海水盐差能（英文：Osmotic power或salinity gradient power）或盐差能（Ocean Salinity Energy）是指海水和淡水之间或两种含盐浓度不同的海水之间的化学电位差能。在海水和江河水相交汇处容易产生咸淡水。据估算，地球上存在着26亿千瓦可利用的盐差能，其能量甚至比温差能还要大。淡水丰富地区的盐湖和地下盐矿也可以利用盐差能。

在实验室环境下，该技术已经被证实。荷兰的逆电析法（RED）和挪威的压力迟滞渗透膜法（PRO）正将此能源用作商业用途。但膜的昂贵成本是一个障碍。而现在研发一个新较为便宜的膜，利用电改性的聚乙烯塑料，它适合于潜在的商业用途。其他的方法已经提出，目前正在开发。主要有双电层电容器技术和蒸汽压力差方法。

Osmotic power, salinity gradient power or blue energy is the energy available from the difference in the salt concentration between seawater and river water. Two practical methods for this are reverse electrodialysis (RED) and pressure retarded osmosis (PRO). Both processes rely on osmosis with ion specific membranes. The key waste product is brackish water. This byproduct is the result of natural forces that are being harnessed: the flow of fresh water into seas that are made up of salt water.