My understanding is the SST are used to evaporate the working fluid to generated the electricity. Alternatively the the warm waters are flush evaporated as in OC OTEC. The relatively colder deep waters just recover the working fluid. So where does the thermal gradient factor in.
I did my master's thesis on OTEC. I created a thermal model of the system and used it to estimate the performance over a range of conditions reported for various sites. The model is an Organic Rankine Cycle. If you do a Google search for "Organic Rankine Cycle" or "ORC" you will find articles. These systems are also used in geothermal plants. I have worked with several of this type geothermal systems (ORC) that are now working. You can make calculations using an Excel spreadsheet. I have attached a paper that I presented and can send you more information if you are interested.
There is much information as this is a large topic. After you read the paper I attached, create a plan for what you hope to accomplish. This should include specific tasks and objectives. I can then see if there is anything I can do to help you achieve any of those goals. I will not do anything that you could do, as this is your education and you need to do those things so that you can master the concepts and prepare for a career.