Too many options. Need some help.

[Bluedog225]

I’ve got analysts paralysis. I’d sure appreciate any thoughts.

Let’s say I’ve got a lot of panels like 60 or 70. Off grid. And I need to maintain a couple of thousand watt load 24/7 during the really hot summer months. 100 days over 100F not that long ago. 95F at sunrise. Texas y’all. (chuckle). Duty cycle of the air conditioning is hard to predict in those conditions…assuming 100%.

And I am going to have the battery capacity to carry me for a bit. Say eventually 16 server rack batteries (48V/100ah). That’s about 40 dark hours. Eventually. Starting with 4 batteries and will see how it goes. The point being, a large potential bank to charge.

The panels are a mix but lots in the 290 watt 40 volt neighborhood.

Here’s where I’m stuck. I plan for 16 panels or so east, 32 or so south, and 16 or so west. As fat a curve as I can get.

How do I choose among the extraordinary variety of series and parallel options?

Do I go high voltage and get a victron 250/100? Or a Midnite 250 classic. Eg-5s, 3p for the south? Or is it dumb for an amateur like myself to be messing around with such high voltage (200V+)?

And then combine in the other arrays (central or south) as possible within the controller limits. Then multiple controllers?

Or does something else make more sense from a safety,cost, or other standpoint?

I feel like there is a smart way to do this but feel like I’m just guessing.

Any thoughts appreciated.

 

[time2roll]

I think you want an off-grid solar storage inverter with 2 MPPT inputs. Maybe E & W could feed one and south feed the other.

Maybe something like this Growatt 12000T but I am far from being an expert on these.
https://www.growatt-america.com/show-42-649.html

 

[MichaelK]

Well, I can recommend what I myself did, which includes running air-conditioning. I build my arrays on rotating mounts, so they can rotate East to West over the course of the day. This is really important for me to maintain the 2000W+ of power I need for running my well-pump to water the orchard trees. In your case it would be to power the air-conditioner. My mounts could hold 6 grid-tie panels if oriented in landscape.

Since I wanted late afternoon power for running the air-conditioner, I have arrays facing due West rather than South. My primary arrays are in an East-West line, so they start getting shade ~5pm, so power production would go way down if it wasn't for the West facing arrays. In my own case, I went with an array voltage of ~120VDC, so I got Midnight200 controllers to handle four panels in series putting out that voltage. If you wanted to put six panels on one array frame, then I would wire them 3S2P, running the solar cables over to a combiner. I use Midnight's 6-breaker combiner utilizing 12A breakers for each string.

How many arrays is going to be proportional to how much air-conditioning you want. I just use a 8000BTU wall unit, and I can power that just fine with a XW+ inverter. In your application, are you talking multiple wall/window units, or central air? Central air will be a tougher design, because we are talking high amperage 240VAC. I'd look at Schneider's XW, Outback's Radian, and the Solar-Ark for supplying that much power. Depending on the size of the system you might need two inverters in parallel to supply the starting surge for BIG air-conditioning. Remember that the starting surge for electric motor units like air-conditioners will be 3-4X higher then the running power.

Here's what I would do/have done. Look at the max number of watts you expect to be pulling, and mount 2X the number of panels needed to supply that. So, for example, you have an air-con that pulls 2500W, then install 5000W of panels. In you case though, maybe 5000W facing more or less South, and maybe another 5000W facing West for late afternoon power when air-conditioning is most needed.

 

[Bluedog225]

Thanks. Very helpful.

I haven’t made any purchases yet other than the panels and 4 rack batteries.

The AC (or 2) will be mini split inverters to keep the surge down.

 

[Bvillebob]

Forget the idea that there's a "right" answer, there are many answers that will work. Your choice among them will depend on what's available to you at the best price, your ability to do the work, how much room you have, etc. Right now panels are dirt cheap, the idea of trying to build a movable platform that will survive the anticipated wind loads versus just adding some more panels is not anything I'd ever consider.

For myself, I've worked with high voltage DC (over 1000 volts) most of my life, so I've kept my solar install in the 120 volt range. It's high enough to keep the amperage of any individual array down to a comfortable level without requiring huge wires, but not so high as to be incredibly scary.

If you have the room, I'd just install 3 arrays, with about 1/2 facing south and 1/4 facing southeast and 1/4 southwest. I have several of the Midnite Classics and I love mine. They're not "state of the art" in terms of tech but they're very rugged and well built, with great USA support.

 

[Bluedog225]

That sounds about right Bville.

I’m very curious given your experience why 120V DC was your number. What gets scarier at 250V DC? Thanks