(Continued from Part One.)
As a direct consequence of this low-temperature difference, most of the considerable amount of research that has been done is around the efficiency of every stage in the process, particularly the heat exchangers and the type of secondary stage liquid used to drive the turbines. With such small temperature differences, the efficiency of the heat exchangers are key to controlling the capital costs and minimizing the requirement for high volumes of water flow. To withstand erosion caused by particulate matter in the sea water and corrosion caused by both the sea water and the secondary stage fluid, copper-nickel alloys were thought to be the best option, but the most recent research is suggesting that although aluminum alloys may suffer faster deterioration the higher heat transfer efficiency and lower material cost may make them more economically viable. Likewise, although early experiments were carried out with ammonia as the secondary stage fluid used to drive the turbines, the greater environmental and corrosion problems associated with that product have meant designers are favoring common refrigerants such as R-22, to the extent that plant costs and modeling are now almost exclusively based on R-22.
A 100 MW OTP power plant would be similar in size to a semi-submersible oil drilling platform of about 28,000 tons, and as a result, production facilities currently producing such rigs would be capable of producing an OTP platform. Likewise, objections stating that transmitting the electrical current back to shore would be challenging prove to be within current technology, as up to 250-MW subsea cables are in operation and manufacturers claim a 100 MW transmission line would not present a problem. The only remaining issue appears to be the economics of constructing and maintaining the deepwater cold water feed pipe, but even here the Andersons have developed a design using existing technology that seems economically viable and able to withstand the wave surge of a non-fixed, ocean-based, semi-submersible platform.
Maybe what is required is someone like the Chinese to take this idea up and create something of an Ocean Thermal Power Race, where once we had a Space Race. A little healthy competition would go a long way to spur federal agencies into providing sufficient tax breaks to attract big investors and private money. We are not talking major technological breakthroughs here; this isn’t fusion power or flexible thin-film solar, there is likely nothing here that modern metals manufacturers and engineers could not solve and make viable. We would welcome contributions from both supporters and critics — the technology deserves debate when so many less environmentally attractive options are receiving huge subsidy.