Off grid - generator and batteries to start

jakenshake

Hello all,

Brand new to forum...lots of detailed information but I'm so new it's hard to follow much of it. I suspect my questions have been asked before, but I wasn't able to find. I'm hoping someone can point me in the right direction.

I have a new off-grid camp in northern Michigan, just framed and fully wired for normal 120 AC. I want to set up power using a battery bank and propane generator, with the option of adding solar panels later. I have a large metal roof slope facing south. Generator will be on south porch, just below a 2nd floor closet where I will store the (sealed) batteries. Camp will only be used a few weeks in summer, fall, and early winter. Camp interior will experience sustained subzero temperatures.

I framed a 335 gallon water storage tank 20' up in the attic for gravity feed hot and cold. Not sure how pressure will work out as plumbing is underway now but hoping for the best. I can fill the storage tank with normal pressure when power is on, or by using a hand force pump at the well in a pinch. Also, the main wood heating stove is kitty corner to a holding tank placed in the bathroom. A thermosyphon coil in the stove warms the tank, keeping the bathroom warm and taking the cold edge off from the water feeding into a power vented propane water heater. The water heater, ceiling fans, and fridge are my only significant 'continuous' power needs.

My long term solar and perhaps wind goals are 6 kw hours/day with peak power load not exceeding 4000 watts. I would be happy with half of these numbers to start...setting up just a propane generator and battery bank this year as funds are tight.

All my appliances are 120 AC, including a grundfos 10SQ05B-160 'soft start' water pump submersed in the well. Biggest power items will be microwave, toaster, washing machine, and water pump. But none of these will be used unless the generator is running...at least until my system is capable.

So my questions are many. Would you agree that a 5500 watt generator is appropriate for now and future? What is a top of the line brand? It appears that AGM sealed batteries would fit my needs. How many and what voltage for a system starting at 3000 watt hours/day and a peak draw of 2000 watts that will eventually be upgraded to twice that capacity with solar/wind instead of just generator charging? Should I go with a 12 volt or 24 volt system? Any recommendations on a high quality inverter/charger for the long haul? I'm guessing I need some kind of gear to tell the generator to kick on when the batteries are at half charge. What other equipment will I need? Are there wiring 'diagrams for dummies' available? I'm a structural engineer and my eyes cross when I see most wiring diagrams.

Any help would be greatly appreciated. I've spoken to a couple of different solar contractors. However, even though they were both given the same scenario, completely different systems were proposed. Maybe someone can recommend a good expandable starter kit or even a good book. Thanks.

Cariboocoot

Re: Off grid - generator and batteries to start

Welcome to the forum.

On the whole it's an entirely feasible plan. The devil is in the details of course.

For instance you need to get a bit more finite numbers on your usage potential. Keeping the large power items for generator only is good, but do you really need an electric toaster at all? The first rule of off-grid is conservation, and that means dropping as many big loads as possible. Anything that heats is automatically a bad idea.

I'll reiterate the standard litany of sizing systems:
Your maximum total Watts used at any one time determines the size of your inverter.
The total Watt hours used per day determines the size of the battery bank.
Once you have that figured out you'll know how to recharge it.

Skipping the panels initially is something I often recommend. But you need to have either an inverter charger or a good stand-alone 3 stage battery charger. It is important the batteries be recharged properly, or else they won't last long.

I wouldn't put much hope in wind power if I were you. Most of the time the site is not suited for it. Couple that with the difficulty and expense involved in installing a turbine properly and you see it rarely is a good value. Then there's the terrible reality of how many of the commercial units out there are just plain junk.

To try and answer some specific questions, with a peak draw of 2000 Watts you will definitely want a 24 Volt system (if not 48). Especially with 6 kW hours daily use (which is quite high for most off-grid systems). You'd be looking at roughly 500 Amp hours of battery @ 24 Volts. That's a need for 50 Amps charging current.

