Recommendations for new system

jcheil
jcheil Solar Expert Posts: 722 ✭✭✭
Was hoping that the two admins here could chime in using their formulas to suggest the proper build for a system that will need to produce 16-20kwh per day (technically an expansion of my existing system but please read on).

System will be located in Orlando Florida, completely off-grid (no grid available for 6+ miles).

Energy conservation has already been done and those numbers are pretty much spot on after measuring usage for the past 2 months (while running on generator and existing off-grid solar install).

Biggest load is AC which is currently window units but will be switching out to a multi-zone mini-split soon. However, that AC usage is really only that high in the few super hot months of summer (Jun-Sep). That is why the range is 16-20kwh because I estimate the reduction in AC consumption in the other 8 months of the year. It's also kind of a catch 22 (in a good way) in that at night I am only running one window-unit (or crank the others up to 82) so most of the AC usage is in the daytime. All 120v System, no 240v devices.

Don't really need more than 1 day of extra storage (if even that) since I will be here all the time and can always start the generator (or auto-start it once that gets installed). Already have a complete Outback 48v system, 3648 Inverter, FM80, Hub4, Mate3 and 2460w of panels. Forget the batteries I have, they are about 2 years old and I know I need a much larger bank and am prepared to buy a new one (I have someone buying the old ones as their "murder-set" for their first off-grid solar install). I'll leave the existing panels on the existing FM80 and just get another FM80 for the new panels (unless by chance 5000w will work for my needs and all panels (old and new) can be put on one FM80 [I can find matching panels]).

Thanks in advance for all your help and opinions.
Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Recommendations for new system

    20 kW hours per day? That's "ow". Or maybe "owe". :D

    Well if you were starting from scratch ...

    First, there's no question it would need to be 48 Volt. Trying to store that kind of energy at lower Voltage is madness. Then we can calculate an approximate battery bank size like this:

    20,000 Watt hours / 0.9 conversion efficiency = 22,222 + 480 for inverter tare = 22,702.
    Might as well call it 23 kW hours. Divide by 48 nominal = 479 Amp hours used. Minimum battery bank (X2) 958 Amp hours, 25% DOD battery bank (X4) 1,916 Amp hours.

    So you'd be looking at forklift or 2 Volt cells here for sure. Need to adjust battery bank up/down to fit. Since 20 is the 'top end' of the estimated power use you could go down. Say you pick 1700 Amp hour 2 Volt cells ($1,123 each, btw; $26,952).

    Okay so we try for 10% peak current (necessary for tall case batteries). That's 170 Amp hours. Problem: just over what two 80 Amp controllers could handle. There's another $600 on the tab (three Classics @ $610 each; $1,830, but they would work best here). Enough array for the current: 10,597 Watts (170 Amps @ 48 Volts / 0.77 efficiency).

    We're at $40,000 and we haven't got an inverter on the list yet, never mind wire, breakers, hardware, etc.

    So, how expensive is it to get grid there?

    Fortunately you've already got about half what you need.

    No, 5kW of panels isn't going to do it: you will definitely need to double up on array and charge controller. The FM80 isn't ideal, but you've already got one so it's best they match. With 10kW of array in Florida and given 5.5 hours good sun it should just work. But the new battery bank is going to be killer in size and cost. Figure the two controllers maxed out, 160 Amps, 1600 Amp hours of battery, 25% DOD gives about 16 kW hours. It's a close-run thing.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Recommendations for new system

    One of the reasons that 2 days and 50% maximum discharge is a better optimum for battery bank sizing is not just for running loads during bad weather, it also allows you to recharge the battery bank quicker after a "day" or use... You have limited hours of sun per day--And need probably >2 hours of absorb time to recharge the battery bank fully.

    Another thing to look at--Perhaps a smaller LiFePO4 (Lithium) battery bank would really interesting for this installation. High current during charging/discharging would be a big help here.

    Sizing of the battery bank (especially if flooded cell lead acid) is going to be a bit difficult to justify. Using most of your power during the day means the bank can be smaller--But I don't think you want a brown out if the sun goes behind a random cloud either.... So some guesses on how I would think about the problem.

    Since you have already running existing system for two years--Have you seen any "problems" so far (batteries recharging well, runs your heavy loads during summer, etc.)?

    20 kWH per day, assuming "all" the power for the A/C + Daytime loads is supplied by solar array (Solarelectrichandbook for Orlando FL, fixed array, tilted to 23 degrees from horizontal facing south gives us only 4.72 hours of sun for September--Lots of summer clouds/humidity/marine layer??? Use 4 hours of sun to be conservative):
    • 20,000 WH * 1/0.77 panel derating * 1/0.85 inverter losses * 1/4 hours of sun 7,639 Watt array for A/C power (no battery)

    Sizing the battery bank for 1 day of storage:
    • 20,000 WH * 1/0.85 inverter eff * 1 days * 1/0.50 max discharge * 1/48 volt bank = 980 AH @ 48 volt battery bank

    To charge such a bank with 13% rate of charge (panels are getting cheap--Lets "over panel" the system):
    • 980 AH * 59 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 9,762 Watt array to recharge battery bank

    And the minimum rate of charge (want to charge bank during day when A/C is running):
    • 20 kWH * 1/8 hours of heavy AC use during daytime = 2.5 kWatt average load during day (guess)
    • 2,500 Watt * 1/0.77 panel * 1/0.85 inverter eff = ~3,820 Watts of array runs AC system during day
    • 980 AH * 59 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge =3,755 Watt array needed to recharge battery at 5% rate
    • 3,820 Watt + 3,755 Watt = 7,575 Watt array minimum array (based on estimated loads+minimum battery charging)

    So--Depending on actual day time and night time power usage--The array should be ~7,575 to 9,762 Watt array with a 980 AH @ 48 volt battery bank.

