Molokai Off grid system design help

Background - I built a hangar on the state airport and the utility company surprised me by a quote of $28K to hook up electrical power to it. This is the only reason for looking at an off grid solar system - I would rather be hooked up to the grid.

The largest challenge was understanding the load and daily max watt/hr needs for the building. My best estimate using a kilowatt meter is about 3000 watt/hr daily max. I multiplied that by 1.5X for a fudge factor to get 4.5K watt/hr.

I believe that Hawaii solar insolation is about 5.6 hrs so 4500 divided by 5.6 is about 800 watts - planning for 1000W pv panels - right now I'm looking at the Canadian solar 245W panels CS6P-245P

To figure battery bank size I used the 3000 watt/hr daily max multiplied by 5 days = 15K watt/hr. To get Amp/Hrs I took the 15000/48V to get 312.5 Amp hrs. I am planning on using AGM batteries since I won't be there during the summer months and have no one to look after the water level. I am planning on using 380 Amp Hr 6V batteries - eight of them in series to get my system voltage of 48VDC.

To figure out the charge controller needed, I took the 1000 watt PV panels and divided that by 48V to get a little over 20.8 Amps. I wanted to have a controller large enough in case my needs went up so I am planning on the Classic 200. The VOC of these panels are 37.1 VDC so multiply that by 4 (in series) to get 148.4 VDC - was going to go with the Classic 150 but it seemed to close.

I am planning to purchase the Magnum MS4448 PAE inverter since I want both 220V and 110V outlets in the hangar. For a panel, I'm planning on the Midnight EPanel MNE175-240.

For the generator, I have a Yamaha 2800W quiet inverter generator and might purchase a large 17KW generator to run some machine tools (with the inverter in bypass mode) - this useage will be very intermittent and infrequent.

I am planning on Iron ridge XRS rails and attachment hardware.

What have I overlooked or just plain screwed up with this design? My biggest fear is that I will pour money into this and then it won't be right and have to do it over again.

Thanks, Molokaisteve
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Comments

  • vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
    Re: Molokai Off grid system design help

    What have I overlooked or just plain screwed up with this design? My biggest fear is that I will pour money into this and then it won't be right and have to do it over again.

    Welcome to the forum,
    I think your array is a bit undersized for the amount of battery you are planning.

    Next question is how far are your panels from the batteries and controller? I would like to see you set your panels in strings of three and use a midnite classic 150. Of course you can't do that with 4 panels... If you run 6 or 9 panels it would work, and you need more panels anyway.

    I think it would be a mistake to start out with AGM batteries for many reasons. You seem concerned about flooded batteries because you think you need to water them in the summer when you are away.... but if you are away and have no loads you can just put the batteries on maintenance mode and they won't need water.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Molokai Off grid system design help

    Let's see what the old man (me) would do. :D

    4500 Watt hours per day includes buffering, so a little straight-forward division and we get ( 4500/48 ) 94 Amp hours of use, meaning a minimum 188 Amp hours. Since that is with buffer and you are in Hawaii and there is good sun you can probably start with 220 Amp hours, the good ol' cheap GC2's. I second vtMaps on avoiding AGM's first time out. In a big ol' hangar there's not going to be any problems with close quarters and you don't need the extra expense and ease of destruction.

    Never mind the multiple days: plan on discharge/recharge daily. You've got a generator in case the sun doesn't shine or the volcano spews ash.

    Magnum 4448 inverter: good choice. Dependable and straightforward. Do you need that much capacity? Do you need its 240 VAC ability? If not there are others that could save a couple of $.

    I also agree with vtMaps that your array is small. Recharging that battery bank would require approximately (22 Amps * 48 Volts / 0.77) 1371 Watts of array. Picking the 245 Watt panels = six of them. Two strings of three in series would give an array Voc of 114, well within the limits of the Classic 150. Unless you have a really long wire run between the array and controller there's no need to go higher. You don't want all the panels in one string because it puts the Vmp of the array much above system Voltage reducing efficiency.

    Some things you may want to consider: pre-wired MidNite panel for the Magnum inverter, combiner box with breakers that will allow the addition of further panels (at 22 Amps you are at about 1/4 the Classic's maximum). This would make adding battery & panels capacity very easy in case your power needs go up or you have inexplicably miscalculated them to begin with.
  • BB.BB. Posts: 28,079Super Moderators, Administrators admin
    Re: Molokai Off grid system design help

    You are looking at a fairly small system--A good choice for solar and keeping your costs down. Some links for you to look at.

