6 Kw Off grid

Erikpope · February 2011

I want to do a 6 kw off grid system and want to know how much it would cost me? I will be doing it just out side of Show Low (5 - 5.5 sun). What parts would you recommend? I will be doing the installation myself.

BB. · February 2011

Re: 6 Kw Off grid

Is that Show Low Arizona or somewhere in Greece/Kazakhstan?

Before designing a solar PV off-grid system, it is really helpful to understand your needs/loads. Just in parts, you could be looking at well over $60,000 for a full sized 6kW inverter/charger/solar pv/battery system (not even including a genset for backup power).

Pretty much (at least in the US), off grid power costs in the range of $1-$2+ per kWH vs the $0.10 to $0.20 per kWH that most people pay for utility power.

Also, seasonal power variations are important. You may get 5+ hours of sun 9 months of the year, but get 2-3 hours of sun during winter.

-Bill

Cariboocoot · February 2011

Re: 6 Kw Off grid

Welcome!

I recommend you read this forum 'til you're nearly blind, to start with.

The short version:
Loads. Determine your loads. Maximum draw, type, and total Watt hours per day.
Conservation. Cut those loads down as much as possible. No electric heating, for example.

Once you know what exactly you're trying to run and for how long then you can start making decisions about design and equipment. You need that load information so you can define an inverter size, system Voltage, battery bank capacity, and array size.

Just using a term like "6 kW system" doesn't work for off-grid. Grid-tie is sometimes expressed that way: 6000 Watt array. This is because it is negating power use from the grid and possibly selling back any surplus. You don't have that ability with off-grid. The balance between usage and production is much more critical.

Erikpope · February 2011

Re: 6 Kw Off grid

This is in Arizona. I grew up in Williams. The whole Greece/Kazakhstan thing is probably because of where I am right now. I'm in the Army deployed to Afghanistan.

Ill give you a little more background of what I plan on doing. I get out of the army next Feb and plan on building on my property. The house will be a rammed earth (solar mass) passive solar home. With a wood stove. So the plan is no ac no furnace. So the main power consumption would be fridge, lights and other small appliances. I will put up a solar water heater and propane for cooking so no extra power there. I plan on living out there 24-7 365.

I hope that helps with consumption. I was hoping I could keep the cost to about $20k. but was not sure what I would need to do.

mike95490 · February 2011

Re: 6 Kw Off grid

Erikpope wrote: »

Ill give you a little more background of what I plan on doing. I get out of the army next Feb and plan on building on my property. The house will be a rammed earth (solar mass) passive solar home. With a wood stove. So the plan is no ac no furnace. So the main power consumption would be fridge, lights and other small appliances. I will put up a solar water heater and propane for cooking so no extra power there. I plan on living out there 24-7 365.

I hope that helps with consumption. I was hoping I could keep the cost to about $20k. but was not sure what I would need to do.

You won't likely need 6kw, 3kw should be good, 4kw would be frosting on the cake. Unless you get an electric car, and need to recharge it from solar.

$20K, that's not going to go too far, maybe 2kw, depends on how much you can do that the building inspectors will let you get away with.

BB. · February 2011

Re: 6 Kw Off grid

For what you describe, you are probably looking at 1,500 to 2,000 watt TSW inverter (mostly to run your refrigerator), around 500-1,000 watts of solar panels, and 130 AH to 500 AH of 24 volt battery bank.

Using PV Watts website, 1kW of solar panels, and 0.52 derating (assuming flooded cell batteries and AC inverter), Albuquerque (pick city nearest you with similar weather), fixed array:

"Station Identification"
"City:","Albuquerque"
"State:","New_Mexico"
"Lat (deg N):", 35.05
"Long (deg W):", 106.62
"Elev (m): ", 1619
"PV System Specifications"
"DC Rating:"," 1.0 kW"
"DC to AC Derate Factor:"," 0.520"
"AC Rating:"," 0.5 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 35.0"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:"," 8.7 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 5.33, 84, 7.31
2, 6.06, 84, 7.31
3, 6.44, 99, 8.61
4, 7.16, 102, 8.87
5, 7.40, 105, 9.13
6, 7.10, 95, 8.27
7, 7.13, 98, 8.53
8, 7.02, 98, 8.53
9, 6.71, 91, 7.92
10, 6.55, 97, 8.44
11, 5.73, 85, 7.40
12, 5.14, 81, 7.05
"Year", 6.48, 1119, 97.35

