Reliable Power Inverter Brands?

[bob g]

Chris
i understand that this is what has worked out for you, however
following your logic no one would build their own wind turbines, they would simply go out and spend what it took to buy an off the shelf solution from the git go.

a lot of folks these days either cannot afford even half a new pickup, or choose not to.

for every guy that can afford a 20k dollar system, i will show you a hundred that is struggling just to put food on the table and still scrape up enough to by a used modified sine wave inverter large enough to make his life a bit more tolerable.

my comments about exeltech was directed at those folks that are struggling to put together a workable system without having to spend large sums of money. if everyone could afford a 20k dollar system, there really wouldn't be much to talk about in my opinion, other than
"hey john, my little green light flickered once yesterday, what do you suppose that means?"  now that would be fun, not!

again, i am glad it worked out for you, and i am glad you and your wife really like it, as this is all that counts for you and her.

it sadly is just not going to be the reality for a lot of other folks, even if such a system is the right solution for everyone, which is arguable to start with in my opinion.

bob g

[ChrisOlson]

it sadly is just not going to be the reality for a lot of other folks, even if such a system is the right solution for everyone, which is arguable to start with in my opinion.

I agree 100% with the cost issue.  And make no mistake, we bought every bell and whistle you can get because, basically, both me and my wife grew tired of piecing things together and living with it.  All I'm trying to get across is that the Big Three have proven off-grid systems.  Maybe most folks can't afford to start with all the stuff we got, but we didn't start that way either.  I made the mistake of using inverters like AIMS that do not provide a system that scales up in the future when you CAN afford to scale it up.

If you start with the proven foundation of a Xantrex/Outback/Magnum inverter you can add the bells and whistles as you go.  And while there are definitely other options, its kind of like in the electrical contractor business where they say "nobody ever got fired for spec'ing SquareD equipment".
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Chris

[Mastiffman]

WOW.


 Thanks for the Read guys!

 You both make great opints on the Same topic but from Different Perspectives and that is exactly how a good thread should grow and produce the knowledge for all to see.

 Chris, you have a very unique life style as a few others do but I'm still tied into the grid and do have a small budget. BUT, I do know that if I choose to live completely off grid one day that your replies in this thread will ring forever in my thoughts as it was very useful information from someone with the right experience! So I thank you for that as I myself love autmation in general.

 Bob, thanks for chimming in and giving encouragement to those that are on a tighter budget and are looking for quality assuming they have the patience to find it...

 That's not to say that You Chris, have not. But that you both have provided proper information but from a different vantage point...

 So would you guys have opinions about whether or not it's better to run mulitple inverters off of one battery bank or one large one?

[ChrisOlson]

So would you guys have opinions about whether or not it's better to run mulitple inverters off of one battery bank or one large one?

Typically, the reason for running multiple inverters is because you need to stack two 120 volt machines for 120/240 split phase power.  Otherwise I think you'll get better efficiency from a single inverter that is properly sized for your loads than you will with multiple units.

No matter who makes it, idle power draw is usually 17-20 watts per unit.  An important consideration is sizing the inverter for your loads so it runs most efficient.  As an example, this is the power efficiency curve for the type of inverters we have:



We have two of these unit "stacked" for 120/240 split phase output.  But let's just consider one unit - if you install one of these things and only run it at 200 watts load most of the time your efficiency is down to 85%  Not very good.  The inverter needs to be loaded between 500 - 1,000 watts most of the time for it to be properly sized for your loads and run most efficient.

When you have two inverters like we have, then the "normal" loads in the home should be 1,000-2,000 watts better than 90% of the time.

So there's no easy answer, really, because it depends on your loads and whether or not you can afford to have one inverter loaded and the other at zero percent efficiency using power in idle mode most of the day, or whether or not both are loaded all the time.
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Chris

[Mastiffman]

So, It's more efficient, although more in initial costs for the inverters, to have two inverters sharing the load (of any given calculated load) at the appropriate Wattage that puts the shared wattage into the highest efficiency operation for those inverter models?

