A solar battery is not magic. It is basically a time-shifting tool. It stores electricity when power is cheap or abundant, then powers your home when SDG&E electricity is expensive or when the grid is down.
In SDG&E territory, that matters because SDG&E’s residential pricing is built around Time-of-Use (TOU) periods where electricity costs more in the early evening and less overnight and, on plans with Super Off-Peak, less during certain daytime hours. SDG&E’s published TOU period table shows the familiar 4:00 p.m. to 9:00 p.m. On-Peak window and defines Off-Peak and Super Off-Peak blocks.
This guide explains what a battery is doing hour by hour under SDG&E rates, how it interacts with solar exports under the Solar Billing Plan, and what settings actually matter.
SDG&E’s rate structure in one minute
Think of SDG&E pricing as three “price zones” across the day:
- On-Peak: the expensive window (commonly 4:00 p.m. to 9:00 p.m.)
- Off-Peak: mid-priced blocks outside the peak window
- Super Off-Peak: the cheapest blocks on plans that include it (often overnight, and in SDG&E’s TOU period table also shown as midday 10:00 a.m. to 2:00 p.m. for certain schedules)
Your bill gets worse when you import lots of kWh during On-Peak. Your bill gets better when you can cover your needs using solar or stored energy during that window.
What the battery is doing, mechanically
A home battery has three “jobs,” and SDG&E’s rate structure determines which job matters most.
Job 1: Store extra solar instead of exporting it
Midday solar production often exceeds what the home is using. Without a battery, the extra solar is exported to the grid.
With a battery, that extra solar can be stored and used later. This is the simplest “plain English” benefit: use your solar later, not just when the sun is out.
Job 2: Avoid buying power during the expensive window
A battery can discharge to power the home during On-Peak so you import fewer kWh from SDG&E when rates are highest. SDG&E’s TOU tables clearly define the On-Peak block.
Job 3: Provide backup during outages
In backup mode, the battery keeps the home running when the grid goes down. This is a separate value stream from TOU savings, but many households buy batteries primarily for resilience and then get TOU benefits as a bonus.
The two big billing situations for solar customers
Before talking “strategy,” it helps to know which solar billing structure you are under.
Situation A: Legacy NEM (older net metering)
The CPUC notes that under NEM tariffs, customers receive bill credits for exports at retail rates and that these tariffs are closed to new enrollments.
If you are on legacy NEM, exports were historically more valuable, so the battery’s “store instead of export” value depends on your specific plan and load shape.
Situation B: Solar Billing Plan (Net Billing Tariff / NBT)
For most newer interconnections, SDG&E uses the Solar Billing Plan, where exports earn export credits based on the value of energy at that time of day. SDG&E explains that export credits are calculated based on time-of-day value and are split into separate buckets for delivery and generation.
Under this structure, batteries tend to matter more because the economics favor self-consumption and peak avoidance over exporting a large midday surplus.
How export credits work under SDG&E’s Solar Billing Plan
SDG&E’s Solar Billing Plan uses a credit system that is easy to misunderstand.
Two separate “credit buckets”
SDG&E explains that export credits are split into:
- Generation Export Credits (can offset generation import charges)
- Delivery Export Credits (can offset delivery import charges)
These buckets do not freely mix. That is why some customers feel like they are “earning credits” but still paying certain charges.
Why export value changes by hour
SDG&E’s export pricing page explains that Energy Export Credits are based on the CPUC Avoided Cost Calculator (ACC) values, and SDG&E aggregates those hourly values into monthly/day-type/hour tables.
Plain English translation: the grid values your exported kWh differently depending on the time and season. Batteries help you choose when you export (or avoid exporting entirely by using energy at home).
The battery strategies that actually matter under SDG&E TOU
Most battery systems have settings that boil down to the same decision: When should the battery charge, and when should it discharge?
Strategy 1: Self-consumption
Goal: use as much of your solar as possible inside the home.
How it behaves:
- Battery charges during solar production.
- Battery discharges later to cover evening household usage.
When it tends to make sense:
- Homes that produce a lot of midday surplus.
- Homes that use meaningful energy after 4 p.m.
Why it matches SDG&E:
- It reduces On-Peak imports during 4:00 p.m. to 9:00 p.m.
- It reduces reliance on exporting when export credits may be low.
Strategy 2: Time-based control (TOU arbitrage)
Goal: minimize cost by charging at low-cost times and discharging at high-cost times.
How it behaves:
- Battery charges when electricity is cheapest (often overnight Super Off-Peak and, for some schedules, midday Super Off-Peak).
- Battery discharges during the On-Peak window.
Important note:
- Some programs or homeowner preferences restrict grid charging. The core idea is still the same: charge when cheap, discharge when expensive. SDG&E’s TOU period table shows clearly when those windows exist.
Strategy 3: Backup-first (resiliency priority)
Goal: keep a minimum battery reserve for outages.
How it behaves:
- You set a reserve (example: keep 20–40% in the battery).
- The system uses the remaining portion for TOU savings.
When it tends to make sense:
- If outages are your #1 concern, but you still want bill benefits.
A simple “day in the life” example
Here’s what a well-configured solar + battery system is trying to do on a typical weekday:
Morning (Off-Peak)
- Home uses grid lightly, solar ramps up.
Midday (solar production is strongest)
- Solar covers the home.
- Extra solar charges the battery instead of exporting.
Late afternoon and evening (On-Peak 4–9 p.m.)
- Battery discharges to run the home.
- Imports from SDG&E drop during the most expensive hours.
Night (Super Off-Peak on plans that include it)
- Battery may recharge depending on settings and rules, or it stays ready for the next solar day.
That’s the whole play: move energy from cheap/abundant hours into expensive hours.
What solar homeowners should check in their battery settings
If a battery isn’t delivering savings, it is usually because of one of these issues:
- Reserve is too high
If most capacity is locked for backup, there is less available for peak shaving. - Battery is filling too late
If the battery reaches full charge after the best solar hours, you may still be exporting when export value is low (or importing during peak because the battery never filled). - Battery is discharging too early
If it empties before the On-Peak window, you lose the main benefit of avoiding peak imports. - Rate plan mismatch
Some SDG&E plans and billing situations change the best strategy. The TOU structure and whether you have Super Off-Peak periods matter.
Quick FAQ
Does a battery always save money with SDG&E?
Not always. Batteries save the most when you:
- use a lot of electricity in the evening peak window, and/or
- export a large amount of midday solar under the Solar Billing Plan where exports are time-valued.
Why do I still have a bill if I export a lot?
Under the Solar Billing Plan, export credits are split into delivery and generation buckets and can only offset their matching import charges.
Why is everyone talking about batteries more now?
Because the CPUC’s net billing structure values exports differently by time, and SDG&E’s TOU rates make evening imports expensive. Batteries help shift value into the evening.
The takeaway
A solar battery is best understood as a rate-structure tool:
- It reduces what you buy from SDG&E during expensive On-Peak hours.
- It helps you keep more of your solar energy for your own use instead of exporting it when export value may be lower.
- It provides backup power when the grid goes down.
Call The Experts
Stellar Solar can help simplify the process and get you a free no-pressure quote. We’ve helped over 17,000 homeowners and are happy to add you to the Stellar family. To get started, call us at (866) 787-6527 or fill out this form.
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