Sizing solar to your usage
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“How many panels do I need?” The right answer comes from your electricity usage, not how much roof you have. Here’s how to think about size — and the Texas trap that makes bigger systems pay off less.
Size to your kWh, not your roof
Start from your annual usage (kWh/year, on your bills). A system is commonly sized to cover roughly 100–110% of that, adjusted for how sunny your roof is. Filling every square foot of roof can leave you making far more than you use — which only helps if your buyback is generous.
The Texas oversizing trap
Because Texas buyback is often below the retail rate (Module 2), the kWh you export are usually worth less than the kWh you offset. So past a certain point, adding panels mostly produces cheap export credit, not full-price savings. The sweet spot is usually “cover your usage,” not “max the roof” — unless you have a strong 1:1 buyback plan or plan to add an EV/battery.
What changes the right size
- Future load — an EV, a pool, or electrifying heat raises your usage; size for where you’re headed.
- A battery — lets you use more of your own solar instead of exporting it cheaply.
- Roof & shade — limit how much you can fit and how much each panel makes.
Get an accurate number
Rules of thumb are rough. The most accurate sizing uses your actual 15-minute usage data — in Texas you can download yours from Smart Meter Texas and upload it, so the estimate matches how you really use power across the day (which matters a lot with a battery or time-of-use plan).
Try it in the editor
Run a free estimate: it sizes the array to your usage automatically (with a “fill my roof” option if you want max production), and you can upload your Smart Meter Texas data for the most accurate result.
Next: reading a solar quote without getting burned.
This is general education, not financial or tax advice. Always get quotes from licensed installers and confirm incentives with a tax professional and your utility.