Have a friend that is on an electric co-op where peak $/kWh is 4x the off-peak rate. Peak hours are 6-10 am in the winter and 12-6 pm in the summer.
He has relocated an older system from his previous house to his new one; circuits were separated out to sub-panel that is connected to the inverter AC output. The reinstallation is very professional. Two Trace SW4024 in series (04/96) 120/240 Vac Grid connected to AC1 of each inverter 575 Ah battery bank Two C40s with digital displays, ~ 4.5 kW STC array total Trimetric The goal is to not use any utility energy during peak times, unless the low battery voltage setting is reached, and in general to run as an off-grid system, minimizing charge time from the grid during off-peak hours as well. The assumption (I know it's a tough one, but I'm coming in after the transition) is that the PV array should at least be able to provide the bulk of the load; using the grid to charge the batteries to ensure they are regularly filled and to maximize their life expectancy. The customer is also managing loads actively. It's been a few years, but I used to work on these all the time; however it was usually off-grid with a genset, or fixing poorly maintained Y2K systems which were always in float. I'm attempting to use the energy management mode. Inverter settings: Clocks: Time is accurate Grid AC1 amps AC: 60 Max charge amps AC: 10 (each inverter) Grid usage: FLT Set start charge time: 23:00 Start bulk time: 23:10 Set end charge time: 05:00 Set float volts DC: 25.4 Bulk volts DC: 28.8 Absorb time: 1.5 hours Low battery cut-out: 22 Low battery cut-in: 25.4 Okay, programmed the system, both inverters are inverting, AC1 is blinking green, looks good. Then a well pump kicks on, registers 70 A DC on the Trimetric. This causes inverter 1 to go into bulk charging and pass through about 10 additional amps from the grid to the load (inverter 2 continued to inverter about 10 amps for the load). Inverter 1 soon cycled into float, then went back to what invertering (amber light) and green blinking AC1 (which is what I want it to be at). Had to leave, both the customer and I had other obligations. He took a picture of the inverter sat 11:15 pm, and they were in bulk, battery voltage rising...exactly as planned. But then in the next set of pictures, taken at 7 am, after the end of the charge time, they were in float, not inverting, even though, based on the Trimetric readings at 11 (64%, 85A charging), and the fact that charging would have been active all night, they were not in anyway at a low voltage condition (Trimetric readings am readings were 85%, trickle charge, 25.6 V). Something seems amiss. Any suggestions or insight? Thanks! Brian Mehalic NABCEP Certified Solar PV Installation Professional™ R031508-59 IREC ISPQ Certified Affiliated Instructor/PV US-0132 PV Curriculum Developer and Instructor Solar Energy International http://www.solarenergy.org
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