At a minimum of 81 kWH per month of AC power in December, or an average of:

81,000 Watt*Hours per day / 31 days = 2,600 WH per day (2.6 kWH)

That should be enough to power an Energy Star Rated refrigerator (look for ~400 kWH per year rated fridge or smaller). And leave lots of power for small electronics.

A good size battery bank would be ~5% to 13% rate of charge. 10% is a nice number:

1,000 Watts of solar panel * 1/29 volt battery charging * 0.77 system derating * 1/0.10 rate of charge = 265 AH @ 24 volt of battery bank

You could go with as low as 5% rate of charge:

1,000 Watts of solar panel * 1/29 volt battery charging * 0.77 system derating * 1/0.10 rate of charge = 530 AH @ 24 volts of battery bank

A 265 AH battery bank running a 1kWH per day refridgerator (365 kWH per year) plus 200 WH of misc. lighting/computer and 50% maximum battery usage would supply your needs for about:

[265 AH * 24 volt bank * 0.50 max discharge] / [(1,000 + 200)WH per day * 1/0.85 eff inverter] = 2.25 days of "no sun"

After that, you could run a Honda eu2000i (manual start) genset with a Meanwell PB-1000-24 (1,000 watt 24 volt) battery charger (long thread started by SteveK on finding the "optimum" battery charger for a Honda eu2000i genset).

By the way, there are other ways of getting low power / low cost refrigerators too... Do a chest freezer conversion (~ 1/3rd the power usage). A great way to have a fridge and save energy/costs--May not be the best choice for your spouse.

The host of our forum is NAWS (Nothern Arizona Wind & Sun out of Flagstaff). You can start there looking there for components (and call for sales support/questions). The forum here is hosted by NAWS but we here are all volunteers with no connection to the store (other than Windsun and Rick, the two administrators here).

They have 30 years experience setting up systems for the Southwest just like you are describing.

-Bill

Erikpope · February 2011

Re: 6 Kw Off grid

I want to build with expansion in mind. I may only start with half the panels/batteries but as far as I understand the core components can only be upgraded so far. I don't want to buy an 3kw inverter and need a 4 or 5 or 6...

I was also thinking about peak amp usage, but that is probably more on the battery side. Such as I know for example air compressors my need 15 amps to run but to start could need 45 or more.

As you can see I am fairly new at this and thats one reason I am starting now, a year out, seeing what I need to figure out.

When I start the project I'll be sure to post about my system

Erikpope · February 2011

Re: 6 Kw Off grid

It's funny you talked about a chest freezer conversion because I was looking at that and my wife did shoot it down. I was also looking at LP refrigerators. Not sure if it is worth it or not. I just have to price out the cost of LP and all other costs too.

What would you guys recommend? The nice thing about this project is that isn't a retro install. Everything is new and I have time to make changes. Thanks

mike95490 · February 2011

Re: 6 Kw Off grid

If you even think about starting a compressor or large tools, you should just start at the top - XW 6048. It will happily run off a modest 48V battery of 4 deep cycle batteries from costco, and start 240VAC deep well pumps (or arc welders, wormdrive saw, table saw, bandsaw...) Add a couple more panels, and use an energy star fridge you can get at any store, and forget the propane fridge.

I also like the morningstar 60A MPPT controller, which will work with even a small array and still be efficient

BB. · February 2011

Re: 6 Kw Off grid

I am not sure if Mike is being funny or serious about a "modest" 48 volt Costco battery bank and a XW 6048 hybrid inverter...

For flooded cell batteries, you pretty much need a minimum of 2.5x the surge power to run heavy startup loads. A 6kW XW system can surge 12kW (at 240 VAC; ~70% of that at 120 VAC). Pretty much the floor to support 12kW of surge is around 600 AH 48 volt battery bank...