    Poster "Adas" a few years ago setup an off grid fabrication business in Hawaii using low cost equipment and used fork lift batteries. If are thinking about going larger, he has lots of thread he started that may be of interest to you:

    http://forum.solar-electric.com/search.php?do=finduser&userid=1074&starteronly=1&contenttype=vBForum_Thread

    Next, you may wish to look at using a AC inverter that has "generator support". Again, for a larger system. It allows you to run your AC loads from the Inverter+battery bank and a genset at the same time. You can use a smaller genset to support the "average loads" and when you have high starting surges (or short bursts of larger power needs), the AC inverter kicks in battery power to prevent the genset from being over loaded.

    Poster ChrisOlson (and others) has some good advice here for "swimspam" :

    Choosing a good generator
    genset alternator failure (and if your generator is not generating AC? What to look for/do--Thread started by "Unicornio" from Spain)
    Demonstration of Generator Support (A couple inverters that will share AC loads with the generator--smaller generator with large load support)

    End result--you get what you pay for.

    And a really nice "mid sized" gasoline powered genset:
    ChrisOlson wrote: »
    BB. wrote: »
    The smallest genset I have seen here so far that can be (more easily) configured to auto-start (automatic choke) is probably the Honda EM4000SX that Chris Olson is using. The choke/mixture is controlled by the electronic engine controller.
    I'd like to point out that the little 46538/46539 Champion generators also have an auto-choke and I have mine configured for auto-start with the Trace/Xantrex GSM on the SW Plus inverter. When our Generac would fail to start in cold weather I used the Champion as a backup with the auto-start and it works fine.

    It is basically a three-wire start generator and you only have to tap into the wires on the back of the Combination Switch to do it, which is quite easy to do.
    --
    Chris

    Of course, you can use Diesel if your fuel prices work better (and can avoid road taxes), plus the higher fuel efficiency of diesel gensets).

    Making a "hybrid" power system (generator+inverter+battery bank+solar power) can give you near utility performance for a moderate price.

    Of course--The larger/more capable you make your power system, the higher the capital and maintenance costs--Which then pushes you into the cost of bringing grid power to your hanger+monthly bills... It is a tough call.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • molokaistevemolokaisteve Posts: 25Solar Expert
    Re: Molokai Off grid system design help

    Wow - thank you all for the advise - I really appreciate it!! Better to understand more now prior to purchasing and installing.

    Here is what I have learned so far:

    1. Don't buy the AGMs instead buy the less expensive flood acid and during the summer when they are not in use, put the system in maintenance mode
    2. I need to plan for more PV panel capacity. Sounds like two strings each with three panels would be better. Also, I like the idea of purchasing a PV combiner with breakers so if more are needed, it would be pretty simple to install. And go with the Classic 150
    3. On BB's advise, I am so new I don't understand enough. Tried looking at the threads posted but I still didn't get it. I like the idea of a inverter that is good with a generator input and will share the load and not need that large of a generator. I take it the Magnum that I was going to use won't do this? Do the inverters that have generator support also put out both 110 and 220V without having two inverters or a transformer?
  • BB.BB. Posts: 28,079Super Moderators, Administrators admin
    Re: Molokai Off grid system design help

    On your inverter options...

    There is for generator support:
    • Schneider XW family. Both 120/240 VAC from one inverter + generator support. Requiries a 240 VAC generator for 120/240 support (or transformer). Can be reconfigured for 120 VAC In/Out (jumpers in unit, different firmware--I believe).
    • Outback GFX/GVFX. Typically 120 VAC need transformer or "stacked" inverters for 240 VAC. May need inverter-generator for accurate frequency?
    • Magnum. Brand new model says it has generator support--Very interesting looking unit. 120 VAC. Need transformer for 240 VAC.

    About all I know--You can read/research about these guys first (and download the manuals/programming instructions). Then call the vendors (like NAWS) and get their recommendations too.

    For various reasons--Sometimes it is better to use an Auto Transformer to mix/match 120/240 Inverter output with 120/240 VAC loads (or just go with a 120 VAC inverter to 120/240 VAC Auto Transformer)... We can talk about the details now (or later) if you wish.

    None of these are "cheap solutions"--But compared to $28k plus monthly bills for grid power--The may be viable options.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • molokaistevemolokaisteve Posts: 25Solar Expert
    Re: Molokai Off grid system design help

    Bill,

    THANK YOU. I will research the manuals on all three to learn how a hybrid system may just be the ticket for me. My load is intermittent and variable. The normal load of LED lighting and a stereo is very small but more consistent and longer duration. The intermittent load of running power tools of various kinds during maintenance will be once a month or less and a couple of minutes maybe five times a day.

    Now, the weird part is that I would really want to install a couple of machine tools (a lathe and a mill) but this makes the load go way up (I will need a 17KW propane powered generator to "start" the 5 hp 3 phase motors one running at a time) but the run time will be in the minutes (like 10-20) and once a month or less so the propane cost should be manageable and the generator cost is less than $4K. I could install them in my shop at home (12 miles away) but the convenience of having them in the hangar would be nice.

