When shopping for PV modules, you must choose between 60 cell and 72 cell modules. The extra cells mean extra wattage and while many people make the assumption that more is better, this isn’t always the case. There are two basic ways that the extra cells will make the solar panels different, voltage and physical size. Both of these factors should be considered when making the choice.
Because all the solar cells in a PV module are connected in series, the 72 cell module will be about 6 volts higher than a 60 cell module. If you are using them with a string inverter this means less panels on each string. If you are using them with microinverters or DC optimizers, you will have to make sure the equipment you choose is designed to handle the higher voltage. Microinverters and DC optimizers for 72 cell modules will typically have a maximum input of 60 volts to prevent issues in even the coldest of temperatures.
So now let’s talk about size, which definitely does matter. All standard solar cells are similar in size and efficiency, so the 72 cell PV module is going to be a bit larger. You may be getting more wattage, but your wattage per square foot is still the same. The typical solar module is 6 solar cells wide, so a 72 cell module is the same width as a 60 cell module, but it is about a foot longer and 8 pounds heavier. The typical size for a 60 cell module is 66” x 40” and weighs in at 40 pounds while the 72 cell module is going to be about 78” x 40” and 48 pounds.
It doesn’t sound like much of a difference, until you are the one that has to move it around. Carrying a standard 60 cell module on a steep sloped roof is awkward, but the 72 cell module, which is likely taller than your biggest crew member, can be a real bear. If it is a two story house, lugging it up to that roof is not going to be fun either.
Another challenge of the size is trying to maximize the wattage that you can fit on a residential roof. With limited roof space, the flexibility of the smaller 60 cell module can be a great advantage. Especially as more states are adopting stricter codes for fire access, using a shorter module often means being able to install a whole second or third row which will result in a larger overall system size.
Transport also needs to be considered. Trucking companies already don’t like our non-standard sized pallets for the 60 cell modules, but the footprint of the 72 cell modules adds a whole new level of complication for shipping companies. Also, a 78” long pallet can’t be turned inside a freight truck. The first time you have to balance one longways on a forklift you will understand that the physics are not working in your favor.
But this doesn’t mean that 72 cell modules don’t have their place. These larger modules can decrease labor costs on large commercial systems where there is plenty of roof space and a crane can bring the pallets up for you. They are also popular on ground mounted systems. In both of these cases, the 72 cell module can be installed just as fast as the 60 cell module which means more watts installed with the same amount of labor hours.
So bigger being better depends on your circumstances and all factors should be considered when choosing whether to go with a 60 cell or 72 cell module.