    Compared to your current system (~2.3x larger battery bank and ~4x larger solar array) vs this paper design--Do you think it will be capable of cost effectively supplying your loads?

    If you run your A/C system very consistently during summer, you could possibly make a case for this size of array (you end up using much more power than planned at night--Hot nights, water pumping, using electricity for cooking, etc.):
    • 9,762 Watt (13% rate of charge battery bank) + 7,639 Watt (for running 20 kWH of A/C power per day) = 17,401 Watt array Max battery charging + daytime A/C loads

    And get 2-3 of Midnite Classic charge controllers with a Wizbang Jr. (current shunt/battery monitor) to limit charging current to the battery bank to 13% rate of charge (assuming that 2-3 Classis in parallel will limit battery charging current based on Wizbang Jr. feedback).

    Probably start with 8-10 kWatt of array and see how system performs. If the batteries are not recharging properly and/or you need to run too much backup generator--Add more panels based on how short you think you are.

    I think the above numbers are conservative (4 hours of sun, 100% of power used during the day)--And an 8-10 kWatt array should be a good start. Look at using a Lithium battery bank. Especially if you do not need much storage (1 day or less of storage).

    Your thoughts?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jcheil
    jcheil Solar Expert Posts: 722 ✭✭✭
    Re: Recommendations for new system
    20 kW hours per day? That's "ow". Or maybe "owe". :D

    Well if you were starting from scratch ...

    First, there's no question it would need to be 48 Volt. Trying to store that kind of energy at lower Voltage is madness. Then we can calculate an approximate battery bank size like this:

    20,000 Watt hours / 0.9 conversion efficiency = 22,222 + 480 for inverter tare = 22,702.
    Might as well call it 23 kW hours. Divide by 48 nominal = 479 Amp hours used. Minimum battery bank (X2) 958 Amp hours, 25% DOD battery bank (X4) 1,916 Amp hours.

    So you'd be looking at forklift or 2 Volt cells here for sure. Need to adjust battery bank up/down to fit. Since 20 is the 'top end' of the estimated power use you could go down. Say you pick 1700 Amp hour 2 Volt cells ($1,123 each, btw; $26,952).

    Okay so we try for 10% peak current (necessary for tall case batteries). That's 170 Amp hours. Problem: just over what two 80 Amp controllers could handle. There's another $600 on the tab (three Classics @ $610 each; $1,830, but they would work best here). Enough array for the current: 10,597 Watts (170 Amps @ 48 Volts / 0.77 efficiency).

    We're at $40,000 and we haven't got an inverter on the list yet, never mind wire, breakers, hardware, etc.

    So, how expensive is it to get grid there?

    Fortunately you've already got about half what you need.

    No, 5kW of panels isn't going to do it: you will definitely need to double up on array and charge controller. The FM80 isn't ideal, but you've already got one so it's best they match. With 10kW of array in Florida and given 5.5 hours good sun it should just work. But the new battery bank is going to be killer in size and cost. Figure the two controllers maxed out, 160 Amps, 1600 Amp hours of battery, 25% DOD gives about 16 kW hours. It's a close-run thing.

    Absolutely impossible to get the grid here :(

    And yeah the 2v/forklift batteries really jump up the cost :(

    I was hoping to be able to do it with something like 2 strings of the Trojan LE16RE-B (370ah each, 740ah total bank). That puts me in the battery bank budget I was thinking of ($5k-ish). I've been getting by fine with my 430ah bank for now. My energy usage daily has been about 10kwh per day (24hour period) and I always seem to be above 80% SOC in the morning, but that was always running the AC from the small generator at night.

    I already planned for another FM80 and like I said I have everything else (including the wiring to be able to manage 2 parallel strings of batteries).

    Let's say I had to really crunch my energy usage (which I could likely do with some lifestyle changes) to be able to fit it into a 48v - 740ah bank. Where would that leave me as far as total energy available each day keeping me at say 50% and 75% SOC respectively in your opinion?
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • jcheil
    jcheil Solar Expert Posts: 722 ✭✭✭
    Re: Recommendations for new system
    BB. wrote: »
    One of the reasons that 2 days and 50% maximum discharge is a better optimum for battery bank sizing is not just for running loads during bad weather, it also allows you to recharge the battery bank quicker after a "day" or use... You have limited hours of sun per day--And need probably >2 hours of absorb time to recharge the battery bank fully.

    Another thing to look at--Perhaps a smaller LiFePO4 (Lithium) battery bank would really interesting for this installation. High current during charging/discharging would be a big help here.

    Sizing of the battery bank (especially if flooded cell lead acid) is going to be a bit difficult to justify. Using most of your power during the day means the bank can be smaller--But I don't think you want a brown out if the sun goes behind a random cloud either.... So some guesses on how I would think about the problem.

