Finalizing my Off Grid System... Thoughts?

Rngr275
Rngr275 Solar Expert Posts: 127 ✭✭
in Off Grid Solar & Battery Systems #1
I have an installer I like who has been living off grid for the past 12 years.

My load calculations called for between 3-5Kwhr a day. (most loads measured, some estimated)

OutBack E-Panel/3648 with Trimetric monitor (120v only right now... may need to expand in the future to 240v)
2-1920W PV arrays on pole top mount.
16-L16RE Trojan batteries ( wired for 48V, 1 parrallel string for 740 Amp Hour
Plus all the matterial and installation (less any and all sweat equity I do... which will be a lot... I hope)

~25-27K

I wanted to build in some cushion so I am going with a little more PV than needed.

Planning on a Propane back up generator because I have jioned a co-op and can get LP pretty cheap (relative).

Looking at a 6Kw Ecogen or an 8.5 Kw Kohler... are these enough generator for the above sysytem?

Thoughts on the system.... questions I should ask?
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Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: Finalizing my Off Grid System... Thoughts?

    I am a little confused with the 16x L16RE battery bank configuration... You say it will be 1 parallel string--But it appears that it has to be 2 parallel strings of 6 volt batteries (L16RE-B type, 8 batteries per string).

    Second, check the warranty for your genset... Over the last few years, some generator manufacturers will void the warranty if the generator is installed in an off-grid application (no utility lines to site).

    Here is a thread about Kohler:

    propane generator warranty for off-grid application

    It may be possible that you can tell them the system is still a "backup" power source for a solar power cabin/home/etc... But at the time, it was not clear that they would honor such a warranty claim.

    To find a "prime power" rated 1,800 RPM (low speed) propane genset in the sub 15-25kW rating seems to be getting difficult.

    By the way, what is the solar array you are looking at/location of system (for PV Watts calculations)?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: Finalizing my Off Grid System... Thoughts?

    Actually you have two parallel strings of L16's. Not sure which ones add up to 740 Amp hours. 640 or 780 is what I get from the A and B models.

    At 780 Amp hours you should have at least 4862 Watts of array. At 640 it would be 3989 Watts. Either way you need an 80 Amp charge controller. You have 3840, so there isn't any "extra" PV.

    You really should not need 6kW of generator, much less 8. Full power output of the inverter is 3.6 kW and the charger in it will use about 4kW more at most. It is extremely unlikely you'll need full charging power and full load power at the same time. Buying too big a generator means spending too much on fuel. Unless you have some other heavy load you want to run off the gen you should look at something closer to 4kW (depending on load size; most of the time you probably won't be using over 1kW from the inverter). I have a similar 24 Volt system (lower battery capacity) with a 2kW gen. It works fine. If I were to up the battery bank to 464 (double) I'd need another 1kW in gen capacity.

    Definitely think about upping the PV capacity. The more charge you get from them the less you have to run the generator, no matter which one it is.
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  • Rngr275
    Rngr275 Solar Expert Posts: 127 ✭✭
    #4
    Re: Finalizing my Off Grid System... Thoughts?

    Sorry I meant 2 Parrallel strings (8ea).

    18-240w panels in upstate NY... Average daily @ ~4.5 hrs annually.... Dec-Feb is in the 2hr range... I think I can't find that nice web site for the month by month detail. Binghamton, Syracuse vacinity.
    I'm nervous about Genarc Ecogen but they are getting some good reviews and are for off grid. I've seen the warranty info on the Kohlers... not sure if they would by the "Stand-by" argument. I found this on but I am not sure how I would protect it or what slow turning really means
    http://www.generatorsales.com/order/04592.asp?page=H04592
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #5
    Re: Finalizing my Off Grid System... Thoughts?
    Rngr275 wrote: »
    Sorry I meant 2 Parrallel strings (8ea).

    18-240w panels in upstate NY... Average daily @ ~4.5 hrs annually.... Dec-Feb is in the 2hr range... I think I can't find that nice web site for the month by month detail. Binghamton, Syracuse vacinity.
    I'm nervous about Genarc Ecogen but they are getting some good reviews and are for off grid. I've seen the warranty info on the Kohlers... not sure if they would by the "Stand-by" argument. I found this on but I am not sure how I would protect it or what slow turning really means
    http://www.generatorsales.com/order/04592.asp?page=H04592

    http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/

    "Station Identification"
    "City:","Syracuse"
    "State:","New_York"
    "Lat (deg N):", 43.12
    "Long (deg W):", 76.12
    "Elev (m): ", 124
    "PV System Specifications"
    "DC Rating:"," 4.0 kW"
    "DC to AC Derate Factor:"," 0.770"
    "AC Rating:"," 3.1 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 43.1"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:","14.5 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 2.77, 275, 39.88
    2, 3.36, 295, 42.77
    3, 4.40, 423, 61.34
    4, 4.98, 445, 64.53
    5, 5.45, 483, 70.03
    6, 5.36, 446, 64.67
    7, 5.66, 481, 69.75
    8, 5.32, 458, 66.41
    9, 4.95, 416, 60.32
    10, 3.79, 347, 50.31
    11, 2.34, 206, 29.87
    12, 2.21, 216, 31.32
    "Year", 4.22, 4491, 651.20
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: Finalizing my Off Grid System... Thoughts?

