Another newbie here

System · November 2011

Hi all,

I've been reading and gotten some good info, but I'm feeling overwhelmed!

-Usage: 2 kWh/day
-Off-grid, generator backup
-Full sun location,
-Latitude: 16 degrees north

-Panels: 3-4 Kyocera 235W (I'm confused about is system sizing. Some calculators say a panel total of ~600W, others 900W)

-Charge controller: Morningstar TriStar45

-Inverter: ExcelTechXP2000 (or Outback2000W)--the inverter site on the wind&sun store is down, and I can't remember which brands are recommended.

-Batteries: Crown 12V renewable energy (12CRP130) 90Ah. Again, not sure about sizing (6-10?).

-Meter: MidNite Solar Battery Capacity meter

-Breakers/disconnects. I'll have to read more about this.

Could someone let me know if I'm on the right track? Thank you!

mike95490 · November 2011

Re: Another newbie here

-Batteries: Crown 12V renewable energy (12CRP130) 90Ah. Again, not sure about sizing (6-10?).

Yow !! NO !!

You want to minimize the number of parallel batteries. Instead of 12V batteries in parallel, look at 2v batteries in series, to get the same capacity.

Another rule of Thumb, is when inverter size is below 1,000w, 12V is OK, but beyond 1,000w, step up to 24V. This reduces the amps the wires need to carry, and increases your system efficency. You do loose the option of 12V appliances though.

Cariboocoot · November 2011

Re: Another newbie here

Step #1: get a fix on your daily Watt hour usage. All of the system design hinges on that. Don't guess; buy a Kill-A-Watt meter and measure what you intend to run under "real world use" conditions. It's $30 well spent.

2 kW hours per day can be done on 12 Volts. It only requires a minimum of about 450 Amp hours of battery. Four golf cart batteries would supply this and be a very inexpensive and simple bank to construct. But like Mike said, 24 Volt could be better. I don't agree with the 2 Volt cells, however, as they tend to be very high Amp hours and rather costly.

To recharge the 450 Amp hours of battery you would need:
45 Amps peak potential current (10%) * 12 Volts (minimum bank Voltage) = 540 Watts, less typical 77% panel derating = 700 Watt array. This would potentially max out the Tristar 45, but again if you shift up to 24 Volts the same batteries would supply the same net power and be recharged from the same amount of panel but with a significant drop in the needed current.

The Kyocera 235's have an "oddball" Vmp of 29.8 and can not be used on either a 12 or 24 Volt system with an MPPT charge controller. You could run three in series to a Tristar MPPT 45 and be good for either system Voltage. No panel fuses would be needed.

The inverter needs to be sized to handle your maximum load at any one time. 2kW will likely be large enough for most things, but may in fact be too large. Both the Exeltech and Outback are good inverters, and available in either 12 or 24 Volt. Again I'd favour 24 for a 2 kW unit.

You will need circuit protection on the wire from the controller to the battery and from the battery to the inverter. The size/type ultimately depends on the final system design and how much current is expected. For example a 2 kW 12 Volt inverter can draw up to 200 Amps, whereas the 24 Volt version of the same thing would draw half that.

mike95490 · November 2011

Re: Another newbie here

I'd mentioned the 2V cells, as an alternative to 10, 12V in parallel. There are also 4V, 6V and 8V cells, in varied amp hour configurations, to get what's needed.

But, for beginner batteries, it's hard to beat golf cart 6v batteries, cheap and plentiful. As BB said, 4 in series would give you 24V @ 200 ah.

But I think there is a typo here, that I corrected in RED

The Kyocera 235's have an "oddball" Vmp of 29.8 and can not be used on either a 12 or 24 Volt system with an PWM charge controller. You could run three in series to a Tristar MPPT 45 and be good for either system Voltage.

Cariboocoot · November 2011

Re: Another newbie here

Wrong typo correction, Mike:
It should say "The Kyocera 235's have an "oddball" Vmp of 29.8 and can not be used on either a 12 or 24 Volt system without an MPPT charge controller."

I need a proof reader; my eyes are gettin' old.

System2 · November 2011

Re: Another newbie here

Thanks for advice. I think I'll go with the 4 6V, 225 Ah batteries, with the 2kW 24V inverter. I'd be concerned about going down to the next smaller size inverter (Exceltech 1100W) because I have a heavy-duty blender (1000W max). I'll keep working on the design. Thanks again!

icarus · November 2011

Re: Another newbie here

2 kw inverter, consistently running smallish loads would be very inefficient. consider a smaller 24/7 inverter for your base loads, and either a larger one for occasional larger loads, or use a genny for the rare larger loads. For example,we run the vacuum on the genny. a few minutes of run time, and we don't have to have a big inverter.

