Marine renewable energies offer alternatives to fossil and nuclear energies. Ocean thermal energy conversion (OTEC) is one of these alternatives, which also provides a range of additional products - food, air conditioning, water, pharmacheuticals included - hence the term deep ocean water applications (DOWA). It is also, unusually, a base-load system. Applications are in both developed and developing nations, but with particular application to island locations. Economics have significantly improved, due to advances in both design and materials, and OTEC/DOWA has many environmental advantages. Small (up to 1 MW) experimental units have been designed and built, and performance has been measured. These results confirm the growing practicality of OTEC/DOWA, and the next requirement is design, construction and operation of a representative scale demonstrator, typically 5 – 10 MW, to evaluate the feasibility of full scale production systems.