    Keep in mind that for off-grid applications the PV Watts numbers are more of a guideline than actual fact. It's designed for grid-tie where there's always someplace for the power to go. This is not the case with a battery-based system.

    I used to live near there myself (Rochester area). The Winters are known for their cloud cover. On a good day you could expect just under 8kW hours AC from that array. On a typical day about half that. You will get some boost from the cold temps of course.

    You might be better off "sizing down" the battery bank to the 640 Amp hour capacity, keeping the 3840 Watt array as is, and getting a generator around 3kW.
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  • Rngr275
    Rngr275 Solar Expert Posts: 127 ✭✭
    #7
    Re: Finalizing my Off Grid System... Thoughts?
    Cariboocoot wrote: »
    Actually you have two parallel strings of L16's. Not sure which ones add up to 740 Amp hours. 640 or 780 is what I get from the A and B models.

    At 780 Amp hours you should have at least 4862 Watts of array. At 640 it would be 3989 Watts. Either way you need an 80 Amp charge controller. You have 3840, so there isn't any "extra" PV.

    You really should not need 6kW of generator, much less 8. Full power output of the inverter is 3.6 kW and the charger in it will use about 4kW more at most. It is extremely unlikely you'll need full charging power and full load power at the same time. Buying too big a generator means spending too much on fuel. Unless you have some other heavy load you want to run off the gen you should look at something closer to 4kW (depending on load size; most of the time you probably won't be using over 1kW from the inverter). I have a similar 24 Volt system (lower battery capacity) with a 2kW gen. It works fine. If I were to up the battery bank to 464 (double) I'd need another 1kW in gen capacity.

    Definitely think about upping the PV capacity. The more charge you get from them the less you have to run the generator, no matter which one it is.

    I read the 20hr @ 370Ah (370x2=740Ah) Am I reading doing something wrong.

    Installer explained to me this way:
    1-1920w array would is just enough Kw for my extimate of 3-5K (3.8kwhr for a 2 hr of sun) and that a 370Ah (8-L19RE-B batteries) 48v would be a good combination of PV and Battery bank.

    1-3000w array would give me ~40% more Kwhr for that same 2 hr but may generat more Ah than the 370Ah (8-L19RE-B batteries) can store during the summer... OK in the winter. He worries about not having enough staorage for the KW generated.

    Higher than 3000w of PV like the one I described... 2-1920w Arrays would need to have the larger battery bank... hence the second string to up the AH of the battery bank to 740Ah.

    My load estimate/measurements are in the 3-5Kwhr a day range. Trying to learn/understand and make good choices up front and not spend $$ on non-value added equipment.

    Appreciate your help and continued help.

    I have a Honda 2000i currently just wasn't shure if I needed more generator ot not for the long dark winter here in the Finger LAkes.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #8
    Re: Finalizing my Off Grid System... Thoughts?

    My 2 cents: make sure that your pole mount allows you to put the panels in a vertical position for the winter. Sheds snow better, and the reflection of sun off the ground snow will be welcome. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #9
    Re: Finalizing my Off Grid System... Thoughts?

    From what I've read the EcoGen 6.5 IS warranteed for Off-Grid use.
    There has been some discussion elsewhere about this genset needing a kit to enable 240 VAC output, and as of about 6 months ago, there were issues with voltage regulation at 240 VAC. This may have been remedied by now.

    Believe that the OB inverter's Charger section is NOT Power Factor corrected, and will need a higher powered genset than one might expect. Personally, would think that 5KW genset might be a bit light, with some AC loads and the PF issue, plus any altitude de-rating. Battery charging is often a long grind -- several hours in Bulk if the batts are discharged a bit. This can be rough on AIr-Cooled engines.

    This is excised from BB's linked Thread,

    "Kohler defines Stand By Rated gensets as those served by " a reliable utility source" . Exceeding the max rating of the genset is "prohibited". Typical run-time per year is 200 hours, except KM powered units = 100 hours, and the Waukesha units at 3500 hrs. For all other other durations, use the Prime Power rating, for which the smaller Kohler gensets ARE NOT RATED.

