Please comment on this off-grid design with gen backup

Not close enough. Minimum panel wattage required for 48 volt battery is 64 volts, preferable up around 90 to 120 volts.

My questions
WHY are you building a High voltage off grid array, using a very expensive charge controller (~$1,200) ? Do you have extremely long DC runs to need 300V ? Try splitting the the panels to 90-120V strings, to use a more conventional (mass produced = <$$) controller: Schneider Electric (Xantrex) Conext MPPT 60-150 $400
Even if you needed 2 of them, that's less than 1 of the 600V-80A And you gain some redundancy. And can use the 150V breakers from Midnight, simplifying the combiner/disco box
And I'd consider scaling up the array just a bit larger, to cover more charging in the winter.

Inverter, the Conext version XW-5548 should be OK, it's a lot less than the XW-6048 I'm used to. Hopefully it's just as solid.

To tie them all together, monitor, program and update firmware:
Schneider Conext ComBox ~$400 (lots of $$, but invaluable features) Along with a $40 wi-fi router, now you are connected. (The SCP is $230, so get the ComBox)
And their battery monitor, if you are staying with all one brand (data buss protocol) Conext Battery Monitor $300 (I don't know if it comes with a shunt)

When your batteries are low, your array could put out nearly 90A at 50V (low battery voltage = high amps from 4400w) Better to split that to 2, 60A controllers. Adjust wire gauge accordingly

You want a Midnight ePanel to wire this stuff into. And several more of the Midnight SPD's (MOV in your dwg)
And wire the high amp stuff intelligently, center loads on the buss bars, don't put the inputs on one end, and the total output on the other (we can all learn from my installers mistakes)
10259224_654873261252797_5715636728126544140_o.jpg

I don't own the MPPT 60-150 controllers, I don't know if you can configure them, to limit the output amps, may be desirable if you are close to the max battery charge amps, or you can split the aim of the 2 arrays by 10-30 degrees, to get a "broader" power band over a larger period of time. But you do need a minimum charge rate to stir the electrolyte in the batteries.

Generator, I've not heard good things about the generac ecogen. They don't warranty them for off-grid (prime) use, and will not honor the warranty. Have you considered a diesel genset ? (there are many good ones) Will the low temps in your area allow the use of propane (vapor pressure when cold) ?

Battery:
There are 2v, 4v and 6v deep cycle batteries to get a single series string example:
Trojan L16RE-2V 2 20 hr:1110ah L11.575" W7.125" H17.7" 119lbs

beware - some are a 3 pack of parallel 2v cells, with 3 filler ports !!

And, you may want to start with a sacrificial set of cheap golf cart batteries for the first year or 2 (if they last that long) which will do 2 things: a) allow you to de-bug the system and fry cheap batteries instead of a pricey set. b) verify your loads and usage, to insure your final set will be sized right.

?? You want to edit that message to say what you mean ??

I do not understand your reply. What I meant was am I running too near the output amperage rating of the MPPT. You said the minimum panel "wattage" is "volts", which doesn't make sense and I am too new to know what you mean. I don't know what the 64 and 90 to 120 represent. Can you please elaborate?

Opps.

Sorry I meant minimum panel voltage. But after looking at the drawing I see what Mike is saying. Unless there is a specific need to run that high of a voltage, you can save some coins using 150 or 200 volt controllers.

Mike,

"Why"? Because I am a beginner! I don't believe I have what you consider a really long run. I've heard you can go 300' or more DC, but I haven't run the numbers. I only have 70'.

What was the evolution? I started by considering two MS Classic 150's, and you may recall I had 4 in a string which Amy pointed out exceeds the VOC. I was confused what the MS HyperVOC actually permits, and now I know. So I am limited to 3 in a string, and I wanted 16 panels. With three in string, that pushes me to 5 strings and I saw the current going up up up. With two controllers, I'd have one with three strings and one with two, and I'm down 275 watts. Yeah, I'll admit - when I saw the high voltage capability of the MPPT 80 600, I was impressed and thought I'd get a lower voltage drop over the run with lower current. But you are suggesting I don't need to worry about it for shorter runs. My solar array will be facing due south on a roof. I would have to add a pole mount to face panels another direction.

I *did* consider briefly that "redundancy" is good for off-grid. I was looking at the Classic 200 and 250 this morning, and noticed I would have to pay more for two than the one MPPT 80 600. However, I get a backup if one dies. With those I get 4 in a string. Bottom line is I didn't like going to 3 in a string and losing a panel. With the Xantrex 60 150 I again am limited to 3. Sounds like I should consider having two, primarily for the redundancy. Beginner's mistake. Better to find out now than when the only one smokes itself.

Thanks for that info about batteries. I did see higher capacity units that weigh 230 or 270 lbs, but I couldn't get near 715Ah and they are more expensive overall. Maybe that was the Rolls 5000 series.

I have propane on site. I don't really like adding fuel, unless there is a good reason. The Ecogen is air cooled, and the little research I did I believe suggested not good for continuous duty. It was only in the last few days I realized it may run for 7 or 8 hours. You have to remember I am a novice here. I also don't want ear-splitting noise. Will possibly using a noiser but more appropriate generator and building a sound proof enclosure be an option? Do you think the capacity is OK?

As far as multiple angles, I am limited to 9am to 2:30pm of unobstructed sky on Dec 21 on this site. Beyond that after 2:30, the sun will be coming through crowns of trees 250' away, and from what I have read that will reduce my output considerably. My plan was a planar array mounted on a roof of a custom building. I need the building to get me up 10' to clear obstructions (house and trees). The array bottom would be at 10', and going up from there. Thus not a lot of flexibility. Also no extra roof space to add panels later. I'd have to add a pole mount.