This is probably even more confusing and over-whelming. But it can be broken down into manageable bites. It all depends on loads.

icarus

Re: Off grid - generator and batteries to start

A couple of points,,

First. Your 350 gallons of water in the attic are going to be heavy,,~3500#, personally I would consider a conventional pressure tank. Second, that tank elevated ~20' is only going to deliver water at ~8 psi, not enough to be terribly useful, so you will need a booster pump, and if you are going to have to go to that trouble,, consider by previous suggestion.

The general rule of thumb (my back of the napkin calc) is, off grid systems deliver sort of like this. Take the name plate rating of the PV, divide that number by 2 to account for all cumulative system loses and detatings, then multiply that number by 4 to represent the average number of hours of good sun, per day, that one can reasonably expect, on an annual basis. So to get 6 kwh/day will need a substantial system.

For example 3000 watts of PV, 3000/2=1500*4=6000 wh/day (6KWH).

Into 12 vdc that will deliver ~ 200 amps. That would require a battery bank in the ~1000-2000ah range. ( A T-105 golf cart battery is ~ 250 ah into 12 vdc as an example)

Your best advantage is to do everything you can to conserve. 6 kwh/day is a pretty big load for a part time cabin. For example, we use no micro-wave, no resistance heating appliances what so ever. ( I have a very nice Propane toaster!) If you reduce your daily loading by 1/2 you save a ton on PV and battery costs. Time shifting loads to peak sun periods is a great way to off set large system sizes. Also, consider using the genny to pump a lot of water, once every few days for example.

Quite frankly, I think a 5 kw generator is way to big for day to day. Consider 2 Honda EU 2000i's. You can run one for every day loads, up to ~ 1800 watts, and then plug them together to get ~ 3600 watts continuously. Running the 5 kw will burn a lot of fuel and will not be loaded much.

Consider 24 vdc to reduce series connections in the batteries, but the down side is that 12 vdc is handy to have for a variety of other uses. We power much of the house with 12 vdc, including ceiling fans, some lighting, radio, telephone, etc.

Good luck and keep in touch,

Tony

mike95490

Re: Off grid - generator and batteries to start

Have you chosen an inverter and charger yet ? Might I suggest the integrated XW6048, 48V, 6KW and a 100A battery charger w/PF correction. With the genset, you can control the amps to the max the batteries will accept , to keep your runtime down & save fuel. Batteries - better to have them in series, than in parallel, building this up in 24V will be a real pain, and require large interconnects.

I think you will find, that you will need some solar to keep the batteries charged while you are away, or else you will come back to find ruined batteries. Figure 2-3% of total battery bank amps to keep a trickle charge. Charged batteries will not freeze, generally, unless you are in a REAL cold situation.

simmtron

Re: Off grid - generator and batteries to start

Don't think you will have a problem with the water tank at 20 feet. Here in Mexico every house has a tanaka tank on the roof which supplies the pressure, we have on at about 20 feet. Fine for shower and normal water use, slow for watering garden. Be careful if you are using an "on demand" water heater as most need more pressure than you will get from a gravity fed tank.

Cariboocoot

Re: Off grid - generator and batteries to start

I'm going to disagree with Mike, which I don't normally do. For a off-grid only application the XW series isn't a good value for the money. Especially if you don't need the 6 kW capacity. Magnum makes some inverters with PF charger built-in and available as 120/240 if needed. About $1,000 less than the XW.
Nor is there need to go to 48 Volts if you don't actually have the power requirements.

But without firm load requirements you can't make any equipment choice. Well you can, but it's likely to be wrong.

jakenshake

Re: Off grid - generator and batteries to start

Cariboocoot:
Of course you are right about power consumption. After throwing out my wife's curling iron and blow dryer (I'll tell her later) and deciding to eat stale bread I could get by with a final system of 4000 watt hour/day and a peak load of 2000 watts. I'll start the initial system with 2000 wh/d and 1500 peak load, and use large appliances when generator is running.

You said peak watts used determines size of the inverter, but does that mean peak watts used at any time even when generator is running? Of course one is 5500 and the other is 2000 watts.

I'll skip the wind idea. Too expensive and noisy.