    Since you have already running existing system for two years--Have you seen any "problems" so far (batteries recharging well, runs your heavy loads during summer, etc.)?

    20 kWH per day, assuming "all" the power for the A/C + Daytime loads is supplied by solar array (Solarelectrichandbook for Orlando FL, fixed array, tilted to 23 degrees from horizontal facing south gives us only 4.72 hours of sun for September--Lots of summer clouds/humidity/marine layer??? Use 4 hours of sun to be conservative):
    • 20,000 WH * 1/0.77 panel derating * 1/0.85 inverter losses * 1/4 hours of sun 7,639 Watt array for A/C power (no battery)

    Sizing the battery bank for 1 day of storage:
    • 20,000 WH * 1/0.85 inverter eff * 1 days * 1/0.50 max discharge * 1/48 volt bank = 980 AH @ 48 volt battery bank

    To charge such a bank with 13% rate of charge (panels are getting cheap--Lets "over panel" the system):
    • 980 AH * 59 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 9,762 Watt array to recharge battery bank

    And the minimum rate of charge (want to charge bank during day when A/C is running):
    • 20 kWH * 1/8 hours of heavy AC use during daytime = 2.5 kWatt average load during day (guess)
    • 2,500 Watt * 1/0.77 panel * 1/0.85 inverter eff = ~3,820 Watts of array runs AC system during day
    • 980 AH * 59 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge =3,755 Watt array needed to recharge battery at 5% rate
    • 3,820 Watt + 3,755 Watt = 7,575 Watt array minimum array (based on estimated loads+minimum battery charging)

    So--Depending on actual day time and night time power usage--The array should be ~7,575 to 9,762 Watt array with a 980 AH @ 48 volt battery bank.

    Compared to your current system (~2.3x larger battery bank and ~4x larger solar array) vs this paper design--Do you think it will be capable of cost effectively supplying your loads?

    If you run your A/C system very consistently during summer, you could possibly make a case for this size of array (you end up using much more power than planned at night--Hot nights, water pumping, using electricity for cooking, etc.):
    • 9,762 Watt (13% rate of charge battery bank) + 7,639 Watt (for running 20 kWH of A/C power per day) = 17,401 Watt array Max battery charging + daytime A/C loads

    And get 2-3 of Midnite Classic charge controllers with a Wizbang Jr. (current shunt/battery monitor) to limit charging current to the battery bank to 13% rate of charge (assuming that 2-3 Classis in parallel will limit battery charging current based on Wizbang Jr. feedback).

    Probably start with 8-10 kWatt of array and see how system performs. If the batteries are not recharging properly and/or you need to run too much backup generator--Add more panels based on how short you think you are.

    I think the above numbers are conservative (4 hours of sun, 100% of power used during the day)--And an 8-10 kWatt array should be a good start. Look at using a Lithium battery bank. Especially if you do not need much storage (1 day or less of storage).

    Your thoughts?

    -Bill

    Thanks for the input. Very interesting ideas.

    I do already have an FM80 and will stick with them because I already have the FNDC, Mate3 etc so I do all that battery monitoring already.

    As I mentioned in the post I made while you were typing yours, my energy usage daily has been about 10kwh per day (24hour period) and I always seem to be above 80% SOC in the morning, but that was always running the AC from the small generator at night.

    I do sometimes run a single AC in the daytime from noon-5 which only seems to add a couple of kwh to the total. Basically, 99% of the time, when that unit is running from noon-5, it is basically running directly off the panels (not literally). I rarely see a drop in charge current to the batteries when it is running.

    My original goal was to expand the system to be able to run the AC at night, but thought maybe it would be nice to be able to run the AC more frequently or more than one unit in the daytime.

    As mentioned in my other reply, I am going to be limited by my "battery bank" budget mostly.
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Recommendations for new system

    740 Amp hours @ 48 Volts, 50% DOD: 17,760 Watt hours DC. In AC probably 15 kW hours. That's cutting it close.

    Are you good with still having to run the generator if needs be?
    Could you stand two parallel strings of 390 Amp hour L16's? Maybe a bit bigger?
    If you expand the array to 10kW and get 160 Amps it would be too high for 740 Amp hours, so you'd want to limit the current. An Outback FNDC may be a good inclusion here, allowing you to better track and manage output from two controllers and the inverter-charger (one of which will have a hard time managing to charge a very large battery bank).
  • jcheil
    jcheil Solar Expert Posts: 722 ✭✭✭
    Re: Recommendations for new system
    740 Amp hours @ 48 Volts, 50% DOD: 17,760 Watt hours DC. In AC probably 15 kW hours. That's cutting it close.

    Are you good with still having to run the generator if needs be?
    Could you stand two parallel strings of 390 Amp hour L16's? Maybe a bit bigger?
    If you expand the array to 10kW and get 160 Amps it would be too high for 740 Amp hours, so you'd want to limit the current. An Outback FNDC may be a good inclusion here, allowing you to better track and manage output from two controllers and the inverter-charger (one of which will have a hard time managing to charge a very large battery bank).

    Yeah I have no issue running the generator if need be and hope to get an auto-start one at some point in the near future.
    And I already have the FNDC (forgot to mention that).
    It's difficult to make this call because it's an expensive one and I don't want to sell myself short. Especially on the batteries.

