Off Grid sytem opinions please???

System
System Posts: 2,511 admin
in Off Grid Solar & Battery Systems #1
Ok this is my first post on this forum and let me just say it’s a great resource for information on renewable energy.
I am after opinions on an off grid system I am planning to put together. My electricity source at the moment is generator consisting of a Lister CS 6/1 diesel 6hp driving a 3Kw 240v 50hz alternator.
I have installed a solar hot water system and all cooking and heating is done via an Everhot 204 slow combustion wood stove with a water jacket for water heating on cold overcast days.
The plan is to install a PV array and battery bank to reduce the need to run the generator as much as possible down to almost nil :D
*I have 8x190w SolarOne SF160 24v Solar panels from a previously grid tied 1.5kw system. I plan to keep them wired in series to give an open circuit voltage of 360v/DC and a short circuit current 46amps. To which I plan to add the following:
* Xantrex 80amp 600v MPPT charge controller
* A refurbished forklift battery 24v 930ah@20hr (size: 12-125-15) That I will cycle no lower than 30% D.O.D
* 24v 1800w Pure sine wave inverter
The idea is to run my AC refrigeration and some low voltage AC lighting charge phone and laptop off the inverter and to cut right back on loads if there are cloudy periods to give me 3 days of autonomy before I fire up the generator. Ok so my questions are as follows:
1) Will my PV array have enough amps to charge a battery of this size from 30% D.O.D? (factoring in losses/inefficiencies)
2) What size (amp) 24v single phase charger would be most suitable to charge this battery from my 240v generator?
Any comments, suggestions, or advice would be greatly appreciated

Thanks

Keith
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Comments

  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #2
    Re: Off Grid sytem opinions please???

    Welcome to the form Keith! You've come to the right place for sure. This is my response to your post, but keep in mind that others may well see things in a different light, and from different angles. :)
    First thing I notice is your expected amps being 46, but since you plan on connecting all your panels in series, the amperage does NOT add, rather you will get (real world) roughly 5 amps @ 36volts X8 panels = 288 volts. That is, 5 amps at 288 volts, under MPP load conditions. 5X288=1440 watts. BUT, there will be system losses and you won't always get this much from your panels. PV output will depend on the relative angle of the sun, clarity of the atmosphere, cleanliness of the panel faces, temperature of the panels etc, and of course the normal system losses. By the way, the current I would expect to be available from your charge controller for charging your battery, would be roughly 1440/24= 60 amps under full sun. More or less.
    http://www.solardesigntool.com/components/module-panel-solar/Hanwha%20SolarOne/SF-160-M195/specification-data-sheet.html;jsessionid=78903FE6AEC112D1BBCF95EEE1B086CB
    Now, a very important question. What will be your daily power consumption? What are your specific loads? How long will you expect your system to go without sun?
    "A refurbished forklift battery"? What was done to "refurbish" it?
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #3
    Re: Off Grid sytem opinions please???

    It's easiest to work this out from your daily consumption, but it seems that we can work backwards from the info:
    930Ah * the 30% you'll be using = 6.6kWh and you want 3 day's of autonomy from that, so daily consumption would be 2.2kWh. (?)

    Assuming you're in the UK (?), you can use this tool to estimate PV production:
    http://re.jrc.ec.europa.eu/pvgis/apps4/pvest.php#

    Use about 20% for the 'estimated system losses' box. The tool will then add even more losses, but I found 20% matches what I see from my system. With 1.5kW, looks like you'll make about 1kWh/day in december and 5kWh/day in July. Factor in 80% charging efficiency, so that's 800Wh/day dec and 4kWh/day July.

    (I've plugged in london as the location, so best you use your real location to get better results)

    It's not a good think to leave the batteries uncharged for a length of time, so for the marginal months where you know that you won't be able to fully charge with solar, you could set the generator to come on at a DoD of say 10%, so that it comes on every day in the morning and you have a fighting chance of using the rest of the day's solar to complete the charge.

    Instead of using a separate charger, a single inverter/charger is more convenient. It will automatically control the switchover between gen and inverter and can also be programmed to automatically start and stop the generator. Another feature of some of htem is that they can boost the gen's output with their own if you need that.