In the end, if you have power tools that you use somewhat irregularly, a large genset may be the better solution. If, however, you use shop tools daily (work/farm related), then you may be able to justify the solar panels+battery bank required to operate both the tools and your home.

The problem is that with large battery banks come large costs... You need a large solar array to properly recharge the bank (5-13% rate of charge rule of thumb), plus you have more batteries to replace every 5-15 years or so (and 10 year batteries seem to cost about 2x the cost of 5 year batteries--so it is hard to come out ahead).

Heavy Surge Current, High Watt Mechanical Loads are just killers for any off-grid power system.

As a good starting point, figure your grid power at $0.10 to $0.20 per kWH and your off grid power at $1-$2+ per kWH... What would you do different for your off-grid home if power was 10x as expensive.

For a typically "small" off-grid home that used propane for heating, no A/C, not too much well pumping, a good aim point is ~100 kWH per month worth of power (3.3 kWH per day) usage... System is still relatively small and maintenenace is not going to kill you.

Remember, my rule of thumb, Batteries will last ~5-15 years, electronics/inverters/etc. will last ~10 years with possible a repair bill in the middle. Have that in your budget... Solar panels may last 25-40 years, but the rest of the support hardware does not have nearly that life.

Making your own power station certainly makes one appreciate what a utility company provides for $0.10 per kWH (virtually unlimited power 24x7 and no other out of pocket costs).

In some cases, if there is power less than 1/2 mile away or your utility has subsidized fees for running lines--Going with grid power and paying $10-$50k for running a line to your home may be the better deal.

-Bill

mike95490 · February 2011

Re: 6 Kw Off grid

I was being serious, get the beefy inverter, and run it as a modest system, kill a set of cheap batteries, then when the shop is built, and life begins in full swing, you can add more panels, replace the batteries with a full blown pack and use it.

Or the other way to start is with a couple panels, a suresine and limit your loads to 400W or so, but you can't expand that, you will be replaceing it.

I'm seriously looking at getting "Things" that will be useful, not $ rotting away in a bank, sort of along the lines, the one with the most toys, wins. But I'm past the toys and into the tools now.

Cariboocoot · February 2011

Re: 6 Kw Off grid

Erikpope;

Look at the specs in my sig.
That runs an electric 'frige (16 cu. ft.) plus up to 200 Watts of computer/satellite equipment, plus a 1/3 HP water pump, plus a 1 HP digester pump, plus a microwave, plus lights, plus radio.
No 6 kW 48V inverter needed (sorry, Mike!)

Now I do it mostly by load management as the system is a bit "iffy" on specs. But Bill's figure of 2.6 kW hours per day is right about what we use in the Summer. If I were to improve my existing set up it would have more panel, certainly, and more battery. Maybe like this:

450 Amp hours of battery (allowing up to 5.4 kW hours per day @ 50% DOD, 2.7 @ 25% which is better).
Double the panel capacity to 1400, which would give about 40 Amps peak charge current and about the max 5.6 kW hours harvest in Summer (high elevation = more efficient panel operation).
Might add 400 Watts of "morning" panels to start charging earlier in the day.
Possibly exchange the VFX3524 inverter for a Magnum MS4024 (better charger).
Wouldn't trade the MX60 for anything (FM60 is the modern equivalent).
Wouldn't trade the Honda EU2000i for anything.

Does that help?

sub3marathonman · February 2011

Re: 6 Kw Off grid

BB. wrote: »

Before designing a solar PV off-grid system, it is really helpful to understand your needs/loads. Just in parts, you could be looking at well over $60,000 for a full sized 6kW inverter/charger/solar pv/battery system (not even including a genset for backup power).

Pretty much (at least in the US), off grid power costs in the range of $1-$2+ per kWH vs the $0.10 to $0.20 per kWH that most people pay for utility power.

Also, seasonal power variations are important. You may get 5+ hours of sun 9 months of the year, but get 2-3 hours of sun during winter.