    I just have this feeling a lot of my consumption in the daytime is being consumed directly from the solar because like I said, I average about 10kwh per day now, with only 430ah of battery and they always stay above 75-80%. I can watch the FNDC and even with the ac running in the daytime, it is usually at 100% (or in the high 90's) until the sun starts going down.

    I have one other possibility, which allows me a bit more time to save some $ to get the larger (proper) battery bank, that I would like your opinions on.
    That is to simply add another string to my existing bank, bring it up to 645ah (will be 3 parallel strings at that point) and do some lifestyle changes for a while (may have to not use the pool for a while - that consumes a couple of kwh per day).

    Then bring my array up to 5000w, maxing out the existing FM80.
    Or, get another FM80 and add another ?? watts of array to properly charge that now 645ah bank (recommendations on array size?)
    Perhaps even over panel a bit to help with the daytime consumption??
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Recommendations for new system

    Problems with adding to an existing bank. How old are they? How 'well used'? If you tack on new ones you will probably be losing battery value from that moment because the older ones will pull the newer ones down. It isn't very noticeable at first.

    Three parallel strings is generally frowned upon, but if done well on a 48 Volt system you won't see any current sharing issues because the resistance variations are small for the Voltage used.

    Now 645 Amp hours @ 48 Volts should have about 4kW of array to charge properly. It appears you have 2460 so that would come up short. If you max out the existing FM80 your theoretical peak charge rate would be 12% on 645 Amp hours.

    So how comfortable are you with adding that additional battery capacity now for a few dollars, knowing the old ones may fail and require all-new anyway? (Knowing nothing about the age & condition of the batteries I wouldn't even hazard a guess at their condition.) At sixteen GC2's you've already got a lot of cells and connections: do you really want more?

    I'd say an absolute yes on maxing the FM80 if you can, and yes to expanding the battery bank at least to 645. The question is how best to do the latter?
  • jcheil
    jcheil Solar Expert Posts: 722 ✭✭✭
    Re: Recommendations for new system
    Problems with adding to an existing bank. How old are they? How 'well used'? If you tack on new ones you will probably be losing battery value from that moment because the older ones will pull the newer ones down. It isn't very noticeable at first.

    Three parallel strings is generally frowned upon, but if done well on a 48 Volt system you won't see any current sharing issues because the resistance variations are small for the Voltage used.

    Now 645 Amp hours @ 48 Volts should have about 4kW of array to charge properly. It appears you have 2460 so that would come up short. If you max out the existing FM80 your theoretical peak charge rate would be 12% on 645 Amp hours.

    So how comfortable are you with adding that additional battery capacity now for a few dollars, knowing the old ones may fail and require all-new anyway? (Knowing nothing about the age & condition of the batteries I wouldn't even hazard a guess at their condition.) At sixteen GC2's you've already got a lot of cells and connections: do you really want more?

    I'd say an absolute yes on maxing the FM80 if you can, and yes to expanding the battery bank at least to 645. The question is how best to do the latter?

    The bank has been WELL taken care of. I murdered my first set a long time ago :)
    The current 16 are about 18mo old, Sams Duracel GC2's. No issues with the bank that I am aware of. I frequently check voltages and current and they are all pretty darn close to the same. I only expect 3-5 years from a set of GC2's anyways so I guess if I get another 2 out of these (including the new string) I will be happy. I know it's gonna hurt the new ones pairing them with the old, but at this point I think it is the best means to an end to be able to save in 2 years be able to afford the "real" bank. At $760 for another 8 Sam's batteries, it's like I would only be throwing away $32 per month over the next two years.

    The 12 new panels I will be getting are 220w each, so that will add 2640w to my 2460w totaling 5100w which will max out (a tad over) the FM80.
    I'm feeling comfortable knowing that I will be at a proper charge rate with this new setup. I think I was just a tad low in my existing configuration.

    Thanks again for all the help.
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,728 ✭✭✭✭✭✭
    Re: Recommendations for new system

    You need to decide how much energy you "really" need to store and how much you can use while the sun is shining. In my opinion you do not have enough solar for the Florida early afternoon storms/clouds. Probably need well over 4.5 KW. It is a challenging place for sure!
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

  • jcheil
    jcheil Solar Expert Posts: 722 ✭✭✭
    Re: Recommendations for new system
    You need to decide how much energy you "really" need to store and how much you can use while the sun is shining. In my opinion you do not have enough solar for the Florida early afternoon storms/clouds. Probably need well over 4.5 KW. It is a challenging place for sure!

    Ok, so my new plan (see above) is to go to 5100w on a 645ah bank which according to coot puts me at a 13% charge rate.
    Would I benefit from going with more solar above the 5100w? At the cost of adding another controller (no big deal cause I will need one in 2 years anyways)? I'm not sure -- BUT would that start pushing the safe charging limits of a 645ah bank now being more than 5100w???
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    Re: Recommendations for new system

    You will also benefit from using mini splits instead of the window rattlers. I would think a 30% reduction at least.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Recommendations for new system
    jcheil wrote: »
    Ok, so my new plan (see above) is to go to 5100w on a 645ah bank which according to coot puts me at a 13% charge rate.
    Would I benefit from going with more solar above the 5100w? At the cost of adding another controller (no big deal cause I will need one in 2 years anyways)? I'm not sure -- BUT would that start pushing the safe charging limits of a 645ah bank now being more than 5100w???