Icarus:
Yes the tank is heavy when full but the support structure has been engineered and can safely carry 1.5x the load. In any case, it's already installed. Also have a drain pan under the tank for condensation. My hydro calcs indicate a conservative 6 psi, even using large pex piping and no remix valves or other restrictions. I believe it will flow fairly well if I can keep the plumbing inspector away. As a kid my dad had a camp with a large exterior tank that was 30 feet away and only 15' of head, and the water flowed just fine for washing dishes, etc. The real question is how much all the water heating equipment will slow down the hot side.

I like the idea of two smaller generators...efficiency and backup in case one fails. I'll look into that propane toaster. Maybe it can double as a hair straightener.

Mike:
Nothing has been purchased or installed yet, except normal 120 AC electrical wiring and outlets. Not even the main wire leading into the underside of the panel...just a conduit pipe.

Temperature in camp will get VERY cold....sustained subzero. If needed I will haul the batteries out of the camp and store in a local relative's (heated) basement.

What exactly is the XW6048? A charger and inverter? Would that be all I need besides the batteries, generator, and wiring?

It sounds like I should be going with a 24 or 48V system. Does that mean some things are more expensive, and others are less? In a nutshell, what is the advantage and disadvantage of a 12, 24, or 48V system?

Simmtron
I wanted to use a tankless Rinnai but could not for that very reason. They require a certain flow rate before the fuel can kick on.

Would anyone be willing to propose a specific battery bank or other equipment they believe I will want or need?

Thanks to all.

Cariboocoot

Re: Off grid - generator and batteries to start

jakenshake wrote: »

You said peak watts used determines size of the inverter, but does that mean peak watts used at any time even when generator is running? Of course one is 5500 and the other is 2000 watts.

Peak Watts expected from the inverter only. Generator size has to be large enough to supply the charging of batteries plus any expected loads. You soon get the hang of keeping things shut off when power is low. When you're properly indoctrinated into the off-grid culture you learn the mantra: "Do not run the generator. Do not run the generator."

I'll skip the wind idea. Too expensive and noisy.

Right on both counts.

I like the idea of two smaller generators...efficiency and backup in case one fails. I'll look into that propane toaster. Maybe it can double as a hair straightener.

Two small Hondas can be linked to double their output power, but remember that's not 240 VAC. If there's any need for that you need a big gen. Tell your wife you love her curly hair, it looks so beautiful.

Temperature in camp will get VERY cold....sustained subzero. If needed I will haul the batteries out of the camp and store in a local relative's (heated) basement.

Normally this is not a worry. But with no solar the self-discharge rate could present a problem in the cold. Bring 'em home with you over Winter, charge them periodically. Batteries are expensive.

What exactly is the XW6048? A charger and inverter? Would that be all I need besides the batteries, generator, and wiring?

Xantrex XW 6048 inverter/charger. http://www.solar-electric.com/xaxwhyin1.html Looks like the price just went up too.

It sounds like I should be going with a 24 or 48V system. Does that mean some things are more expensive, and others are less? In a nutshell, what is the advantage and disadvantage of a 12, 24, or 48V system?

Got to write a paper on this someday: it's one of the top 10 questions! The basic answer is: as power needs go up it is better to increase system Voltage than to parallel a bunch of batteries and add Amperage. Amps inevitably means heat, inefficiency, big wires, connection problems. In term of power, 4800 Watts is 4800 Watts. It can be 48 V @ 100 A, 24 V @ 200 A, or 12 V @ 400 A. That last one, 400 A, is nearly impossible to accommodate in wire sizing and fuses.

Would anyone be willing to propose a specific battery bank or other equipment they believe I will want or need?

Not at this point. When you have a firm "I need 'X' Watts peak and 'Y' Watt hours daily" you can start looking at component choices. You may be overwhelmed; there's always six answers to one question. And that's not including the wrong ones.

RCinFLA

Re: Off grid - generator and batteries to start

With regards to water storage tank. "Not sure how pressure will work out" and "support structure has been engineered and can safely carry 1.5x the load" are concerning contradictions.