    Darn, sure wish I could hook up to the grid but $28K and doing everything myself seems like so much. I am planning on installing all the solar components myself (I am pretty capable) and so far the cost is about $8K. So $8K and $4K is $12K. Less than half the cost of the grid tie... But cost over time with battery changes and such - still seems to make sense.

    Thank you again and this is such a great resource. Any and all comments from the members are appreciated. It is much better to figure this out before purchasing components.

    I've added the PV combiner (3 string capable) with CBs, 6 Canadian solar panels 245W, 2 strings of 3 ea, more IronRidge mounting HW and changed to the Classic 150. Will research the best inverter for my application.

    Anyone want to comment on whether a Midnight Epanel or the Magnum mini panel is the way to go. I want to mount/wire myself. Right now I'm leaning toward the Epanel.
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Molokai Off grid system design help

    I'd stick with running the big generator when you need to power the big tools.

    The other process, generator support of the inverter, requires not only the right inverter but also the right generator (one that can be started automatically and is sized right for the inverter).
  • vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
    Re: Molokai Off grid system design help
    It is much better to figure this out before purchasing components.
    I wish more of our new members realized this. We see quite a few 'ready, fire, aim' new members here.
    Anyone want to comment on whether a Midnight Epanel or the Magnum mini panel is the way to go. I want to mount/wire myself. Right now I'm leaning toward the Epanel.

    The ePanel exists because it is a better, more flexible solution than that offered by magnum, outback, and SMA. It is much easier to wire and customize. Be sure to order the 'stretched' version of the epanel. Also, take advantage of the support pages and the forum over at Midnite.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • BB.BB. Posts: 28,079Super Moderators, Administrators admin
    Re: Molokai Off grid system design help

    Yep--Agree with Marc/Cariboocoot--A genset is the way to run your large equipment.

    You might be able to look at using a smaller single phase genset if you normally run the equipment at less than full load.

    I have a machinist friend who I helped setup an entire production machine shop in his two car garage at home. All he has was single phase 120/240 VAC power. We did a combination of a three phase idler motor (get a 5 HP Wye wound motor--Use a small AC motor or even pull cord on the motor shaft to get it spinning--then hit with 240 VAC single phase power--Motor gets up to speed and provides "good enough" three phase power to start other 3 phase equipment and the motors help each other to generate the 3rd phase where they seem to operate pretty normally).

    You can also get a start capacitor (provides enough phase shift to start the 3 phase motor, which continues to run on single phase)--Used with with a Bridge Port mill for years just fine (as I recall).

    And there are VFD's -- Variable Frequency Drives... You can get one that takes 240 VAC single phase in and outputs 3 phase (typically MSW) output to the 3 phase motor. The VFD's also provide "soft start" (and variable speed frequency control) too... Not too expensive. Note that VFD's on three phase motors can be a mix bag--Not everyone who uses one is sure that the motors will have a long and happy life (MSW modified square wave output can cause heavily loaded induction motors to run hot).

    Anyway--Some more options.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • molokaistevemolokaisteve Posts: 25Solar Expert
    Re: Molokai Off grid system design help

    Bill, vtmaps and Cariboocoot,

    Thank you all for the advise! Again! This forum is so good.

    Sounds like I will stick with the plan to run the machine tools off a large generator. I have a rotary phase converter that will provide the three phase power to them. They basically are the second option Bill mentioned all packaged up nice. I do like the VFDs a lot, my variable speed drill uses one and I used two to make a variable speed bridge crane is my shop - they are amazing.

    I will stick with the EPanel from Midnight and ask for the stretched version - thank you!

    I am still researching if I can reduce the generator size with matching it with the right inverter - a 17Kw propane powered generator is only $3500 on Amazon. Electric start and their quiet series. But it is a big generator so it will probably suck fuel like there is no tomorrow.

    Thank you all again,
    Steve
  • BB.BB. Posts: 28,079Super Moderators, Administrators admin
    Re: Molokai Off grid system design help

    Here is a nice set propane guidelines:

    http://www.yamaha-propane-natural-ga...onsumption.htm

    And, your 17kW genset probably would run around 1-3 gallons per hour (zero to 100% loading).

    Also, you will have to check to see if the genset you are looking at uses liquid or gaseous propane.

    I would guess an engine that size would have its own vaporizer (I don't know, I have not researched larger propane gensets).

