Nextek Power Systems recently installed a solar photovoltaic system at a large retail store in El Cajon, CA. The system directly converts sunlight into electricity and consequently emits no climate change gases or pollutants that can contribute to environmental damage. Based on the roof installation of the modules, the anticipated net ac energy savings to Target is approximately 104,200 Watts. The annual energy production is estimated to be 181,926 kWh/year. The Photovoltaic system features 828 BP Solar Model BP2150S PV modules, each generating 150W at Standard Test Conditions, and were produced by BP Solar. 804 of these modules are connected to a 100 kW Xantrex inverter (Model PV-100208), and the remaining 24 panels are Directly Coupled to 56 fluorescent lighting fixtures via four Nextek Power Systems NPS-1000 power modules. The lighting fixtures have been equipped with Nextek high efficiency DC ballasts.
Many of these lights are controlled by occupancy sensors. The Nextek Power System is well-suited to occupancy sensor because both the occupancy sensor power, and switch is handled through one 'telephone' wire between the ballast and the sensor. No other wiring is needed.
The PV modules for this system each have the following electrical Characteristics:
|Open circuit voltage||42.8 V direct current (DC)|
|Operating voltage||34 V DC|
|Short circuit current||4.75 A DC|
|Operating current||4.45 A DC|
|Maximum power||150 W|
|Maximum system voltage||600 V DC|
The PV system is divided into five sub-arrays physically occupying on space on the roof. Sub-Array 1 is connected to the PV inverter. Sub-Arrays 2 - 5, are each connected to a NPS-1000 Power Module. The array is attached to concrete forms, placed over roof supports. Concrete forms are glued to the roofing material to accommodate local earthquake protection codes.
Sub-Array 1 is connected to an inverter
120.6 kW DC. A 100 kW Xantrex inverter (Model PV-100208) is connected to a daylight sensor that shuts the unit down when there is no sunlight. This prevents the inverter from using any power at night.
|Open circuit voltage||514 V DC (600 V after CEC correct. factor)|
|Operating voltage||408 V DC|
|Short circuit current||318.25 A DC|
|Operating current||298.15 A DC|
|Maximum power||~120,600 W DC|
Sub-Arrays 2 through 5
900W DC each (Total 3600 W DC) connected to NPS-1000 Power Systems.
|Open circuit voltage||85.6 V DC (600 V after CEC correct. factor)|
|Operating voltage||54 V DC|
|Short circuit current||14.25 A DC|
|Operating current||13.35 A DC|
|Maximum power||~900 W DC|
Each Nextek NPS-1000 is monitored by the Nextek MCM monitoring board. The MCM's report AC and DC power to the Nextek MEC control module, which reports to the local building management system and to our live data website.
To see live data from this system, contact Nextek Power Systems