For each Midnight Shard, you can gain 300⋅L experience; L being the character's level. Players above level 200 will receive the same amount of experience as a level 200. A character can trade up to 40 shards for experience per year. However, an arbitrary amount of shards can be traded for gold.
Note that the formula is not ∑Ni=300Li (for N shards). If you level up by using one shard, you will not gain 300 more experience per shard for the next level. Thus, it is slightly better to trade them incrementally, than all at once. Check the table for better results.
In resume, you get 300 points * Level you have, example:
You are lvl 150 so you will get 300*150 = 45000 exp for each shard.
And if you are 200 or more level the amount will be always the same , for the maximum shards you can give you will get 2.4kk exp.