I personally would not have 2700 lbs hanging overhead in a wood structure. 8.5 psi is not much water pressure. A pressure tank would be a better solution. I had a pump running a bladder pressure tank on a 4kVA 48vdc inverter and the kWH's are really quite small compared to general kWH consumption.

You did not mention on how you plan to fill the 20' high overhead tank.

General rule of thumb is 12v per 1 kW. 24vdc for a 2-2.5 kW, go with 48 vdc for higher kW inverter. It is determined by battery line current and wire size to handle such current.

jakenshake

Re: Off grid - generator and batteries to start

Cariboocoot
So higher voltage, less amps, more efficiency. But flip side is more expensive inverter and batteries with higher voltage?

I am firm on 1500 Watts peak and 2000 Watt hours daily.... expandable to future 2000/4000. Leaving in August to install so I have to purchase fairly soon. If you are willing, please fire away with specific components.

RC
No contradiction. My reference to 'pressure' was in regards to how much water pressure will be available at the faucets and showers ....completely apart from the capacity of the supporting structure. It's actually closer to 3000lbs when the tank is completely full, and it is easily carried with wood...properly designed of course. Technically not "hanging", but "bearing" on designed platform, beams, and walls which provide a direct load path into the foundations.

Storage tank will be filled either with normal electric pressure (from the submersible) or via a hand pump (baker monitor attached to the well casing) in the case of no electricity.

By that rule of thumb and looking to the future I should consider a 48V inverter/charger. Thanks for that.

Cariboocoot

Re: Off grid - generator and batteries to start

jakenshake wrote: »

Cariboocoot
So higher voltage, less amps, more efficiency. But flip side is more expensive inverter and batteries with higher voltage?

Yes. When you go up in Voltage there is a certain minimum additional expenditure, like the need to buy two T105's for 12 Volts but four to get 24 Volts. As well as increasing the panels to recharge and buying a more costly inverter. There is an addition of power, but it comes at expense.

I am firm on 1500 Watts peak and 2000 Watt hours daily.... expandable to future 2000/4000. Leaving in August to install so I have to purchase fairly soon. If you are willing, please fire away with specific components.

With those figures I'd go with 24 Volt. Even at 2 kW you'd be under 100 Amps (maximum Watts drawn divided by minimum battery Voltage), and it's not likely you'd be running that much all the time.

For 2000 Watt hours a day you'd need at least 167 Amp hours @ 24 Volts.
For 4000 Watt hours a day you'd need at least 334 Amp hours @ 24 Volts.
That is at a maximum Depth Of Discharge of 50%. As you can see, four of the basic "golf cart" batteries would get your system going and not cost a lot of money.
I'll be the first to stick my neck out and suggest:
Four Crown 225 Amp hour 6 Volt batteries: $540
Outback FX2524 inverter/charger w/MATE $2200 or
Magnum MS4024 $2100

There are advantages/disadvantages to each inverter, particularly in respects to future expansion.
Do you need 240 VAC output for anything? You could use either an autotransformer or go for the 120/240 version of the Magnum for slightly more money.

And yes this could be done on 12 Volts, but with the future expansion plans it's probably not a good choice.

jakenshake

Re: Off grid - generator and batteries to start

I have no need for 240. How do you get 2000/167/24?

Also, (4) 225 batteries equal 900 amp hours...or 450 at 50%. Is this right? How does 450 convert to 167?

I'll buy the (4) T105 225 amp hour 6 volt batteries. Are Trojans worth it?

I'm sold on the Outback inverter. I've read many good things. Any advice on wires or other required equipment?

Thanks again.

Cariboocoot

Re: Off grid - generator and batteries to start

jakenshake wrote: »

I have no need for 240. How do you get 2000/167/24?

Also, (4) 225 batteries equal 900 amp hours...or 450 at 50%. Is this right? How does 450 convert to 167?

I'll buy the (4) T105 225 amp hour 6 volt batteries. Are Trojans worth it?

I'm sold on the Outback inverter. I've read many good things. Any advice on wires or other required equipment?

