Charge rate questions?

verdigo
verdigo Solar Expert Posts: 428 ✭✭
Currently I have four 300 watt panels and four 280 watt panels on a Classic 150 for a total of 2320 watts (rated). I was playing with my sell feature today and I seen as high as 40 amps (very briefly) at just shy of 2100 watts on the classic's display. My battery bank is at 464 ah so I need 46 amps to meet the 10% charge rate.

Using BB's standard calculations I see in many of his posts for sizing arrays I come up with a need for four more panels in the 300 watt range to meet 10% charge rate. It seems as though one more string of two 300 watt panels at 7.8 amps would get me to the 46 amps.

Was that 40 amps that the Classic indicated something I should take as gospel or should I stick to the math and go ahead and go for two more strings of two 300 watt panels? This would put me at 3520 watts (rated).

Then again BB's math may be above my head, or the Classic's display could be off?

Dennis

Comments

  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Charge rate questions?
    verdigo wrote: »
    My battery bank is at 464 ah so I need 46 amps to meet the 10% charge rate.

    Yes, but 10% is a rule of thumb, not a required number. What's important is that you make enough power to satisfy your loads and your battery.

    As far as BB's calculations, he usually derates the solar panels to about 77% of their capacity. That is also a rule of thumb that may not apply to every system. Your 40 amps today is 90% of your panels rating, but was transient... you won't see that all day every day.

    Bottom line: Are your batteries getting charged all the way? If so, you do not need more panels.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Charge rate questions?

    All displays on all charge controllers are off somewhat.

    40 Amps - at what Voltage? If you divide 2100 Watts by 40 Amps you get 52.5 Volts.
    A 2320 Watt array putting out 2100 Watts is 90% efficiency; don't count on that continuously. I have seen my display show greater than 100% efficiency, but on average it's 82% (high elevation advantage).
    For selling back to the grid you will have that average efficiency, not any occasional peak (which may be due to edge-of-cloud event for example).

    By my standard calculations the minimum size for that battery bank is:
    46 Amps * 48 Volts / 0.77 efficiency = 2868 Watts. Another 600 Watts will do you no harm.
  • verdigo
    verdigo Solar Expert Posts: 428 ✭✭
    Re: Charge rate questions?
    All displays on all charge controllers are off somewhat.

    40 Amps - at what Voltage? If you divide 2100 Watts by 40 Amps you get 52.5 Volts.

    Yes 52.5 (bouncing around a bit) but yes thats pretty close.

    By my standard calculations the minimum size for that battery bank is:
    46 Amps * 48 Volts / 0.77 efficiency = 2868 Watts. Another 600 Watts will do you no harm.

    Thats good news to me. I can tie that 600 watts into the lower rack of my array without a lot of modification or extra expense to the mount.

    Another issue I noticed about the same time was that the inverter was only selling 1600 watts according to the display on the Mate. That was more than I had seen it do so far, but will the inverter not sell up to it's rated output? I did check the AC line voltage at 129 volts, so it was putting out a little more than 12 amps on the AC side. Is there something I am missing in settings that is limiting the output, or does it need the AC grid input voltage to be lower in order to be all it can be? Without the inverter selling I checked the AC line voltage at 123 volts. My house is the only one on this particular transformer.

    Thanks for all the help

    Dennis
  • verdigo
    verdigo Solar Expert Posts: 428 ✭✭
    Re: Charge rate questions?
    vtmaps wrote: »
    Yes, but 10% is a rule of thumb, not a required number. What's important is that you make enough power to satisfy your loads and your battery.

    As far as BB's calculations, he usually derates the solar panels to about 77% of their capacity. That is also a rule of thumb that may not apply to every system. Your 40 amps today is 90% of your panels rating, but was transient... you won't see that all day every day.

    Bottom line: Are your batteries getting charged all the way? If so, you do not need more panels.

    --vtMaps

    The system is being set up primarily as a backup, and also as a bit of a hobby as I am here pretty much all of the time I am not working. I care for my Father who is on oxygen 24/7, who needs AC and a dehumidifier as well. The house is otherwise all electric with one big window shaker air conditioner using a couple of fans for air distribution to the rest of the small house.

    Heat is currently a couple of 240 volt forced air resistant wall heaters. There use to be one in each room, but I have removed all but two. I replaced the refrigerator a couple of years ago when I connected it to my little 2500 watt generator, and it would killed the engine.

