Hi All. (Semi) Solar Newbie from Australia.

Lumpen
Lumpen Registered Users Posts: 4
in Solar Beginners Corner #1
Hellow,

I've been reading these forums for the last few weeks as I'm looking to piece together an off-grid solar system for my first house (well, backwoods cabin to be honest).

Although this is the first system I'll have installed, I've been living in a off-grid solar house for the last 25 years, so I'm already well aware of its limitations. The system there consits of 24 BP 40W panels, a Plasmatronics PC2430 PWM regulator, a Latronics M2(?) 1500/6000 inverter, back up is by a 2.5kVa cheapie genset running into a 10A! charger. Batteries are a sad state of affairs. The bank consists of four near new Sunextender PVX-2120L and four Remco 200A/H AGM's of unknown age, set up in series/parallel to give 24V (trust me, you don't want a photo!) The system runs ar 24V for lighting and the fridge and freezer with 240V out of the point for computers, TV's etc. Basically a stoneage set-up that hasn't changed that much since it was first installed, with the panels now maxing out at about 30A on good day.

As for my cabin, I'm planning on designing the appliances around the system to some extent. Cooking is either on LP gas or wood stove, heating is via a radiant Nectre slow combustion heater and hot water will be via "instant" LPG system. I would like to have a decent 240V fridge that I plan on filling with water bottles to take up excess space and keep cool, its yearly power consumption is given as being 269kW/h (740wh/day?). Lighting will be exclusively by LED lights, typically in the 3W-6W range, outside lights will probably cheapie solar motion spotlights from ebay. I'll also need to use a pressure pump for water pressure to the shower/gas hot water but I'm undecided if that's going to be a 24V bilge pump style or a proper pressure pump.

Property location is approximately 28.6S, 151.9E and I'm planning on permanently ground mounting the panels to keep them accessible and also give them best chance at sun for longest time. Sunshine average: 7 hours winter/12MJ day, 9 hours summer/20MJ/day.

I (think) I know what I'd like to use and most of the electronic side I plan on buy from the states (NAWS) simply due to the cost (though panels and batteries are probably going to be sourced locally).

I am planning on:
Outback VFX3024 (International 240V) Inverter - Look solid, 240V and good inbuilt charger too.
Midnite Classic 150 MPPT - Good rep and can take alot of Amps in the one unit, wish to keep this as "simple" as possible.
2x5 Panel Strings of 250W 24V Panels (initially 1x5panel string?) - Midnite Charger Sizing PDF is attached with details.
24V battery bank, probably 12x2V AGM but unsure on exact sizing/style as yet. 600 to 800A/H?

I have a few questions though, as the more I read, the more I seem to get confused.

1/The charger component of the VFX inverter, will it take AC from a generator or is it grid only? I have looked at the manual and though I'm far from technical, there didn't seem to be anywhere to plug it in?
2/I like the look of the pentametric battery monitor, though not nessecary, is it worthwhile? Should I just trust the Midnite MPPT?
3/Is it possible to set up automatic generator startup at say 75%SOC on this system? If so, does that require other gadgets?
4/How do you go about sizing battery banks when you have no idea of the REAL draw of appliances? I find it very hard to track down draw numbers (W or A) for things like TV's etc, about all I can use is the federal government electricity rating system which typically gives kW/h per year on a standardised system (eg. all TV's are on 10 hours use, 14 hours standby)


All input, ideas, experience and knowledge GREATLY appreciated.


Thanks,
Brendan
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Comments

  • Lumpen
    Lumpen Registered Users Posts: 4
    #2
    Re: Hi All. (Semi) Solar Newbie from Australia.

    I actually quite like the look of the Outback pre-built system: http://www.solar-electric.com/outback-flexpower-preassembled-inverter-system-fp1-vfx3024e.html

    It would take out alot of the hassle I'm sure. However, I'm wondering about the charge controller. The Flexmax80 is rated at 80A@24V = 1920W but Outback state that 2500W is the maximum sized solar array. Would I get away with 2500W of panels or would it be better to drop it back to say, 2000w (8x250?).

    Summer temps are typically 22-26c (71-79f) and only rarely above 32 (90) while winter is typically 10-18c (50-68f) in the day, dropping to -6c (20f) overnight.