    Yes it would be more current than you want. You'd be getting near the point where it would do more heating than charging, should the batteries get all the current and the loads get none.

    Trying to balance running loads in daylight against charge controller supply without going too high or too low is tricky. One forum member is getting away with murder having far to small a battery bank for the current potential of the array. One day the loads will be too low and the current will be too high and the batteries will cook. Or more likely, will cook a little bit every so often neatly cutting years of the lifespan without being an obvious problem.

    Now if you want to get crazy and rig the 'extra' PV to be active only when the loads call for it ... Well it can be done. But it isn't easy. Wiring AC controls to 'cut in' extra PV and all that.

    And no you can't AC couple to FX inverters as they were never meant to regulate that.
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: Recommendations for new system

    The possibility of over paneling with a second controller being a midnite classic, might work with the Whiz Bang Jr, I asked before it was released over on the Midnite forum if, since it was monitoring the current going into the battery if it would work well in conjunction with a charge controller that is not controlled by it... since it would 'see' maximum current going into the battery would it shut down the Classic, I think it was boB(or maybe Ryan?) who wasn't sure but thought it was logical... They are likely to have more information on this now.

    If those single 2 volt cell prices bother you check out 48volt forklift batteries Here.

    Florida weather is interesting, lots of micro climates there from the sea breeze effect, while I was in Tallahassee we would regularly have afternoon showers in the summer. I like that your considering a minimal battery bank, but don't know if it would work well in your area of Florida, though I've never lived there, I know I would have issues in Tallahassee.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • jcheil
    jcheil Solar Expert Posts: 722 ✭✭✭
    Re: Recommendations for new system
    Photowhit wrote: »
    The possibility of over paneling with a second controller being a midnite classic, might work with the Whiz Bang Jr, I asked before it was released over on the Midnite forum if, since it was monitoring the current going into the battery if it would work well in conjunction with a charge controller that is not controlled by it... since it would 'see' maximum current going into the battery would it shut down the Classic, I think it was boB(or maybe Ryan?) who wasn't sure but thought it was logical... They are likely to have more information on this now.

    Well, I am on an Outback system and don't really want to change to the Midnights at this point.

    I am 99% sure that the Outback FNDC has that same ability, you can set the maximum charge current going to the battery and it will regulate it.
    However, I am not sure exactly if that is just regulating the INTERNAL charger current + solar to not exceed the maximum or if it is all charging devices combined and regulated. If so, then perhaps I could benefit from a bit of overpaneling for the daytime load.

    And Those forklift battery prices look good, however the price list is from 2011 and says subject to change due to lead prices. Wonder what they cost now - I shall check.
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • jcheil
    jcheil Solar Expert Posts: 722 ✭✭✭
    Re: Recommendations for new system
    Now if you want to get crazy and rig the 'extra' PV to be active only when the loads call for it ... Well it can be done. But it isn't easy. Wiring AC controls to 'cut in' extra PV and all that.

    This is an interesting idea....

    Now, if the FNDC cannot regulate all current sources (see other post), what would be required to make this happen?
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Recommendations for new system
    jcheil wrote: »
    This is an interesting idea....

    Now, if the FNDC cannot regulate all current sources (see other post), what would be required to make this happen?

    We probably just shouldn't even go there.
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: Recommendations for new system
    jcheil wrote: »
    Well, I am on an Outback system and don't really want to change to the Midnights at this point.

    I am 99% sure that the Outback FNDC has that same ability, you can set the maximum charge current going to the battery and it will regulate it.
    However, I am not sure exactly if that is just regulating the INTERNAL charger current + solar to not exceed the maximum or if it is all charging devices combined and regulated. If so, then perhaps I could benefit from a bit of overpaneling for the daytime load.

    And Those forklift battery prices look good, however the price list is from 2011 and says subject to change due to lead prices. Wonder what they cost now - I shall check.

    I wasn't suggesting changing, I was saying it would work in conjunction with your Outback, Outback will only know how much is coming out of the charge controller, it will not measure the current going into the battery like the Midnite will. I think it might have some communication with the inverter and be able to adjust somewhat, but couldn't output more than 80 amp regardless, with a Midnite along side. it would measure the amperage going into the battery, So if you tell it not to allow more than 80 amps it would shut down(I believe) Since it is measuring the input to the battery it would adjust to the loads. so if you have a possibility of 120 amps and only want to charge at a 80 amp rate, if you have the Air conditioner running, it would see only 40 amps gong into the battery and charge, if your air shuts down it would shut down seeing too much current running into the battery.

    Anywho I would ask the guys over at Midnite if one doesn't pop in to correct me...

    About that price list, I suspect it's still good, I think someone else I directed to them has bought one I the last year, I think I was a 2-3 year old list when I bought mine in 2010(?)
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: Recommendations for new system
    jcheil wrote: »
    Now, if the FNDC cannot regulate all current sources (see other post), what would be required to make this happen?
    Kinda' what I was suggesting, though I would put the bulk of the array on the Midnite and set end amps high on the outback... I would think the Midnite would see the charging through the charger and shut down... But first I would ask the brain trust at Midnite.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Recommendations for new system
    jcheil wrote: »
    I am 99% sure that the Outback FNDC has that same ability, you can set the maximum charge current going to the battery and it will regulate it.
    However, I am not sure exactly if that is just regulating the INTERNAL charger current + solar to not exceed the maximum or if it is all charging devices combined and regulated.