    I am the first residential solar customer that I know of in my little town and maybe the county that will be grid tied. So far the inspector doesn't really know what to do with me, so I haven't been able to see what the system will support because it is not connected to the house yet. I am waiting on the inspector to approve or modify my plan.

    I realize I have a lot of conservation work to do yet, but I gave up with the "kill a watt" pretty soon into the project. I would like to be able squeeze as much as possible out of the system without murdering the battery bank. Then again if I do kill the bank I may go up in capacity which will once again require more panels. This just keeps going round and round.

    Thanks

    Dennis
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Charge rate questions?
    verdigo wrote: »
    Another issue I noticed about the same time was that the inverter was only selling 1600 watts according to the display on the Mate. That was more than I had seen it do so far, but will the inverter not sell up to it's rated output? I did check the AC line voltage at 129 volts, so it was putting out a little more than 12 amps on the AC side. Is there something I am missing in settings that is limiting the output, or does it need the AC grid input voltage to be lower in order to be all it can be? Without the inverter selling I checked the AC line voltage at 123 volts. My house is the only one on this particular transformer.

    Thanks for all the help

    Dennis

    It won't sell its rated output (3600 Watts) if it can't produce it: you can't get 3.6 kW from a 2.3 kW array. Pulling power from batteries means the Voltage sags below the SELL level. To actually sell full capacity you'd need an array around 4.6 kW. At that point you'd be better off contemplating adding the 2kW 'extra' to a standard GTI if you don't need the back-up capacity; it would be more efficient.
  • verdigo
    verdigo Solar Expert Posts: 428 ✭✭
    Re: Charge rate questions?
    It won't sell its rated output (3600 Watts) if it can't produce it: you can't get 3.6 kW from a 2.3 kW array. Pulling power from batteries means the Voltage sags below the SELL level. To actually sell full capacity you'd need an array around 4.6 kW. At that point you'd be better off contemplating adding the 2kW 'extra' to a standard GTI if you don't need the back-up capacity; it would be more efficient.

    This is something new to think about. Even on the Outback website there is very little operational information about their equipment. It more or less states that you can sell power to the grid without any specific info on how much.

    Using the information you just shared I will likely increase the array to 3500 watts, (four more panels) and leave it at that. If I ever need to go further I would consider buying another inverter and stacking for split phase 240. This would give me some redundancy.

    Then again new emerging technology is changing pretty fast and that in itself can change your plans. If I had known 6 months ago when I bought this inverter I could have got a 4 KW Radian for $2700.00 I would have given one of those a hard look. Who knows someone might come out with a 20 gigawatt cold fusion generator next week that runs on septic tank sludge for a hundred dollars, and make solar power a mute point.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Charge rate questions?
    verdigo wrote: »
    Who knows someone might come out with a 20 gigawatt cold fusion generator next week that runs on septic tank sludge for a hundred dollars, and make solar power a mute point.

    My solar power is already very quiet (as in mute). I doubt that the 20 gigawatt generator will be as quiet, but that's a moot point because it isn't going to happen.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Charge rate questions?

    English lesson:

    The word "moot", contrary to popular usage, actually means debatable; not non-debatable.
    In other words exactly the opposite of how it is continually (mis-)used. ;)
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Charge rate questions?
    The word "moot", contrary to popular usage, actually means debatable; not non-debatable.
    In other words exactly the opposite of how it is continually (mis-)used. ;)

    The Meaning of the Word "Moot" is Moot.
    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Charge rate questions?

    Do you know how its meaning got twisted?

    If an issue came up that was moot it would be shelved for later discussion. People picked up on the shelving part, but ignored the notion it would be tabled later for further debate. (And isn't it fun how we use furniture metaphors? Documents on the table are currently active, documents on the shelf are not.)

    These days the Internet misinformation super highway encourages incorrect spelling, grammar, and punctuation to the point where it is documented as accurate (such as the continual use of 'impact' as a synonym for 'affect' and/or 'effect') until it becomes accepted. What is worse is that even venerable reference sources re-write their content rather than fight the uphill battle of correcting misuse.

    When you live in the linguistically schizophrenic land of Canada it's even more fun. :p
  • verdigo
    verdigo Solar Expert Posts: 428 ✭✭
    Re: Charge rate questions?

    Brain successfully updated on the spelling and true meaning of "moot". This http://www.extremetech.com/extreme/171660-1-megawatt-cold-fusion-power-plant-now-available-yours-for-just-1-5-million is interesting though.
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Charge rate questions?

    Ah , yes Mr Rossi and the E-Cat, we haven't heard from him in several years, since he seemed to go into hiding....
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada