An innovative, collaborative effort combines six rivers, six intakes, one steel tank and a powerhouse to create the 9.7 MW Choloma hydroelectric project in Guatemala.
By Jane Kreller, Rudolf Jacobs and Rodrigo Tormo
This article describes the design and construction process for a new and innovative 9.7 MW hydroelectric project that was constructed in 2010 and 2011 and came on line for the first time in October, 2011. The project, called “Choloma” is located in northwestern Guatemala in the Santa Cruz Mountains. The private developer, Hidroelectrica Choloma, SA is an experienced hydropower developer in Guatemala, with two other projects already constructed and on-line.
|The upper reservoir storage tank (20,000 cubic m, 200 ft diameter, 35 ft tall) for the 9.7 MW Choloma project is reported by the manufacturer, TIPIC SA, to be the largest steel water tank in Central America.|
Near the village of Senahu, on the slopes of the Santa Cruz Mountains in northeastern Guatemala, experienced hydropower developer Hidroelectrica Choloma SA (a subsidiary of Secacao Group) saw potential. Nearly 500 m of drop provided ample head for a hydro project, but the main water source in the area, the Choloma River, could only sustain a hydroelectric project of 3 to 4 MW, not enough to make the project economically feasible.
Several other small very rivers flowed down the slopes in the 6 kilometers west of the Choloma. The solution? Six intakes were constructed on six streams and all flow was collected in a 6 km long HDPE pipeline (24¨to 48¨diameter) running across the slope generally following an existing serpentine gravel road. The combined flow allowed an economic project 9.7 MW in size to be constructed. The original intention was to collect all the water at the end of this collector pipe at a small reservoir and dam, which would serve as the headworks for the project. Hydraulics dictated the dam crest be at elevation 647.0 meters, so there was only one suitable location to construct it on the Choloma River. Geotechnical explorations showed poor subsurface conditions for a dam, no bedrock and lots of clay, sand and subsurface water. The solution? On a nearby ridge, a site was cleared, bedrock blasted away, and a large steel water tank was constructed with its top elevation at 647.0 The tank is 200 feet in diameter and 35 feet tall and was the largest steel water tank in Central America at that time. With 20,000 cubic meters of live storage, this tank will allow the project to generate at nearly full load every day of the year during the 4 hour daily peak demand hours in Guatemala, even in the dry season. In the dry season the plant will only operate from 6pm to 10 pm daily, and then shut down for the tank to refill. During the rainy season the plant will operate at full load all day.
|The powerhouse contains a single generator two-jet Pelton turbine unit rated at 9.7 MW.|
In 2010, Rudolf Jacobs, vice president of Hidroelectrica Choloma, contracted with Jack Snyder and Don Jarrett with EES Consulting (EESC) of Seattle, Washington, USA, to develop a design to harness the water flowing through the several small rivers within about 6 km west of the proposed project site. Together, they developed a design to build six small dams with water intakes on six streams. The water would be transported in a 6-km-long high-density polyethylene (HDPE) pipeline purchased from ISCO Industries of Louisville, KY (with a diameter of 24 in to 48 in), which was routed across slopes near an existing road. With the additional flow, a 9.7 MW project could be built – providing enough clean energy to be economic and to help serve the Guatemala grid even during periods of peak demand.
The original intention was to collect all the water at a headworks consisting of a small reservoir and dam with enough capacity to store one full day of water needed to run the project at full load (a day reservoir). This would allow a 4 hour daily peaking operation of the plant, even in the dry season. Hydraulics of the intake and collector pipe locations dictated the dam crest to be at 647 m elevation, so there was only one suitable location to construct it on the Choloma River. Unfortunately, geotechnical explorations at the site performed by Rodio-Swissboring of Guatemala showed poor subsurface conditions for a dam – no bedrock and lots of clay and subsurface water. Not to be deterred, Hidroelectrica Choloma and its team came up with a solution to store water for the powerhouse.
On a nearby ridge, a site was cleared, bedrock blasted away, and a large steel water tank, manufactured by TIPIC SA of Guatemala, was constructed. At two hundred feet in diameter and 35 ft tall, it was the largest steel water tank in Central America according to TIPIC. “I think that using a large tank to collect water from six dams on six creeks, and using the tank as the project reservoir, were the innovations that made this project a success,” Snyder said.