    Victron multiplus' are very popular in the UK, they have local service centres for repair and are widely used in the boating/off grid market.
    Regarding the XW MPPT 600, it's a really REALLY expensive charge controller for this type of system and I don't see a compelling reason to choose it. The normal XW MPPT charge controller with a Voc limit of 140V, or the outback FM or the morningstar MPPT chargers will do the same job for close to a third of the price. You'd have to have some parallel strings though, e.g. 4 parallel strings of 2 panels in series.

    Victron do a 2kW 24V inverter/charger with a 50A charger = roughly 1.2kW from your gen. If your gen can handle more prolonged current than that, then the next option up is the 3kW unit with a 70A charger.
    Other makes to consider in the 2kW range: SMA sunny island, Studer Inno (although I have heard that you can have issues getting the things repaired in switzerland because of added VAT costs...or something, clarify with dealer before purchasing.)
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #4
    Re: Off Grid sytem opinions please???

    Not to be cryptic, but start with your expected daily loads, and work backwards. All calcs. stem from the loads. Pv sizing, battery sizing, controller sizing, inverter sizing etc.

    Tony
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: Off Grid sytem opinions please???

    Will you have enough PV to charge that battery? Nope.
    Look at it as a whole: eight 190 Watt panels is 1520 Watts. Usually these will operate at about 77% efficiency on average, so that's 1170 Watts. Charging Voltage for the 24 Volt system is around 28.8. Divide Watts by Voltage and get 40 Amps peak potential charge current. That's around 4% of the 930 Amp hour rating of the proposed battery; below the recommended 5% minimum and well below the desirable 10% target.

    Do you need that much power? Probably not. 930 Amp hours is roughly 11 kW hours of potential power at 50% DOD. I run the cabin off 2.4 kW hours, including refrigeration and water pumps. At 25% DOD you'd still have double that. Forklift batteries, btw, are capable of a maximum 80% DOD. I recommend you rethink your battery bank, starting by getting a Kill-A-Watt meter and measuring some real-world power consumption of what you plan to use. You won't get it 100% right, but it will be close. You need to have target numbers for maximum Watts at any one time and total daily Watt hours.

    What charger should you get? You're going to be in the "big power" category here, with refrigeration (high start-up surge which won't show up on the K-A-W meter). You will be better off buying an inverter with built-in high capacity charger.

    The Xantrex controller you're looking at is tres expensive: $1300+ It will be much cheaper to reconfigure the array a bit and use a Midnight Solar Classic to handle the unusually high Voltages of your panels. If we had all the panels specs (Voc, Vmp, Imp, Isc) we could get more specific about configuration.

    Welcome to the forum. Hope you haven't already spent the big $. :D
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #6
    Re: Off Grid sytem opinions please???

    > To which I plan to add the following:
    > * Xantrex 80amp 600v MPPT charge controller

    I think he's got the high voltage PV DC covered, or does the Classic go higher than that ?
    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 ,

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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Re: Off Grid sytem opinions please???
    mike90045 wrote: »
    > To which I plan to add the following:
    > * Xantrex 80amp 600v MPPT charge controller

    I think he's got the high voltage PV DC covered, or does the Classic go higher than that ?

    No, the Classic is lower than that: in both Voltage max (up to 250) and a significant amount of dollars. The Classic 250 is roughly 1/2 the price of the Xantrex 600. Worth rearranging the panels for in my opinion.
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,892 ✭✭✭✭✭✭
    #8
    Re: Off Grid sytem opinions please???
    Cariboocoot wrote: »
    No, the Classic is lower than that: in both Voltage max (up to 250) and a significant amount of dollars. The Classic 250 is roughly 1/2 the price of the Xantrex 600. Worth rearranging the panels for in my opinion.

    On the other hand the XW -80-600 has much more capacity to grow later.
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
    Re: Off Grid sytem opinions please???
    Dave Sparks wrote: »
    On the other hand the XW -80-600 has much more capacity to grow later.

    Providing you can get past the persistent problem of being able to match the existing panels on the controller. Of course you could buy a second Midnight Classic and still not have spent the money the one Xantrex unit costs and not have to worry that the next batch of panels you buy isn't a close enough match to the old ones.
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