumption patterns and identify your peak usage times. This information is vital for discussing battery sizing with a qualified solar installer. You can also monitor your energy usage through smart home devices or utility portals if available.

However, determining the precise battery capacity, inverter compatibility, and system design for optimal NEM 3.0 performance requires the expertise of an accredited solar installer. They will perform a detailed energy audit, consider your specific utility's Time-of-Use rates, and design a system that complies with all local regulations and interconnection requirements. Do not attempt to size or install battery systems yourself, as this involves high-voltage electrical work and complex system integration.

What the published sources do not tell you

The CPUC's official documentation outlines the framework and general principles of NEM 3.0. However, it does not provide specific guidance on optimal battery sizing percentages or detailed financial modelling for individual homes. The exact payback period for a solar-plus-storage system under NEM 3.0 will vary significantly based on factors such as your specific utility's Time-of-Use rates, your household's unique energy consumption profile, the cost of your installed system, and future electricity price fluctuations.

While the CPUC highlights the dramatic evening export rate spikes, the precise monetary value of these spikes is dynamic and determined by the Avoided Cost Calculator, which changes over time. Homeowners should consult with solar professionals who have experience with NEM 3.0 and access to detailed modelling tools to get an accurate projection for their specific circumstances.