Quality is based on the differential temperature between source and what it will be after being used. The ocean is not that warm so it has a small differential temp between pre-use and after use. This makes it difficult to transfer the energy....bigger radiators, heat exchangers etc, compared to what is needed with high temperature fluid. Quantity: Well, there is a lot of ocean out there so there is a lot of usable heat energy even if it is low quality heat.
