We had a client ask us to provide a flowchart of how the energy flows through a Powerwall 3 system, so we built this simulator. You can play with different scenarios by selecting the buttons or adjusting the sliders. Let us know what you think in the comments below!
1 PW = 5 kW · 1 PW + expansion = 8 kW
2 PW = 10 kW · 2 PW + expansion = 13 kW
3 PW + expansion = 18 kW
Extra expansion packs add stored energy (13.5 kWh each), not charge rate.
The simulator above is not a stock graphic. It is a working model of how a Tesla Powerwall 3 whole-home backup system actually routes electricity, under the rules that apply to real Florida homes with net metering. Drag the sliders, and you are watching the same decision logic a real system uses, just sped up and put on a screen.
I built it because the number one source of confusion I hear from homeowners is not about panels or price. It is about where the power goes. People assume their battery runs the house every night. In a net metering scenario, it does not, and the reasons why are worth understanding before you spend money on batteries.
What the Simulator Shows
Four circles: Solar, Grid, Home, and Powerwall. The moving dots on the curved lines show which direction power is flowing at that moment, and how much. Faster, denser dots mean more power. Each number lives next to its circle, so you can read the whole system state at a glance.
The battery circle shows state of charge as a percentage with a green ring around it. The banner across the top narrates what is happening in plain English, because a diagram should not require an electrical license to interpret.
How to Use It
Start with the four scenario buttons. Sunny day, night, and the two outage scenarios cover the situations that matter. Then start dragging sliders.
Solar production runs from zero to 30 kW. Home usage runs from zero to 25 kW, which covers everything from an empty house to a big home running two AC systems, a pool pump, and an EV charger at once. Battery charge sets the current state of charge as a percentage. The grid toggle is the interesting one: flip it to outage and watch the whole system reorganize itself in about a second, which is roughly what the real hardware does.
You can also change the equipment. Pick one to four Powerwall 3 units and zero to three expansion packs, and the simulator recalculates what your system can store, how fast it can recharge, and how much power it can deliver during an outage. Those three numbers are the entire sizing conversation, condensed.
Why the Battery Sits at 100 Percent
This is the part that surprises people. In this simulator, when the grid is up, the battery does not power your home. Ever. It sits at full charge, reserved.
That is not a limitation. It is the correct configuration for a Florida home with full retail net metering. When your utility credits you at essentially the same rate for exported solar as it charges you for imported power, cycling your battery every night accomplishes nothing financially. Every cycle you avoid is battery life you keep. So the intelligent move is what Tesla calls full backup mode: the battery holds its entire capacity in reserve for the one job that actually justifies its existence here, which is keeping your home running when the grid fails.
Excess solar does not get stuffed into the already-full battery for later. It goes to the grid, you bank the credit, and you draw it back at night.
The grid is your battery for economics. The Powerwall is your battery for hurricanes.
What Happens After an Outage
Set up an outage scenario, drain the battery a bit, then flip the grid back on. Notice the priority: solar goes to recharging the battery first, at the maximum rate the equipment allows, while your home runs on the grid in the meantime. The system’s first job after an outage is getting your reserve back, because in Florida the next outage is not hypothetical. Storms come in clusters.
The Overload Lesson
Try this: switch to a grid outage, then push home usage past what your Powerwall configuration can deliver. The system does not partially power your house. It shuts down completely.
This is the single most important thing the simulator teaches, and it reflects reality. An inverter operating off-grid cannot serve half a load. If your home demands more than the hardware can supply, the system trips offline, and everything goes dark until you reduce the load. Two Powerwall 3 units can deliver up to 23 kW, which handles most homes comfortably, but a large home with everything running at once can exceed that. This is exactly why we do load calculations before quoting a backup system instead of guessing.
Charge Rates, Expansion Packs, and Why They Matter
Click the little info icon next to Your System and you will see the charge rate rules. A single Powerwall 3 recharges at up to 5 kW. Add at least one expansion pack and that rises to 8 kW. Two Powerwalls get you 10 kW, two with an expansion 13 kW, three with an expansion 18 kW.
Why care? Because during an extended outage, your recharge rate determines whether a day of sun refills your reserve or barely dents it. Expansion packs are usually pitched as storage capacity, and they are, at 13.5 kWh each. But the charge rate bump from the first one is a real and underappreciated benefit for outage resilience.
What This Is Not
The simulator is a teaching tool, not a design tool. It uses conservative, simplified modeling, and it is not connected to any live system. Real behavior depends on your specific configuration, your loads, and conditions on the day. When we design an actual system, we run real numbers on your real house.
It also ignores grid-charging, which is possible. You can charge your depleted Powerwall from the grid if it is working.
This also does not simulate time of use rates, differing buy and sell rates, and battery arbitrage, which are not things we do in Florida. With full net metering, the calculus is much easier.
The Bottom Line
If you take one thing from playing with this: in a net metering scenario, batteries in Southwest Florida are outage insurance, not daily energy savings. Size them for the loads you genuinely need during a storm, understand the shutdown behavior when you exceed capacity, and let the grid handle the day-to-day economics. If you want to know what the right configuration looks like for your home, that is a conversation we have with a load calculation in hand, not a guess.
