I was trying to upload a PowerPivot file of 1 GB to SharePoint, this didn’t work because SharePoint is by default set to maximum of 50 MB. To increase this limit you have to do the following configurations:
Out of the box, SharePoint allows you to upload files up to 50MB in size and Excel Services allows you to view files as large as 10 MB in a browser. Our new farm setup increases the Excel Services limit to 50MB. You can change these settings even further if users will be publishing and interacting with larger files.
To increase Web Application limits:
a. Navigate to SharePoint 2010 Central Administration > Application Management > Manage Web Applications.
b. Select SharePoint-80 and then, on the Ribbon, select General Settings > General Settings.
c. Change the Maximum Upload Size setting to the MB limit you want to set. (The maximum allowed by SharePoint is 2047MB.)
To increase Excel Services limits:
a. Navigate to SharePoint Central Administration > Application Management > Manage Service Applications.
b. Select your Excel Service Application.
c. On the Ribbon, click Manage.
d. Click Trusted File Locations and on the following page, select your trusted location. (Typically, this is listed as http:// in the Address column.)
e. In the Workbook Properties area, set the Maximum Workbook Size property to 2000 and the Maximum Chart or Image Size to 100 MB
Found at the excellent powerpivotgeek blog: http://powerpivotgeek.com/server-installation/single-server-install/