Also consider, a 2 kw load on a 225 ah battery bank (24 vdc) is a pretty big load on a fairly small battery bank. (83 amps)

Tony

waynefromnscanada · November 2011

Re: Another newbie here

icarus wrote: »

2 kw inverter, consistently running smallish loads would be very inefficient. consider a smaller 24/7 inverter for your base loads, and either a larger one for occasional larger loads, or use a genny for the rare larger loads. For example,we run the vacuum on the genny. a few minutes of run time, and we don't have to have a big inverter.

Also consider, a 2 kw load on a 225 ah battery bank (24 vdc) is a pretty big load on a fairly small battery bank. (83 amps)

Tony

I agree re smaller inverter for base loads, that's where my SS-300 (one of them) comes in. I have the PS 1800 on for the heavy loads only.
Re big loads on smaller battery banks, consider that with the smaller bank, if you apply heavy loads, the voltage will quickly drop to where the inverter kicks out because of low input voltage. Think of that your car headlights do when as you crank the starter, at least with the older cars, most of the newer ones automatically shut them off while cranking. A 1000 watt load will be 100 amps @ 12 volts, + probably 10% for losses = 110 amps, and that size load is going to have a major impact on battery voltage. I'd consider a smaller blender for sure.

hillbilly · November 2011

Re: Another newbie here

You didn't mention much about your generator, but do realize that this part of your system may well end up being one of the more important aspects (albeit, not quite as glamorous as the PV panels and such). Consider how you'll charge your batteries from the Genny; you'll need another charger of some sort or another here. One option is that some inverters(Outback, Xantrex, and Magnum all have inverter/charger units) have a charger built in, which can make life a bit simpler. I've had positive, but limited success with Iota chargers (which are a couple hundred bucks); the only issue is that you don't have much control over charging voltages and can't Equalize via this charger. You may or may not need to use the generator in this fashion, depending on your weather and your array size compared with your usage and battery bank size.

You mention your location as being in the tropics, so I take it that you have a fair amount of rain and showers. How long might you go between sunny days at worst? Just some thoughts to consider, for us with our system it ended up working out much better to go with an Outback inverter-charger which allows us full charging options with our generator during winter weather.

I agree with others about recommending 24V system, but if you're using 2kwh a day I'd probably look at more than 4 225ah 6V batteries. I'd think probably more like 8: making two parallel 24 batteries adding up to a total of 450ah. Thats roughly 10kwh, which you'd really want to use about half of: thus 2-3 days of no sun before you'd need to recharge them up. With your proposed bank, you'd end up running the genny almost every time you had a single cloudy day...

EDIT: Forgot to mention that I would recommend a trimetric or other type battery meter that will show a lot more than the Midnite solar battery meter. Nothing against that meter, but imo it's extremely helpful to have a meter that will show you amps in/out, amp hours withdrawn, and a few other features that you don't get on most battery monitors.

On the CC, I've heard nothing but good things about the Tristar units, but you may want to strongly consider the 60 amp vs 45 amp unit. If you think that you may end up adding more PV panels at any time you might find that having some "head room" is worth the extra $100-$200. Otherwise you'd end up needing an additional CC AND a second wire run, which gets more expensive... food for thought.
good luck

System2 · November 2011

Re: Another newbie here

Thanks again, all. I took your suggestions and sent along the info to NAWS for a quote. I was a little concerned when I got back the quote, and they had substituted in a ProStar (not MPPT) for the TriStar controller, since as cariboocoot pointed out (and it says on the NAWS website) that the MPPT MUST be used with the Kyocera 235W panels. It made me question the ability of their technicians in helping design the rest of the system. Are they generally reliable?

Also, as hillybilly said, they thought the bigger bank was better (4 Crown 6V 395Ah), although I think I'd prefer the 8 Crown 6V 225Ah.

I'll plan to get the Trimetric meter.

As for the Iota battery charger, they recommended the 24V, 25amp. The 40amp version is almost double the price ($400 vs $225), but it would charge the batteries that much faster, right?

BB. · November 2011

Re: Another newbie here

What size generator are you planning? That will affect your ac battery charger choice too.

-Bill

Another newbie here

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