Thanks again.

Ah, the secret battery formulas! Should have included them.

Four 225 Amp hour 6 Volt batteries put together in series equals one 225 Amp hour 24 Volt battery:
series connections increase Voltage but not Amperage; parallel connections increase Amperage but not Voltage.

2000 Watt hours divided by nominal 24 Volts = 83.3 Amp hours. With a maximum allowable 50% DOD that means a 167 Amp hour battery bank to accommodate power needs (83.3 * 2 = 166.6). Keep in mind this is not an exact calculation as it doesn't take into account system efficiency (idle current on the inverter, for example).

Trojans are excellent batteries in my opinion. I've never had any trouble with them nor have I heard of anyone else having problems. Can not say the same for the expensive Surrettes, regrettably. Crown batteries are also good, and often cheaper than Trojan. To that end, your local warehouse club may have some really low priced golf cart batteries that will suit. People here have reported good luck with those, especially for the price.

I'm sold on Outback equipment too, but it's not always the best choice. You do need a MATE to program it, the technology is "dated" (but dependable), and it can be a bit pricey for the power. But they're tough as tanks! Install and programming manuals are like a sequel to the encylopaedia.

jakenshake

Re: Off grid - generator and batteries to start

ah ha! The numbers now make sense and thanks. So with 225 amp hour batteries I will actually have a 2700 wh/day system.

I just priced the Trojan T105 225 6 volts at $150 a piece if I buy at least 3. Not as bad as I thought but I'll still check at costco and sams club.

I have an upstairs interior closet the batteries will be in...would the inverter be best placed on a covered exterior porch next to the generator or inside the closet with the batteries?

BTW, I'm sold on using two Honda EU2000i in parallel with propane conversion kits. Can use gasoline or propane, and are said to run almost indefinitely with propane...less wear and tear because propane is so clean.

icarus

Re: Off grid - generator and batteries to start

If you are putting your batteries in an upstairs closet, make sure you provide for some venting. Battery banks of that size will off gas hydrogen in enough quantity to become dangerous. Consider a voltage controlled exhaust fan (like a Zepher) to vent the battery closet to atmosphere.

Tony

Cariboocoot

Re: Off grid - generator and batteries to start

As close to the batteries as possible: keep those high Amperage DC lines short. And like Tony said VENT it.

I like my Hondas. The EU1000i has over 6,000 hours with just gas, oil, and spark plug changes. Propane efficiency can vary from place to place; I'll stick to gasoline. It's bad enough getting robbed of Watts due to high altitude.

jakenshake

Re: Off grid - generator and batteries to start

I thought the T105s were sealed batteries..and here I was all happy only spending $600 on the batteries. That is why AGMs are twice the price or more. doh!

I believe I would prefer sealed and forget punching a fan hole in the wall. Unless there is some other drawback to AGM besides the steep price?

Does anyone know of any basic schematics available that show how a system such as this is put together ...to include generator, inverter, batteries, and camp electric panel?

Cariboocoot

Re: Off grid - generator and batteries to start

A couple of drawbacks to AGM's: you can't check the SG with a hydrometer (so you should really have a battery monitor to keep track of the SOC) and they are unforgiving of recharge errors. Too much, and they vent. Then they're done.

As for schematics ... it's a matter of piecing together the hook-up instructions that come with the major components using the guidelines of the NEC and some common sense electrical practice. Since every install is different, there isn't any one-size-fits-all wiring diagram. Lengthen a wire run, change the Voltage or current ... suddenly it's different. The basic connections are quite straightforward.

jakenshake

Re: Off grid - generator and batteries to start

I guess what I'm looking for is a better idea on the general layout. Does the generator feed the inverter AND electrical panel, or is it a line from the generator to the inverter, lines from the battery bank to the inverter, and the inverter sending the final power (be it from the bank or from generator) to the electric panel? The reason I ask is that I plan to set everything up myself, if I can find enough information to feel safe doing so. My dad has wired many homes and he will help.

