New off grid home

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Re: New off grid home

Postby franks » Fri Nov 15, 2013 11:40 am

Its overkill using breakers for 2x200watt string (arc not really a issue with Voc of 90), I would use 10amp DIN fuses & holders..cheap as dirt.
With such a large PV array wanted..I suggest going for 250w panels (60 cell) 4 in series (Voc 148v, Vmpp 120v) Midnite supports hyper Voc..for the odd times its very cold and Voc excceds 150volts.
48 volt system you can have 4kW array thats 16 250 watt panels as 4 strings of 4..less cabling and less fusing/breakers.
3.04kW Grid Tie system 16 of 190W PVs, Samil 3.3kW
3.8kW PV Stand Alone Off Grid.. 5-8kWHr Per day
24 of 190W PVs
Midnite Classic 150 & Lite MPPT
8 of 6V 600 AH flooded cells (24 volt 1200 AH)
Outback VFX3024E Inverter Charger
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Re: New off grid home

Postby offgridQLD » Fri Nov 15, 2013 11:54 am

Yes its overkill but I don't mind a bit of overkill if its anything to do with safety. I already have the panels. yes its 4 more panels 200w panels than using 250w but the 200w only just fit were I want them at the size they are now.

I find my classic works really well with a voltage closer to charging voltages more so it stays very cool doing so. Also I don't particularly like having 150v Dc running all over the place. Yes less fusing less cabling but for a few hundred dollars more I'm happy to keep it 2s - 1p config.

If the shit hits the fan with one of my classics I can throw one or two of my old PL40s charge controllers back on line and they will still work as a backup with 1p-2s config.

Kurt
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Re: New off grid home

Postby franks » Fri Nov 15, 2013 12:33 pm

10 strings of 5.3 amps Impp for each string... thats 53 amps I trust your using good cabling..anyway the difference between Vmpp 120 vs Vmpp 72 volts input into the charge reg is less than 0.5% in effecency, also watts is watts, higher voltage-less current or lower voltage-more current..still the same heat.

Im suprised the assumptions people on here make ???
3.04kW Grid Tie system 16 of 190W PVs, Samil 3.3kW
3.8kW PV Stand Alone Off Grid.. 5-8kWHr Per day
24 of 190W PVs
Midnite Classic 150 & Lite MPPT
8 of 6V 600 AH flooded cells (24 volt 1200 AH)
Outback VFX3024E Inverter Charger
franks
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Re: New off grid home

Postby offgridQLD » Fri Nov 15, 2013 12:53 pm

Where are you getting that 0.5% number from?

I'm not talking about heat in the cable . I understand the simple equation for wattage. I talking about heat created in the classic when its down converting from 120v to 50-60v. 0.5% that you mentioned of a 4000w array is 20w I'm sure the classic is shedding more than just 20w of heat down converting from 120v - 50-60v charge voltage. I could be wrong but it sounds to small.

6mm2 for each string to the combiner and them a minimum of 32mm2 more likely 50mm2 for the 15m to the breaker before the classic.


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Re: New off grid home

Postby franks » Fri Nov 15, 2013 1:08 pm

The power graph for the classic 150 difference between Vmpp 120 & Vmmp 72 volts input, also as the classic is a buck DC-DC converter a head room of 30% is suggested
ie 62 volts equlise for 48 volt flooded battery bank..I think you have
ie 62x1.3 =78 volts min, also expect your PV array will be running NOCT values not STC (Ideal).. setup will drop yeild when cell temp is very high cell temp, cell temp typically aprox Tambiant +25
3.04kW Grid Tie system 16 of 190W PVs, Samil 3.3kW
3.8kW PV Stand Alone Off Grid.. 5-8kWHr Per day
24 of 190W PVs
Midnite Classic 150 & Lite MPPT
8 of 6V 600 AH flooded cells (24 volt 1200 AH)
Outback VFX3024E Inverter Charger
franks
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Re: New off grid home

Postby offgridQLD » Fri Nov 15, 2013 1:15 pm

Well I can give it a try I have 21 panels if a want to go 3s .

Though the old 4000w system is working fine on 2s and they are even lower voltage just 35.2v panels than the new ones are 36.7v.

looking at the classic 150 graph at 48v nominal why is it capable of 5022w at 70v input and only 4438w at 110v ? That's 584w less at 110v more than 10% derating. Can only be one reason why its derated the higher the voltage goes above 70v and it must be heat! and whats heat - inefficiency. You an clearly see the max wattage rating gets smaller as the voltage increases Above 70v. Now it's a different story with the classic 200 it's sweet spot looks to be around 140v and the classic 250's sweet spot is about 180v.

Image

The new panels are 36.7v - (73.4v) I want it working best from 50v - 60v as the meat of my charge is done at 55-60v. EQ I only do a couple of times a year if that. Once I go to 16s lithium battery bank. I wont be doing any EQ and will only need 59v- 60v in a short absorb stage to get each cell to 3.65 and balance the cells and the meat of the charge will be done at 50v- 55v with lithium.