-Bill

This may be risky, but I would respectfully disagree with Bill, at least on the $60K for a system. And, even off-grid, it is apparently possible to claim the 30% Federal Tax Credit, which even at $60K would bring it back down to $42K. I think it can be done for MUCH less.

This is what I came up with in about 10 minutes of looking at the NAWS site, which Ericpope would probably use since he is in Arizona too. I didn't research the quality of the panels, but I thought Kyocera was supposed to be fairly good.

A 4.4kw system, 24 Kyocera KD185GX-LPU panels, $11040, Xantrex XW4548, $3000 (93% efficient), XW Power Distribution Panel, $1140, Control Panel, $228, XW 150-60 Charge Controllers, two, $1058, for a total of $16466.

Then you need the batteries, which is where you can go cheap or expensive. A minimum set of 8 Trojan L16RE-B would cost $2590 (there is a quantity discount from NAWS). A Rolls-Surrette 6CS-17PS Battery (10 year warranty instead of 7), eight would cost $6624, but you would have a 546 AH system instead of a minimum 370 AH system.

So even with the expensive components, it would total $23090 for the components. You would probably have to add for the mounting system, wire, and labor for an electrician and roofer, but I can't see that going over another $5000.

That would seem like a pretty nice off-grid system in my opinion, at less than $20K after the tax rebates.

Erikpope · February 2011

Re: 6 Kw Off grid

What do you think of this as an end state?

Magnum MS4448PAE 4400 Watt Sine Wave inverter/charger 120/240 Volt
$2,159.20

Morningstar TriStar 60 Amp MPPT Solar Charge Controller
$545.00

Kyocera KD210GX-LPU, 210 Watt Solar Panel * 20 = 4200w
$9,500.00

Concorde Sun-Xtender PVX-560T 58 AH, 12 Volt * 16 = 928 AH
$2,800

Other parts
$5,000

=
About $20,000

What would you change?

Oh by the way I am planning on putting in a well. So I would have a pump for that too. I forgot to add that part.

P.S. didn't see the last post before posting.

sub3marathonman · February 2011

Re: 6 Kw Off grid

Erikpope wrote: »

What do you think of this as an end state?

Magnum MS4448PAE 4400 Watt Sine Wave inverter/charger 120/240 Volt
$2,159.20

Morningstar TriStar 60 Amp MPPT Solar Charge Controller
$545.00

Kyocera KD210GX-LPU, 210 Watt Solar Panel * 20 = 4200w
$9,500.00

Concorde Sun-Xtender PVX-560T 58 AH, 12 Volt * 16 = 928 AH
$2,800

Other parts
$5,000

=
About $20,000

What would you change?

Oh by the way I am planning on putting in a well. So I would have a pump for that too. I forgot to add that part.

I would definitely change the batteries. You don't want to have more batteries than absolutely necessary. I wish I could buy 2V cells instead of the 12V batteries that I bought. You want to avoid connecting batteries in parallel.

It is interesting that we both almost simultaneously came up with Kyocera panels. I would go with the more expensive Xantrex inverter, I'm not sure about the one mentioned, but I would definitely be checking into the efficiency and the idle consumption, which starts to add up at 24 hours / day.

sub3marathonman · February 2011

Re: 6 Kw Off grid

After a bit more checking, I think the Kyocera KD210GX-LPU is a better choice, at $2.31/watt instead of the $2.49/watt. I guess I should have keep checking a few more seconds.

Erikpope · February 2011

Re: 6 Kw Off grid

Thanks for the help everyone. I'm off to bed, its midnight here. More research tomorrow.

This really has been a lot of help.

Thanks
Erik

BB. · February 2011

Re: 6 Kw Off grid

Sub3marathonman,

Not hurting my feelings... I was trying to get a feel for what Erik was looking for--Both what the system needed to do and what he wanted/can pay.

Your system with the batteries you recommended would do about 6kW of surge (roughly C/2.5 surge for a flooded cell bank) and around 400-500 watts average load (C/10)...

So, yes a less costly system, but also less capable of running a shop...

Also, we need more details... For example 15/45 amps (run/surge) for an air compressor can be at 120 or 240 VAC.

