Its easiest to compare modules on a dollars per watt basis. (Divide the module's price by its power rating) Just because one module is cheaper than another means nothing without comparing the price per watt. Also mono crystalline is worth 10% more per watt, because it will make more power throughout the day and throughout the year than the same wattage module in polycrystalline.

Wiring Modules

Solar modules are wired in different combinations to get the voltage & current needed. They are wired in series to increase voltage; up to 30 modules can be strung together for voltages as high as 600 v (the highest voltage most modules are rated for). The voltages of each module are added together. (see Wiring Diagrams for series and parallel wiring)

Modules are also paralleled to increase current. The voltage stays the same, but their currents are added. Some 12 volt systems can have dozens of modules in parallel for currents close to 100 amps. To avoid too much current in a single module that can overheat and melt connectors, the modules are wired into subarrays. Each subarray carries as much current as the modules are designed for including a safety factor. This factor includes both a 25% safety factor and a 25% factor in case the modules produce more than their rated power in special sunlight conditions (see edge of cloud effect in glossary).

Example:
If a module's series fuse rating is 20 amps, then you divide that by the combined safety factor of 1.56. so you could safely wire 12.8 amps of modules together in parallel. If each module's short circuit current is 4.2 amps, then you could parallel 3 modules. Regardless, we don't recommend ever wiring more than 4 modules in parallel in one sub-array, and some inspectors don't allow any parallel wiring within a sub-array.