🔋 New SGIP Battery Sizing Rules for Standalone Storage: What California Homeowners Need to Know in 2025
California’s Self-Generation Incentive Program (SGIP) continues to be one of the best ways to reduce the cost of installing a home battery. But if you're planning to apply for a rebate in 2025, it’s crucial to understand the new sizing rules introduced by the California Public Utilities Commission (CPUC) under Resolution E-5360.
These changes took effect on December 19, 2024, and they significantly impact how large your battery system can be — especially if you're installing standalone storage (a battery not connected to solar panels).
⚖️ What Changed?
Under the new rules:
SGIP now sizes battery systems based on energy (kWh), not power (kW)
The old 10 kW sizing threshold has been replaced by a 15 kWh threshold
If your system is larger than 15 kWh, you must justify the size with actual energy usage data
There is now a 30 kWh cap for all systems applying through the residential equity budget
📐 How to Justify Standalone Battery Size
If you're installing a standalone battery and want a system larger than 15 kWh, here's what you need:
You must use:
The average daily energy consumption from 4 PM to 9 PM
during a summer calendar month (June, July, or August)
This specific 4–9 PM window aligns with California’s peak demand period, when the grid is most stressed and energy is most expensive. SGIP wants to ensure batteries are used during these hours.
🧠 Example:
Let’s say you're applying in July 2025 and you provide usage data from June 2025.
Your utility data shows that during June, your household used an average of 15.6 kWh per day between 4–9 PM
Based on this, you’re eligible to install a battery up to 15.6 kWh in capacity
If you wanted to install two Tesla Powerwalls (which total 27 kWh), you’d need to prove your average usage during that time window was at least 27 kWh/day
⚠️ If you don’t have enough usage to justify the size, SGIP will not approve your rebate for the full system.
🚫 Residential Cap: 30 kWh Max
Even if your data supports a larger system, SGIP limits residential equity projects to a maximum of 30 kWh.
✅ When No Justification is Needed
If your standalone battery system is 15 kWh or less, you don’t need to submit any usage data at all. This makes one Tesla Powerwall (13.5 kWh) an easy choice for many homeowners who want to skip the paperwork.
🧾 What You’ll Need to Apply
Interval usage data from your utility (typically Green Button format)
A simple calculation of your average daily 4–9 PM energy use during a summer month
A sizing worksheet or justification form (varies by program administrator)
💡 Should You Pair Storage With Solar?
If you're having trouble justifying a larger standalone battery, you might consider pairing it with solar. Paired systems follow different rules — sizing is based on excess solar production, not your load. That can sometimes allow for larger batteries (we'll cover this in a separate post).
🏡 Bottom Line
If you're planning to install a standalone battery system in California and apply for the SGIP rebate, make sure you:
Understand your 4–9 PM summer usage
Stay below the 30 kWh cap
Use June, July, or August data to justify your system if it’s over 15 kWh
Have questions about your usage data or whether your home qualifies for SGIP? We can help you analyze your numbers and design a right-sized system that qualifies for incentives.
