Hidroeléctrica Choloma, a hydropower developer, held rights to a potential small project on the slopes of the Santa Cruz Mountains in Guatemala. But the site came with a few problems that needed to be solved before the project could move forward.
The site had plenty of head, but the main stream of the nearby Coloma River had enough flow to accommodate a project able to produce only three or four megawatts.
McMillen, serving as project manager, and other team members decided to take advantage of several smaller streams flowing down the slopes about six kilometers west of the river. They came up with a design for a small dam with water intakes on each of the six streams, with all of the flow then collected in a six-kilometer-long collector pipeline. The combined flow was large enough that it allowed the project to expand to 9.7 megawatts.
The project team thought the pipe could send all of the collected water to a small reservoir and dam that would serve as the project’s headworks. Hydraulics of the intake and collector pipe locations dictated that the reservoir and dam be built at an elevation of 647 meters. But there was only one suitable location on the Choloma River that hit that mark. And the conditions there were less than ideal: no bedrock and lots of clay, sand and subsurface water.
The project team decided to look in another direction. On a nearby ridge, workers cleared a site, blasted away bedrock and constructed a large, steel water tank at an elevation of 647 meters. A 42-inch, 2,950-meter-long steel pipe was installed to carry the water to a powerhouse 460 meters below the tank.
The project was designed and constructed to meet international standards for green power. The project owner has applied for green certification to be able to sell output as sustainable energy.