It has recently been proposed that OTEC could be used to produce ammonia, a chemical currently manufactured from natural gas at a total energy consumption of about 2.5% of the U.S. natural gas consumption. Since the manufacture of ammonia could be accomplished anywhere, the plant could be located in a favorable location, for example, off the coast of Brazil, where the difference in temperature between the upper layer of the ocean and the layer at the 600 m depth is approximately 20 K. Using an OTEC power plant of 500 MWe capacity, estimate the number of tons of ammonia that could be produced per year. For a price of $165/ton of ammonia, estimate the time required to regain the capital investment in the OTEC production plant and compare your estimate with the claim that the capital could be repaid in 2.5 years.