Obviously, the most important ratings when doing calculations for a power system are the voltage and current at maximum power
. A system is rarely calculated using panel wattage ratings, as this is a function of both the voltage and current. Some panels are rated at slightly higher or lower voltages than others, and this affects the amount of current available. The open circuit voltage and short circuit current ratings are important from a safety point of view, especially the voltage rating. An array of six panels in series, while having a nominal 72 volt rating, can output over 120 volts DC more than enough to be dangerous.