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An EPRI White Paper

DC Power Production, Delivery and Utilization

A PV-DC case study, distribution warehouse, Rochester, NewYork

Nextek Power Systems recently designed and installed their high- efficiency renewable energy lighting system at a distribution cen- ter in Rochester, New York.This facility is equipped with a lighting system that utilizes DC fluorescent ballasts, roof-integrated solar panels, occupancy sensors, and daylight sensors for high efficiency. The building, including the innovative lighting system, was designed by William McDonough and Partners of Charlottesville,Virginia.

The facility has 6,600 sq ft of office space and 33,000 sq ft of warehouse. The warehouse is equipped with skylights and 21 kW of solar panels bonded to the roof material (SR2001 amorphous panels by Solar In- tegrated Technologies).A canopy in the office area is equipped with 2.1 kW of Sharp panels.

The power from the solar panels is distributed in three ways:

  • 2.2 kW is dedicated to office lighting.

  • 11.5 kW powers warehouse lights.

  • 11.5 kW not needed by the lighting system is inverted to AC and used elsewhere in the building or sold back to the utility.

The entire system consists of 35 NPS-1000 Power Gateways.These devices take power from the solar panels and send it directly to the lighting without significant losses.Additional power, when needed at night or on cloudy days, is taken from the grid.

In the office,6 NPS-1000’s power 198T-8,four-foot fluorescent lamps, illuminating most areas at 1.1 watts per square foot. Each of the fix- tures is equipped with one high-efficiency DC ballast for every two lamps. Most of the fixtures are controlled by a combination of manual switches, daylight sensors, and occupancy sensors in 13 zones.

Figure 14. Sharp panels—canopy

In the warehouse area 29 NPS-1000’s power 158 6-lamp T-8 fix- tures.These fixtures have low (2 lamps on), medium (4 lamps on), and high (all 6 lamps on) settings so that they can be dimmed by 3 daylight sensors and 30 occupancy sensors located throughout the area. The goal of the control architecture is to maintain a lighting level of 0.74 watts per square foot, using daylight when available, whenever the area is occupied.

The logic of the lighting system is designed for optimum efficiency. Sources of light and power are prioritized such that:

  • 1.

    Daylight from the skylights is used.

  • 2.

    If daylighting is not sufficient and the area is occupied, power from the solar panels is added.

  • 3.

    If daylight and solar power are not enough, additional power required for lighting is taken from the grid.

Figure 15. Office and warehouse lighting systems use DC power

June 2006

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