    If the generator need gaseous propane--Then the size of the propane tank becomes important and how quickly it can boil off propane without icing up and dropping pressure.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Posts: 7,967Solar Expert ✭✭✭✭
    Re: Molokai Off grid system design help

    (heretic mode on)
    Or by the time you buy batteries, inverter, generators, a shed to store gear/fuel in, you may find the Grid install to be less expensive, but not nearly as fun. $28K isn't going to go too far, if you are building a largish system.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • molokaistevemolokaisteve Posts: 25Solar Expert
    Re: Molokai Off grid system design help

    All,

    Still trying to learn. Here is the equipment list I plan to purchase - again my load is approx. 3000 watt hours daily max and is intermittent with some days almost nothing and most days about 1000 watt hours

    6 ea - Canadian Solar 245W panels - 2 strings of 3 ea
    8 ea - Flood acid type GC2 batteries 225 ah - 48V system voltage - looking at Costco or Sams Club - if not powerstridebattery.com (free ship to Hawaii-amazing)
    Magnum MS4448 PAE inverter to power both 120VAC outlets and 240VAC (for like a drill press used maybe five minutes once a week)
    Midnight Classic 150 charge controller
    Midnight EPanel MNE175-240
    Magnum Advanced control panel ARC-50
    Magnum Battery monitor
    Midnight PV combiner box (in case I need to add more PV panels)
    IronRidge rails and hardware with quick mount hangar bolts for roof mount to a steel 36" panel type roof
    Backup generator already purchased and on site is a Yamaha Inverter type quiet generator EF3000is
    Looking at later to purchase a 17KW propane generator to run machine tools (lathe, mill, etc) - may or may not do this...

    A couple of questions:
    1. If I hook up my Yamaha generator to the Epanel geny input, do I have to put my inverter in bypass each time I fire it up since it is not a hybrid type inverter - and if I don't will I hurt the inverter?
    2. Is two strings of 3 ea panels better (I think so - the VOC total should be under the Classic 150) or three strings of two panels better
    3. If I have cloudy days but little to no load and the batteries are less than 80% full, should I run the generator or can the batteries stay at like 60% for a day or two without hurting them?
    4. I like the Xantrex XW 4548 inverter for the surge capacity to start motors and since it might sync with my geny's but it is more $ and the panel for it is more $. Over a $1000 more which I could put towards the big geny for the machine tools.

    So far I'm at $5329 plus $1300 for batteries - total so far is $6629 - vs $28K for the utility company to hook up (with me doing the trenching, purchasing the conduit, filling the trench with cement at $250/yard).

    Thank you all for the help!!

    Steve
  • vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
    Re: Molokai Off grid system design help
    A couple of questions:
    1. If I hook up my Yamaha generator to the Epanel geny input, do I have to put my inverter in bypass each time I fire it up since it is not a hybrid type inverter - and if I don't will I hurt the inverter?
    2. Is two strings of 3 ea panels better (I think so - the VOC total should be under the Classic 150) or three strings of two panels better
    3. If I have cloudy days but little to no load and the batteries are less than 80% full, should I run the generator or can the batteries stay at like 60% for a day or two without hurting them?

    1) The magnum has a built in automatic transfer switch. Should be seamless.
    2) I believe that those panels have Vmp about 30. If so, 2 strings of 3 panels each is mandatory. The voltage of 2 panels in series will sag in the heat and be unable to charge batteries.
    3) It won't hurt batteries to stay at 60% for a day or two.

    Other thoughts: make sure you have remote battery temp sensors for both midnite and magnum.

    Are you ordering the epanel kit (with all breakers, shunt, etc)? If not, be sure to order some some midnite lightning arrestors. Also, buy a lightning arrestor for the combiner box.

    The bypass switch in the epanel is a nice touch, it allows you to remove the magnum (for service) while the generator passes through to your power distribution panel. Actually, I'm not sure how that works with a 120 volt generator and a 240 volt power distribution panel :confused:

    Before you pull the trigger, price out a prewired ePanel with the magnum included. I sense that you are a DIY type, but those prewired epanels are huge timesavers, even if you've done a few already.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • molokaistevemolokaisteve Posts: 25Solar Expert
    Re: Molokai Off grid system design help

    vtmaps,

    THANK YOU! OK - so 2 strings of 3 each it is. I priced out the EPanel and Magnum combined but it is over $500 more plus I do like wiring and am pretty good at it.
    I am ordering the Magnum battery monitor kit (which includes battery temp, I believe?) but you mentioned the midnight and magnum temp sensors - do I need both?
    I'm buying the epanel kit with the shunt and breakers and planning to use it as the load center for the Hangar as well since it has spaces for up to six AC breakers and that should be enough to power the lights, the outlets and a 240VAC outlet.

    Wow, you brought up a good point I never thought about - a 120VAC generator (Yamaha EF3000is) for a 240VAC power distribution system. How does the inverter like/dislike that and what you probably only hook it to one of the legs like L1? Does the inverter act as a charger when that happens or does it need 240VAC input (I will have no grid tie)?

