Is This System Balanced?

help!

I'm making purchases to set up an off-grid solar system in southern Colorado, average 6+ hours of sun/day, at 8500 ft. altitude. Solar panels will be mounted on the porch roof of a small building (which will house the controls and batteries), and on two poles.

The system will power a nearby parked 5th wheel trailer w/30amp 110/120vAC plug (microwave oven, electric blower/fan on propane furnace, small kitchen appliances, HDTV/ DVD player, computer, occasional vacuum cleaner and small clothes washer, etc.); in the building, a 17 cft refrigerator, 12 cft chest freezer, small 110/120v hot tub w/cover (not run continuously); a 3/4 hp 220/240v deep-well pump run 10-15 min/day, and occasional use of 110/120v hand power tools.

The trailer has its own 2 deep-cycle, flooded-lead-acid batteries (not AGM), inverter and charge controller (which my husband says doesn't matter to the system, but the batteries do provide some charge, since they power 12vDC lights, radio, refrigerator (when put on 12vDC or 110vAC settings), the antenna, and the slide motor).

The 24v system I'm planning is only partially purchased, and I'd appreciate advice on whether I have too much or too little of each component on my list (right now, I think I'll need more batteries). Also, please let me know if you think a 500 watt 24v wind turbine mounted on the building roof or nearby pole could be wired to the second MPPT charge controller, or if it needs to be put on its own. (Does a wind turbine NEED an MPPT controller to maximize its effectiveness as PV do?)

Components in question:

8 205 watt/12v panels TOTAL 1640w (22.80 Voc, 12.10 Isc, 18.40 Vmp, 11.15 Imp), mounted on 6" pole (sun tracking, if we can afford it; otherwise, manually moving), wired to 1st controller

8 205 watt/12v panels as above TOTAL 1640w, mounted on 2nd 6" pole, wired to 2nd controller

8 130 watt/12v panels TOTAL 1040w (VOC 24.10V, VMP 18.80V, ISC 7.11amp, IMP 6.55amp), mounted on porch roof, 6 wired to 1st charge controller, 2 wired to 2nd controller

2 Outback Power Flexmax 80 Amp MPPT Charge Controllers

1 6000 watt continuous/12000 watt surge, pure sine wave inverter, 24v DC input, 110/120v AC output

1 transformer for 220/240v AC output

20 Sun Xtender PVX-890T AGM batteries (12v, 89 amp-hour)

1 500 watt wind turbine, wired to 2nd controller

THANKS FOR ANY ADVICE or COMMENTS!

BB.

Re: Is This System Balanced?

Hold up here--It is going to take a bit of reading to put everything together and figure out what you are trying to do...

But, it is probably not balanced. 6kW inverter on a 24 volt battery bank is a lot of current (12kW at 22 volts surge current will be on the order of 680 amps--very heavy cables and large battery banks to support that amount of energy). The AGM batteries will barely be able to support the 6kW inverter (if you want to use full power) but wiring them into 10 parallel strings will be difficult and expensive...

It is getting too late for me to give you a coherent response tonight.

But, would like to understand the loads you want to support... You have lots of loads and a good amount of solar panels. Have you worked out the Watt*Hours per day (or kWhr) that you want from the system. Will this be a 9-12 month residence or weekend/seasonal?

And, can you take a look at the PV Watts website and find the city in Colorado (or nearby state) the most closely matches your location and weather type? It will hep us to estimate your average solar PV power.

Regarding the Wind Turbine and MPPT controller... Historically, DC battery charging wind turbines have not use MPPT charge controllers. However, Midnite Solar is developing an MPPT wind charge controller that could really help increase the total power available from a wind turbine via MPPT. It should be out by summer (last we read here). Outback Power may also have an MPPT Wind charge controller or upcoming project (contact them for more info). There may be other suppliers--I am not in the industry so my knowledge is limited.

The Wind Turbine would need it's own MPPT charge controller (when such a product becomes available). The Wind Turbine needs it own pole and should be 60' or higher, and 30' minimum above obstructions less than 300-500 feet away. Trees should be "flagging" from prevailing winds as a sign that your average wind speed may be high enough to support a wind turbine with useful power output.

If you have not purchased an inverter yet... You might want to look at the Xantrex 6kW 48 volt 120/240 Hybrid inverter with at least 600 Amp*Hour 48 volt battery bank (probably a lot more battery). It supports 120/240 VAC circuits without additional hardware/transformers.

Lastly, and really firstly, Off-grid electricity is not cheap (very roughly $1-$2+ per kWHr (or roughly 10x utility power costs). Conservation is usually the first recommendation around here (we are a cheap group ) -- it is much cheaper to conserve a watt than to generate a watt.

Next, knowing your load requirements (watts peak and WattHour/kWHr per day, seasonal variations, etc.) before spending the money helps too.

-Bill

mike95490

Re: Is This System Balanced?

nope.
Cant/should not, mix different panels on the same charge controller.