[bob g]

i will go first, and again this is from my perspective and not necessarily how others should do anything

because i have exeltech mx series inverter bank, technically i have multiple inverters... and

i believe in multiple battery banks as well,  for a variety of reasons

as for multiple inverters i like redundancy, if one goes down i am not waiting for a replacement, i can continue on while waiting for a replacement or service.

when the crap hits the fan, it is far more important to me to have redundancy than the best support in the industry and having to wait.
in a bad time, that wait may be significantly longer than either i or the manufacture would like.  as for exeltech i believe i have both, that being the best redundancy and also the best support in the industry.

as for battery banks, having one that can be on charge while the other is being used to power a load, makes for maintaining both banks easier and in the long run longer lived.  much like rotating a full size spare tire out of the trunk increases the mileage on all the tires. 

i also like redundancy when it comes to battery banks, should a battery fail, i don't have a short string and the problems related to that, and again if the crap hits the fan i really don't wont to deal with extended down times because of shipping or other issues.

truth be told, i am much more about having multiple quality charge sources, in that i believe that if one has one battery bank that he is relying on, he ought to have at least 2 charging sources that are capable of quality charging.. by that i mean true 3 step, temperature compensated charging with sufficient capacity to get the battery charged as quickly and efficiently as is safe and recommended by the battery manufacture.  this does not include standard battery chargers,  or solar panels and charge controllers that are dumb as a box of hammers and woefully undersized for the bank they are expected to charge.  this also precludes the use of a smart charging system that  is too small to get the acid stirred up and keep stratification issues at bay with flooded lead acid batteries.

btw, i wouldn't walk across the street for a set of nife batteries, even if they were half the price of a quality lead acid battery, which we all know they are not.
fwiw

bob g

ps. looks like Chris got in there first! 

[ChrisOlson]

So, It's more efficient, although more in initial costs for the inverters, to have two inverters sharing the load (of any given calculated load) at the appropriate Wattage that puts the shared wattage into the highest efficiency operation for those inverter models?

In our case, they did not make a single inverter large enough, and in the right price range. to carry our heavy intermittent loads.  So dual units ended up being the best way to go.  Our loads typically run from zero to 300 watts when we're sleeping, 1 - 12 kW during the day, and around 1,600-2,000 watts in the evening hours.

We went with the system where the generator fills in the difference for the extreme loads, as those loads are intermittent (things like the electric clothes dryer) and not that expensive from the standpoint of generator hours required to power them.  However, only Xantrex has that feature - Outback and Magnum don't have it.

I'm going to say that for most people who live off-grid, a single inverter is going to be more efficient simply because most off-grid folks don't use electricity for anything but the basics - lighting, basic low powered appliances, well pump, and limited electronic stuff like TV's or computers.  We did that for 7 years and it's no fun.
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Chris

[ChrisOlson]

as for multiple inverters i like redundancy

Bob makes this point about redundancy, and there's several ways to go about that too.  Our inverters have built-in bypass:



The bypass allows us to bring the generator online and restore power within minutes in a situation where both inverters have failed.

And then to make it better we installed a big manual transfer switch:



The transfer switch allows me to completely remove the inverters and batteries from the picture and switch all our loads over to genset power without having to go thru the inverter bypass system at all.

The reason we went with gensets for power redundancy instead of inverters is because gensets are way cheaper than inverters and you only might need the redundancy once in a blue moon.
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Chris

[birdhouse]

i think a very key point in this whole discussion, which chris stated earlier:  chris doesn't use propane for water heating, cooking, or clothing dryer (unless indirectly from a propane back-up genset). 

i'm sure if his lovely lady allowed propane lines in the house, his inverter(s) could be sized much smaller.  it also seems he has over come this obstacle fairly well, by inverter dumping from the turbines to heat water ect. 

i don't know every detail about chris's system, and chris, i don't mean any of this as any sort of disrespect to you of your wife, but just thought it might be a key thing to consider in the general discussion. 

in my offgrid ranch, where i don't live!, though feel like i could pretty easily, i use propane for hot water, cooking, and heat to some extent.  i use a xantrex prosine 1800 (24v) and love it.  i wish it was just a hair larger to run my mig welder at full blast, but aside from that it does all my power tools, and about anything else i plug into it!  though my place is small, and loads aren't near to a full on offgrid lifestyle.

adam

[ChrisOlson]

i'm sure if his lovely lady allowed propane lines in the house, his inverter(s) could be sized much smaller.  it also seems he has over come this obstacle fairly well, by inverter dumping from the turbines to heat water ect.

