Voltage regulation is a measure of how much an alternator's output voltage changes from no load to full load, expressed as a percentage. It is calculated by taking the difference between the no load voltage and full load voltage, dividing by the full load voltage, and multiplying by 100. The example shows an alternator whose voltage rises from 3300V at full load to 3350V at no load, resulting in a voltage regulation of 1.5% at unity power factor. The regulation depends on the load power factor.