    I ran across a thread about sizing the battery bank correctly:

    "one other note is that it is recommended to have a 100ah minimum capacity per kw of inverter power capability with 48v battery banks. you may have ripple problems going with only 250ah as it really should be twice that. it would become obvious to you that the 250ah will not handle the full 4400w of load anyway. battery voltage would quickly get sucked down until the inverter thinks there's insufficient voltage to operate. it may help if you limit your loads to about 2kw max and if using the built in charger then cut the charge current back there to roughly 13% of battery ah capacity or .13 x 250ah = 32.5a. i'm not sure of the actual settings allowed on the charger, but i wouldn't go higher than 35a or 40a unless you have loads present to the batteries to offset the high charge rates."

    I was going to initially get a 380ah battery bank (of course I was so new I was going to go with AGMs - now have learned that would have been a costly mistake) but now plan on going with 232AH battery bank with GC2's. This goes against the rule of 100ah per kw of inverter power. Is this true that my MS4448PAE magnum won't be able to put out 4400W even for a short time (like 5 minutes) to run a larger power tool like a drill press or table saw because my battery bank is not large enough?


    Steve
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Molokai Off grid system design help

    An inverter that requires 240 VAC gen input won't do anything with only one leg energized.

    I know some of the guys have re-wired the Xantrex XW's to take 120 VAC input. Not sure it can be done on a Magnum. You may have to use an autotransformer on the gen's output (not always a good solution) or get a 240 VAC generator.

    Then there's the horrible gen-runs-battery-charger-direct-to-batteries-only solution. Needs to be the biggest charger you can manage in that circumstance as it has to take on any loads first before there's power going to charge the batteries.
  • molokaistevemolokaisteve Posts: 25Solar Expert
    Re: Molokai Off grid system design help

    Cariboocoot,

    Thank you for your help. I am so new that I don't yet understand much.

    I ran across a thread today that has me confused. It read:

    one other note is that it is recommended to have a 100ah minimum capacity per kw of inverter power capability with 48v battery banks. you may have ripple problems going with only 250ah as it really should be twice that. it would become obvious to you that the 250ah will not handle the full 4400w of load anyway. battery voltage would quickly get sucked down until the inverter thinks there's insufficient voltage to operate. it may help if you limit your loads to about 2kw max and if using the built in charger then cut the charge current back there to roughly 13% of battery ah capacity or .13 x 250ah = 32.5a. i'm not sure of the actual settings allowed on the charger, but i wouldn't go higher than 35a or 40a unless you have loads present to the batteries to offset the high charge rates.

    The rule of having 100ah per 1KW of inverter power? I'm am now planning on using a 232ah battery bank (8-GC2's). Does this mean the inverter won't give me 4400W of power even for a short duration of let's say 5 min (ie: running a larger power tool).

    Thank you,
    Steve
  • vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
    Re: Molokai Off grid system design help
    An inverter that requires 240 VAC gen input won't do anything with only one leg energized.

    Don't have a magnum, but I thought that it accepts 120 VAC but puts out 120 or 240 VAC. Am I wrong about that? My concern was how does generator pass through (and the epanel bypass) work with a 120 volt gen and a 240 volt power distribution panel? I guess I have the same question on the new Schneider Conext SW which takes 120 from the gen and puts out 240.
    but you mentioned the midnight and magnum temp sensors - do I need both?

    You have two chargers (midnite & magnum). each should have one (they're cheap). When you have an integrated system (such as outback or xantrex) the two chargers can share a single temp sensor. btw, I have an outback controller and an outback inverter and each has it own $25 temp sensor. It would cost me much more than $25 to buy the outback network hub that allows the two to share a sensor.
    Is this true that my MS4448PAE magnum won't be able to put out 4400W even for a short time (like 5 minutes) to run a larger power tool like a drill press or table saw because my battery bank is not large enough?

    Yes. If your high wattage needs are few and far between, use a generator... its not worth over building a system for something you hardly ever need.

    You mentioned that you have a yamaha 2800 watt generator... maybe you should rethink the Magnum and buy an inverter that offers generator support... That means that the generator supplies the first 2800 watts and the battery/inverter helps out with the additional wattage over 2800.

    Another option is to stick with the magnum and do DC coupling... that means you buy a standalone battery charger and run that with your generator. With the sun and the generator both charging your batteries the inverter will handle the load, drawing down the batteries (if needed) to make up any charging deficit while the loads are running.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • molokaistevemolokaisteve Posts: 25Solar Expert
    Re: Molokai Off grid system design help

    Thank you!

    Would you help me with the 100ah per 1kw inverter size question? Am I sizing my bank correctly? I am planning on 8ea 6volt GC2 batteries (232ah). My load is 3000 watt hours daily max but the load is intermittent and variable. I am thinking of the Magnum MS4448PAE since it provides 240VAC output and want to run a larger power tool for a small (5min) duration that may be up to the 4400W capacity of the inverter.

