Generator Power Limits on Outback Inverters

richardimorse
richardimorse Registered Users Posts: 98 ✭✭
edited November 2018 in Solar Beginners Corner #1
48Vdc System
After installing three new FRX3048E inverters with a 4.5 kW generator, I noticed there is an issue that the inverters could burn out the generator charging the batteries and operating in passthru with the inverters, the inverter internal transfer switches are protected with 6 * 30 Aac breakers, the protection for the generator is its own internal 20 Aac circuit breaker, three configuration items exist in the mate3s that are relevant.

Per PORT (inverter)
Max AC input (Amps)
Charger On/OFF
Max AC Charge (Amps)

Here the Generator is 20Amps, and the 0.2C continuous max charge rate for the batteries is 46A (daily charge) with the 0.3C once off max charge rate being 69A (fast charge), with the stacking not working if Max AC input is set below 6 Aac

So I guess to prevent the generator tripping (or burning out if the trip switch is faulty) and allow for 0.25C battery charging by the generator, the settings should be:

Inverter 1
Max AC Input = 7 Aac
Charger On/Off = On
Max AC charge = 7 Aac

Inverter 2
Max AC Input = 7 Aac
Charger On/Off = On
Max AC charge = 7 Aac

Inverter 3
Max AC Input = 6 Aac
Charger On/Off = Off
Max AC charge = 0 Aac

(Revision to Inverter 3)
If the batteries are in 5 parallel strings, then the actual max charge rate is multiplied by the number of strings = 46A *5 for C 0.2 hence

Inverter 3 revised
Max AC Input = 6 Aac
Charger On/Off = On
Max AC charge = 6 Aac

Which got me to thinking about the Charge Controllers which have a similar Max Output Current setting, however this time it is from the panels as the power source and defaults to the rating of the charge controller (e.g. 80A for a flexmax 80) and then thinking about panel sizing in general for 12V batteries with low Ah ratings

I am under the controller Voc and Ioc limits and have 4725 Watt Panel on two controllers, soon to be moved to one controller, with 3 panels due for decommissioning leaving Wp = 4,200W (24 * 175Wp panels) on a single 5,000W controller (the FlexMax 80).

Q) 80Adc at 48V is 3,840W output, so with 4,200Wp input on the Flexmax 80 (8 strings) I should be getting near maximum output of 80A
I am due to add new panels using 355Wp/360Wp/365Wp panels for the other controller in this case 12panels (4 strings) was thinking of using the 355 Wp panel version (same panel, lower efficiency, slightly cheaper) to get 4260Wp.  Then I realised that 80A is above the existing 12V battery 0.3C maximum charge rate of 69A

Should I be setting the max current figure for the flexmax 80 down to 69A for one controller or even 40A and 29A for two controllers used in parallel, or is this not required.

I noticed their is a global ac output coordination function with the mate 3s but this requires the "flexmax dc" monitor and setting the flexmax 80 to grid tied mode which causes the float voltage to remain at the absorption voltage, should I be using this for my off grid configuration in case the operator starts the generator when the sun is shining and the flexmax 80's are charging the batteries.

The new batteries (Narada REXC 1200Ah) I am planning to install in January are C 0.2 = 240Adc so won't have an overcharge problem, the new replacement generator will only be able to charge them at 30Aac = 120Adc with three inverters = C 0.1 and the panels at 160Adc with 2 charge controllers C 0.133 for a total of C 2.33 hence no overcharge problem

Comments

  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    edited November 2018 #2
    @richardimorse said,  80Adc at 48V is 3,840W output, so with 4,200Wp input on the Flexmax 80 (8 strings) I should be getting near maximum output of 80A
    I am due to add new panels using 355Wp/360Wp/365Wp panels for the other controller in this case 12panels (4 strings) was thinking of using the 355 Wp panel version (same panel, lower efficiency, slightly cheaper) to get 4260Wp.  Then I realised that 80A is above the existing 12V battery 0.3C maximum charge rate of 69A