    For gensets with Prime Power ratings, it is permissible to use them for applications "where utility power is unreliable or unavailable"

    That was from an older warranty statement from Kohler ... have not looked in the intirim.
    YMMV, etc, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
    Re: Finalizing my Off Grid System... Thoughts?
    Rngr275 wrote: »
    I read the 20hr @ 370Ah (370x2=740Ah) Am I reading doing something wrong.

    No, it depends on which model of L16 you get. There are several and Trojan keeps expanding the line (to my consternation).
    Installer explained to me this way:
    1-1920w array would is just enough Kw for my extimate of 3-5K (3.8kwhr for a 2 hr of sun) and that a 370Ah (8-L19RE-B batteries) 48v would be a good combination of PV and Battery bank.

    1-3000w array would give me ~40% more Kwhr for that same 2 hr but may generat more Ah than the 370Ah (8-L19RE-B batteries) can store during the summer... OK in the winter. He worries about not having enough staorage for the KW generated.

    "Not enough storage for the kW generated". There never is. The batteries reach full, the panels stop producing. Unless you can take advantage of opportunity loads you will always lose some of the power potential (even if you can you can't use it all).

    Your needs of 5 kW hours per day AC come down to: 5 / 0.52 over-all system efficiency = 9615 / 2 hours of sun (pessimistic even by my standards) = 4800W array. Anyway he's doing it a bit backward, as the battery bank is the source of power:

    5000 Watt hours AC = 5600 Watt hours DC / 48 Volts = 117 Amp hours * 4 (25% DOD) = 467 Amp hours. A 640 Amp hour bank should be more than enough. The PV is then designed to recharge it. Usually:

    64 Amps (10% peak current potential) * 48 Volts = 3072 plus efficiency factor = 3989. That's pretty close to what you've got.

    If you try to design a system entirely around Winter numbers it will be too large (and expensive) for Spring, Summer, and Fall. If you design entirely around Summer numbers it will be too small for Fall, Winter, and Spring. You've have to average things a bit and know that sometimes you will be running that generator; that's why you've got it.

    The problem with the larger battery bank is that these tall case batteries really do need some serious current to recharge properly. You might even go with a 15% calculation based on "Summer numbers" so that you'd have enough for Winter.
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #11
    Re: Finalizing my Off Grid System... Thoughts?

    In this link from the OB Forum, the second post indicates that happy EcoGen 6.5 user experienced a sieze-up at 44 Hrs of use, but notes it is being replaced by Generac:

    http://www.outbackpower.com/forum/viewtopic.php?f=17&t=6304

    And, Marc, the only reference I've seen to charging Tall-Case batteries, like the L-16 regards the need a reasonably high Asorb voltage and/or more frequent EQs. The aggressive bubbling of these higher volatge and LOWER current charge stages is what mixes the electrolyte, not the C/10-ish charge currents in Bulk. YES, if the array is so small that one never reaches Asorb, and EQ is impossible, this is not good, but stratification is not the real concern.

    The main batteries in use here are considerably taller than L-16s -- the Jar is 24 inches tall. And have never noted any stratification with my anemic PV array. Bulk currents peak around 3.5% of 20-hr capacity.

    Larger arrays that yield around 10% of capacity are essential when the bank is discharged to 80% SOC or below, no arguement there. Is'nt this fun, we go round and round on this rate/mixing in tall batts.
    Back to work, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #12
    Re: Finalizing my Off Grid System... Thoughts?
    Rngr275 wrote: »
    1-3000w array would give me ~40% more Kwhr for that same 2 hr but may generat more Ah than the 370Ah (8-L19RE-B batteries) can store during the summer... OK in the winter. He worries about not having enough staorage for the KW generated.

    Higher than 3000w of PV like the one I described... 2-1920w Arrays would need to have the larger battery bank... hence the second string to up the AH of the battery bank to 740Ah.

    My load estimate/measurements are in the 3-5Kwhr a day range. Trying to learn/understand and make good choices up front and not spend $$ on non-value added equipment....

    ...I have a Honda 2000i currently just wasn't shure if I needed more generator ot not for the long dark winter here in the Finger LAkes.

    It is a fact of off grid living that there will be waste, usually lots of waste. If your willing to run the genny(and your Honda maybe all you need dependent on max loads) I'd say, go with half the battery bank.

    Use to be, you size your array for the minimal amount of sun exposure to recharge 20-25% of your battery bank in one day, 80 Amps x .7 battery charging effiecency X2.2 hours of sun light, your around 33%, in these days of $1-1.50 a watt solar panels I'd say that's smart.