    Cheers,
    Brendan
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #3
    Re: Hi All. (Semi) Solar Newbie from Australia.
    Lumpen wrote: »
    1/The charger component of the VFX inverter, will it take AC from a generator or is it grid only? I have looked at the manual and though I'm far from technical, there didn't seem to be anywhere to plug it in?
    2/I like the look of the pentametric battery monitor, though not nessecary, is it worthwhile? Should I just trust the Midnite MPPT?
    3/Is it possible to set up automatic generator startup at say 75%SOC on this system? If so, does that require other gadgets?
    4/How do you go about sizing battery banks when you have no idea of the REAL draw of appliances? I find it very hard to track down draw numbers (W or A) for things like TV's etc, about all I can use is the federal government electricity rating system which typically gives kW/h per year on a standardised system (eg. all TV's are on 10 hours use, 14 hours standby)

    Welcome to the forum.
    1) the VFX works very nicely from a generator. It is meant to be hard-wired to the generator. Take a look at the Midnite ePanel. You can buy it pre-wired with the Outback inverter and Classic charge controller. It comes with all breakers, bypass switch, shunt, etc. Just screw it to the wall, hook up the batteries, ground rod, and generator, and run the AC output to your circuit breaker panel.

    2) I highly recommend a battery monitor such as the pentametric. Midnite is about to release their new shunt based battery monitor, so it might be worth waiting for.

    3) You can set up AGS, but how you do it depends on the generator. I don't think you can set it to start at 75% SOC without a battery monitor. You can set it to start based on battery voltage.

    4) Unfortunately you cannot size a battery bank until you know your loads. You design a system to meet a need, and the need is the load. If you don't know what you need, you don't know what to buy.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Hi All. (Semi) Solar Newbie from Australia.

    Actually if you're determined to limit your array to 2500 Watts you can set the battery size by that. It will not hurt either an FM80 or Classic controller to be "maxed out" on array: extra power available is simply 'clipped' (not utilized). Too much panel is, of course, a waste of money.

    2500 Watts should supply about 80 Amps peak current @ 24 Volts, and using the 10% rule-of-thumb that would 'limit' you to 800 Amp hours of battery. That would normally supply about 4 kW hours @ 25% DOD. I get by on about half that. :D

    The panels themselves would supply roughly 5 kW hours per day, so if you can take advantage of daytime loads your system would be even more efficient.

    Don't start out with less panel than your batteries need. If you halve the array, halve the batteries as well. You might find 2 kW hours daily to be a bit of a stretch what with the TV and all. Check the specs on your panels carefully: one string of five could be 190 Voc which is over the limit for anything but a Classic 200 or 250.

    You might consider going with a 48 Volt system if you're looking for that 4 kW hours stored capacity.
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  • petertearai
    petertearai Solar Expert Posts: 471 ✭✭✭✭
    #5
    Re: Hi All. (Semi) Solar Newbie from Australia.

    Hi I think the victron battery moniter can be used to start a generator at a predetermined SOC.
    2225 wattts pv . Outback 2kw  fxr pure sine inverter . fm80 charge controller . Mate 3. victron battery monitor . 24 volts  in 2 volt Shoto lead carbon extreme batterys. off grid  holiday home 
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  • Lumpen
    Lumpen Registered Users Posts: 4
    #6
    Re: Hi All. (Semi) Solar Newbie from Australia.

    Thanks for the input all, just a quick note while I'm thinking over it. I blued earlier when I said the Midnite sizing calculator thing said 2 strings of 5 panels would work, it was actually 5 strings of 2! I just did it again and it says 10 strings of 1 (I guess all in parallel?) is feasible, though is it practicable? That string would be putting in nearly 100A at the last panel, which is some serious cabling, can MC4 Y connector (splits) cabling take that kind of amps? Is there a prefered way to wire panels in general? Panel I'm considering using is here (local Australian link,hope it's ok?): http://www.lowenergydevelopments.com.au/index.php?route=product/product&path=59_77&product_id=78

    I just used an online calculator (another local australia solar provider, won't link unless needed) using worst case scenarios (Fridge, Laptop and all lights running constantly, TV running 2 hours and a pedastal fan running 12 hours and 1000W pressure pump running for 1 hour) which suggested I'd use 245A/H or 5897 watt hours per day and for 3 days autonomy I'd need 1228A/H of storage, or 2047A/H for 5 days of autonomy (I guess at C100 rating?). This included 8% inverter losses and 10% battery losses. Does this sound about right? I was expecting around 1000A/H given what the other house uses/

    For the fridge I back calculated from 269kw/h per year to give 730w/h/day or about 31W average draw per hour. I know they cycle using more power for less time but this is the only figure I could get for its power use, does it look right at least for calculation?