I assume I can just keep an eye on the MATE, and when I see the batteries going low, fire up the generator to charge them? Maybe there is an audible alarm at 50% battery charge?

I looked up that zepher vent. It only turns on when the batteries are charging which is much more appealing. The cost of installing a fan is far less than the extra cost of AGMs...and apparently better batteries to boot.

I really appreciate all of your time and willingness to help me out.

Cariboocoot

Re: Off grid - generator and batteries to start

Using an Outback inverter it's fairly simple: generator output goes to AC IN. When the inverter senses Voltage there is switches loads to the generator and switches operation from 'invert' to 'charge'. You can have the system start the generator automatically when a certain low Voltage point is reached, providing you have a generator capable of it. This lets out the Hondas, of course; no autostart.

The MATE allows you to set the parameter of the inverter, and there are many. If you add solar with an Outback charge controller you can use the MATE to adjust that as well; they'll connect via a HUB and share data regarding Voltage set points, et cetera. The OB charge controllers can do many interesting things too, like operate things via the programmable AUX output. The only down side is the amount of reading you have to do to find and understand all the functions!

rbtrrer

Re: Off grid - generator and batteries to start

What about the water pump?

I think that's how the 240Vac came up

jakenshake

Re: Off grid - generator and batteries to start

After a bit more research I'm leaning toward the Outback FX3048 or even VFX3648. I'll have the potential for a large system, and I can always add another inverter for 6kw or more later. Besides a more expensive inverter I don't see the downside with going to 48V, but maybe I'm missing something.

I'd like to purchase (2) Honda EU2000i with the propane conversion and a parallel kit for a total of 4000W charging capacity.

Making system 48V from the start, but don't really want to lug around (8) 63lb batteries. Is there any downside to purchasing (4) 12V 225amp instead of the 6V? Later when I expand the system I would add (8) 6V. Is there a way to calculate how much charging power is sufficient for a given set of batteries? I'll only have 4000W for years to come, assuming the Hondas hold up.

rbtrr...no 240 needed. Submersible is 120

Cariboocoot

Re: Off grid - generator and batteries to start

The downside of a 48 Volt system is pretty much what you've noticed: you need more batteries.
Now, you do get more power if the batteries are the same size:
Two 225 Amp hour 6 Volt batteries for a 12 Volt system = 1344 Watt hour potential.
Eight 225 Amp hour 6 Volt batteries for a 48 Volt system = 5376 Watt hour potential.
But nothing says you have to use those batteries (@ 67 lbs. each) if you don't need 5 kW hours of power potential. Minimally you could use four of these: http://www.solar-electric.com/unbamo45agms.html (32 lbs. each). At 50 Amp hours, you'd have 1200 Watt hour potential.

Charging a 48 Volt system is another challenge, because you must have enough Voltage to charge the batteries. This usually means at least two panels in series, and they will be the big (expensive) panels. Or four of the Kyocera 135's - which would be more array than you need for those minimal batteries. So getting a good panel-to-battery ration becomes a bit more complicated. Especially since you'd want the panels to be usable when you do increase the battery bank size.

jakenshake

Re: Off grid - generator and batteries to start

This is in the Great Lakes region with lots of gray winter weather. I wonder if that argues against a 48V system in any way? If not, I'm still inclined to go that way.

The Kyocera's are ~$370 a piece. I don't think four would be unbearable for me next year. Do you know if they have quality (non damaging) brackets for attaching to a standing seam metal roof at a 10:12 pitch?

Is it experience or do you have a secret formula for determining that such and such panels would appropriate for a given battery bank?

Also, what do you mean when you say "want the panels to be useable"? How could increasing the bank size make them un-useable? If you mean not enough panels, I would always have generator. And that brings me back to whether 4000W charge capacity is enough for a system that may grow to be quite large.

Cariboocoot

Re: Off grid - generator and batteries to start

Sorry; forgot the magic formula.