Yes, this is true.  Many years ago we had a gas valve malfunction on a water heater and fill the house with gas.  Ever since, my wife will not have a propane line coming into the house.  Last winter she even bought a new range from Sweden that has an induction cooktop on it and the induction cooking is twice as efficient as gas and considerably more efficient than conventional electric cooktops:



As Adam said, the "normal" for off-grid is to use propane for cooking and water heating, and possibly even home heating.  I have tried lots of different things to come up with ways to use electricity for everything and it took me a few years to arrive at a system that works and is efficient.

We went with relying on the generator to power the big loads on-demand, and have been very happy with it.  Our LP tank holds 400 gallons of LP gas and it is dedicated to the generator.  The last time we had it filled was June 2011 and it still shows about 25% left in it.  We'll probably have it topped off here pretty soon while LP prices are lower before the winter heating season.  But I'm guessing we could make it thru the winter on the 25% that's left in the tank.

About 90% of the time the inverters will run these heavy loads OK, as long as my wife doesn't turn on two of her Big Power appliances at once.  So even though we technically use LP gas to sometimes cook, heat water, or run the clothes dryer, I think we are about as efficient (from the gallons used per year standpoint) as somebody who uses the LP gas directly to fuel an appliance.
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Chris

[bob g]

Chris
maybe i missed something or read into something that you didn't write?

are you suggesting that you can cook with your induction cooktop
with power from your inverters, being fed by your propane fueled generator as efficiently as you could had you just used a propane cook top/range?

did i miss something here? 
or did i misunderstand?

if this is what you are stating i would like to see how you arrive at that conclusion, because i cannot see anyway that you can power that cooktop with less propane use than simply using a propane range.

bob g

[ChrisOlson]

are you suggesting that you can cook with your induction cooktop
with power from your inverters, being fed by your propane fueled generator as efficiently as you could had you just used a propane cook top/range?

You misunderstood.

If you consider the "normal" off-grid home where propane would be used for cooking, water heating, firing a gas clothes dryer, PLUS fuel a standby generator - I don't think we're doing too bad considering that our totally electric home uses about 20-25 kWh/day and we only only burn roughly 250 gallons of LP gas per year in the generator.

So my point is that when a person is looking at buying an inverter system it is important to size the inverter so it operates at peak efficiency powering your normal loads.  Don't size it for peak loads.  Using generator power for on-demand peak load management is more efficient in the long run than operating over-sized inverters 23 hours per day at well below their peak efficiency because the normal loads are too small (see the power efficiency curve I posted for a typical inverter).

I really think that most people who set up off-grid systems totally miss the fact that an inverter is more efficient from 15-100% load than it is idling with less than 200 watts load most of the day.  Put in a big inverter and be proud that you got the inverter capacity to run anything - then load it at 200 watts most of the time and you're blowing all your hard earned kWh generated form renewable sources right out the window.  Buy a smaller inverter and turn some lights on for pete's sake, and use the generator for the intermittent heavy loads.
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Chris

[bob g]

ok, that makes absolutely more sense to me!

your point about inverter efficiency makes a certain level of sense, however getting caught up in absolute efficiency of one part of the system often gets folks in trouble.

the first 200 watts of any inverter that has a standby mode capability will always be the most inefficent

the inverter section likely will be somewhere around 90% across the whole spectrum of output, however at or under 200 watts, those 20 watts of idle current equate to at least another 10% of losses, taken together explain the 80% efficiency of the unit below 200watts.
at 100 watts, if we have a 90% inverter section and the same 20 watt idle current, we end up with an efficiency of 70% which on the surface sounds horrible...

but ought we not take this efficiency in context?

that same 20 watts idle when factored against the full load output of say a 1k watt inverter works out to what  2%?  or .2% with a 10k inverter?  and it works out to be the same on the lower end of the sprectrum with small outputs.