15 amps * 120 VAC = 1,800 VA (possibly watts)
45 amps * 240 VAC = 10,800 VA (possibly watts)

So--we sort of have a big range to fill in with guess work.

Erik, your equipment list is all good stuff... The AGM batteries are high end and about the best you can get for off grid (they also have very good surge current support, much better than flooded cell)... But, as others here have said, you might want to start with "trainer" batteries (cheaper flooded cell).

Add a generator + AC battery charger.

Well, do your research now. There are big 240 VAC pumps (cheap on grid power) which can become a nightmare on Off-Grid power (high power, high starting surges, etc.).

There are a few options. DC (/AC) pumps from Grundfos (very nice flexible pumps, not cheap). 3 phase 240 VAC pumps (or 3 wire 1 phase pumps) behind a VFD (Variable Frequency Drive). Or less expensive DC in well pumps.

If you can pump to a cistern and then use a small DC pump for home pressurization (and pressure tank(s)).. That might be the best of both worlds. Trying to run home pressure from an in-well AC pump is "expensive" for Off-Grid power.

Basically, much of your system costs will be based on surge current requirements... 2x surge current, 2x costly system.

Regarding the electric/propane refrigerator--if this is a full time home (>9 months of the year), then it is probably a better choice to go electric. Summer home (<3 months a year), then propane.

In any case, doing the research now before you buy/build will put you farther ahead in the game no matter what you end up doing later.

Lastly, you might need to brush up on the difference between VA (volt*amps) and Watts. For AC, electric motors draw their current out of phase with the AC voltage wave form... Basically they draw more current and need heavier wire, inverters, generators, to operate without overheating the wiring. Solar panels and batteries pretty much run on Watts... The formula is:

Power = Volts * Amps * Power Factor (aka Cosine of voltage/current phase angle).

And keep safe over there so you can make back home in one piece.

-Bill

sub3marathonman · February 2011

Re: 6 Kw Off grid

BB. wrote: »

Sub3marathonman,

Not hurting my feelings... I was trying to get a feel for what Erik was looking for--Both what the system needed to do and what he wanted/can pay.

Your system with the batteries you recommended would do about 6kW of surge (roughly C/2.5 surge for a flooded cell bank) and around 400-500 watts average load (C/10)...

So, yes a less costly system, but also less capable of running a shop...

And keep safe over there so you can make back home in one piece.

-Bill

A couple of questions for Bill.

Wouldn't my system be able to supply about 3000 watts or more during the day when the solar panels are producing? Also, as far as surges, isn't it possible for the batteries to withstand a huge draw for just a few seconds? So during the day, wouldn't the XW4548 be able to supply up to the 9kw surge rating?

And the Concorde are high quality batteries, but don't you really want to avoid having batteries connected in parallel?

mike95490 · February 2011

Re: 6 Kw Off grid

I know for example air compressors my need 15 amps to run but to start could need 45

That's what lead me to the XW6048 For only a couple $ more than the 4548. Sure, 4 12V batteries won't run much, I guess 45A 120V starting surge (a compressor that big could likely be rewired to 240V for less line losses) is 5400w which at 50V, is 108A. One or 2 starts a day, the batteries should handle that, but the well pump will be another factor..... how deep, and how many GPM??

BB. · February 2011

Re: 6 Kw Off grid

Yes, I agree the AGM can supply a whole bunch more current for surge... However, there appears to be possible voltage fault error with the XW system when you have a lot of solar panels an few batteries...

The Concord AGM are known to simply stop taking current when they are 100% charged--They therefore are not really able to help regulator the system voltage and the (what appears to be) slower response times of the XW charge controllers (and the Hybrid inverter in GT "sell" mode) appears to be problematic if you do not have a "large" (600 AH @ 48 volt) minimum battery bank with 6kW of solar panels and 6-12 kW (or 1.0 to 2.0) range of peak and surge ratings.

