Who we are>Environmental Commitment>Photovoltaic Plant
The Process

Photovoltaic systems generate electricity when sunlight falls on solid-state silicon-based chips. The sunlight causes an electrical charge in the chips and direct current (DC) electricity flows through the chip. In Platte River's system, the DC power is changed to alternating current (AC) in an inverter. The electric power then flows into the grid system which supplies Platte River's headquarters building.

The Study

The evaluation phase of Platte River's photovoltaic project was conducted from June 1988 to November 1990. During this period, a computer controlled data acquisition system monitored energy production and weather conditions from each of the four systems. A detailed report has been written and is available upon request.

System 'A' uses concentrating collectors which focus the sun's energy on silicon chips. These collectors are mounted on a two-axis tracking mechanism which follows the sun. System 'B' includes flat-plate collectors mounted on the same tracker. System 'C' uses the same type of flat-plate collectors as system 'B', but they are mounted on five single-axis passive trackers. These trackers turn to face the sun as it warms freon in tubes along each edge of the panel. The expanding freon moves from one side of the panel to the other, and gravity pulls the unit around its pedestal.

System 'D' uses the same flat-plate collectors as system 'B', but they are mounted on an adjustable-tilt, south facing surface. The tilt is adjusted twice a year to compensate for the changing elevation of the sun.

Of the four systems monitored, the two top performers remain today. They are:

System 'C', a one-axis passive, flat-plate system; and System 'D', an adjustable-tilt, south facing system.

Both of these systems are simple, rugged and provide the best cost performance of the four systems monitored. The remaining two systems, 'A' and 'B', both required an expensive and complex two-axis tracker that was not well-suited for the windy Colorado front range.

 

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