New off grid system

BoFuller · March 2015

I'm almost finished building my log home. I've had a million battles with the County and one of them is time. I have to be finished by May 5. So I subbed out a few projects - electrical, plumbing, and solar.
My system will have the Outback FLEXpower FP1 VFX3648 3,600 Watts 48 Volts For Off-Grid, 12 Kyocera 235 panels and 16 Trojan L16REs.
I know the Outback unit has the FlexNet DC for monitoring. My concern is that it is mounted out in the solar shed, and I would like something like my current Trimetric tthat I have for my trailer setup. I mentioned to the solar company the possibility of a Trimetric unit located inside the log home and he said the main shunt already was being used by the Outback meter and hooking up a second meter to the same shunt would cause reading errors.
Any suggestions?

zoneblue · March 2015

The flexnet is a prt of outbacks monitoring system yes, but its really driven by the mate. The fndc's primary purpose is to monitor the shunt. If you go with the mate3, you can hook ethernet cable to it, and this can run up to 100m, and be used to monitor the system using a variety of monitoring solutions. Im not sure how long the mates own cable can run, i think its serial or RS485. Youd need to check.

inetdog · March 2015

Two meters which look at the voltage across the shunt, using a high impedance voltmeter, will not have much if any interaction between the two meters.
But there may be a problem with the grounding setup of the two meters if you do not carefully look at which side of the shunt is grounded.
And a device which generates a proportional current based on current division with the shunt (not at all common!) will lead to interaction between the two meters.

jberg85 · March 2015

Just hook up the mate inside your cabin. That is what I have done and my power room which houses all of my batteries, generator, and all controllers/inverters etc is over 200 feet away. Just have to run a cat5e cable between the two buildings.

Also, your planned solar panels of 2,820w seams very low for 740ah at 48v battery bank which essentially is 35,520w making you only at about a 8% charge rate in a perfect sunshine and no clouds day. I have the same exact battery bank and I currently only have 4,725w of solar panels going to it as I have not installed the other panels just yet and if I get a few cloudy days I'm having to run generator quite a bit. Just a thought.

BoFuller · March 2015

Thanks for all the input.

BoFuller · March 2015

The tech showed up yesterday to start installation and he first looked around, like at the water pump, and said I was in trouble. The pump alone would trip up my system since it was a one HP unit. He said I needed 8 more batteries and probably a second inverter.And I should switch to a 1/2 HP pump.
I called his boss, who originally told me I only needed 8 batteries (Trojan L16RE-B (6V)), and 6 panels. I insisted on 12 panels and 16 batteries. He redid the worksheet and said except for the pump, I was okay. I didn't put the pump on the worksheet because I didn't think of it. He does off-grid systems on a regular basis, so I figure he should have had it on his worksheet.
Anyway, I found a 1/2 hp pump that draws 7 amps and now I'm undecided as to whether I should up my batteries from 16 to 24. And should I get a second inverter?
The worksheet said I would use 7,327 watt-hours/day
I don't mind if I have to use the backup generator on an occasional basis. He says my array will average 6900 watt hours/day in Dec and 10,200 watt hours/day in June.
Suggestions?

BB. · March 2015

I am a big believer in conservation as a means to reduce initial and ongoing maintenance costs.

So, a question for you... If you have to replace 16 batteries or 8 batteries in ~5 years--Which would you prefer. A "larger" system that can handle more loads, or a smaller system and lower costs.

Charging the battery bank, roughly 5% to 13% rate of charge is a good range--And for a full time off grid home with daytime loads, I would be suggesting 10% + rate of charge:

8x 6 volts * 220 AH batteries * 1/0.77 panel+controller derating * 0.10 rate of charge = 1,571 Watt nominal array (one string)
16x 6 volts * 220 AH batteries * 1/0.77 panel+controller derating * 0.10 rate of charge = 2,743 Watt nominal array (two strings)

Lets say you have a minimum of ~4.5 hours of sun per day (winter), then:

7,327 WH per day (120 VAC power) * 1/0.52 average system efficiency * 1/4.5 hours of sun per day = 3,131 Watt array minimum (winter break even array based on load+sun)

And sizing the battery bank for 2 days of power, 50% maximum discharge based on 7,327 WH per day (really charge during day, use power at night):

7,327 WH per day * 1/0.85 AC inverter eff * 1/48 volt battery bank * 2 days storage * 1/0.50 max discharge = 718 AH @ 48 volt battery bank

If you use less power at night, a 220/440 AH @ 48 volt battery bank would supply:

220 AH * 48 volts * 0.85 inverter eff * 1/2 days of storage * 0.50 maximum discharge = 2,244 WH per night (poor sun day)
440 AH * 48 volts * 0.85 inverter eff * 1/2 days of storage * 0.50 maximum discharge = 4,488 WH per night

What is your actual solar array size?

And do you have a split daytime/night-time load plan?

If you wanted to use 7kWH per day (including on dark/stormy days) without firing off the genset, the battery bank seems a bit on the small side.

If you plan on relatively small night-time loads and supply power during a sunny day from solar array (irrigation, daytime office/home loads,etc.)--Then a smaller battery bank may work OK.