Would what is pictured here be along the lines of what I might do? Two Classic 200's are about $1200 at least online - about the same cost, some additional wire and more labor to install, a different manufacturer so monitoring is more complicated. But it will be in my basement and not out 50' through the snow in an unheated garage as originally planned. And most important I get 40-50 more amps (Classic 200 is 65A max @ 48V).

Please ignore everything grayed out, which needs to be updated.

Can I do the two different hot circuits inside one combiner box as far as the NEC goes? With AC house wiring it wouldn't be allowed. Thanks.

If you complain about the cost of the battery. Why are you want to size 700+amp hours for 7 KWH per 24hours? I just don't see the sense of it. I am assume some of the power are used during the day in the sun hours. We Off grid folks have to manipulate the use of the power. Try use the heavy load during the sun hours and only use light load during the night.

Peukert's Law yield a little more amp hours if you use it less than the 20 hours rate. Like the Rolls S-605, it rated 468 AH at 20 hours rate, if you load is average in 24 hours, it is only 300 watts, even calculate with 500watts, the power draw will be around 10 amps at 48 to 50 volts. it will be 50 hours rate on the Rolls S-605 which will yield you to 547 AH.

If it were me, I will save some money by use only 15 panels and wired 3 in series and 5 series in parallel, use one Classic 150 charge controller which can easily handle 4600 watts at 48 volt system. use only one string Rolls S-605 and use the generator to charge the battery when ever is overcast. just two to three hours generator can supply the rest of the day. I will use the money saved buy another small inverter to run it in the night when the load is very small.

When you lay out your panels and wire them, wire from side to side,

1 - 2 - 3 * 4 - 5 - 6
7 - 8 - 9 * 10-11 -12

That way, as the sun and shadows shade the lower row, you still have active strings on the upper row that can continue production

not
1 4
2 5
3 6 Where the first bit of shadow on the lower row of 3 6, shuts down all harvest from 123 & 456.

Does that make sense ?

I get what your intent is, but I don't understand the example. You didn't comment on using 4 in series, which I think is ok with the Classic 200 (but it may result in less efficiency than strings of 3 with the 150 - I have to go back and look at the manual, which has several curves in it), but let's assume I am using a 4 x 4 array with 2 strings of 4 into each MPPT.

If my array spatially is:
01-05-09-13
02-06-10-14
03-07-11-15
04-08-09-16

Are you recommending wiring 4-8-9-16 in one string, as opposed to top to bottom, so that shading of the bottom row doesn't slam all strings?

Everyone has their own opinion. Look at Mike's comment that he would up the size of the PV, to use a generator less. I don't mind running a generator, but I don't want to run it every day by any means - especially not in winter.

I used two different methods to determine the battery bank size. One was a rough guideline Sunking posted a while ago, which I can't recall at the moment but yielded 715Ah. The other is a formula takes the Ah needed in day (144), divides by the inverter efficiency to find true Ah needed (160). Then multiply by the battery multiplier (1.11 @ 60 deg) and the days of autonomy (2), and divide by the DOD allowed (0.5). This gave me 709 Ah, which agreed well with Sunking's guide, even though I believe his was for 3 days or of autonomy and also 50% DOD. By the way, if I had chosen 3 days which many people suggest, I'd be over 1000Ah. So I felt I was undersizing this already, but not by far. But you may be right, and all I need is 4000W. Someone else suggested not going balls out with the batteries at first. Perhaps good advice, considering the cost.

I only get 2 hours worth of insolation in the winter, maybe less, and that is when the sun shines. I hear what you mean, in that I may be able to get along with less, and that when the generator is running I'm taking excess from there. I have no idea what running this day to day will be like, so I am relying on people with experience, and trying to mash together their opinions. It's a shame they all aren't the same

a) working on 3rd week now, no sun. Got 14 minutes today, been about 3- 4 hrs daily generator runtime. Larger array would not be of help at the moment. No sun forecast for the next week either !

b) Yes, if the bottom row 4-8-9-16 is shaded, even parallel with 3 other strings, the controller will only be 25-30% reduced. Any string with shade will be disabled. Even shade from a twig can be enough to shut down a string.

And a item I learned, is that the higher the PV voltage, the more loss (heat) in the controller downconversion. My 140V strings into my batteries, has the cooling fan in the controller screaming all the time. For a 48V bank, EQ at 65V, you don't want to go much over 120Vmp in the strings, unless you have really long runs that you can't afford copper for.

And in winter, or cloudy conditions, you run the genset on day 2, and reserve day 3 for when the weather is so bad, you can't get to the genset. If your batteries are already flat, you are in the dark. As much fuel as I have been using and transferring, even though diesel stinks, it doesn't explode like gasoline can. And gas stinks too.

OK, I did some looking at something I haven't investigated enough yet. Generators. The ecogen is relatively cheap, but cheap doesn't mean good. I found a thread here http://www.solarpaneltalk.com/archiv...p/t-13837.html with some interesting comments, and there appears to be a lot out there on the web written by people looking for a solution.

Unfortunately, more gray area. Turns out those of use who charge batteries for hours using generators may be using them as what the manufacturer calls "Prime Power", not "Backup," and this voids the warranty (as mentioned above). Furthermore, a small (<18,000W) generator that is water cooled, which appears to be desirable for long run times, is as easy as finding a gold doubloon when you excavate to build a house.

Anyway, I see there are a lot of generators out there to peruse. Time to dive in.

Start here for generators. For homeowners you basically have two manufactures, Generac and Kohler. They both make residential and commercial products. Fo rprime power you want commercial grade which is going to cost you. Make note non eof the manufactures offer a gasoline model for stationary generators. There is a good reason for that.