    Steve
  • vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
    Re: Molokai Off grid system design help
    Would you help me with the 100ah per 1kw inverter size question? Am I sizing my bank correctly? I am planning on 8ea 6volt GC2 batteries (232ah). My load is 3000 watt hours daily max but the load is intermittent and variable. I am thinking of the Magnum MS4448PAE since it provides 240VAC output and want to run a larger power tool for a small (5min) duration that may be up to the 4400W capacity of the inverter.

    Perhaps you missed my post (post #19) while you were typing yours. I don't think it will work very well. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • molokaistevemolokaisteve Posts: 25Solar Expert
    Re: Molokai Off grid system design help

    OK - battery temp sensor for the Classic 150 is now on the list - thank you!

    My little Yamaha EF3000is won't supply the 240VAC voltage needed for a larger power tool so it looks like getting a larger Generator may be just the ticket - I was considering one for the machine tools anyway so I should just plan on using it for all the larger power tools and take the Yamaha home for backup power.

    Steve
  • molokaistevemolokaisteve Posts: 25Solar Expert
    Re: Molokai Off grid system design help

    Yes, I was typing and should have been reading - thank you!
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Molokai Off grid system design help

    The rule-of-thumb about 100 Amp hours per kW of inverter is mainly for hybrid GT systems where the inverter is expected to run full-out for as long as possible as it converter all the 'extra' DC array power to AC on the grid. Without sufficient battery capacity the AC ripple on the DC side presents some problems.

    With an off-grid system it is less of a concern because the inverter usually is not operating at maximum capacity for any extended period. Instead we have to look at whether or not the battery bank will 'go flat' from current demand. So if you actually do plan on pulling 4kW out of the inverter that's >84 Amps on the DC side (@ 48 Volts). On a 232 Amp hour battery bank that's 36% of capacity. Under that much load the real battery capacity is greatly reduced (while the load is on) and the Voltage sag can be significant - perhaps enough to trigger LVD on the inverter if the batteries aren't fully charged.

    Keeping the maximum current draw to <20% of the battery capacity is a good way to avoid these problems. Strangely that works out to about the same ratio as the GT recommendation: 100 Amp hours per kW of inverter (used). [at 48 volt battery bank. -Bill]
  • vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
    Re: Molokai Off grid system design help
    My little Yamaha EF3000is won't supply the 240VAC voltage needed for a larger power tool so it looks like getting a larger Generator may be just the ticket

    Not so fast... reread the last part of post #19... I mentioned two options that will work with the yamaha. I know the second option (DC coupling) will work. I'm less certain about the gen support option (I know gen support can work, but I'm not sure how it works with 120 in and 240 out).

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • molokaistevemolokaisteve Posts: 25Solar Expert
    Re: Molokai Off grid system design help

    Oh, I reread it and now I think I understand. A stand alone charger that the Yamaha runs and charges the battery and the sun charging the battery from the PV panels and Classic 150 - then the inverter should have enough juice to run a larger powertool for a short time. Did I get this right? Any suggestions on a stand alone charger?

    Thank you, thank you. Boy, so much to learn and easy to overlook things...

    I was reading the Classic 150 and it says it comes with a battery temp sensor. Yeah!
  • BB.BB. Posts: 28,079Super Moderators, Administrators admin
    Re: Molokai Off grid system design help

    With Magnum, it appears you have two options. There MS-PAE family appear to support 120 VAC generator with 120/240 VAC split phase output... What any limitations/functional issues there may be with this setup--I cannot say--But you may end up with 1/2 the DC charger output with 120 VAC input power:

    http://www.solar-electric.com/maenms4040wa1.html
    1.0 Introduction

    Congratulations on your purchase of the MS-PAE Series inverter/charger from Magnum Energy.
    The MS-PAE Series is a “pure” sine wave inverter designed to provide 120 and 240VAC in a single

    unit to power loads when inverting and also while charging. It has two 120VAC lines (L1 and L2), a
    neutral and a ground. The two 120VAC output lines are 180° out-of-phase with each other, so that
    the combination of the L1 and L2 lines total 240VAC and the voltage between either L1 or L2 and
    neutral is 120VAC. The MS-PAE Series charger can accept 120VAC input (to L1 or L2) or 120/240
    VAC split-phase input power (to L1 and L2), the incoming AC power is shared with the charger and
    the output continues to be 120/240VAC with either a 120VAC or a 120/240VAC inpu
    t.

