The short answer
A Powerwall 3 system is three things: the battery, which has its own solar inverter built in; the solar panels feeding it; and a Tesla device that separates your home from the grid when the power goes out. How those three connect to your panel decides what stays on during an outage and what the installation involves.
This guide covers how it fits together. Whether solar and a battery pay off under PG&E's current billing is a separate question, worked through in Is solar worth it under NEM 3? and the NEM 3 battery math.
What Powerwall 3 is
- BATTERY: 13.5 kWh of nominal battery energy per unit[1].
- POWER: continuous AC output configurable at 5.8, 7.6, 10 or 11.5 kW on the grid[1], and a load start capability of 185 locked-rotor amps for motors[1].
- SOLAR INVERTER BUILT IN: up to 20 kW of DC solar per unit, across 6 MPPT inputs[1][2].
- WHERE IT GOES: indoor and outdoor rated, NEMA 3R, floor or wall mount[1]. Tesla's design guide says Powerwall is not installed in habitable locations[2].
- SCALING: up to 4 Powerwall 3 units in one system, plus up to 3 Expansion units of 13.5 kWh each, which add energy but no inverter[1].
Two of those numbers do different jobs. Battery energy is the amount stored; how long it lasts depends on what is running and any solar recharge. Continuous power limits how much can run at once. Sizing a backup system is a balance of the two against what you want running, which is why we start from your list of loads rather than from the size of the house.
Tesla requires a grid-connected system and does not support fully off-grid Powerwall 3 systems[2]. During an outage, the backup device isolates the home from the grid.
With new solar
With new panels, the solar wires straight into the Powerwall's built-in inverter. Tesla calls this DC-coupled and says it is strongly preferred over AC-coupled solar[3]. One unit takes up to 20 kW of DC solar[1], so new solar that meets Tesla's electrical and compatibility requirements needs no separate solar inverter.
Tesla's design rules require its Mid-Circuit Interrupters on each solar string connected to Powerwall 3, even where rapid-shutdown rules would not otherwise apply, and third-party optimizers cannot be wired to it[2]. Those rules shape the panel layout, so the solar and the battery are designed together.
With solar you already have
Tesla says Powerwall 3 works with all major solar inverter brands and with various existing system sizes[4]. Existing solar on another brand's inverter connects on the AC side, which Tesla's design guide lists as supported[3].
There is a limit that matters during an outage. Tesla allows a maximum of 7.68 kW AC of third-party solar per Powerwall on the backup side, or 10 kW AC when Expansion units are installed, and it says a Powerwall damaged by excess solar during an outage is out of warranty[3]. A large existing array can need a design that keeps part of it off the backup side.
If you already have a Powerwall 2 or Powerwall+, note that Powerwall 3 cannot be added to those batteries[4]. On billing, Tesla says adding battery storage does not affect an existing NEM 1.0 or NEM 2.0 customer's status[4].
The device that keeps the lights on
During an outage the home has to be separated from the grid before the battery can power it. Powerwall 3 supports three Tesla devices for that, and Tesla says no third-party equipment can stand in for them[1][2]:
- GATEWAY 3 detects outages and transfers to backup automatically. It has its own 200-amp panelboard and a service-entrance-rated main breaker, and it can be installed for whole-home or partial-home backup[1][5].
- BACKUP SWITCH plugs into the meter socket, with the meter plugging into it[6]. Tesla's system-design page describes it in whole-home backup, and says it may not be approved by some utilities[5]. Tesla lists PG&E among the territories that allow it[6].
- BACKUP GATEWAY 2 does the same job, and Tesla's datasheet shows it in a partial-home configuration[1].
Whole-home backup keeps the main panel powered, so any circuit can run, within the system's power limit, until the stored energy runs low. Partial-home backup moves the circuits you choose onto a backup panel. Which is better depends on your loads and how long you want to last, and we price both at the inspection.
How it runs day to day
- SELF-POWERED stores solar you do not use during the day to power the home at night[7].
- SAVINGS, called time-based control in Tesla's warranty[11], charges from and discharges to the grid at certain times to maximize savings[8].
- BACKUP RESERVE sets how much stored energy is held back for outages, anywhere from 0% to 80%, and Max Backup holds 100% for up to 72 hours[9].
- STORM WATCH, when enabled and activated, charges the Powerwall to full ahead of severe weather. Before enabling it, your phone has to be paired with the Powerwall and Grid Charging enabled, and your installer sets whether Grid Charging is available[10].
From install day to switched on
A solar and battery system has two sign-offs. First the building department's inspection: PG&E says the system must pass city or county inspection to get a final building permit[12]. Then PG&E's: it reviews the interconnection application and gives final permission to operate[12], and the paperwork includes a copy of the final building permit[12].
PG&E is explicit that the system must not be turned on before its permission to operate letter[13]. It says that permission typically takes 5 to 10 business days, up to a maximum of 30[12]. We handle the permit, the inspection and the interconnection application.
On billing: since April 15, 2023, new interconnection applications go on the CPUC's Net Billing Tariff[14], which PG&E calls the Solar Billing Plan[15]. Exported energy is credited at values from the CPUC's Avoided Cost Calculator that vary by month and hour, and residential customers on it take service on PG&E's E-ELEC rate[15]. That pricing is why the battery math looks different from older solar advice.
What the rules do and don't require
California's 2025 Energy Code has a battery-ready provision for newly built single-family homes with one or two dwellings and electrical service over 125 amps, and homes built with a battery installed are exempt from it[16]. The provision does not apply to additions or alterations[16], so it does not require an existing home to add a battery.
The federal residential clean energy credit, Section 25D, does not apply to expenditures made after December 31, 2025[17], so there is no federal credit for a 2026 solar or battery install.
Who installs it, and the warranty
Tesla says Powerwall 3 installation must be carried out only by Tesla Certified Installers who are licensed electricians[18]. Tesla's limited warranty is 10 years, with 70% of the 13.5 kWh capacity at 10 years for solar self-consumption, time-based control and backup use. It covers a Powerwall purchased from Tesla or a Tesla certified installer, excludes modification or repair by anyone else, and depends on the system being registered and connected to the internet: without that, Tesla commits to at least four years[11].
We are a Tesla Certified Installer, and the solar, the battery and the panel work are all in-house under our C-10 licence.
What to have ready
- Your last 12 months of PG&E usage
- If you already have solar: the inverter brand and model, and the system size
- A list of what you want running in an outage, and for how long
- Where the equipment could go, outside or in a garage