    Cheers,
    Brendan
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #7
    Re: Hi All. (Semi) Solar Newbie from Australia.
    Lumpen wrote: »
    it was actually 5 strings of 2! I just did it again and it says 10 strings of 1 (I guess all in parallel?) is feasible, though is it practicable? That string would be putting in nearly 100A at the last panel, which is some serious cabling, can MC4 Y connector (splits) cabling take that kind of amps? Is there a prefered way to wire panels in general?

    Those panels have a Vmp of 30.7. Therefore you must put them in 5 strings of two panels per string. All 10 panels in parallel won't be adequate for a 24 volt system. You will need to use a MPPT type controller to drop your input voltage (about 60 volts) to battery charging voltage.

    The proper way to connect them is to put a combiner box close to the panels. Each string goes directly to the combiner box and has its own fuse or circuit breaker in the combiner. Midnite Solar makes a very nice combiner that can handle 6 strings. Midnite will custom make the combiner with MC4 connectors .... just plug each string into the bottom of the box.

    Do NOT cut your MC4 cables. If your combiner does not have built in MC4 connectors, buy some MC4 extensions and cut them in half. Take the cut end and run it into the combiner.

    How far will your panels be from your charge controller? You need to pick the right sized cable to go from the combiner to the controller.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #8
    Re: Hi All. (Semi) Solar Newbie from Australia.

    hi brendan,
    that pv looks ok spec wise, but we here don't know the make or reliability of it or the company that made it. be advised that they say it is a 24v nominal pv. it isn't. that pv would not be able to reliably keep a 24v battery charged as most 24v nominal pvs will have about 35v vmp or higher. you can still use it with an mppt controller, but you need to use at least 2 pvs in series to get the proper voltage. anytime we refer to 2 or more in series this is called a string and you may be able to put 3 in series too as the controllers can down convert the voltage. 4 may be too high for outback controllers and the classic 150, but the midnite classic has more models that can go higher and have a safety over voltage feature called hypervoc to help prevent damage to the controller from accidental over voltage periods.

    you are going with 10 pvs so this would be 5 strings of 2. this is right to the edge on the capability of 1 classic 150 and will be too much for the outback. even with the 10 pvs there will be times the classic will be at its 94a maximum current and freeze at that current level. 2500w/94a=26.6v so if the batteries show below this 26.6v while charging the classic will be clipping at that 94a level. if you go to expand on your pvs you will need another controller as there's no room for expansion unless you would consider a 48v battery bank and use an inverter with 48v input. this would necessitate 3 pvs in series for each string to get the proper input voltage btw.

    your watthour draws don't look too concrete so you may want to try and pinpoint your loads better. just remember that it is not advisable to draw your batteries below 50% soc to try and preserve the battery life. once you've better determined your daily loads you can just multiply that number by the number of days of autonomy. thus also means that the 50% minimum buffer also gets multiplied by the same number of days. if the bank gets too large it can affect the size of your pv array as you may then need more to meet the charging needs of the larger battery bank.
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  • Lumpen
    Lumpen Registered Users Posts: 4
    #9
    Re: Hi All. (Semi) Solar Newbie from Australia.

    Thanks for the replies everyone, I'm very slowly starting to get an idea together about what goes with what.

    There are two panels that I'm leaning towards currently, both from the same distributor.
    The Midnite sizer (pdf attached) indicates both will function with the Classic 150 on 5 x 2 panel strings. Is there are reason to prefer one over the other? Higher voltage, less current for wiring perhaps? They are more expensive though.

    I like the look of the combiner box, does seem to make things much simpler. As for length of wiring I'm planning on having the panels either on the ground in front of a dedicated "solar" shed. So probably less than 6 foot from the panel to the combiner which for all intents and purposes should be in the same room as the charge controller, inverter, batteries and just off the side of the house.


    Cheers,
    Brendan
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #10
    Re: Hi All. (Semi) Solar Newbie from Australia.

    watts are watts. given 2 relatively unknown manufacturers then go with the lower cost of the 2. you can get higher voltages with the cheaper pvs by placing more in series. not worth paying more for the pv with higher voltage.
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