    With the FNDC the Outback charge controllers will cut back, but the outback inverters will NOT cut back. Look for 'Global' charge control in the Mate. Of course, this is all relevant to Bulk charging... during absorb or float all charge sources will regulate without communication.

    --vtMaps

    edit: see this post: http://forum.solar-electric.com/showthread.php?p=152925#post152925
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • jcheil
    jcheil Solar Expert Posts: 722 ✭✭✭
    Re: Recommendations for new system
    vtmaps wrote: »
    With the FNDC the Outback charge controllers will cut back, but the outback inverters will NOT cut back. Look for 'Global' charge control in the Mate. Of course, this is all relevant to Bulk charging... during absorb or float all charge sources will regulate without communication.

    --vtMaps

    edit: see this post: http://forum.solar-electric.com/showthread.php?p=152925#post152925

    Interesting. I think I will give a call to outback tomorrow and find out the best way to do this with the FNDC.
    The reason I am asking is because I am going to pick up my other panels this week, and with such a good price and local pickup (no freight), I wouldn't mind getting some extra ones now if there will be a use for them without damaging anything. Ultimately, in about 2 years when I get the "real" battery back I will need the panels anyways.
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Recommendations for new system

    All you have to do is stage the voltage for each source, a little lower ( .02 or so ) on one source or two if you have 3 and it will drop it's amperage based on the voltage of the other. When you have a current draw on the bus they will all contribute.

    Added: I do it often with banks where I want to Bulk at maximum current and then will drop one source to finish the absorb at a different voltage and current once above gassing voltage. You have to play with it a bit because the display voltage is not always what the source thinks it is. You can calibrate them sometimes. Watch any RTS you use, it should be on the master source you use for the final absorb. Setting the absorb time is about the same thing you can play with. Remember once you go into float some sources will not re-trigger until they drop to a certain voltage. On a source with a Fixed algorithm voltage ( Bulk, Absorb, float ) that is RTS capable you can replace the thermistor with a potentiometer and fake them out with a fixed ohm value to change the voltage settings.
    .
  • jcheil
    jcheil Solar Expert Posts: 722 ✭✭✭
    Re: Recommendations for new system
    solar_dave wrote: »
    You will also benefit from using mini splits instead of the window rattlers. I would think a 30% reduction at least.

    I'd really like to explore these, however being that I am in the middle of nowhere, I am concerned about service (if I need it).

    Also, there are so many out there now I don't know where to begin and I have spent hours looking. I know I would want an inverter based one. I would also think a multi-zone one since I have 3 rooms that I would want to cool and not always at the same time. They are not very large rooms, one is 140sq.ft, the 2nd is 150sq.ft and the third is only 65sq.ft. (my office, the one used from 8:30am to 5pm M-F).

    Plus I would need to stay on 120V unless I got a transformer, but then I might need another FX anyways. Ugh, I just don't know. If you have a suggestion on a unit, please chime in or PM me so this thread doesn't get too sidetracked.
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • jcheil
    jcheil Solar Expert Posts: 722 ✭✭✭
    Re: Recommendations for new system

    Just a quick clarification please:

    Bill mentioned a formula:
    980 AH * 59 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 9,762 Watt array to recharge battery bank

    and if I apply that to my proposed 645ah bank it would be:
    645 AH * 59 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 6,425 Watt array to recharge battery bank

    Coot mentioned:
    Now 645 Amp hours @ 48 Volts should have about 4kW of array to charge properly. It appears you have 2460 so that would come up short. If you max out the existing FM80 (my proposed 5100w) your theoretical peak charge rate would be 12% on 645 Amp hours

    Why is there such a difference in array size for the difference in 1% charge rate?

    I guess I just want to make sure I have enough panel so that I do not come up short (and I am ordering in the next couple of hours).
    Using Bill's formula, I would need to get another controller (which I am OK with since I will need another one in 2 years anyways), but Coot mentioned more than 5100w would start pushing the limit for overcharging current with a 645ah bank. So I am a tad confused.
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    Re: Recommendations for new system
    jcheil wrote: »
    I'd really like to explore these, however being that I am in the middle of nowhere, I am concerned about service (if I need it).

    Also, there are so many out there now I don't know where to begin and I have spent hours looking. I know I would want an inverter based one. I would also think a multi-zone one since I have 3 rooms that I would want to cool and not always at the same time. They are not very large rooms, one is 140sq.ft, the 2nd is 150sq.ft and the third is only 65sq.ft. (my office, the one used from 8:30am to 5pm M-F).

    Plus I would need to stay on 120V unless I got a transformer, but then I might need another FX anyways. Ugh, I just don't know. If you have a suggestion on a unit, please chime in or PM me so this thread doesn't get too sidetracked.