    Are the panel output calculations based on ideal conditions 25°C? Real output at a higher temperature say 33°C, given the location, could be significantly less, this along with the controller being able to accept over paneling to some degree, it would be a matter of observation, it is a dynamic calculation which really needs to be observed in real time, the recommended  charging rate of the batteries themselves could be exceed within reason as well. What about loads during charging? Some current could be diverted lowering actual charging, again dynamics, understandably every day is different and there needs to be a ballance point. Perhaps erring on the side of caution is the best approach, only you can make that decision, pushing the envelope is generally not  recommended. Just some thoughts.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • richardimorse
    richardimorse Registered Users Posts: 98 ✭✭
    edited November 2018 #3
    mcgivor said:
    @richardimorse said,  80Adc at 48V is 3,840W output, so with 4,200Wp input on the Flexmax 80 (8 strings) I should be getting near maximum output of 80A
    I am due to add new panels using 355Wp/360Wp/365Wp panels for the other controller in this case 12panels (4 strings) was thinking of using the 355 Wp panel version (same panel, lower efficiency, slightly cheaper) to get 4260Wp.  Then I realised that 80A is above the existing 12V battery 0.3C maximum charge rate of 69A

    Are the panel output calculations based on ideal conditions 25°C? Real output at a higher temperature say 33°C, given the location, could be significantly less, this along with the controller being able to accept over paneling to some degree, it would be a matter of observation, it is a dynamic calculation which really needs to be observed in real time, the recommended  charging rate of the batteries themselves could be exceed within reason as well. What about loads during charging? Some current could be diverted lowering actual charging, again dynamics, understandably every day is different and there needs to be a ballance point. Perhaps erring on the side of caution is the best approach, only you can make that decision, pushing the envelope is generally not  recommended. Just some thoughts.
    I will re-check the combiner boxes to see if one 8 way combiner box without surge arrestors can squeeze 9 panel string isolators into it, keeping the 4725Wp that already exists (bearing in mind that some 8 years life has passed panel efficiency will be lower). Putting in 5 panel strings of new 355Wp panels isn't going to work because it is well over the 5000 maximum, (that leaves an option of going for 15 * 320Wp panels at 4,800Wp to match the power of the old panels as probably the best approach.

    Leaves 9,525Wp on a 9,000W inverting system which is enough given the batteries used are REXC with 19 year life at 30% DoD cycle life or 8.5 year at 50% DoD they also have a very fast charge rate 2-4 hours, choice of generator is a bit more of a problem for single phase due to losses.  The system is not sized for the 2 "dark months" when it rains a lot, they can use the generator in 2-wire AGS support mode during that period.  During the rest of the year they won't have to use the generator at all.

    That said you have to put a stake in the ground somewhere on battery bank size, given the plentiful sunshine, it is more about how much power you are going to need so that the generator doesn't start on its own every day, although there is something to be said for a 1 hour or 2 hour generator run to keep the battery bank size down, I would rather the generator doesn't start more than once per week on a generator exercise run all year round apart from the 2 dark months where it can run for 2 hours per day to support the panels.
  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,731 ✭✭✭✭✭✭
    It takes all kinds and there are many who live in places that do not need a generator if the designer/installer knows to go this way.

    Large resorts or applications with many uninformed users may need a genset. Many of my clients never have used the genset they have.
    I think, that is a good thing!

    To do this days of autonomy need to be designed in. 
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

  • richardimorse
    richardimorse Registered Users Posts: 98 ✭✭
    I guess so but even one dark day autonomy is going to need a big battery bank at 40% DoD

    Lets say peak hours use 4kW*8 hours solar hours use 3 kW*8 hours, Sleeping uses 1kW*8 hours  thats 64Kwh per day at 40% requires a battery bank close to 200 kWh = 2 sets of 2000Ah 2V batteries using 6 parallel strings (3 terminal sets per battery). 