7 kWH per day loads is pretty large, and a 220/440 AH @ 48 volt battery bank is a bit on the small size for such loads (I think, if I understand your needs/post correctly).

-Bill

BoFuller · March 2015

Array size is 12 Kyocera 235GX-LPB Panels VMP 29.8V.
7kWH is worst case scenario.
I hadn't thought about daytime/nighttime split. All dishwashing, laundry, etc would be midday, and the evening hours would be limited to ceiling fans and TV.
I'm just worried about the water pump overloading the system.

BB. · March 2015

For flooded cell batteries (your two string 16x battery bank), more or less the loading is approximatly:

440 AH * 48 volts * 0.85 inverter eff * 1/20 hour discharge rate = 898 Watt average 120 VAC load (5 hours per night, 2 nights)
440 AH * 48 volts * 0.85 inverter eff * 1/8 hour discharge rate = 2,244 Watt maximum average load (roughly 3 hours to 50% discharge)
440 AH * 48 volts * 0.85 inverter eff * 1/5 hour discharge rate = 3,590 Watt maximum sustained loads (minutes to hour)
440 AH * 48 volts * 0.85 inverter eff * 1/2.5 hour discharge rate = 7,181 Watt maximum starting load (seconds)

Just a rough recommendation/sizing...

-Bill

Surfpath · March 2015

zoneblue wrote: »

The flexnet is a prt of outbacks monitoring system yes, but its really driven by the mate.

Hi BoFuller,
I also have a Flexpower1/REB set up - small config though: 2,000watts of pv charging 370amp hrs.

Seems like if you sort out the pump issue you will be able to keep your system size/costs low.

My observations over the past 2 years of using my system:

The Flexnet DC is not really a SOC monitor. It is only minimally useful as a sort of "dial" to set end amps. Go to the Outback web site and read the experience of users there. It comes with the FP1 system anyways, and it has some cool lights on it, but expect VERY little out of this unit.

I have a 8.5% Charge rate and it works OK for me (I dont even have a generator). But there have been a few days that I have wished for more, so I am panneling up to a 10.5 % charge rate this Summer. I wished I would have done this from the start. So think "more PV" when possible.

The REB seems to be a good battery, so far I'm happy. They cycle from 70% to 95%/100% each day. I'm expecting 6-7 years from them (fingers crossed).

Another reason why I think a 8.5% charge rate works for me is that, apart from the fridge cycling, I actually use "search" for much of the day. I do have a few items plugged in but they are all very small wall wart loads (< 4-5 watts each?) that seem to work well in Search. That little pulse of electricity powers them fine. I try to not plug in any other loads, like laptop/ipad chargers because they seem to dislike search.
Anyway, there you go. SP.

706jim · March 2015

Just how long does that 1 hp pump have to run? I have a 1 hp centrifugal spa pump in my wood fired hot tub. I would run it for as much as 15 minutes on the high setting from my 12 GC's and 1500 watt Trace Dr 1500 inverter. Far less battery than you have here. And as far as array size goes, you have a LOT more than I do although you obviously have larger loads.
I would try what you have now before I expanded the bank.

Alaska Man · March 2015

You are going to have to run a genny from time to time anyway. If it was myself, I'd get a smaller pump and a holding tank. Run the genny/bulk charge/pump up water to holding tank. You'll have way less to spend in five - seven years when your bank is no longer performing for you.
I have a 200 gallon water tank in the corner of a linen closet, from there I use a 120V R.V. pump with an expansion tank (2gl). works fine.

Graham Parkinson · April 2015

Alaska Man has the right suggestion - small DC pump and a cheap big plastic holding tank up high somewhere. We run a 24V Dankoff Slow pump off of two 50 watt panels here in coastal BC. It pumps water up off our beach collection tank up 150 feet vertically onto a ridge behind our places and 600 feet laterally via a 3/4" pipe. Runs all summer day in and day out, pumps about a third of what you would get from a garden hose but it is steady. Ran for about 10 years with no maintenance, just replaced impellers recently. You can get these types of vane pumps as submersibles or as surface pumps like ours.

BoFuller · April 2015

I sent the one hp pump back and ordered a 1/2 hp one. It draws 7.4 amps but I figure it's not going to run more than 15-20 minutes a day. I have a 44 gal pressure tank so I think I'll be okay.

I told the guy to go ahead with the original plan. They came yesterday but the clamps to hold the panels on the steel roof were not the right ones, so they had to order another type. They left the batteries but will probably not be back until Monday with the new clamps.

Thanks for the input.

BoFuller · April 2015

I don't remember how to edit the information in the sig line.
Can someone remind me how I got the info there?

Photowhit · April 2015

BoFuller wrote: »

I don't remember how to edit the information in the sig line.
Can someone remind me how I got the info there?

Left click your name in the upper right hand corner choose "User Settings"
Choose "Account"
...about half way down there is a link to change your sig line.
Looks like this;
Attachment not found.

BoFuller · April 2015

Photowhit wrote: »

Left click your name in the upper right hand corner choose "User Settings"
Choose "Account"
...about half way down there is a link to change your sig line.
Looks like this;
Attachment not found.

Thanks. I started editing but didn't finish yet.

New off grid system

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