Note: You must be an "admin" on your account to add users.
First, open the Users tab in the upper right by clicking on the Key-shaped Icon.
This will take you to the Users page, where you'll select "Invite User."
Enter their email in the window when prompted, and they'll receive an email invite to join your account in SolarDesignTool. Sometimes this email can get snagged by spam filters, so be sure to check!
Note: Additional users are $50/mo, as outlined in our Pricing Page.