"How many panels can I add?" is the wrong first question. With a battery-coupled system — panels wired straight into your home battery, no grid export — the amount of solar you can actually use is set by two ceilings, and you hit whichever is lower. Here's how to think about it, running this at my own house in Charleston.
Ceiling 1: the battery's DC input rating
Every battery system has a maximum solar (PV) input, measured in kilowatts — that's how much panel power the built-in charge controller can take at once. Connect panels up to that rating and you're set. Go beyond it and the controller clips the extra at midday: you simply can't harvest more than the input accepts at peak sun.
You can connect a bit more panel than the rated input — it's called overpaneling, and it's standard practice. The clipped midday peak is a small loss, and in exchange you get more output in the conditions that usually starve solar: cloudy days, early mornings, and winter. Two caveats: there are diminishing returns past a modest overpanel, and you must never exceed the input's voltage limit — too much current just clips, but too much voltage can damage the unit. An installer sizes this safely.
The exact input rating depends on your specific system and how many units you've stacked, so it's not one universal number — but it's a hard ceiling on harvest no matter how many panels you bolt down.
Ceiling 2: how much you actually use
Here's the one people forget. Because battery-coupled solar doesn't export to the grid, you can't bank or sell a surplus. Any energy your panels make beyond what your home uses — directly or stored in the battery for later — is simply wasted. There's no net-metering meter spinning backward.
So the second ceiling is your own consumption. Solar that overshoots what you'll realistically use, even with the battery time-shifting it into the evening, isn't buying you anything. This is exactly why "just buy a huge array" advice falls apart for non-grid-tied systems: past the point where you're self-consuming it all, extra panels are extra cost with no extra savings.
The battery is what raises your usable ceiling
This is where the battery earns its keep on the solar side. Without storage, you can only use solar as it's produced — so a sunny afternoon while you're at work is wasted. The battery soaks up that daytime production and lets you run on it into the night, which raises how much of your solar you actually consume. More self-consumption means more of your panels' output turns into real savings. Panels and battery work as a pair: the panels make it, the battery makes it usable when you need it.
So what's the right size?
There isn't a universal answer, because it depends on your usage shape and your system's input — which is the whole point. The honest way to size it: enough to meaningfully offset what you use, without overshooting either ceiling. A modest array that you fully self-consume beats an oversized one that clips and spills.
That's what the analyzer estimates — it reads your real usage and gives a rough, honest solar figure on top of your battery numbers, capped at what you'd actually use (never a fantasy export number). And it ties back to the bigger sizing question for the battery itself, which I cover in what size battery you need to cover a Rate 7 peak.
My approach
I'm growing solar in stages rather than maxing it out on day one — starting with a ground-mount array to see real output, then the main house roof later. The battery already delivers most of the value through backup and the rate switch; solar stacks on top, sized to what I actually use, not to a spec-sheet maximum. If you want the full picture of why the battery is the foundation, start with is a home battery worth it on Dominion Rate 7.