If you have 3kW of panels, and expect 3/6kW from your inverter (peak, surge), then I would expect the kWH rating of the battery bank to go down by 1/2 too (remember 600AH*48V=28.8 kWH of storage per 6/12 kW rated inverter). If you go to a 24 volt battery bank (3kW 48 vs 3kW 24), you still have the same "amount" of energy storage (xxkWH), but with 1/2 the battery bank voltage, the AH rating of the bank is 2x larger (P=V*I).

So, from backing out other's experiences here (not mine directly), I have seen that C/2.5 or C*0.40 seems to be the limit that I would suggest is the maximum surge current that a generic flooded cell storage bank should be expected to reliably supply over time/age/state of charge.

C/8 seems to be the maximum continuous current that most (average) storage batteries can produce continuously without overheating (also appears to be the maximum charging current too without external cooling).

AGM's would appear to address a small bank with large current spikes (C*4 or 10x the current with Concorde AGM's from the Wind-Sun FAQ).

In general, continuous power usage of C/10 or C/20 seems to be a good assumption for most people's off grid solar systems. Still fairly efficient, a couple days of storage, and not too large (expensive) of battery bank. Also goes with long battery life.

However, I would be hesitant to go the otherway and assume that a small Concorde AGM bank can accept large solar arrays in a Grid Tied configuration (because they do not accept, very much, charging current when "full" and may allow to battery bank to well exceed 72 VDC causing various items to shutdown). AGM batteries in UPS type situations (15-20 minutes of max power then shutdown) do not seem to last more than a couple years before they need replacement.

Again, this is my humble opinion, and I have been wrong before

. My recommendation if somebody needs to go with a small AGM bank and a large solar array to support surge current/power usage during the day--Put down the specifications of the system (including expected output performance) and then let people who know more than I (Solar Guppy, Solar Sparks, etc.) speak to their experiences.

-Bill

mike95490 · February 2011

Re: 6 Kw Off grid

BB. wrote: »

.... However, there appears to be possible voltage fault error with the XW system when you have a lot of solar panels an few batteries........

I think that's only for grid tie sell mode, not off grid stand alone. And the fault is more the charge controller's, allowing too high of voltage - I EQ at 62.5V, and have yet to see the XW fault , except for when the pump was left on after dark and ran the batteries down to 40V !

But back to the OP's idea of starting a small system, and then growing it, I think the 6048 and 60A tristar MPPT is a good combo with any small battery bank, learn on a small cheap bank, then buy the expensive bank. If the OP is going to be selling to Grid, then you have to go all XW gear and much larger starting bank.

BB. · February 2011

Re: 6 Kw Off grid

Sounds good... I was concerned that a "large" array with "small" battery bank plus heavy/surging loads could cause a similar event as a varying GT inverter + clouds passing overhead.

In any case, lots of panels and a small bank would be for a system where most of the loads are used during the day (shop/business).

-Bill

Erikpope · February 2011

Re: 6 Kw Off grid

About the well, what I had planed to do is just what you suggested. I plan to pump to a storage tank and then pressurize it after that. About running it at night all I would have to do is put it on a timer.

I also plan on using a gray water system. That should help with how much I need to pump up.

About batteries, the ones I chose didn't show warranty/life of battery info. If I did 8 Trojan L16RE-B 370 AH 6-Volt Deep Cycle Solar Batteries would I keep it as a 6 volt system or put it in parallel and have a 12v system? at 12v would my total AH be 1480 or is my math wrong?

About a shop, I would like to do some wood working and stuff out there but If I did do that I would have a generator for the time I was using those tools.

Now heres a Question. Would it be better to have the generator separate from the solar and just run my tools (table saw, compressor, drills) or connect the generator to the inverter? Ether way I am buying a generator first. I will need it while I build the house.

