Info

long cloudy periods, using PV modules as the only power source would not provide the year-round reliability that the farm needed. Since a large battery bank exceeded the budget, the crew decided to take advantage of the cabin's preexisting grid connection and devised a plan that allows the farm to manually switch the power source between the small PV system and the grid. An 115 Ah Millennium battery was used, providing up to three nights of lighting at 50% depth of discharge if the grid goes down.

Installing the System

Finding a suitable location for the array among the dense tropical flora and fauna proved challenging. The crew settled on a sunny spot not far from the cabins and bathroom buildings—one of the few clearings on the developed portion of the farm. At the equator, the sun is very high in the sky and shading is less likely during midday, so there was less need for a detailed solar site analysis.

In the classroom, Carol Weis of SEI explained to the locals how the power from the PV array goes through the controller to the battery, and then through an inverter to a manual transfer switch. She also illustrated how the grid power comes into the other side of the transfer switch. Following the discussion, the students—including the farm's maintenance workers, who participated in the course and installation— split into three groups and got to work.

The power center, with each component labeled in Spanish and English.

The power center, with each component labeled in Spanish and English.

LEDs, Lumens & Performance

According to the U.S. Department of Energy, incandescent lamps typically produce 12 to 15 lumens per watt of electric power. Compact fluorescent lamps (CFLs) produce at least 50 lumens per watt, while currently available high-brightness LEDs can produce about 30 to 35 lumens per watt.

In task-lighting applications, LEDs may be able to provide enough light on the task, even though the total lumens are less than comparable incandescent or fluorescent sources. This is because LEDs emit light in a less diffuse pattern than conventional light sources. In contrast, standard incandescent bulbs and fluorescent lamps emit light in all directions, and much of the light output is absorbed inside the fixture or escapes in an unintended direction.

Mounting the modules. The two 50 W modules were mounted on Direct Power & Water feet on a 12-foot bamboo platform, which was high enough to minimize shading from huge umbrella-shaped saman and palm trees.

Wiring the power center. The incoming PV array got wired first into a donated MidNite Solar DC disconnect box, where the PV-to-charge-controller circuit breaker is housed. The PV wiring from the DC disconnect was run to the 10 A Steca controller. The charge controller to battery wiring was also completed through its own circuit breaker in the DC disconnect box. Wiring was then run from the battery to a 600 W inverter via a third breaker in the DC disconnect box.

On the AC side, the transfer switch was connected to the output of the inverter, which allows for the manual transfer between grid power and the PV system. Finally, wiring between the transfer switch and the AC loads was completed via an AC disconnect box.

New wiring to the cabins. Working in the developing world often means working with pre-existing wiring and equipment that may not be ideal or up to standards. The wiring on the farm was typical of rural Latin America: a jumble of indoor-rated wires running from tree to tree— pretty unsightly and unsafe. Nicola and Dario wanted the wires routed underground in conduit for safety and aesthetic reasons.

Working with PV

The finished system—which took less than two days to complete—allows the farm to manage their electricity needs by switching between sources. When the sun is shining, energy can be sourced from the PV array. During cloudy weather, or other times, like when the battery charge gets low, the farm can switch over to the grid until the battery is recharged by the PV modules. Likewise, if the grid goes down, the farm can easily switch over to the PV system and still have electricity for lighting. On the rare occasions when the cabins are not being used, the inverter can be turned off and the loads switched over to the grid to avoid unnecessary drains on the battery from the inverter, which uses 3.6 W on standby.

Nicola and two technicians from the farm took part in the class, and Sergio, the main technician, also received additional training in system maintenance and troubleshooting. Taking into account the remote location, the crew left behind extra equipment for unexpected problems—a controller, fuses, and replacement LED lamps.

After the success of the PV lighting system, Nicola and Dario are eager to power the whole farm with renewable energy, including the water pumps for filling the cisterns. Next year, SEI plans to return to the farm to install more PV systems for the cabins, and to build a pedal-powered water pump.

Access

Laurie Guevara-Stone ([email protected]) is the international program manager at Solar Energy International, a nonprofit RE educational organization. Laurie, her Ecuadorian husband Anibal, and their son Camilo try to spend as much time as possible near the equator.

Solar Energy International • www.solarenergy.org Rio Muchacho Organic Farm • www.riomuchacho.com

The truck is free—time to go home.

International Renewable Resources Institute • www.irrimexico.org System Components:

C. Crane Company • www.ccrane.com • LEDs

Kyocera • www.kyocerasolar.com • Modules

MidNite Solar • www.midnitesolar.com • Combiner box

Steca • www.stecasolar.com • Controller

Techman Electronics • www.techman-usa.com • Inverter n

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