Generally you try for a potential peak charge current of 5-13% of the battery bank's total Amp hours. I usually "shoot for" 10% because, what with one thing and another, you usually get between 5 and 10 that way. Thus:

50 Amp hours charged at 5 Amps (10%) * 57 Volts (typical charging Voltage on a 48 Volt system) = 285 Watts. Since panels don't put out their nameplate rating you have to take a certain amount of derating in to account. Usually this is 77% (some places will do better, others worse). That makes for a 370 Watt array. Two 185 Watt, "24 Volt" panels in series should do ... but not all panels are created equal. One panel here http://www.solar-electric.com/kyocerakc170gt.html has a Vmp of only 23.6 - which means it won't actually work! Four of the Kyocera's is actually much more capacity than you'd need for those batteries, but the Voltage is right. See the balancing act?

Then when upgrade to a larger capacity battery bank, will those same panels be available for adding on? Mixing different panels can be problematic if the Vmp and/or Imp are too far different from the original panels.

So when you're planning on future expansion it's a good idea to work out both systems in advance: what you want/need now and what you'll want/need then. That way you can see what components can be retained and what will have to be changed. And of course that means you may buy one or two "over sized" items initially, and suffer some efficiency loss there knowing you will be adding on later.

4kW worth of generator is a lot for most off-grid applications, btw. I like your plan of using two of the Hondas to get it, as it gives you flexibility in capacity.

jakenshake

Re: Off grid - generator and batteries to start

The Kyocera you recommended has a vmp of 17.7, which is lower than the one you said wouldn't work? It wouldn't work for a 48V system because a multiple of it has to be closer to 57? (2 x 23.6=47.2...not close enough to 57, but 3 x 17.7 = 53.1 is?)

So if from the start I had 255 amp hour batteries...the math would go like this:

255 x 10% = 25.5
25.5 x 57 = 1454
1454 / .77 = 1887

Using the 135 Kyocera = 135

1887 / 135 = 14 panels

But since the amp hours is independent of the number of batteries, how does the number of batteries fit in here?

I'm going to be muttering "amp hour....voltage...EU2000!" in my sleep tonight.

BB.

Re: Off grid - generator and batteries to start

For a lot of reason, ~17.5 volts Vmp is around the optimum voltage for a solar panel to charge a 12 volt battery at ~14.5 volts (~15.0 volts for equalization). Solar panels loose voltage at they get hot, and you have wiring+controller voltage drops too...

So, for charging a "48 volt bank", you are looking at ~4x17.5v=70volts... That is the "optimum" voltage for a PWM controller, and the Minimum Voltage for a MPPT type controller.

Your formulas are correct:

255 x 10% = 25.5
25.5 x 57 = 1454
1454 / .77 = 1887]

The AH * Voltage * # of batteries is what matters... If you have 8x 6 volt @ 255 AH batteries--whether they are organized as:

• 6 volt string => 6 volts * 8 batteries * 255 AH = 12,240 Watt*Hours of storage

Or as a 48 volt string:

• 8 batteries * 6 volts * 255 AH = 12,240 Watt*Hours of storage

So--how you organize the battery bank as 12/24/48 volts--You will get:

• 2 batteries in series x 4 parallel strings => 4x 255 AH = 1,020 AH @ 12 volt bank
• 4 batteries in series x 2 parallel strings => 2x 255 AH = 510 AH @ 24 volt bank
• 8 batteries in series x 1 parallel strings => 1x 255 AH = 255 AH @ 48 volt bank

So--the batteries, no matter how you organize them will still store the same amount of "energy". The difference is the amount of current/AH storage will require heavier copper wires to carry more current at the lower voltage battery bank.

The Number of Batteries--In series, they add voltage. In parallel--they add current... In series/parallel, they add a bit of each.

AH can be a bit deceiving. People talk about using "AH" from their battery bank and talk about pumping AH back in (recharging).

However--when we talk about systems here--we are always asking what voltage was the Battery Bank you are talking about--Knowing Amp*Hours is not enough:

• Power = Voltage * Current
• Energy = Power * Time = Power * Hours = Volts * Amps * Hours = Watt*Hours

So-- Amp*Hours does not tell us every thing....