i suppose a good case might be made for a second small inverter, if chosen carefully to run all the loads that the larger inverter might be asked to run that are under perhaps a couple hundred watts, maybe up to 500 watts "if" a smaller inverter can be chose with a very small idle current draw, "and" its full load efficiency is very high across its output spectrum.

your use of the generator to power heavy loads makes perfect sense, particularly in the winter when you could harness and put to use the waste heat of the generators engine. that is if it is water cooled or some  other heat recovery scheme is used.

it always amazes me when folks want an inverter large enough to run their welder too, when buying a used miller or lincoln engine driven welder would be far cheaper and a better overall solution to the problem.  when one considers just how much welding he will be doing over the course of a year, it just doesn't make sense to ask an battery/inverter system to be sized and responsible for providing for that load.

not to me anyway.

surely if one will discipline himself a bit, he can get by with a much smaller battery/inverter system, if he would schedule his loads, do a bit of load management and make appropriate use of a generator.

i think generator use has gotten a bad rap, many folks equate their use as a 24/7 proposition, when in reality, with proper scheduling of loads, (along with a now smaller AE/battery/inverter system) one can get a lot of stuff done in a couple hours per week of run time. this would allow for a much smaller, less costly and more efficient system. especially if coupled to a generator large enough to cover those heavy loads efficiently as possible. 
if the generator also has a heat exchanger that can recover the waste heat and use it to do things like heat wash water, or space heating in winter...

 Doing so equates to the proper and responsible use  of a generator in my opinion.

my advise to anyone interested would be not to avoid generators like the plague, but rather accept they are often a necessary evil and embrace them as being something that will probably be a necessity. then take the time to pick one that integrates effectively into their overall system design, and use it responsibly.

if that makes sense?



bob g

[ChrisOlson]

i think generator use has gotten a bad rap, many folks equate their use as a 24/7 proposition, when in reality, with proper scheduling of loads, (along with a now smaller AE/battery/inverter system) one can get a lot of stuff done in a couple hours per week of run time. this would allow for a much smaller, less costly and more efficient system.

This hits the nail right on the head with the point I'm trying to make!  The generator is an integral part of the off-grid power system!

I've run into some folks who equate "success" with their off-grid system by the fact that the generator does not run for months at a time.  Then the system is not designed right.  The inverter(s) are probably WAY over-capacity for what is needed and running at less than optimum efficiency most of the time.

In the world of grid powered homes a 8 kW standby generator would be considered too small for a home that uses 20-25 kWh/day like ours.  But we can do it with 8 kW of inverter capacity by integrating the generator with it.

We have found that, for instance, drying a load of clothes with the electric clothes dryer takes about an hour at 5.5 kW draw from the dryer.  For most off-grid folks this is unthinkable to use an electric clothes dryer.  But here's what happens - my wife washes a load of clothes and this might cause the water heater (also 240 volt electric) to kick in.  We have 2,000 watt elements in the water heater.  The clothes get done with the spin cycle and she throws them in the dryer and turns it on.

So have our other normal loads which might be 1.2 kW, plus the water heater at 2 kW, plus the clothes dryer at 5.5 kW.  The generator starts because of the peak load management system.  The generator will run until either the water heater or clothes dryer turns off.  And more than likely it will be the water heater than turns off first so the generator will run for maybe 30-40 minutes and burn about .55 gallons of LP gas.  The rest is done with RE power.

It ends up being not all that bad considering that it would be dang hard to fire the clothes dryer and the water heater directly with LP gas to do this job and only use .55 gallons.  .55 gallons of LP is only roughly 60,000 BTU.  And heating the 12 gallons of water it took to wash and rinse the clothes from well temp to 125 degrees takes 17,000 BTU input alone with gas water heating at about 40% efficiency.  Electric water heating is 97% efficient.

If you use just LP gas for this job in the water heater and clothes dryer you don't have the option of using RE power to help out.  I do because I'm using electric and the solar panels and wind turbines can finish the job while the generator is only required to provide the heavy lifting for a brief time that the solar and wind can't do.

