A team of researchers from Robert Gordon University in Aberdeen have recommended that the Maldives seriously consider marine current energy as part of meeting its ambition to become carbon neutral by 2020.
The team visited the country in April and met with assorted energy stakeholders, interviewed divers, fishermen and boat captains, and hired a vessel to conduct current measurements.
According to the pre-feasibility report, “marine current energy in particular might provide a potential resource to add to the national energy mix.”
“Marine renewable energy has the distinct advantage of being very scalable, being to small mini-grid applications in communities, as well as larger scale installations for areas of high demand such as Male’. Furthermore, it is the only renewable energy that can have no visual footprint, an important consideration in a tourist dependent country such as Maldives,” the report stated.
The researchers noted that existing investigations of renewable resources, such as solar, wind and biogas, each had particular limitations in the Maldivian context.
“Solar shows the best resource potential of these but its implementations is restricted due to space restraints,” the report noted, while “despite numerous proposed wind projects, NREL (the National Renewable Energy Laboratory) indicates that the Maldives wind resource is ‘poor to marginal’.”
Biogas was more promising, the scientists said, particularly plans for a 3-5 megawatt waste energy plant near Male’, but this represented only a fraction of the current 38.76 megawatt installed capacity of STELCO’s existing fossil fuel setup.
The team investigated the potential for marine current and ocean thermal generation.
Marine current
The team modelled a number of channels to determine the power resource that would be technologically and economically exploitable, and found a significant variation depending on which direction the current was flowing.
The difference in total extractable resource was significant: when the current flowed east to west, the extractable power of all channels modelled was 106 MW, but only 28 MW when the flow was reversed.
The largest resources for east to west currents were found at Dhiffushi Kandu (31 MW), Gaadhoo Koa (25 MW), Thilafushi (14 MW), Emboodhoo Kandu (13 MW) and Gulhi Falhu (12 MW), while few of the channels provided much resource when the flow was reversed: just Kandu (15 MW) and East of Vadoo Island (9 MW). Gulhi Falhu and Emboodhoo Kandu, as marine protected areas, were unable to be developed as marine energy installations due to existing legislation, the report found.
“The reduced power available when the current flow in the west to east direction is partly due to the lower mean current speed in this direction, and partly due to the position of North Ari Atoll to the west of Male’ and South Male’. When the flow is from west to east it is slowed by North Ari Atoll before it reaches the Male’ and South Male’ Atolls,” the researchers noted.
They did however note that the monsoonal current model used for the calculations “did not take into account the effect of the other factors that affect the overall current speeds, such as tidal currents.”
The researchers suggested that the most applicable technologies for developing marine renewable resources in these channels would be “those designed for slower current speeds and shallow water sites”, but advised the government to remain “technology agnostic” until a detailed study of flows was completed over a longer period, “ideally a year”.
“Partnering too early with specific technology providers could result in a scenario whereby the Government of the Maldives is obliged to use technology that is not suited to the particular channel and current characteristics, and will not deliver maximum energy at the most economical cost,” the researchers warned.
Ocean thermal
The researchers also examined the potential for ocean thermal in the Maldives, a technology that converts thermal energy into kinetic energy by taking in deep cold water at depths of up to 1000 metres.
However a small 40 megawatt commercial facility requires a large displacement of water and can have a large environmental impact on the immediate area, due to noise and changing water temperatures, the scientists noted.
Moreover, the technology is exceedingly expensive with even a small 5-10 megawatt demonstration plant costing upwards of US$200 million.
“[Ocean thermal] was conceived over a century ago, yet there are still no operational commercial plants, and only one operational pilot plant (Hawaii). This is despite numerous feasibility studies and investigations by both countries and private enterprises, none of which have resulted in an actual installation,” the researchers noted.
“One of the main reasons that commercial OTEC power plants have not been built to date is their unfavourable economics in comparison to fossil fuel. Thus the challenge is to finance a capital intensive technology that does not have an operational record. The plant would need to be >50MW to be cost competitive in terms of $/kWh,” the report said, suggesting that this would price out the Maldives.
A small-scale water cooling system working on the same principle was trialed at Soneva Fushi resort, the report noted, whereby the cold water was to be used for air-conditioning and thus reduce the resort’s electricity consumption by 25 percent.
“Cold water (11-12°C) was pumped through a pipe from the 300m shelf approximately 3 km southeast of Soneva Fushi Resort. From the pump station, it was distributed to guest rooms and offices via an insulated underground piping system,” the report explained.
“Non-corrosive fan units in each room enabled the heat exchange between water and the surrounding air to bring the temperature down to comfortable levels. Unfortunately the project had some design flaws that resulted in it not delivering on cooling requirements as anticipated and it was thus decommissioned by Soneva in 2009.
“One of the problems encountered was that the pipeline wasn’t weighted down sufficiently, as with all the weights on it was still floating. Because the anticipated depth wasn’t reached, the water that was pumped in from the deep water intake pipe was not cold enough,” the researchers noted.
The report observed that while the current installed fossil fuel plants met Maldivian needs, “a very ambitious transition towards a renewable energy portfolio is needed to deliver on the ambition to become carbon neutral in 2020.”
“The Maldives is blessed with abundant renewable energy resources, but the ongoing energy programs in the Maldives until recently have had a substantial focus on electricity generation through diesel-run generators,” the researchers observed, “and little attention was given to promoting renewable energy production in remote islands to meet their energy needs.”
“There was a glut of proposed renewable energy projects announced subsequent to the declaration of the Maldives’ carbon neutral ambitions. Numerous MOU’s were signed, however, the absence of progress in these projects is causing concern,” they concluded.
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