Phil, Good advice. Assuming 48V and a large system, what would you use as a diversion load and controller in this application? As I understand it, this would be a DC diversion load, such as a wind gennie air heater, that would be gradual, resistive, and noncritical for occasional use in this rare scenario.
Thank you. Allan Sindelar al...@positiveenergysolar.com NABCEP Certified Photovoltaic Installer EE98J Journeyman Electrician Positive Energy, Inc. 3201 Calle Marie Santa Fe, New Mexico 87507 505 424-1112 www.PositiveEnergySolar.com <http://www.positiveenergysolar.com/> Kirpal, The biggest challenge when mixing brands is dealing with the 300 second timeout after grid disturbance (what I call 5 minute PWM) make for less than ideal system operation. There needs to be a better way to regulate power than kicking the string inverter offline. Imagine, say, a 7kW array pumping energy into the home on a beautiful sunny day. The grid goes down, but the battery based inverter (BB) picks up the slack and the grid-tied batteryless inverter (GT) stays online. Home is drawing less power than the array's output (~6kW worth), and the batteries are full. Battery voltage hits the regulation voltage, and the BB inverter (or the voltage controlled switch) activates a relay to open the circuit to the GT inverter, effecting a blackout on that circuit. Suddenly the BB inverter and the battery bank is hit with the full 6kW of load. The batteries are a little undersized because that was the easiest portion of the system to cut costs on, and they're a little old and dried out from years of sitting in an uncooled garage, so their voltage sags under the load. The voltage controlled switch senses the drop, and closes the relay to the GT. However, the GT has to stay offline for another 299 seconds and the battery voltage continues to fall... I've been worried about just this scenario for some time, especially as systems age. Therefore, I've been suggesting to anyone interested in using mixed brands of inverters (or those who don't want to use RS485 communications with SB/SI combos) that they strongly consider installing a diversion load and controller capable of absorbing at least the majority of the expected surplus energy. A blackout relay can be used as a secondary control mechanism. I think that this is going to provide the most reliable operation, ultimately. Phil Undercuffler Director, Battery-based and Off-grid Distribution Sales Group Conergy
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