Underwater power generation

1. A method for providing auxiliary electrical power to an underwater well installation, the installation being linked to a surface location via an umbilical cable, to supplement any electrical power received at the installation from the umbilical cable, the method comprising:

providing a chemical flow battery at the installation;

providing a chemical supply channel for supplying the flow battery with operating chemicals for the purpose of electrical power generation, the chemical supply channel comprising a flowline housed within the umbilical cable;

supplying the operating chemicals to the flow battery via the chemical supply channel; and

providing an electrical power output line for transferring electrical power generated by the flow battery to the installation, wherein the electrical power generation is caused by a chemical reaction of the operating chemicals.

2. A method according to claim 1 , wherein the chemical supply channel comprises a spare chemical or hydraulic fluid flowline.

3. A method according to claim 1 , further comprising mixing the flow battery operating chemicals with a further chemical at the surface location, wherein the chemical supply channel comprises a chemical injection line in the umbilical cable for transporting the further chemical to the installation.

4. A method according to claim 1 , comprising providing a chemical resource at a location remote from the installation.

5. A method according to claim 4 , wherein the chemical resource is provided at the surface location.

6. A method according to claim 1 , further comprising providing a chemical removal channel for removing spent chemicals from the flow battery subsequent to electrical power generation.

7. A method according to claim 6 , wherein the chemical removal channel comprises a flowline which carries the spent chemicals to a surface location.

8. A method according to claim 7 , wherein the flowline is located within the umbilical cable.

9. A method according to claim 8 , wherein the installation is for producing a production fluid, and the flowline transports the production fluid to the surface in use.

10. A method according to claim 1 , comprising converting the DC output of the flow battery to AC, and phasing this current with electrical power received at the installation from the umbilical cable.

11. An underwater well installation, the installation being linked to a surface location via an umbilical cable, the installation being provided with means to supplement any electrical power received at the installation from the umbilical cable, said means comprising:

a chemical flow battery at the installation;

a chemical supply channel for supplying the flow battery with operating chemicals for the purpose of electrical power generation, the chemical supply channel comprising a flowline housed within the umbilical cable;

means for supplying the operating chemicals to the flow battery via the chemical supply channel; and

an electrical power output line for transferring electrical power generated by the flow battery to the installation, wherein the electrical power generation is caused by a chemical reaction of the operating chemicals.

12. An installation according to claim 11 , wherein the chemical supply channel comprises a spare chemical or hydraulic fluid flowline.

13. An installation according to claim 11 , wherein the umbilical cable is connected to an umbilical termination assembly, the umbilical termination assembly being linked to the flow battery by a chemical flow line for the supply of operating chemicals thereto.