Hello Greg. Our system both supports local data logging on the SD card of the emonPi and/or data logging on a remote server such as emoncms.org. This page explains the difference in a bit more detail 2. Log Locally - Guide | OpenEnergyMonitor Local storage on the emonPi allows you to keep the data within the privacy of your home.
In both cases you can export the data as CSV both at full resolution (e.g 10s data) or as say daily averages or totals. See the documentation here on the graph module Emoncms Graphs - Guide | OpenEnergyMonitor and exporting as CSV Exporting CSV - Guide | OpenEnergyMonitor
If you are interested in the technical detail of how data is stored on the emonPi (the data format itself) you might be interested to read Learn | OpenEnergyMonitor