    I don't have a back up and had planned on 4Kw array for my 24V 800Ah battery system, though I'll use maybe 2-3Kw 9 months of the year, I'll likely be closer to 10-12Kw during the summer, running an AC, I added 2+ Kw to the array when I found them dirt cheap, and actually have a greater 'over sized' array. I'm mostly content, I keep thinking about a larger battery but I have no real need. It's rare to have heat with out sun here, and with the extra array I can be assured that the battery is topped off most days.
    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.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #13
    Re: Finalizing my Off Grid System... Thoughts?

    Vic;

    My info on the tall case batteries is from Trojan, and they generally know what they're talking about. It isn't about mixing the electrolyte, which as you say is a matter of getting it to bubble, but rather of getting the sulphor off the plates to begin with. Trojan always recommends 10% as a minimum peak (not an oxymoron in this case) charge current. Being able to get through the Bulk stage quickly is essential in off-grid, as you may have only 4 hours of sunlight. The longer spent in Bulk the less available for Absorb and then you won't get a proper remixing. The net result is the same.

    Forgive my habitual shortcuts to the end result; the older I get the less time I have for anything, including explanations. ;)
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #14
    Re: Finalizing my Off Grid System... Thoughts?

    And from Surrette/Rolls, I believe they recommend 5% rate max. of charge for equalization (to not overheat the batteries?).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #15
    Re: Finalizing my Off Grid System... Thoughts?
    BB. wrote: »
    And from Surrette/Rolls, I believe they recommend 5% rate max. of charge for equalization (to not overheat the batteries?).

    -Bill

    Yes. Although current limiting during EQ usually isn't an issue.
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #16
    Re: Finalizing my Off Grid System... Thoughts?
    Cariboocoot wrote: »
    The problem with the larger battery bank is that these tall case batteries really do need some serious current to recharge properly.

    OK, guess that I misunderstood -- saw the "tall case batteries" and felt that you were speaking of tall case batteries being somehow unique in charge rate requirements. Believe that the case dimension ratios have very little to do with required recharge currents. Have read all of the Torjan, batt manuals/guides over the years ... must have missed this.

    I did think that you were mentioning at one point recently that gentle recahrge being easier/better for batteries. And most off-grid systems often have this gentle recharge in Summer. Here the Bulk is about five hours, and Asorb is about one hour on typ Summer days. Anyway different strokes ... Thanks, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #17
    Re: Finalizing my Off Grid System... Thoughts?

    Well yes and no, Vic. :D

    The tall case ones need better mixing because (according to the makers) they are more likely to stratify. So to get enough of that higher Voltage mixing time in Absorb you have to get through Bulk quickly. All of it is relative is the thing. Batteries do seem to prefer the solar charging with its climb and decline in current to the sudden onslaught of Amps from a charger, but darned if I know why. Were you thinking of the case of a certain someone who was advocating some quite high current rates (without rationalization) and my repeated rebuking of it? I know; it all gets muddled after awhile.

    On another not, if you were using an Outback controller the Absorb time is set to the Bulk time (with maximum time limits and end Amps capability) so 5 hours of Bulk would run up 5 hours of Absorb time. That would be a definite problem if you've only got 5 hours of good sun. :p
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #18
    Re: Finalizing my Off Grid System... Thoughts?

    Just to add to the confusion, Trojan recomends NOT equalizing their batteries unless the cells are out of balance, most battery manufacturers recomend a Equalizing chared every month to 6 months (Rolls, Crown, etc) Perhaps this is the reason Trojan wants a higher charge rate, normally 5-13% or c/20 - c/8. Trojan likes 10-13%.
    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.
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #19
    Re: Finalizing my Off Grid System... Thoughts?

    Marc,

    I DO use an MX-60 for the system where most of my time is spent. AND, thank goodness my MX does NOT do this horrible thing to my batteries. Bulk starts at/near Sunrise. At about 10 Watts PV power. In the Summer, at the beginning of the second hour, the power is probably 150 watts, and it is not until about the fourth hour is the power at/above 1400 watts. From that point, Bulk proceeds fairly quickly. Asorb REQUIRES about an hour or a bit more time.

    This MX has 5.10, or 5.11 FW, forget which MX has which code, BUT, EA works great (set Min time =00 Mins). And correctly ends Asorb when it should.

    All of this discussion really hinges on the DOD of the battery being charged. The deeper the discharge, the longer will be Bulk and Asorb for a given max available charger current. And, of course, if one does not make it to or through the correct amount of Asorb time at the correct Asorb V (for that exact battery bank, given its DOD), then the mixing that takes place later in Asorb will be missed or reduced. But if this happens rarely on a single day, then no big deal. The next day will catch up on mixing. And so on.

    And Photowhit, Trojan used to spec a very high Asorb voltage -- approaching 60 V for every recharge. Bet this gives good mixing. Had wondered i the past if this was one of the reasons that they discouraged EQ. Hot here, computer is switching to off. Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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