I don’t know how many crystals you earn a day but even with low income from arena you can afford one or a few 50 refresh in yellow energy.
Moreover, farming gear with a 50 refresh is better gem-wise than buying by gems. This is true for gear items like cuffs and pistols (i did the math).
Of course depending on which state of the game you are sitting in you also need tons of energy to farm important characters in hard nodes. So overall doing the 50 refreshes in yellow energy is close to a ‘must do’. I strongly suggest you to spend all the gems you get daily into the three 50 yellow energy refreshes (once you earn more gems it is not reasonable to do the 100 refresh since it is too expensive, unless under exceptional circumstances like a panic farm).
Red and blue energy refreshes are too expensive unless you have a nice gem income from arena. But mod refreshes are extremely important in the long run. Mods are the way to go to increase your income in the long term: meta teams go away, mods are forever. But in order to make this investment you already need a bigger gem income from arena (Around top 200 i think, taking into account that you get gems from gw and daily activities.)
