CERL PROJECT PROVES DIRECT CURRENT TECHNOLOGY CAN CHARGE ELECTRIC VEHICLES AND SUPPLY EXCESS SOLAR TO THE AC GRID

OVERVIEW

A Nextek Power Systems test has shown that a solar powered DC infrastructure can charge DC electric vehicles. A second test showed that excess solar when vehicles are not being charged can be used to power other DC loads, and also be returned to the AC power grid. The tests were authorized by the U.S. Army’s Construction Engineering Research Laboratory (CERL) in Champaign, IL.

The test was conducted in two phases. The first was designed to determine the ability of a solar powered DC system to power two DC charging stations. The second added loads such as overhead 380 VDC lighting, along with 24 VDC loads for lighting and office applications. Any remaining solar power was designated to be inverted back to the AC grid.


SOLUTION

Nextek’s Direct Coupling® technology utilizes DC-compatible equipment that eliminates the need for most conversions/inversions, regulating the solar array and the power to the load, thereby reducing power loss in the system, which translates to energy and equipment cost savings.

The Nextek solution included a 6 KW solar array with a module-level Maximum Power Point Tracker (MPPT) in conjunction with two 75 KW rectifiers in an N+1 configuration, producing 380 VDC from 3-phase 480 VAC. This powered a 380 VDC and a 240 VDC EV charging stations. Power Server Modules (PSM) were used in 24 VDC office load situations to distribute and monitor power usage. 380 VDC ballasts were used to power overhead lighting. A 10 KW inverter was used to feed excess power from the solar array back to a 208 3-phase AC panel.

An Amatis data collection reporting system generated data and continues to export it to an Excel file every 5 minutes at the following points: DC lighting loads, 75 KW rectifiers, the vehicle charging stations, and solar.


RESULTS

The tests proved definitively that solar can provide adequate power for main bus requirements, while also feeding electric car charging stations, or returning excess electrical power to the AC grid.