By NEIL HARTNELL

Tribune Business Editor

nhartnell@tribunemedia.net

The Inter-American Development Bank (IDB) has warned many Abaco residents will be without power "for a year or longer", as it called for a "unified" grid to eliminate the four voltages used pre-Dorian.

The multilateral lender, in documents accompanying the $170m project to expand renewable energy penetration and rebuild critical infrastructure post-Dorian, revealed that the pre-storm reliability of Abaco's power grid had been compromised because Bahamas Power & Light (BPL) used no fewer than four voltage transmission frequencies.

These ranged from 4.16 kilovolts (kV) to 13.2 kV, and the IDB reports urged that BPL's transmission and distribution (T&D) infrastructure be rebuilt to condense these into one uniform frequency island-wide. Besides improving grid reliability, it argued that such a strategy would also improve the availability of spare parts as BPL would no longer have to source equipment for four different frequencies.

"A key activity is the voltage unification across the island," documents seen by Tribune Business argue. "Rebuilding most of the Abaco distribution grid is an opportunity to unify distribution voltages, from presently four levels in service (4.16 kV, 7.2 kV, 12.5 kV and 13.2 kV) to a single level. This will significantly improve uniformity and availability of spare parts, while improving grid reliability.

"Operating Abaco's grid with multiple voltage levels causes issues with spare parts and system maintainability, and it is recommended to unify distribution levels as part of reconstruction efforts. The likely single voltage level that may be adapted is 12.7 kV, which is becoming industry standard in the Caribbean, but since this particular voltage level is not presently used on Abaco, consideration can also be given to 13.2 kV as that voltage represent a significant percentage of Abaco's distribution grid."

The IDB paper added, though, that even non-damaged equipment such as transformers and distribution lines will have to be replaced if this objective is to be achieved and Abaco's energy infrastructure made more resilient, thereby increasing restoration costs.

"There are some challenges associated with this effort," it admitted. "Grid reconfiguration will require replacement of the equipment which is not necessarily damaged beyond repair. Specifically, many distribution transformers on Abaco, either pole of pad mounted, would have to be replaced or adapted for the selected single distribution voltage.

"As for distribution lines, those which operate at 4.16 kV and 7.2 kV will have to be uprated even if they did not sustain any damage during the storm. Also, a significant upfront engineering effort is required to redesign existing systems to operate at the common voltage, which may impact the effort to rebuild the lines and restore power supply as soon as possible."

The IDB was also somewhat pessimistic on the timeline for electricity services restoration, warning: "Due to severe destruction and limited rebuilding resources, many Abaco residents will be without power for a year or longer. It is therefore important to improve grid resilience along with rebuilding the grid to minimise impact in case of future high intensity storms.

"More than 75 percent of all dwellings on the island were somehow affected by Dorian, and approximately 57 percent of the houses were severely damaged. Most of the electricity transmission and distribution infrastructure in those areas needs to be rebuilt, and BPL estimates that a total of about 1,000 transmission or distribution poles and more than 90 percent of the transformers in these areas were destroyed or damaged.

"However, the bulk of the power generation capacity on the island based in Wilson City is still available and in good condition as the plant was not directly hit by Hurricane Dorian." The IDB's pessimism stands in contrast to that of Dr Donovan Moxey, BPL's chairman, who told the recent Bahamas Business Outlook conference that "all of Abaco should have power back up by BPL at the end of March".

Still, the IDB study said one of the two 20-kilometre transmission lines running from the Wilson City power plant to Marsh Harbour had been completely destroyed in Dorian, with another suffering 70 percent damage. While designed to take 69 volts, they had been operating at just 34.5 kV.

The northern transmission line, which branches off to Treasure Cay, also requires a "complete rebuild", while the IDB said BPL had informed it that "at least six of the 13 substations and switching stations were damaged beyond repair and will require total replacement".

As for the submarine cable network serving Abaco's cays from the mainland, the report added: "As per BPL Abaco office staff, all submarine cables have been tested and 80 percent of them are found to be damaged.

"No further information was provided on the extent of the damage, but it is reasonable to assume that not all submarine cables will have to be replaced as some are likely repairable. Most of the transition structures on shores, which transition from overhead lines to submarine cables and include necessary switching and protection equipment have also been damaged beyond repair."

Describing the rebuilding of Abaco's electricity infrastructure from Wilson City to Crown Haven as requiring "a massive level of effort, and specific logistics and planning", the IDB said BPL's own estimates pegged the cost at $83m.

The majority of this sum, some $80.285m, is required for the transmission and distribution (T&D) system. Of this, substation repairs and replacement is estimated at $34.56m, while restoring the transmission line from the Wilson City power plant to Crown Haven is pegged at $26.274.

The IDB report also warned that developing a more hurricane-resilient energy infrastructure could be sacrificed by the need to rapidly restore power so that businesses and homeowners can proceed with their reconstruction and recovery efforts.

"For Abaco, significant additional challenges arise in the planning and co-ordination of grid improvements in conjunction with present ongoing work by BPL. Efforts to fast track restoration of power supply to residential and commercial customers is a top priority at this point in time," it said.

"Presently ongoing efforts are concentrated on rebuilding the grid in mostly a 'like for like' approach as it minimises engineering and procurement efforts, and increases the speed in which they can rebuild.

"Introducing new approaches to distribution will add resiliency to the system but will require front-end design and system integration and constructability efforts, and additional time for procurement and implementation."

To harden Abaco's energy grid, the IDB report recommended burying critical overhead lines underground to reduce their vulnerability in major storms, while also providing redundant capabilities to ensure power is not distributed from a single source.

"Almost all potential improvements listed above will depend on BPL's plans, methodology, progress and pace of ongoing reconstruction, as well as a decision to unify or not distribution voltage on the island," the report warned.