GN Condenser(s) is a energy capacitor(s) that allow a mobile units to reserve and exploit excess GN particles when needed. Mobile units that have high particle requirements can't efficiently utilize the full power of their mobile units without risk draining power from various or all systems. To compensate, the condensers are used to help maintain consistent power to systems and can be used to charge a high particle consuming function. Most GN Mobile Suits have smaller GN Condenser units built all over its body in to maintain the power consistancy, and these are even more important for high volume particle suits like Gadessa and Virtue who rely on large stored particle amounts for some of their high particle functions. Basically GN Condensers are tanks where you can keep GN particles to use them later.
Large volume GN Condensers are also used in order to act as a power source for GN Units that are not equipped with a GN Drive such as Celestial Being's Ptolemaios, 0 Raiser and GN Archer in order for them to function for a certain limited time before needing recharging from units who do possesses GN Drives.