Ocean currents are a convection system caused by thermal gradients in the oceans and the rotation of the earth. Unlike tides they are almost constant in their direction and their velocity fluctuates only by small amounts according to the seasons of the year.
Ocean currents help to distribute heat around the Earth and circulate massive amounts of warm and cold water. Ocean current flow rates are measured in Sv units where one Sv is equal to 1 million m3/s. Two of the fastest flowing ocean currents are the Florida Current running into the Gulf Stream off the USA eastern seaboard and the Agulhas current off the south and east coast of southern Africa.
Beginning in the Caribbean and ending in the northern North Atlantic, the Florida Current leading into the Gulf Stream is a north flowing ocean current that reaches speeds in excess of 2.0m/s, particularly in the Florida Current region closest to the USA’s eastern seaboard. The Gulf Stream begins upstream of Cape Hatteras (North Carolina), where the Florida Current ceases to follow the continental shelf and heads out into the Atlantic. The transport varies from 30 Sv in the Florida Current to a maximum of 150 Sv at 55°W in the Gulf Stream.
The most appropriate location for deploying Evopods would be the Florida Current off from Miami where it adheres to the continental shelf in no more than 150m water depth. Extracting 1GW of power (8.8TWh/y) from the Florida Current in the region where it flows at 2m/s would require turbines with an accumulated cross section area of about 1.6M m2 (1500 twin turbine Evopod units each rated at 1500kW) or about 10% of the total flow cross section and would take out 3.3% of the energy from the stream.
The Agulhas current flows in a southerly and westerly direction from the Mozambique channel between Africa and Madagascar, down round the south east coast of South Africa past the industrial cities of Durban, East London and Port Elizabeth and eventually interacts with the cold north flowing Benguela current off the southern tip of Africa at Cape Agulhas. The Agulhas current has a volume flow rate of between 70Sv to 85Sv and has a peak speed of about 2m/s in the region off East London.
Extracting 1GW of power (8.8TWh/y) from the Agulhas Current in the region where it flows at 2m/s would require turbines with an accumulated cross section area of about 1.6M m2 or about 4% of the total flow cross section and would take out 1.5% of the energy from the stream. Much more research is required into this area before it can be confirmed that it is appropriate for deployment of tidal current devices. However, Eskom, South Africa’s national utility company has claimed that the Agulhas current has considerable potential for bulk power generation and have commissioned studies to investigate routes to exploitation.