A 2,950-m-long, 42-in-diameter steel pipeline manufactured by Ameron International carries water from the tank to the powerhouse 460 m below, down steep slopes. A cable crane was used to haul steel pipe up the steep slopes for installation. The general contractor, CONASA, constructed the penstocks and pipeline as well as powerhouse, which contains a single two-jet pelton turbine-generator unit manufactured by Gilkes, Inc. rated at 9.7 MW. The plant started up and produced first power on Oct. 5, 2011.
Snyder and Jarrett helped develop the conceptual design, prepare equipment specifications, assist with bidding the equipment supply contract, and manage that contract. EESC also performed dam and intake design, powerhouse foundation design, pipeline specifications and layouts and powerhouse foundation design.
Snyder and Jarrett joined McMillen in early 2011, and the company assumed management of the equipment contract; assisted with coordination of the various project team members; developed facility testing and commissioning procedures; attended and conducted testing of the pipelines, intakes, tank and generating equipment; assisted in operator training and led the plant commissioning and startup team.
|Six intakes were constructed on six separate streams, allowing for all flow to be collected in a 6 km-long high-density polyethylene collector pipe before being transported to the steel storage tank.|
A team effort
The McMillen team and Hidroelectrica Choloma worked closely to bring together a team of local, regional and international experts to turn the project from the initial 3 MW conceptual facility into a fully functional 9.7 MW plant and to get it completed on time, over a tight 14 month construction schedule and within the $25 million budget. Financing was obtained from a combination of developer equity and loans from Guatemalan commercial banks. A list of the participants is as follows:
– Hidroelectrica Choloma SA; Guatemala City; Owner
– McMillen LLC; USA; Design and startup
– EES Consulting, Inc.; USA; Design engineering
– CCASA, SA; Guatemala City; Civil engineering
– CONASA; Guatemala; General contractor
– Gilkes, Inc.; Kendal, England; Turbine equipment
– Hyundai-Ideal Electric Co.; USA; Generator equipment
– Alstom Power; USA; Electrical and controls
– ISCO Industries; USA; HDPE pipe supply
– Ameron International; USA; Steel pipe supply
– DISMME; Guatemala; Electrical installation
– TIPIC, SA; Guatemala City; Supply of steel tank
– RODIO-Swissboring Guatemala, SA; Guatemala City; Geotechnical
– EMS Provectos e Inspecciones SA; Guatemala; Inspection/X-ray tests
– D2FC; France; Main shutoff valve
At the onset of this project, the roadblocks seemed to indicate the Choloma Project wasn’t viable. It was too small, wouldn’t be economically feasible and the location was too unstable. With tenacity and creativity, Hidroelectrica Choloma and the McMillen team made this project a success. Industry providers from around the world combined with local Guatemalan talent to get the job done. For example, the powerhouse, roads and parts of the diversion dam structures were designed by a Guatemalan engineer, the steel pipe was supplied Ameron International from southern California, the turbine manufacturer , Gilkes Inc., was from England. The generator and controls were provided by suppliers in the USA, Hyundai-Ideal Electric (generator) and Alstom Power (controls).
The development group included 15 team members; the team structure included three key consulting engineering teams: McMillen (Idaho, USA), EESC (Washington), and CCASA (Guatemala). All had to coordinate designs and worked closely together by reviewing each other’s work, providing critiques and suggestions for improvement.
The ability of team members on all sides to speak at least some Spanish and some English contributed to the success of this approach. The team agreed to use USA design standards as many of the typical U.S. design standards – such as ASME pressure vessel and welding code, American Concrete Institute (ACI) concrete standards, and American Water Works Association (AWWA) water systems standards – were fully in use and accepted throughout Guatemala. This facilitated design coordination.
Small, but not simple
For a small hydroelectric project, Choloma has considerable complexity. Material was ordered and delivered from the U.S., France and England. Delivery of heavy components like the generator and turbine case, as well as hundreds of loads of pipe, had to be carefully coordinated to deal with small wooden bridges and narrow and steep gravel roads. About 180 truckloads of pipe had to be shipped from the Atlantic port to the site. Large items such as the turbine case (40,000 lb.), generator rotor (50,000 lb.) and generator stator (65,000 lb.) had to be transported with extreme care.
Flows from six streams have to be monitored, collected and transported to the collection tank. The tank level has to be carefully monitored and controlled to prevent overtopping but to ensure that it is full and ready for peak operation. Although it is situated in the jungles of rural Guatemala, the power plant is fully controlled by computerized programmable logic controllers (PLCs). A fiber optic-based LAN connects plant controls and protective relays to the PLC inside the powerhouse. Power and fiber optic cables run to the tank 3 km away to ensure critical tank levels and fill rates can be tracked from the powerhouse.