Transformer:
1) needs to be sized for the pump STARTING current. if sized for run current, it will not pass starting current - core saturation.
2) idle loss of large transformer. 50 - 100 Watts, just powered up. If you switch it on manually, each AM, for a pump cycle to fill an overhead tank, OK, but if it's on and "cooking" 24/7, waiting for the pump, that's a LOT of wasted power.

Batteries - Shoud be Series 6V batteries, not parallel lots of 12V batteries.
it's very hard to keep parallel strings balanced, but series strings inherently are. May need to go to 4V or even 2V batteries to get the needed AH

Wind turbine :
needs it's own controller and dump load.

hillbilly

Re: Is This System Balanced?

I would agree with the suggestion to look into a 48V system, not just for the battery amp hours but also to use 1 single charge controller if possible (I think an FM 80 will handle somewhere in the neighborhood of 4KW at 48V, elevation/ high temps would lower this limit to possibly near 3KW?) Seems like a big PV array for a 5th wheel. I'd double check your charge controller specs for your specific installation, and double check your load totals. I would think that you could likely do well enough with a single Charge controller if you were using a 48V system.

Do you have the PV panels already? If not, then don't bother with the 130w panels. If so, then either wire them to a separate charger. You could wire them in sets of 4 paralleled with your 205's, for a bit of a loss, as the output would be limited by the slightly lower voltage of the 205's:
18.4*4panels in series= 73.6V for all 4 parallel sets (2 sets of 130watt, and 2 sets of 205 watt)
so 73.6V * 6.55amps = 482 watts * 2 sets = 964 watts for a loss of about 76 watts on the 130 watt panels, with the 205 watt panels at full output.
Wiring the 130's in series with the 205's would loose a huge amount of power, not a reasonable option at all.
Again if you do not have the panels already I wouldn't mix and match like that if you don't have to.

I don't think that a tracker would likely be cost effective, but there are lots of variables (and variable opinions) regarding this.

I'd probably skip the small wind turbine personally, as it will quite likely make your system more complicated and present more a dramatic increase in system hassles. At the very least, make absolutely certain that you have a good wind site, and factor in the costs associated with a properly sized tower. Don't consider mounting it on your roof, nor a small lightweight pole.

You might look into replacing that well pump (your only 240V load?) for a small solar h20 pumping system. Could be a pretty small array with a large tank, a much more efficient "battery" for the energy you need for your water. Would likely be much cheaper in the long run than buying a battery bank sized for a few days of autonomy plus the PV array to power that. You could also simply buy a storage tank, and just run the well pump when you are using a generator to fill that tank up (I'm assuming you will have a generator?).

icarus

Re: Is This System Balanced?

As we suggest so often,

"do the math". With the aid of a Kill-a-watt measure your loads both for draw and duration. Add up your total loads, calculate in some head room to grow (as loads always do!) and then work backwards.

Here is the quick back of the napkin calc. If you take the name plate rating of your PV, multiply that number by .53 to account for all systems loses, then multiply that number by the average hours of GOOD sun you can expect ( seldom more than 4!) and get a total.

So a quick figure for your system might look like this, 4000 watts of PV * .52=2,080*4=8320 wh/day. Can you get your loads down to ~8 kwh day? (Hint, pretty hard with a hot tub!)

Tub 1500wt*8 hours=6kwh
Fridge type .75 kwh
Furnace fan 30 wt/24= 700wh
TV 150*4=450wh
DVD computer etc 60 wt*6=360
Misc??? 1 kw
Leaving a quick total of at least 9.2 kwh.

My best guess is your loads are likely to be much bigger (I haven't done any lighting/water pump etc) So I would guess that you need ~twice as much Pv.


So let's use 8 kwh just for round numbers. If have to decide how deep you are willing to draw down your batteries. Some suggest that a 50% routine discharge is ok, other like myself favour a 25% discharge.

So, lets say that you wish to have a 3 day reserve and you wish to draw your batteries down to 50% in that 3 days. 3*8=24kwh So you would need a battery bank of 1000 ah ~48 vdc to be in the ball park. (V*A=W) 48*1000=48,000 wh/2=24,000 wh.

My first hunch is you have ~1/2 as much battery as you will need.

Finally, you mentioned that some of the hardware hasn't been purchased yet. My suggestion is that you buy nothing else, until you figure out what it is that you need. If not you will fall into the "ready, fire aim" trap that gets so many. You are likely to end up with a system that doesn't do what you expect it to do, and will require expensive changes that could have been addressed earlier.

Most folks, make a series of mistakes. They under estimate their loads, they over estimate the amount of real energy they can harvest, they over draw their batteries, and then they chronically under charge their batteries. These lead to premature battery failure, and a much greater net/net cost.

Good luck, welcome to the forum. There are some very smart folks here (not me!) who have forgotten more about RE than most of us will know. Use this knowledge well and you will be rewarded with a well thought out, well planned, well sized system.

Just as an FYI: We live off grid, and use ~.6kwh of power/day. We do this with ~300 watts of PV, 450 ah of battery (12vdc) (~5.4kw) Our system is just about perfectly balance between charge and draw. But the loads continue to grow every year~ (.6 kwh is tiny by most normal standards!)