Kurt
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Re: New off grid home

Postby offgridQLD » Sun Nov 17, 2013 1:47 pm

Got to test the hail impact resistance of our BP solar panels yesterday. The largest stone were golf ball size. We were lucky up in the hills down on the coast the hail was the size of tennis bals :shock: .

Was A little nerve wracking watching them smack into the glass panels at terminal velocity.It didn't sound good at all. Happy to report no damage but it did hold me back on installing my new panels.

hail at our house golf ball size
Image

Hail down the hill tennis ball size.
Image

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Re: New off grid home

Postby offgridQLD » Wed Dec 04, 2013 12:21 pm

Just an update on the 4200w PV array.

I have been gathering parts over the weeks some of the component spec decisions like breaker ratings and cable size were dependent on what PV configuration I settled on 2 series (73.4v at pmax ) or 3 series for (110.1v at pmax). After a lot of procrastinating and partly due to the cable run lengths, easier to obtain reasonably prices DC CB in the sub 100A range and the fact I don't really have a use for the extra 200w panel I purchased to enable 3 series 21 panels total. I decide to go with 3 series configuration. 3 series 110v limits my 2nd classics output to 76A (4438w) vs 83A at 2 series 73v (5022w) but I can live with that. Not often will I hit that 76A limit (4438w) from a 4200w array without it being a cloud edge effect situation anyhow.

So I purchased 6mm2 cable to run from the PV to the junction boxes in the shed (one separate run for every 3 series panels). some of the runs from the most distant panels add up to close to 20m (12m or so for the closer panels) So 6mm2 gives me just under %2 voltage drop.I found some nice 8pole distribution boxes and settled on two of them. One will hold 4x10A dual pole Dc CB. From 4 strings of 3 series (12 panels) on the lowers roof. The second box will be populated with 3x10a dual pole DC cb. From 3 strings (9 panels) on the upper roof section. below the combiner boxes are two boxes with the buss bars to parallel all my 6mm2 outputs to a nice 10mm stud to run my 50mm2 cable from.


From the underground run from the buss bars down to the power room around 15m distance (I have allowed 20m of cable as you always need a little more to tie off each end) I have purchased 50mm2 cable this gives me under 2% loss. I then have a total from PV to charge controller of under 4% loss very worst case.

I will have 50A dual pole DC breaker just before the new classic charge controller. Just for some isolation down there. Though both new and old classics will get there own 125A primary fuse on there outputs. Before there outputs are paralleled at the main secondary large knife switch style fuse isolator and 200A fuse.

Originally with just the one classic charge controller there was two 250A fuses for the main battery feeds to the inverter and the 3rd fuse slot of the 3 gang isolator had a 125A fuse for the PV. I like this isolator arrangement as both PV & battery are isolated at once at the pull of the one lever. I wanted to maintain this style of isolation. Now with two classic charge controllers to the one PV fuse I needed to up the final fuse rating and add the smaller primary fusing on each classic. (I think this is the best way to go about it and use whats there but open to ideas)

I'm getting there slowly.

ps, I added the new (wiz bang ) current shunt modal by midnite solar last weekend. It's a 500A shunt tapped just off the main battery negative feed. There was just one sense wire back to the classic 150s Axillary 2 input (5 min installation job). Now when I set a end amps setting to trigger the end of absorb. It now takes all loads on the battery into account to calculate when the end amp trigger point it reached. Regardless of what loads are on the battery. This is a great feature as we often have our EV charger or washing machine, dishwasher and so on running or during the week perhaps very little running while the classic is trying to switch to float .This made it imposable to calculate just one amp trigger value that would take all the load variations into account.Often timer based float triggering would be the unnecessary fallback.The problem is solved now and the true end amps value is always what triggers float.

Other features are being slowly added to the classic monitoring software to take full advantage of the new shunt model in a logging sense.

Kurt
Last edited by offgridQLD on Wed Dec 04, 2013 1:30 pm, edited 8 times in total.
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Re: New off grid home

Postby jimbo » Wed Dec 04, 2013 12:35 pm

Hi Kurt,

Can you see any of the Shunt data on mymidnite or the Local app?
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Re: New off grid home

Postby offgridQLD » Wed Dec 04, 2013 12:47 pm

For now the shunt data is available just through the latest local app (vs 0.3.33 from memory) (and the latest firmware on the classic) On the local app 0.3.33 A little window just under the status tab and Shows up as WBJR and live + or - amps reading along with net amps.

For example it might show -3.5A at night with base loads and no pv input. Or +70A in the day when charging. It's interesting to see the classic pumping say 50A+ output from PV but then see the shunt only showing +30A due to 20A of inverter loads. It's also interesting to watch it try and hover around 0Amps at the shunt when in float and loads come on while the classic ramps up its output to cover loads but not charge the battery any more.

Improvements/utilization they want to make are. More averaging in its output readings for more stable numbers (though I find it ok as it is) They also mentioned tying the data into the logging and perhaps my midnite. It's early days and they just wanted to get it out there and solve the triggering of end amps under fluctuating loads issue. As it was something that many people were asking for a solution.

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