    I don't think you will find a 3 zone split in 120V AC, most are 240 V. I have seen 120V units as low as $749 for single zone 13 seer models. I would suggest a more efficient one like a 19 seer unit single.
    http://justminisplits.com/home/
  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,728 ✭✭✭✭✭✭
    Re: Recommendations for new system
    solar_dave wrote: »
    I don't think you will find a 3 zone split in 120V AC, most are 240 V. I have seen 120V units as low as $749 for single zone 13 seer models. I would suggest a more efficient one like a 19 seer unit single.
    http://justminisplits.com/home/


    You should be split phase with a couple of the 28 Seer 9,000 BTU LG's. That would be an exact copy of a system I have going in Pensacola. It uses less than 12 KWH per day for everything. Runs dawn until midnight. On the really nasty days they shut one heat pump down and close off rooms of the house.
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Recommendations for new system
    jcheil wrote: »
    Just a quick clarification please:

    Bill mentioned a formula:
    980 AH * 59 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 9,762 Watt array to recharge battery bank

    and if I apply that to my proposed 645ah bank it would be:
    645 AH * 59 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 6,425 Watt array to recharge battery bank

    Coot mentioned:
    Now 645 Amp hours @ 48 Volts should have about 4kW of array to charge properly. It appears you have 2460 so that would come up short. If you max out the existing FM80 (my proposed 5100w) your theoretical peak charge rate would be 12% on 645 Amp hours

    Why is there such a difference in array size for the difference in 1% charge rate?

    Cariboocoot was using PEAK array power. You should always plan your controller size and wiring and fuses etc for peak power. You should plan to actually harvest much less than peak power. Bill's formula derated the array size to account for that.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Recommendations for new system
    jcheil wrote: »
    Just a quick clarification please:

    Bill mentioned a formula:
    980 AH * 59 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 9,762 Watt array to recharge battery bank

    and if I apply that to my proposed 645ah bank it would be:
    645 AH * 59 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 6,425 Watt array to recharge battery bank

    Coot mentioned:
    Now 645 Amp hours @ 48 Volts should have about 4kW of array to charge properly. It appears you have 2460 so that would come up short. If you max out the existing FM80 (my proposed 5100w) your theoretical peak charge rate would be 12% on 645 Amp hours

    Why is there such a difference in array size for the difference in 1% charge rate?

    I guess I just want to make sure I have enough panel so that I do not come up short (and I am ordering in the next couple of hours).
    Using Bill's formula, I would need to get another controller (which I am OK with since I will need another one in 2 years anyways), but Coot mentioned more than 5100w would start pushing the limit for overcharging current with a 645ah bank. So I am a tad confused.

    Marc/Cariboocoot and I have a slightly different set of assumptions when making the calculations. Also I gave a maximum 13% rate of charge and he gave a 10% rate of charge:

    645 Amps * 48 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 4,021 Watt

    The 48 vs 59 volt charging voltage--If you cycle the battery to 80-75% state of charge, and have a heavy charging current, the system will spend most of its time in the 54 to 59 volt range of charging. If you have deeper cycling or AGM batteries, the average charging voltage may be less.

    10% rate of charge is a very healthy number (many vendors recommend 10% as either minimum or optimum rate of charge for their battery bank). 13% is C/8 rate of charge--Generally about the maximum rate of charge before batteries need a remote battery temperature sensor and/or active cooling (fans) to keep them from getting too hot (this is charging from something like 50% or less SOC to 100%--Like deep cycling a forklift battery).

    So Marc's number here was a nice healthy rate of charge--Mine was the "cost effective" maximum for a standard off grid home (charging during the day and discharging at night).

    Because a large amount of your load is during the day--You have to support both the A/C loads and give the battery bank a minimum of 5% (5%-13%) rate of charge over your A/C usage to recharge the bank after its night time loads. So, in this case your array size would be larger than normal (day-time planned load current + Battery charging current). If you only ran enough solar panels to support your day time loads, the batter bank would not see enough current to properly recharge from its night time/1 day of cloudy weather use.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jcheil
    jcheil Solar Expert Posts: 722 ✭✭✭
    Re: Recommendations for new system
    BB. wrote: »
    Marc/Cariboocoot and I have a slightly different set of assumptions when making the calculations. Also I gave a maximum 13% rate of charge and he gave a 10% rate of charge:

    645 Amps * 48 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 4,021 Watt

    The 48 vs 59 volt charging voltage--If you cycle the battery to 80-75% state of charge, and have a heavy charging current, the system will spend most of its time in the 54 to 59 volt range of charging. If you have deeper cycling or AGM batteries, the average charging voltage may be less.

    10% rate of charge is a very healthy number (many vendors recommend 10% as either minimum or optimum rate of charge for their battery bank). 13% is C/8 rate of charge--Generally about the maximum rate of charge before batteries need a remote battery temperature sensor and/or active cooling (fans) to keep them from getting too hot (this is charging from something like 50% or less SOC to 100%--Like deep cycling a forklift battery).

    So Marc's number here was a nice healthy rate of charge--Mine was the "cost effective" maximum for a standard off grid home (charging during the day and discharging at night).

    Because a large amount of your load is during the day--You have to support both the A/C loads and give the battery bank a minimum of 5% (5%-13%) rate of charge over your A/C usage to recharge the bank after its night time loads. So, in this case your array size would be larger than normal (day-time planned load current + Battery charging current). If you only ran enough solar panels to support your day time loads, the batter bank would not see enough current to properly recharge from its night time/1 day of cloudy weather use.

    -Bill

    OK, I see, so somewhere between the 5100w minimum that would max out my existing FM80 and the 6,425w number you recommend would be good and not cause any harm in potential overcharging, etc?
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Recommendations for new system

    The Outbacks have a remote battery temperature sensor--So you have that issue covered (as batteries get hot, the charge controller will dial back the Absorb voltage).