Choloma’s Rudolf Jacobs said; “The project also required high volumes of earth movement (over 100,000 cubic meters), and pipeline trenches required removing the foot of slopes over long stretches along a 6 km-long system. Slope stability was an area in which much care and investment was expended to avoid problems during operations, and this effort has paid off as slopes and earth-movement sites have been very stable, with only minor issues during the rainfall seasons (May through November) of 2012 and 2013.”
Satellite links provide connectivity to the internet so remote monitoring and troubleshooting of the plant can be accomplished from Guatemala City or even from the U.S. if, for example, control system program changes are needed from Alstom Power.
An eye on the environment
As a hydroelectric project, Choloma uses a renewable resource and does not contribute to global warming, nor does it produce any carbon dioxide during generation of electricity. But the design went above and beyond to protect the rural location and minimize impacts.
For example, the six small dams and intakes each create a small pond upstream from the diversion less than an acre in size, with three of the six having ponds less than 0.25 acre is size, so the footprint of affected lands is minimal.
Environmental impact studies were completed by the project developer to help identify and minimize impacts to fish and wildlife. The dams are all located upstream of a series of waterfalls on each stream that prevents the use of these streams by fish, so no fishery mitigation was necessary.
And finally, the Choloma project was designed and constructed to meet international “green power” standards and has applied to the United Nations under their Clean Development Mechanism (CDM) for a green certification, which will allow the sale of the green attributes of the project.
The benefits continue
The completed Choloma project is operating today and the ripple effects are still felt.
TIPIC reports that the innovative concepts developed for Choloma, such as use of a steel tank headworks structure, are being investigated by other developers in Central America for adoption in their projects. Although steel storage tanks have not been used very often as hydropower reservoirs, they provide the ability to better meet electrical system daily peak load demands at less cost than conventional dams and reservoirs, when they fit the circumstances. The use of tanks for high head, low flow projects are being studied and could become a viable alternative based upon operating experiences gained at Choloma.
HDPE pipelines had not been widely used in Guatemala before this project. The USA-based HDPE pipe manufacturer, ISCO Industries, reports strong interest from other hydropower developers in Guatemala and nearby Costa Rica for the use of HDPE due to its flexibility, ease of field welding, and material cost.
Construction work created much-needed employment for more than 400 local workers for a year, injecting needed cash into the severely depressed economy.
The completed project not only helps the local residents; it also provides reduction in greenhouse gas production by offsetting burning of coal and petroleum products, two major sources of electricity in Guatemala. The Choloma project is a strong example of how engineering innovation, cooperation and coordination can be used to create a unique project that economically provides real benefits to the local residents and the global environment.
“The Choloma Hydroelectric Plant has been running well since it became operational in the third quarter of 2011.” Jacobs said. “The Choloma Project is a successful venture for the Hidroelectrica Choloma/Secacao Group and a project that has evoked the interest and of the many visitors that toured the site. The energy produced is critically important to help the people of this region address serious issues with environmental quality, economic development, jobs, education and even quality of life.”
Jane Kreller is marketing coordinator at McMillen LLC, Rudolf Jacobs is vice president of Hidroelectrica Choloma SA, and Rodrigo Tormo is general manager of Hidroelectrica Choloma SA.
Hydro Growth in Latin America
Guatemala is not the only Latin American country seeing exciting growth in the hydropower market. With power consumption in the region predicted to double by 2025, the demand for additional energy sources is resulting in an increase in investment throughout the region, as shown below in some key examples:
– Argentina: 52 approved projects with an investment of $21,356,000,000
– Bolivia: 10 approved projects with an investment of $6,784,000,000
– Brazil: 457 approved projects with an investment of $89,848,000,000
– Chile: 68 approved projects with an investment of $10,656,000,000
– Columbia: 37 approved projects with an investment of $15,485,000,000
– Ecuador: 73 approved projects with an investment of $25,620,000,000
– Paraguay: 5 approved projects with an investment of $580,000,000
– Peru: 105 approved projects with an investment of $39,832,000,000
– Uruguay: 2 approved projects with an investment of $5,000,000
– Venezuela: 18 approved projects with an investment of $11,434,000,000
Resource: Industrial Info Resources
By Bethany Duarte.
Bethany Duarte is associate editor of HRW-Hydro Review Worldwide.