    The new 120/120 Magnum inverter + a 240 VAC transformer? Note, Magnum calls this a Hybrid Inverter--Hybrid in the sense that this integrates with a genset and can do "Generator Support" (hybrid as in gas generator + battery bank power)--And not a Hybrid Grid Tied+Off Grid inverter (like the Schneider XW and others) that can feed power back into utility lines and turn the utility meter backwards.

    http://www.solar-electric.com/magnum-energy-msh4024re-hybrid-inverter.html
    The Magnum Energy MSH-RE series hybrid inverter is designed for off-grid and backup power systems. The pure sine wave 60Hz, 120 volt output ensures that you can run all standard 120 volt devices. It has two separate AC inputs, one for a generator and one for utility power. This allows you to charge your batteries from either AC source. The hybrid function of this inverter is what makes it stand out. If you have a total electrical load that exceeds the inverter output, the inverter can start your generator and match its AC output with the inverter's AC output. Instead of running all loads from the generator, it combines the generator output with the inverter output. So if your generator is rated for 2,000 watts and you add that to the 4,000 watts from the inverter, you can run a total of 6,000 watts of electrical loads.

    Specifications and Features:

    4,000 watts
    24 volts DC
    120 volts AC output at 60Hz
    Two 60 Amp AC inputs for generator and utility hook up
    Built-in 110 Amp battery charger


    Throw a 240 VAC transformer of some time on your 240 VAC tools... In some ways, this may be a more flexible unit in that you can pull full inverter power on 120 VAC -- Where a typical 120/240 split phase inverter setup will only allow you to draw ~50% to 70% of system available power from one leg (you can use an auto wound transformer to balance the 120 VAC load across 120/240 split phase inverters--But if you already have to buy a transformer to do this--Why not look at 120 VAC only inverter in the first place+transformer--You may pay less and have lower inverter idling losses).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
    Re: Molokai Off grid system design help
    Any suggestions on a stand alone charger?
    Do a google search... there are quite a few industrial chargers on the market. Be sure to get a PF corrected charger if you want to use the full capacity of your generator.

    One problem I see... You would like to have a charger that can put out as much as your generator can handle, but that is probably more power than your batteries can take. When you shut off your power tool you may be suddenly pushing too much current into your batteries. That won't be an issue if your batteries are in absorb or float (because the batteries won't accept too much current then), but it is an issue if your batteries are in bulk charge mode.

    There is a lot of talk on this forum about 'balanced' systems.... 4400 watts with a 220 ah battery bank is not what we would normally call balanced. It can be done, but you need to understand well what you are doing. One other thing... if your tool draws 4400 watts continuous, what is the startup surge like?

    The more I think about it, the more I think that you need a larger battery bank and/or a larger generator. Generator support is a possibility, but not with the Magnum you have in mind. Among the inverters that do provide gen support, I am not knowledgeable enough to advise you... especially with 120 in and 240 out. btw, if gen support is attractive to you but is limited to 120 out, you could make it work with a step up transformer.

    Have you read the 'Generator Support' thread?

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • molokaistevemolokaisteve Posts: 25Solar Expert
    Re: Molokai Off grid system design help

    Well, I wish this stuff would stick in my brain better but it doesn't. I've read the generator support thread and about gen set supported inverters and a bunch of other stuff. I think I should just stick with a larger generator for all the larger power tools and machine tools. The use is infrequent enough for this to be not much of a bother. The inverter I chose is oversized for the rest of my load but I like having the 240VAC output and hopefully it will let me learn what can and cannot operate with it and what it does to my battery bank. Hopefully this doesn't scare anyone...

    I think I've narrowed down my needs thanks to all of you. Here is what I plan to purchase for my normal load - 3000 watt hours daily max.

    Six Canadian solar CS6P-245P panels - two strings of 3 each
    Magnum MS4448PAE inverter
    Classic 150 controller (with a battery temp sensor included - I'm told)
    EPanel MNE175STM-L-240
    Magnum battery monitor kit
    Magnum ARC50 panel
    Eight GC2 220AH batteries - wired in series to make 48V - questions on this down the post...
    PV combiner box (MNPV3) - in case I need to add another string of PV panels
    MNSPD300 surge protectors
    Iron ridge mounting rails and HW

    Please help me on the following:

    I'm planning on purchasing two 10AWG UL4703 with H4 connectors 600VDC 50' cables to run the PV panel strings to the PV combiner box mounted externally on the building with feed out the back into the building to the Epanel. Then from the PV combiner box to the EPanel, I plan on purchasing bulk wire of same type and gauge to use? In the EPanel, I plan to use a 30A DC breaker for the PV array input and in the PV combiner box, 15A fuses for each string. Are these sized properly?

