Study in 2011 saw year-round water flow for Amaila

A study done in 2011 of hydrology studies over the years concluded that the Amaila Falls Hydropower Project would have year-round river flow to enable it to produce at least 884 gigawatt hours annually even in periods of low rain and hence low river flow volumes.

However, it said that there would be losses in the order of 7 percent from the total rated generation capacity of the facility, said to be 165 megawatts. The US$858 million project has been shelved by developer Sithe Global and as a result, two potential financiers, China Develop-ment Bank (CDB) and the Inter-American Development Bank (IDB), have ceased work they have been doing in preparation for making their portion of the financing available.

Government last week released the report entitled Amaila Falls Hydropower Project Hydrology Review dated June 2011 and done by Halcrow Group Limited of the UK following this newspaper’s publishing of an article on August 26, 2013 which, referencing another study, said that river flow might be a problem for all-year power generation. It is unclear why it was that this report, not unlike the one that preceded it, was not released in a more timely fashion, given the concerns of the Opposition over the non-disclosure of key documents regarding the project.

“We have estimated the energy yield based on the baseline flows of 41 years and obtained that: an average annual energy yield at the generator terminals is estimated as 1141 GWh, with the minimum and maximum yields being 884 GWh and 1343 GWh, respectively,” the report said.

It said that an average annual energy output from the power plant taking account of machine outages and transformer loss is estimated as 1090GWh yearly. Further, it noted that an average annual power available at the distribution points – Linden and Georgetown – is estimated from 1017 GWh to 1047 GWh taking account of transmission line losses.

“For a dry year (90% dependable annual flows), the annual energy yield is estimated at 994.8 GWh when the monthly average flows are used for simulation. However, when daily flows are used for simulation the annual energy yield estimate reduces to 952.8 GWh,” it said.

It noted that other factors, such as the turbine-generator efficiency, rate for scheduled and unscheduled outages of the plant, are considered to be reasonable. “The power loss rates are considered low for such a long distance transmission line,” the study said.

The study said that the long term distribution of sediment in the reservoir is unclear meaning that this may affect power generation if coarse sediment settles in the upper backwater region which may be part of the live storage of the reservoir.

“Sedimentation is not expected to affect power generation in the early life of the turbines; however for a long term if sedimentation reaches the deeper region of the dam, bed level at the dam is anticipated to reach draw off intake level and therefore may affect draw off requirements to the powerhouse,” the study found.

 

Losses

“We have estimated the power output from the turbine-generator unit by taking account of the hydraulic head losses using typical turbine and generator efficiencies; our estimate indicates that at the rated design flow of 50.2 m3/s the unit achieves approximately 153.5 MW output while the reservoir is at full supply level, which is about 7% lower than the quoted value of 165MW,” it said.

The purpose of the Hydrology Review “is to assess the capability of the Project to produce the energy that will be purchased by Guyana Power and Light (GPL) under the long-term Power Purchase Agreement (PPA).”

It was meant to be a key element of the overall analysis and design of the Project “as hydrology will have a direct impact on the financial obligations of GPL.”

The main tasks of the Halcrow study were to review the existing results, and any relevant studies, advise on the quality of the data obtained and methodology applied, and provide input to the Inter-American Development Bank regarding any modifications to the Project’s generation/ dispatching figures that would serve as an input for the Project’s pro-forma financial projections.

Halcrow was tasked also with providing an opinion indicating if the currently available Information or models for climate change could be incorporated into the hydrology scenarios and “provide a preliminary opinion on how the potential changes in rainfall patterns expected due to climate change could affect, in the long term, the project’s hydrological projections and the level of confidence with which such an impact can be assessed.”

The Halcrow authors acknowledged that the data that they had to work with was not necessarily itself complete and accurate. The Executive Summary of the Halcrow report said thus, “It should be noted that the analysis and assessments presented in this report are subject to the accuracy and completeness of the background information and data provided.”

An independent analyst who examined the Halcrow report said that the study gave the impression that there was very little field work done and it has been mostly a desk study of previous studies. The person who spoke to Stabroek News on the condition of anonymity said that the report has tucked away in it many of the concerns which had been brought up by other observers. He said also that some of the information looked at in the Halcrow review might be too dated to be of value, since conditions would have changed over those years.

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