Erikpope · February 2011

Re: 6 Kw Off grid

What do you think of a Honda EB4000 MSRP $2109.95

Specifications:

Engine Honda iGX270
Displacement 270cc
AC Output 120/240V 4000W max. (33.3/16.7A) 3500W rated (29.2/14.6A)
Receptacles 20A 125V Duplex (2), 30A 125V Locking Plug, 20A 125/250V Locking Plug
DC Output N/A
Starting System Recoil

I started looking at the well pumps and I think ill have to go deep, So, the
Grundfos SQF (SQFlex) Solar Submersible Well Pump

3 SQF-3 Helical Rotor 600 Feet 2 GPM 130-900w 3" (1" NPT)
or
6 SQF-3 Helical Rotor 820 feet 6 GPM 100-1400w 3" (1" NPT)
Same price $1,848.90

To pressurize it should I use a pump with a pressure tank or just elevate the storage tank and let gravity do the work? I know this question was a little off topic but who knows someone in here may have experience with it.

Thanks
Erik

mike95490 · February 2011

Re: 6 Kw Off grid

Now the juggling begins.

Generator, the hondas are nice, and the inverter gensets with the auto throttle use a lot less fuel. (honda, yamaha make them along with some others)

Well Pumps, the Grundfos SQF (SQFlex) Solar also need a Grundfos SQF control box which houses the MPPT ckt. Add some $$ for that. And some extra panels you can't use for anything else. $$$ I went with a standard well pump, $400, the big inverter , and an Intermatic $90 clockwork timer to only allow noon time pumping.
And it's hard to beat gravity feed, to not have a pressure pump cycling on and off, or a storage bladder leak down after 15 years. i have a float switch in the tank, with about 500 gallons between on-off cycles, so it only comes on once in a while.

I've found shop tools run fine of the big inverter, and it's quiet, no genset running all the time. Saws and such are only on for a minute or so, and then it's move, set up, measure, stack......

Batteries, in series, the voltage adds up, 8, 6V batteries = 48V @ 370ah. In parallel, the amps get added. But - in parallel, you can have problems with not sharing the current (load & charging) well, and you can spend a lot more time troubleshooting.

BB. · February 2011

Re: 6 Kw Off grid

You may end up with several gensets... For light loads (1,600 to 400 watts or less), the Honda eu2000i is really hard to ignore (120 VAC only). Really good for smaller loads and banks. The eu2000i and eu1000i (and the Yamaha and others) have an Inverter that allows the engines to throttle back if they are running light loads. Makes them more fuel efficient and quieter.

And a larger genset to run your tools and (if you choose it) to run the 240 VAC input of your inverter/charger. If you can keep them loaded to around 50% minimum loading, your fuel usage is fairly efficient.

Others can speak to raising the tank vs using a local pump for pressurizing the system... However, raising the tank would seem to be an advantage with less system complexity. By the way, do you have a local requirement for fire water storage (for your use or department use)?

One thing to watch out for---Most pressurization pumps do not do very well if they have to lift the water above the tank level. They can cavitate/draw in air from fitting leaks. Cavitating pumps are noisy, do not move as much water, and do not last as long. Putting inlet filters/fine screens on the pump can make the the cavitation problem worse.

If you can put the pump below water level... Watch what happens if there is a leak... I.e., if pump is in a pit, will the pit flood and ruin your pump if the pipe or seals fail.

Regarding batteries... Read these couple of FAQs:

Deep Cycle Battery FAQ
www.batteryfaq.org

About inverters:

All About Inverters
Choosing an inverter for water pumping

And a good reference--Sort of the Everything People Ask about Solar thread (lots of pointers to FAQ's, reading material, alternative DIY projects, etc.):

Working Thread for Solar Beginner Post/FAQ

Say you have 8x 6 volt 225 AH golf cart batteries. You can arrange them in 6 volt, 12 volt, 24 volt, and 48 volt banks.

When you put two batteries in series, the Voltage doubles and the AH capacity (amperage) remains the same.

When you put two batteries in parallel, the AH capacity doubles but the voltage remains the same.