    That is for 1 day autonomy.
  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    There are pros and cons to either choice I guess, one size fits all really doesn't apply. Having a battery bank large enough for 3 days autonomy in a regon of plentiful sun may mean the extra storage goes unused for the most part, slowly aging without being used. Then again a lightly used bank would theoretically last longer than a deeply cycled one, there is the saying if you're not using them you're loosing them, so a contradiction in itself. Personal preference of the end user, wether they want the noise and maintenance associated with a generator or not may be a determining factor, having a generator that never gets used is in itself a waste in itself, yes/no?

    Given the location, along with the nature of business application of @richardimorse, the generator inclusion without battery autonomy makes sense, a generator can get you through times of no battery, better than a battery can get you through times of no generator.



    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,731 ✭✭✭✭✭✭
    It really is the design choice, the budget, and the feasibility. They are the tools that let you accomplish the task.
    The complexity of a generator and its hazards might be enough to tip the scale. 
    Only the designer can make that decision, with guidance from the owner.

    I think it is a bit crazy to not have some breathing room. Better be ready for some last minute plane flights when the genset goes..
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    It really is the design choice, the budget, and the feasibility. They are the tools that let you accomplish the task.
    The complexity of a generator and its hazards might be enough to tip the scale. 
    Only the designer can make that decision, with guidance from the owner.

    I think it is a bit crazy to not have some breathing room. Better be ready for some last minute plane flights when the genset goes..
    When operating a business it would be prudent to have a qualified operator on staff, generators need to be maintained to be reliable, it's been my responsibility in the past to ensure critical generators are ready for their task, monthly run tests, bi annual load tests etcetera, still there is no gaurentee, there is no gaurentee likewise with a battery bank, not attempting to argue one way or the other, both would need someone to keep a finger on the pulse, so to speak.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • richardimorse
    richardimorse Registered Users Posts: 98 ✭✭
    We are going to start them off with 58kWh of Lead Carbon Narada REXC batteries, they currently have about 9kWh usable in their existing battery bank if they are lucky, so having storage will be a great start and a new generator to replace the knackered 4.5kW 

    50% increase in Inverting capacity to from 6kW to 9kW
    Triple the daily discharge cycle of usable storage to 27kWh instead of 9kWh
    Double the panel generation capacity at 9kW instead of 4.5kW
    Triple the Generator COP capacity at 9kW instead of 3kW

    As they get used to their "high power" scenario and load increases we will may need more usable storage
  • richardimorse
    richardimorse Registered Users Posts: 98 ✭✭
    mcgivor said:
    It really is the design choice, the budget, and the feasibility. They are the tools that let you accomplish the task.
    The complexity of a generator and its hazards might be enough to tip the scale. 
    Only the designer can make that decision, with guidance from the owner.

    I think it is a bit crazy to not have some breathing room. Better be ready for some last minute plane flights when the genset goes..
    When operating a business it would be prudent to have a qualified operator on staff, generators need to be maintained to be reliable, it's been my responsibility in the past to ensure critical generators are ready for their task, monthly run tests, bi annual load tests etcetera, still there is no gaurentee, there is no gaurentee likewise with a battery bank, not attempting to argue one way or the other, both would need someone to keep a finger on the pulse, so to speak.

    100% correct on this, the system will blow up sooner or later, having a 10kVA generator and a 5kVA generator as backup leads me to thinking about charging the old battery bank once a week as part of a generator exercise period for the 5kVA generator.

    Here it is interesting to see what maritime users do because their installation is literally - life critical.
    Most have a battery switch which says battery bank 1 or battery bank 2 (emergency).

    Mission critical and autonomy are completely different subjects.
    Autonomy will get used up before anyone calls for help.
  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,731 ✭✭✭✭✭✭
    It is your business so it is hard to really say much more.
    As a business owner, I think education of how the system works and monitoring is one of the most important things you can do for a client.
    If they can't handle it, I would move on.
    Good luck!
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

  • richardimorse
    richardimorse Registered Users Posts: 98 ✭✭
    You have your customers well trained 
  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,731 ✭✭✭✭✭✭
    They all are trained!
    The ones that could not handle it or did not care, I referred them to another business.
    I am lucky enough to be able to do that where I live. 
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net