Try unplugging your battery and take the reading, might be the battery pulling it down.

Usually looking for about 13.8volts

 

I wouldn't be tempted to run it with the battery disconnected if you value the vans electronics.

 

Plus the battery shouldn't be able to pull it down that much unless it is knackered.
What is the battery voltage with the engine off?
And what is the voltage after driving for 1/2 hour or more?

 

How long has it been like that, has it read higher at any time ? are you having a flat battery problem ?
Are your headlights dim when engine is running ?
What are you using to read the voltage, does the vehicle have a voltmeter, or are you using a multi-meter ?
14.0V to 14.3V is correct voltage with a fully charged battery (measured with a reliable meter).

 

Hi
Alternator output is generally governed by demand. Have you got anything hefty running in the background directly linked to the vehicle battery? What happens to voltage when you turn lights and fan blower on? You would expect to see a constant output of between 13.3 and 13.9 volts to maintain a fully charged battery and run systems but it will fluctuate dependent upon draw and immediately after starting the vehicle.
You dont mention flat battery issues?
Likewise, a faulty battery will cause demand. Unfortunately these days with sealed batteries and drop testing not recommended it is difficult to test a battery directly. Ideally get the battery discharge tested to confirm the state of the battery.