New forumite here

BillG

Hi all, I am currently off grid, with just a 24v battery, 15kw generator, and Outback fx 3500w inverter. When I built a few years ago there was a slight possibility of tieing into the grid, but that is not going to happen. So at the time I didn't think a solar array would work for me, now I'm looking at adding pv and don't really know where to begin. Any advice is appreciated. (I'm sure there'll be ???'s about my setup and loads)\
Thanks,
Bill

Cariboocoot

Re: New forumite here

Welcome to the forum.

What you need to know is your power consumption in Watt hours per day and your existing battery's capacity in Amp hours. With that information it's fairly easy to calculate an appropriate array size for recharging the battery.

A 15kW generator is pretty big. Do you have heavy loads you use this for? If not you might also want to look into a more fuel-efficient generator. BTW, I have the same Outback VFX3524 inverter.

BB.

Re: New forumite here

And a rough location where your system is located (hours of sun per day, by month).

-Bill

BillG

Re: New forumite here

I have a string of twelve surette (same as rolls?), I think they are 395AH 2.6v cells. I confess I am not sure how to figure the total AH for the battery, add them or is it still 395? I got a deal on the generator, and used it when building the house, I'm pretty happy with it, a Kohler 15res. I have been using the genset when doing things like laundry and sometimes cooking. Otherwise the big load is the refrigerator, TV if I am watching a movie, and the well pump when there's water demand for showers and toilet, or washing dishes.
I have a recent issue with the inverter, too; it's not picking up the AC from the generator, maybe the frequency is off a bit, but does show ac in on the mate when I have the inverter in bypass, which allows me to charge the battery. Except it won't let me equalize so it's something I need to address soon.

BB.

Re: New forumite here

Can you run a Kill-a-Watt type meter on your loads and get an estimated daily load? Or do you have your Inverter's consumption logs?

Regarding the battery bank, if they are all 2 volt cell in series--Then the voltage adds to 24 volts and the AH capacity is 1 string (parallel) x 395 AH = 395 AH.

-Bill

Cariboocoot

Re: New forumite here

A single string of 395 Amp hour batteries is 395 Amp hours; only when you start paralleling them do the Amp hours go up. Do you have a model number for the batteries?

Assuming a 395 Amp hour 24 Volt bank you're looking at about 1250 Watts of panel and an MPPT type charge controller. This assumes a 10% peak charge rate and 25% maximum DOD. That much panel would supply roughly 2.6 kW hours AC per day, depending on your location.

A refrigerator will use up about half that, depending on the particular one and the conditions it operates under. It's a good idea to get a Kill-A-Watt meter and do some actual measuring. The well pump can be an issue too, because there are many different types/sizes. Depending on how long it runs this can be a significant amount of power. I control mine so it only comes on when the batteries are in Absorb stage (nearly full) or Float (full). In six minutes it will store enough for a typical day.

Not picking up the generator shouldn't be an issue with Equalization specifically. Fortunately the Outback inverters can be programmed to accept a pretty wide range of generator power. If you've been doing this for some time with just the inverter you must have a MATE to program it with; it would be impossible otherwise.

I mentioned a more fuel-efficient generator before. I don't see a need for 15kW of gen power here. I do much the same thing and use a Honda EU2000i for generator power. It works fine and sips fuel. It would be a bit pressed for charging 395 Amp hours, but could do it with load management. Otherwise go up one size.

vtmaps

Re: New forumite here

BillG wrote: »

I have a string of twelve surette (same as rolls?), I think they are 395AH 2.6v cells. I confess I am not sure how to figure the total AH for the battery, add them or is it still 395?

I don't think your cells are 2.6 volts. If they are 2 volts, I don't think they are 395 ah. Rolls does not (as far as I know) make any cells like that. I wonder if you have 12 batteries that are 6 volts at 395 ah. If so, your 24 volt bank is three parallel strings of 4 batteries per string, and your ah capacity is 1185 ah.

--vtMaps