• Volts * Amps * Hours = Watt * Hours

MPPT charge controllers can take high voltage/low current from the solar array and down convert it to low voltage/high current needed to recharge the battery bank. More or less, think of a MPPT controller sort of like the DC like a variable AC transformer.

A PWM is simple "on/off" switch that basically turns on and off to control the charging of the battery bank... That is why you need to match the solar array Vmp to your Vbatt-charge voltage.

Note that you would be connecting your array into a reasonable series/parallel combination of Vmp*Imp...

For a PWM controller:

• 1x 17.5 Vmp = 12 volt bank
• 2x 17.5 Vmp = 24 volt bank
• 4x 17.5 Vmp = 48 volt bank

Now--if you want "More Power"--You would connect additional panels in parallel strings...

For a MPPT type controller, the minimum Vmp is as above. The maximum for many controller is ~150 VDC Maximum... Or around Vmp~100volts maximum which is ~5x 17.5 Vmp panels in series...

So, for an MPPT controller connected to those 135 watt Kyocera panels:

• 1-5 panels in series = 12 volt bank
• 2-5 panels in sereis = 24 volt bank
• 4-5 panels in series = 48 volt bank

And, again, you can add strings in parallel to get the mix of Vmp/Imp you need for your controller and battery bank combination.

And--it does get more complex... The larger >100 watt solar panels are typically designed for Grid Tied AC systems--and are not designed for Vmp in multiples of 17.5 volts... instead, typically, higher voltages for more efficient power transfer (higher voltage means lower current, smaller copper wires, less copper costs). So, typically large panels are less costly ($$$/watt) and can be less costly to wire (fewer electrical connections).

So know, you may be looking at Vmp of 24 to 70+ volts (depending on brand/model you pick).

There are some more rules--but the above gives you an idea of what the basics are for designing your system.

By the way--Here is a neat thread about picking the "ideal" charge controller to match with a Honda eu2000i:

Question about battery charger selection with EU2000 generator

-Bill

techntrek

Re: Off grid - generator and batteries to start

He could design the system to charge at 24 volts in sets of 2, or each individual battery at 12 volts. No reason from a technical standpoint to charge at 48 volts just because the system is 48 volts. Charging each individual battery also gives the advantage of making sure each one is optimally topped off which isn't possible with strings. But you must be sure to use only one charge controller per battery (or pair of batteries) to prevent wiring it up as one big short. Zap.

The flip side is this could cost more, but not necessarily. Just have to run all the numbers on panels and charge controllers at 12, 24 and 48 volts to see how it turns out.

jakenshake - I currently have a battery/generator system (no PV) for emergency use. 192 volt string of 16 batteries, and if the existing charger gives out before I redo the system I will most likely move to 4 charge controllers at 48 volts (with the inverter still running at 192 nominal), or 16 12 volt chargers. Just letting you know you have some additional options.

Cariboocoot

Re: Off grid - generator and batteries to start

What techntrek suggests is not for the uninitiated to tangle with. There are some real concerns with not keeping the negatives and grounding isolated leading to shorts and, as he said, zap.

With the Kyocera 135's you'd use four, as in Bill's post; one is good for 12 Volts, two for 24, four for 48. Nice, even multiples. Simple wiring. Could run off either PWM or MPPT controller. But you would then have more Wattage than you actually need for 50 Amp hours of battery. They could support the 90 Amp hour series in that line. These cost more, weigh more, and give more power.

techntrek

Re: Off grid - generator and batteries to start

Not just the negatives, but the positive terminals, too. Try to share just one pair of batteries hooked in series with one charger wired in parallel to both and you have a dead short on the positive side and a dead short on the negative side of the charger.

Cariboocoot

Re: Off grid - generator and batteries to start

techntrek wrote: »

Not just the negatives, but the positive terminals, too. Try to share just one pair of batteries hooked in series with one charger wired in parallel to both and you have a dead short on the positive side and a dead short on the negative side of the charger.

Right you are! See how easy it is to get confused?
Happens to me at least once a day. Fortunately it only lasts for 24 hours.