In both cases the amount of energy remains the same:

power = voltage * current (single battery)
2*power = 2x Voltage * Current (double the power by 2x voltage)
2*power = Voltage * 2x Current (double the power by 2x the current)

So--your 8x batteries--the amount of energy available remains the same no matter how you arrange them:

8x 6 volts @ 225 AH in parallel = 6 volts @ 1,800 AH = 10,800 Watt*Hours
2x 6 volts in series * 4 parallel strings = 12 volts @ 900 AH = 10,800 WH
4x 6 volts in series * 2 parallel strings = 24 volts @ 450 AH = 10,800 WH
8x 6 volts in series (one string) = 48 volts * 225 AH = 10,800 WH

Now the reason we go with higher voltage is because Power=Voltage*Current. If we have 4x the voltage (48 vs 12 volts), we have 1/4 the current for the same amount of load.

Also voltage drop... Roughly for a 12 volt system, you can have 1.0 volt drop in your wiring. More than 1 volt drop, your loads/inverters may shut down.

12 volt bank) 11.5 volts minimum battery voltage - 10.5 volts cutoff = 1.0 volt drop
24 volt bank) 23 volts minimum battery voltage - 21 volts cutoff = 2.0 volt drop
48 volt bank) 46 volts minimum battery voltage - 42 volts cutoff = 4.0 volt drop

With 24 volt, you have 2 volt drop to work with. With 48 volt, you have 4 volt drop wiring drop maximum.

So, as your system increases in size, the higher voltage battery bank makes it easier to bus your energy around (and save money on heavy copper wiring).

Also, I would recommend that you try for one battery string, and 2-3 parallel strings maximum. Parallel battery strings are more expensive (you need wiring and fuse per string) and more of a pain to maintain (2-3x more cells to check water level in).

And parallel strings need to be checked for current balance and you need to check once in a while for dead cells (open/shorted). A bad cell can damage the string or even the bank (depending on what went wrong).

Plus you need to wire parallel banks correctly so that you get good current sharing:

http://www.smartgauge.co.uk/batt_con.html

Regarding Genset and inverters... There are inverters (DC in, AC out) and Inverter/Chargers (AC in, DC Battery bank, AC out). They typically have internal transfer switches and an internal battery charger that can take AC Grid or AC Genset power and both recharge the Battery bank and even run the AC loads directly (more efficient to run the AC loads directly from the generator vs AC to battery back to AC).

There are some very nice separate Inverters and Chargers... And there are some vary nice combination Inverter/Chargers/Transfer Switches.

The XW Hybrid Inverter (/Charger) can even do neat things like allow you to use a 4kW inverter and still run 6-12kW (surge) AC loads... The Inverter will "help" the generator run the loads (program inverter with lower genset rated current)...

If you think you will ever get Utility Power to your property... Picking a Hybrid inverter that can perform both Off-Grid and, later, Grid Tied operation may be of interest too. Grid Tied operation with a Hybrid inverter is much efficient/cost effective than running from batteries. And you still maintain the ability to go off grid if the utility fails (basically a whole house UPS).

Anyway lots of stuff to study.

-Bill

Cariboocoot · February 2011

Re: 6 Kw Off grid

Erikpope wrote: »

About batteries, the ones I chose didn't show warranty/life of battery info. If I did 8 Trojan L16RE-B 370 AH 6-Volt Deep Cycle Solar Batteries would I keep it as a 6 volt system or put it in parallel and have a 12v system? at 12v would my total AH be 1480 or is my math wrong?

Whoops! Two 6 Volts is series gives you 12 Volts (at the same Amp hours). Batteries connected in parallel ups the Amp hours but keeps the Voltage the same. The "B" Trojans are 375 Amp hours, so eight of them configured for 48 Volts is still 375 Amp hours as all would be in series. But that's roughly 9 kW hours of power @ 50% DOD. Slightly more than 3X what I use.

About a shop, I would like to do some wood working and stuff out there but If I did do that I would have a generator for the time I was using those tools.

Now heres a Question. Would it be better to have the generator separate from the solar and just run my tools (table saw, compressor, drills) or connect the generator to the inverter? Ether way I am buying a generator first. I will need it while I build the house.

Depending on how much you use the tools, that's a good plan. But you can have separate generator outlet and connect it to the inverter so that any time it's running it will also help charge the batteries. Or you can run all loads through the inverter and have the gen available "if needed". It depends on the size of the loads and how much they'll be used. There's no way around that.

6 Kw Off grid

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