Optimizing Schneider AC Support

Dan001Dan001 Registered Users Posts: 3
I recently added additional capacity to my battery bank moving it from 200ah to 400ah.  My setup consists of a Schneider 4048, ~2.5kw of solar tied to a Schneider 80-600 charge controller and a carbon-AGM based battery bank.  My system was built with two key objectives: 1. provide back-up power as we have power outages from time to time and 2. reduce my utility bill utilizing the excess solar to provide a payback for the system.  I have been running the system in Enhanced AC Grid Support mode with good results.  On the 200ah battery pack, the system would discharge the batteries each night to 60% SOC and then I had a charge block set to wait until 9am each morning to give the solar a chance to charge the batteries and then utilize the solar for AC support once the bulk charge phase was complete (usually 3 hours each morning).  Generally, we have the power outages in the late evening so I attempted to ensure that the batteries had at least a 90% SOC around 9PM as they discharged in AC Support.  Under this configuration, the system always exited AC support as the batteries hit 60% SOC early each morning.  I upgraded the batteries to ensure that under full load support the pack would last at least 6 hours in a power outage as the 200ah pack did not perform quite as well as I expected under this scenario.  When I upgraded the batteries to 400ah I started to see that the majority of days the system would invert on AC Support and make it to 9am when the solar came on line.  I noticed that the 4048 continued to invert splitting the power between the loads and the batteries for charging where before it would pass the AC through to the loads and use 100% of the solar to charge.  It seems to me that I would want to exit AC Support each morning as the best way to maximize my two objectives using the solar to charge the batteries as much and fast as possible and then using the excess to support the loads to reduce my power bill, but I do not see a way to do this.  I am still a relitative novice in the solar arena and looking for advice on how best to configure the 4048 and 80-600 to best perform against my objectives with the new batteries.  Any and all feedback would be most appreciated.  Thanks, Dan.. 

Comments

  • EstragonEstragon Registered Users Posts: 4,451 ✭✭✭✭✭
    I can't help with the Schneider specific stuff, but I'm wondering about the general concept of "enhanced AC grid support" given your objectives.  It seems to me you'd want to preferentially use pv power to the extent available, but otherwise use grid to the extent needed, with batteries providing any deficit only if grid is unavailable.  In other words, batteries would cycle only in the event of an outage, and be otherwise kept full.

    As described, your settings seem more appropriate to a situation where a generator is powering loads, and batteries are used to provide power to loads as needed to the extent they exceed generator capacity, or to avoid grid peak load and/or time-of-use charges.  I may well be misunderstanding the way the mode works though.

    Unless your grid power has onerous peak charges, it seems to me the long run cost of cycling batteries daily may exceed any grid savings.  Generally speaking, battery based power is considerably more expensive than grid over time.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • Dan001Dan001 Registered Users Posts: 3
    Estragon - Thanks for the response.  Actually, I started with thoughts much like yours but came to a different conclusion (maybe erroneously) given my circumstances based on the following:

    1. My neighbor spent $12K on a natural gas generator to solve the power outage issue.  That generator just sits and gets old and does nothing to pay him back while it is not performing its primary mission and while it is performing its primary mission it costs him to use.  I spent a fraction of that and had the pleasure of learning; still occurring :) about solar and how to install these systems and getting the chance to meet fascinating people like you.  If nothing else, this will be a very fun learning experience.
    2. The various solar rebates cut the cost of entry for a solar/battery solution considerably.
    3. In my situation, grid-tie was not an option as it did not meet my objectives otherwise, I would have gone that direction.
    4. During the day, my PV produces many multiples of what my house actually consumes despite that I have a very small 8 pannel PV array (I have worked hard over the years to do everything I can to reduce my consumption).  If I do not store this excess PV energy, the benefit from it’s usage is lost.  I sized the PV in alignment with what it would take to charge the batteries based on my understanding of the incentive requirements versus the PV needed for average load during PV production.
    5. Looking at my batteries discharge / cycle life specifications I figured that it would not be overly detrimental to cycle them (to some extent) to maximize energy capture and usage versus longer battery life and excess PV loss.  Part of this calculation is baed on expectation that future battery cost and efficiency will be better.   
    6. My objective is not to actually #save# money rather offset the expenditure of having a back-up solution to the greatest extent possible.   

    One issue that I encountered late in the installation is that the Enhanced AC Support mode is disengaged on SOC or battery bank cutout voltage.  Originally, I had planned to set SOC cutout value higher to say 75% to help maximize battery cycle life against the benefit of capturing the excess PV.  As it turns out the maximum SOC value that you can set is 60% (I have not been able to figure out why this is the case).  Given this limitation I figured that I would just leave it at the maximum value and accept the fewer cycles.  My calculations indicate that I should get at least 5-6 years out of these batteries cycling them 60% everyday.  Given the incentives, I should #save# more than the batteries cost (and almost all of the system cost) during the 5 years.  All on paper though so the proof will be in the experience.  If nothing, I will have fun learning along the way.
  • EstragonEstragon Registered Users Posts: 4,451 ✭✭✭✭✭
    Having fun and learning is always a Good Thing  :)  I've enjoyed it.

    What some people do to capture pv potential is use an "opportunity load" (typically water heating) running on otherwise unused power.  Off-grid, we also try to arrange bigger loads (eg pumps, air conditioning, running big tools, etc) for when there's extra solar potential.  

    Batteries will eventually die of old age, even just floating for their whole lives, so getting some cycles out of them isn't such a terrible idea.  Seems to me it comes down to how often and for how long your outages typically last.  As a rule of thumb, we try not to discharge lower than 50% or so, and spend most of the bank's life at >75% or so in daily use to maximize cycle life.  In a standby application, cycle life would be less of an issue, so going to (eg)  20-30% SOC a few times/yr for a day or so and otherwise floating might give you more years of use than daily cycling.

    Given the main objective is covering outages, I'd load test the bank periodically (eg annually) by putting a known load (eg heater) on the bank for a defined period of time, then check resting voltage (no charging or loads for several hours) to ensure voltage agrees with expected SOC.

    Your neighbour with the NG generator may find the NG piped pressure won't run his generator for the duration of an outage (compressor stations take power to run, which depending on the scope and length of the outage may or may not be available). 
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • mcgivormcgivor Solar Expert Posts: 3,274 ✭✭✭✭✭
    edited July 2019 #5
    What AC support voltage setting are you using ? If too low the support will continue until the  battery voltage drops to the set value. 
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • Dan001Dan001 Registered Users Posts: 3
    Hi Mcgivor - I have the AC Support voltage set at 53.0v.  I arrived at this setting as the battery specs indicate that ~13.0v is the 100% SOC value.  They do say that this value should be measured after a 12 hour rest period.  I took this and added 1/4v per monobloc as I was not sure how much to add to account for what battery voltage would be after immediately after a charge.  Am I thinking about this correctly?  I have the cutout voltage (Recharge Volts) set to 50v. 

    I have a AC Support SOC initiate set to 100% and SOC cutoff set to 60% (max value allowed).

    To be honest, I still am not 100% certain from just a read of the owner's guide on how AC Support Volts and Recharge Volts interact with the SOC from the battery monitor when operating in Enhanced AC Support.  Thanks for the guidance!  

    Dan..  
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