Skimming the early reports, it appears that some number of polling places opened late due to some logistical issues and some people who presented themselves at the polls were not able to pass muster with the biometric verification.
The Ghana News Agency (GNA) is doing a lot of data-centered reporting from a lot of polling places scattered around the country. Their Politics page is here.
Here’s a good example of what GNA is reporting:
Peaceful voting so far but not without hitches (GNA)
A thorough analysis of the biometric voter systems’ performance is, of course, going to have to wait.
Good background story at Modern Ghana from Accra, the capital: Ghana votes in tightly contested presidentials poll.
While many polling stations opened on time, a number started late due to the delayed delivery of materials, causing frustration among voters and officials. Voter biometric fingerprinting was also being used for the first time.
Ghana Web also has a good page: Ghana Elections Updates: Five Presidential Candidates Vote. Scroll down to the bottom for minute-by-minute updates from different places — a woman going into labor and voting with her sister before going to the hospital, politicians voting, technical problems, etc. The earliest updates are at the bottom.