    What other circuit breakers should I purchase and what do they support/protect? Right now, for the PV output out of the Classic 150, I have 63A, 150VDC MNEPV63 breaker chosen. The Epanel comes with 50A AC breakers for the output out of the inverter and a 50A AC breaker for the output from the generator (bypass) and I will most likely use the Epanel as the load center for the building and purchase up to six AC breakers to power the 110VAC outlets, lights and a 240VAC outlet. Do I need a circuit breaker mounted inside my battery bank enclosure? There is a main battery shutoff inside the Epanel for the battery bank to hook in but nothing to protect the wire from the battery bank to the Epanel.

    What size and type wire should I purchase for the battery bank. I want to locate my battery bank into a separate plastic shed type cabinet as close to but not under the Epanel and vented to the outside. Are 10" long battery cables long enough to connect the GC2's in series? Can they be a smaller gauge due to the short length as compared to the cables from the battery bank to the Epanel (I'm thinking these will be about six feet in length?)

    What gauge of wire should I use for wiring Classic 150 into the Epanel.

    Is it possible (if I've undersized this darn thing) to add another bank of eight series tied GC2 batteries in parallel to the first string of eight a month or two from now? I'm thinking of purchasing the golf cart batteries from Costco - anyone have any luck with them - less than $100 ea even with the core charge and in Honolulu already - hard to beat the price but I know, you get what you pay for... For that cost, maybe two strings of eight batteries might make sense from the get go (only $1600 and that would be over 400ah correct?) That probably changes the wire size - correct?

    Do I need anything else? Were leaving in about a month and there are minimal supplies on the island in case I've forgotten something...

    Thank you all again,
    Steve
  • vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
    Re: Molokai Off grid system design help
    I'm planning on purchasing two 10AWG UL4703 with H4 connectors 600VDC 50' cables to run the PV panel strings to the PV combiner box mounted externally on the building with feed out the back into the building to the Epanel. Then from the PV combiner box to the EPanel, I plan on purchasing bulk wire of same type and gauge to use? In the EPanel, I plan to use a 30A DC breaker for the PV array input and in the PV combiner box, 15A fuses for each string. Are these sized properly?

    Personally, I would put the combiner (and its lightning arrestor) very near the panels and run a single 50 ft cable to the epanel, but your scheme is OK.

    The PV array input breaker should be sized to protect the wiring from the combiner to the epanel. Both the breaker and the wiring must be sized greater than the PV output... the breaker should never trip because there is too much sun... it is there mostly as a switch, but it does provide some protection from the controller failing and allowing current from the battery to run into the panels. I would bump it up to the largest size that will protect the wiring.
    I will most likely use the Epanel as the load center for the building and purchase up to six AC breakers to power the 110VAC outlets, lights and a 240VAC outlet.
    That will work, but an external small load center is inexpensive and will give you greater flexibility for future changes in the epanel and the load center.
    What size and type wire should I purchase for the battery bank. I want to locate my battery bank into a separate plastic shed type cabinet as close to but not under the Epanel and vented to the outside. Are 10" long battery cables long enough to connect the GC2's in series? Can they be a smaller gauge due to the short length as compared to the cables from the battery bank to the Epanel (I'm thinking these will be about six feet in length?)

    Make the battery cables to the epanel as short as possible. If you put the battery box on a stand 20-30 inches off the floor, the batteries will be easier to service and closer to te epanel. Some folks build a four ft wall perpendicular to the exterior wall and put their electronics on one side of the wall and their battery box on the other side.

    Are you planning to make your own cables, or order them pre-made? Your Magnum manual (available on line) will have the recommended size for the battery cables.
    Do I need a circuit breaker mounted inside my battery bank enclosure? There is a main battery shutoff inside the Epanel for the battery bank to hook in but nothing to protect the wire from the battery bank to the Epanel.
    The cable from the battery box to the epanel is in conduit, so you are not required to have a fuse in the battery box. Its not a bad idea though. There is an extensive, unfused battery bus in the epanel. I won't even look inside my epanel without first disconnecting the battery bank. One of my future upgrades will be to put a fuse and disconnect switch between the battery box and the epanel.
    What gauge of wire should I use for wiring Classic 150 into the Epanel.
    The classic can handle 4 guage. I think that if the classic is close enough to the epanel, you can use 6 gauge, but check the classic manual.
    Do I need anything else? Were leaving in about a month and there are minimal supplies on the island in case I've forgotten something...
    Ground rods, cable, etc. Also, are you buying the batteries on the island or the mainland? If possible, don't buy them until everything else is wired up and ready to charge them.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • molokaistevemolokaisteve Posts: 25Solar Expert
    Re: Molokai Off grid system design help

    vtMaps,

    Thank you as always for all the information! Depending upon cost, may have to make my own cables. Like the 20-30 inches off the floor - would not have thought about that - having a disconnect at the battery bank another good idea (thank you) and a ground rod - crap, forgot that one too.

    Heard of anyone with experience with the low cost Costco GC2 batteries?

    Steve
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