Professional off-grid energy design
Size solar, battery, and backup systems with confidence
Model load, production, and storage across every hour of the year—then turn results into actionable system recommendations.
Try the full calculator instantly on this device. Create a free account when you want multiple saved projects and access anywhere.
- Hour-by-hour modeling for the full year
- PVWatts-ready solar workflows
- No account required to start
How it works
Five steps from site to sized system
A guided flow designed for installers and property owners alike.
- 1
Project info
Location and site details
- 2
Energy usage
Load profile and demand
- 3
Solar system
Array size and production
- 4
Analysis
Battery and generator sizing
- 5
Results
Reports and recommendations
Capabilities
Built for serious system design
Depth when you need it, without a steep learning curve.
Location-based analysis
Solar production tuned to your address, roof orientation, and regional factors.
Smart load profiling
Archetypes, appliances, and seasonal patterns for realistic usage models.
Advanced solar modeling
PVWatts integration or quick estimates, including multiple roof facets.
Battery sizing
Recommendations grounded in solar surplus and your load profile.
Hour-by-hour year-round analysis
See how solar, load, and storage align through every season—not just monthly averages.
Generator modeling
Backup generators with auto-start/stop and battery charging logic.
Why PAX
From back-of-envelope to defensible numbers
Replace guesswork with transparent calculations you can share with customers, stakeholders, and install partners.
- Hour-by-hour load and solar alignment
- Battery sizing driven by real surplus data
- Generator logic with configurable auto-start
- Location-aware production and seasonal load
Start free on this device
No sign-up wall. Run the calculator now—upgrade to an account when you want more projects saved online.
- Save projects in the cloud
- Create and manage multiple projects
- Open your work from any device