Question: Can you use two 72 cell modules in series with a TriStar MPPT to charge a 48V battery system, or do you need three modules?
Answer: Yes, unless the system is located in an exceptionally hot desert climate, or you are worried about voltage drop from a long wire run from the array to the controller. But as long as your voltage at max power (Vmp) is slightly higher than your target battery voltage, two 72 cell modules will serve you well. For a 48 volt nominal battery, your target battery voltage will likely be close to 60 volts depending on the battery brand. And two 72 cell modules should supply much more than 60 volts even in hot temperatures as long as you’re not in Death Valley or some similar extremely hot climate. We have received a number of questions about this over the years, where people thought they might need 3 modules, when it fact 2 modules would suffice.