    My "13%" limit is really a cost effective limit vs a hard limit that will damage batteries. Many people run 20-25% charging when using AC + Genset/Utility for quick battery charging. Running long hours at over C/8 (12.5%) rate of charge is not "great" for the batteries (longer hours at 10% is probably less harsh than fewer hours at 20-25% rate of charge).

    But with limited hours of sun per day--We sort are left with relatively high charging currents to get the batteries fully charged by the end of the day. And why it can be somewhat better to have a 2 days/50% discharge battery bank (4x daily loads) vs a 1/50% (2x daily loads) battery bank. It is easier (requires less time) to recharge a battery bank 25% of capacity vs 50% of capacity every day. Also you can feed higher charging currents (larger battery bank) to more quickly recharge when the sun comes back up (if you have weather patterns with clouds and sun--requiring more battery usage).

    And that is one reason why poster Dave Angelini (owns an off grid installation/maintenance company in the California Sierra Mountains) likes tracking solar panels--Gives more hours during the day of charging current (or virtual tracking--1/2 array facing south west, other 1/2 facing south east now that solar panels are so "cheap"--my two cents).

    I would still be interested in your actual Day Time vs Night Time KWH loads... You have two calculations to make... How much you need to recharge the bank during the night (array sizing) and what is your estimated average Wattage for day time (again array sizing).

    Then you would add the Night+Day array needs together for your optimum sizing.

    Note, your night time array sizing still needs to look at your 5% to 13% base charging rate for the battery bank. If you night time loads are really low--Then your minimum array sizing could fall towards 5% rate of charge... If your night time loads are significant, then you should look at 10-13% rate of charge:

    Array Size = Day Time Wattage + Either Night time loads or 5-13% rate of charge--which ever makes sense for you

    Your day time A/C power draw may be variable too... Few days of really hot/humid weather then a few days of cooling breeze--You may not need to maximize your day time array for worst case needs.

    In the end, your solar array has a 20+ year life... The battery bank may last from 3-8 years (or more if fork lift batteries). So your whole power management strategy is to ensure a reasonably long life for the battery bank.

    And frankly, a Solar array sized a bit towards the large size--Means you probably will need to spend less time managing your daily power budget (i.e., turn it on and forget vs looking at weather/humidity/cloud cover forecasts/the battery bank state of charge/generator run-time, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jcheil
    jcheil Solar Expert Posts: 722 ✭✭✭
    Re: Recommendations for new system
    BB. wrote: »
    The Outbacks have a remote battery temperature sensor--So you have that issue covered (as batteries get hot, the charge controller will dial back the Absorb voltage).

    My "13%" limit is really a cost effective limit vs a hard limit that will damage batteries. Many people run 20-25% charging when using AC + Genset/Utility for quick battery charging. Running long hours at over C/8 (12.5%) rate of charge is not "great" for the batteries (longer hours at 10% is probably less harsh than fewer hours at 20-25% rate of charge).

    But with limited hours of sun per day--We sort are left with relatively high charging currents to get the batteries fully charged by the end of the day. And why it can be somewhat better to have a 2 days/50% discharge battery bank (4x daily loads) vs a 1/50% (2x daily loads) battery bank. It is easier (requires less time) to recharge a battery bank 25% of capacity vs 50% of capacity every day. Also you can feed higher charging currents (larger battery bank) to more quickly recharge when the sun comes back up (if you have weather patterns with clouds and sun--requiring more battery usage).

    And that is one reason why poster Dave Angelini (owns an off grid installation/maintenance company in the California Sierra Mountains) likes tracking solar panels--Gives more hours during the day of charging current (or virtual tracking--1/2 array facing south west, other 1/2 facing south east now that solar panels are so "cheap"--my two cents).

    I would still be interested in your actual Day Time vs Night Time KWH loads... You have two calculations to make... How much you need to recharge the bank during the night (array sizing) and what is your estimated average Wattage for day time (again array sizing).

    Then you would add the Night+Day array needs together for your optimum sizing.

    Note, your night time array sizing still needs to look at your 5% to 13% base charging rate for the battery bank. If you night time loads are really low--Then your minimum array sizing could fall towards 5% rate of charge... If your night time loads are significant, then you should look at 10-13% rate of charge:

    Array Size = Day Time Wattage + Either Night time loads or 5-13% rate of charge--which ever makes sense for you

    Your day time A/C power draw may be variable too... Few days of really hot/humid weather then a few days of cooling breeze--You may not need to maximize your day time array for worst case needs.

    In the end, your solar array has a 20+ year life... The battery bank may last from 3-8 years (or more if fork lift batteries). So your whole power management strategy is to ensure a reasonably long life for the battery bank.

    And frankly, a Solar array sized a bit towards the large size--Means you probably will need to spend less time managing your daily power budget (i.e., turn it on and forget vs looking at weather/humidity/cloud cover forecasts/the battery bank state of charge/generator run-time, etc.).

    -Bill

    Thanks for the clarification (and everyone's input).

    So I guess I am going to just go with the 5100w right now, and the 645ah bank (since it will all fit on one controller).

    I do 1min data logging of usage to my PC, etc so after about 2 weeks of logging, I will take a look at the results and see what my day vs night usage is.
    At that time, maybe we can look at the data together and you could give me your insights as well as to if more panel will be needed at that point.
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html