Electrical and Fiber Optic Connections for the Marine Renewables Industry
By Dave Pye, Renewable Energy Business Development Manager, SEACON
SEACON will be exhibiting at All Energy in Aberdeen, Scotland on the 22nd-23rd May where SEACON’s Dave Pye has written an article that will be appearing in Enterprising Energy Magazine which will be issued at the show.
The development of any number of Wave and Tidal generators is progressing in many countries worldwide and some of these are nearing the stage where the installation of the first arrays can be considered a possibility. However, in my opinion, insufficient effort is being concentrated on how to get the power generated ashore.
In order to make the arrays commercial it is important that the individual generators can be installed and retrieved for maintenance or repair with the minimum of effort. This has two main implications on the design of the generator and its base structure or mooring (a) a design that can utilise smaller vessels for installation and recovery and (b) a reliable method of connecting and disconnecting the electrical and fiber optic cabling. It is the second of these that I will be concentrating on here.
“There are many connectors available at present in the Oil & Gas sector that we can use”
This statement was heard early on in the life of the Marine Renewables industry and is about as incorrect as it is possible to be for two main reasons :
• The Oil & Gas industry is fully developed and is able to afford the high costs of the most advanced connectors and cable termination devices. Marine Renewables cannot stand these costs
• The environment in which the connectors have to survive is far more benign than that to be found in Marine Renewables – the only real problem being water depth which can be overcome by the use of pressure compensation.
The costs of the connectors are mainly driven by the high specification materials used, the need for protection when un-mated in the subsea environment, the level of testing and qualification required and the comparatively low quantities that are ordered at any one time. An order of more than 10 of the same item is rare.
The working environment for the connectors has probably the most effect on the design and cost of any product to be used in Marine Renewables. The relatively shallow water has the following consequences :
• Temperatures can be far higher than in deep water and this promotes both marine growth and corrosion. Corrosion can be resisted by the use of high specification materials such as Titanium or Super Duplex stainless steel but his comes at a cost. Marine growth is more difficult to combat without the use of environmentally unfriendly materials so is by far the most difficult to mitigate. Both corrosion and marine growth MUST be controlled in this environment by material selection or other methods.
With both wave and tidal there is a constant refreshing of the oxygen content in the water which is not present to such an extent in deep water – again this encourages corrosion and marine growth.
• In relatively shallow waters there is continuous pressure cycling due to wave and tide variations. This will have some effect on the sealing of the connectors.
• The power generated by the devices is also not constant. With Wave power the power level is constantly varying and with Tidal it goes from zero to maximum twice per day. I am not sure if this has any serious effect on the connectors but it must be considered as a potential problem.
Marine Growth and Corrosion
So , overall what we can see is that this industry sector requires products that will work as well (and as long) in a far harsher environment as those used in the Oil & Gas sector but at a far lower cost, possibly something like 50% less. To achieve this the connector industry needs both quantity and, most importantly, standardisation.
Quantities at present are of necessity very low as most requirements are for prototypes. It is possible in these applications to utilise connectors with lower grade materials as the deployment times are much shorter. However, serious marine growth and corrosion has still been seen even after periods of weeks. Even with the first array installations quantities will still only be quite small so it will be difficult to reduce costs significantly.
The factor that will serve to bring the greatest reduction in cost will be standardisation. By this I do not mean putting constraints on how the connectors function or are designed but by reducing the number of variations in things such as current, voltage, numbers of contacts, cable types, test requirements etc. The Oil & Gas industry has introduced a number of specifications which have allowed connectors to be procured from a number of manufacturers with confidence that they will perform to specification. These industry-standard specifications have been developed both by the major users of the products and the Oil Companies themselves but there have also been Joint Industry Projects (JIP) with the same objective.
For the connector industry to be able to produce what is needed for Marine Renewables I strongly recommend that something similar is set up – a JIP involving connector manufacturers, generator developers and installation contractor would be very welcome.