It works, and we're happy with the way it works - especially my wife.  Using that generator for peak load management has made such a huge improvement in convenience and comfort for us in being able to do what we want without having to worry about if we got the power to do it, that it's just unfathomable for us to go back to the "old way" of having to wait until the sun is shining bright and the wind is blowing good to wash clothes.
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Chris

[ChrisOlson]

my advise to anyone interested would be not to avoid generators like the plague, but rather accept they are often a necessary evil and embrace them as being something that will probably be a necessity. then take the time to pick one that integrates effectively into their overall system design, and use it responsibly.

Bob, there another point when it comes to generators, and that you have done a lot of work with;

Things can be done to generators too, such as using some sort of heat recovery system on the exhaust to heat water, or whatever.  This is something we have not done - partly because it would void the five year warranty on our generator if I started modifying it.  But doing these things can also help with inverter sizing, or selecting the right inverter for your loads.

I know some people are doing things with Lister diesel generators in using cooling system water for home heating, as well as driving a generator with the engine to provide electricity.  And these setups can be quite efficient.

There is also the issue of using DC generators to charge batteries vs using an AC unit thru an inverter charger.  Some folks believe the DC units are more efficient, but I question that.  Typically, with a DC unit you are generating AC power anyway and rectifying it to DC for battery charging, and you do not have the option of switching your loads over to AC genset power directly during battery charging, which improves efficiency by not having to invert every kWh produced by the generator.

The DC units also provide no redundancy to keep AC loads on in the event of an inverter failure.

So I think the standard inverter/charger is typically a pretty well thought-out unit that obviously makes some compromises in some areas to get redundancy and decent efficiency in other areas.  It is my opinion that selecting an inverter for off-grid that does not have AC pass-thru capability and built-in battery charging is going to be a mistake for most folks that want some level of automation in their system.
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Chris

[Mastiffman]

Chris,

 You mentioned it taking about 17k BTU's to heat the water from the well with 2kw heating elements for the laundry load...

 Would it be possible to have a Second, "pre" Hot Water Heater that doesn't actually heat the water coming from the well but allows it to warm up to room temp first and then gets put into the Hot water tank, ultimately not taking as long to heat up?

 Woud, that cut down on the BTU's to heat the water for the laundry or does that even matter at this point?

[ChrisOlson]

There's probably a lot of different ways to do things.  We have two 55 gallon water heaters.  All the standard 4,500 watt elements in them have been replaced with 2,000 watt 240 volt elements.

The top element in the primary heater (that feeds the hot water pipes to the house) is always on with the thermostat set at 125 degrees.  That insures that we always have roughly 30 gallons of water at 125 degrees, even if the generator has to run to heat it.

The bottom element in the primary heater, plus both elements in the pre-heater, are controlled in stages by my Classic controllers.  The thermostats on all of them are set as high as they will go (about 170 degrees).  The bottom in the primary heater comes on first when the Classic goes into what is called Waste Not Hi mode.  Waste Not Hi is when the there is excess power from the solar and wind that the batteries do not need for the particular charge stage the controller is in (either absorb or float).  The controller turns on the element which adds load to the system, and keeps the solar panels and wind turbines at full power output instead of "throttling them back" to maintain the charge stage voltage.

When the bottom element in the primary heater gets up to where the stat kicks it out, the power then goes to the top element in the pre-heater, and finally the bottom element in the pre-heater.  When the bottom element in the pre-heater kicks out (which happens quite regularly when we have both good sun and wind), both heaters are up to about 170 degrees and the Classics then throttle the panels and turbines back because there's no place for the power to go anymore.

No matter how you do it, it still takes one BTU to heat one pound of water one degree F.  And there are 3,412.14 BTU/kWh of electricity.
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Chris

[Mastiffman]

There's probably a lot of different ways to do things.  We have two 55 gallon water heaters.  All the standard 4,500 watt elements in them have been replaced with 2,000 watt 240 volt elements.

The top element in the primary heater (that feeds the hot water pipes to the house) is always on with the thermostat set at 125 degrees.  That insures that we always have roughly 30 gallons of water at 125 degrees, even if the generator has to run to heat it.

The bottom element in the primary heater, plus both elements in the pre-heater, are controlled in stages by my Classic controllers.  The thermostats on all of them are set as high as they will go (about 170 degrees).  The bottom in the primary heater comes on first when the Classic goes into what is called Waste Not Hi mode.  Waste Not Hi is when the there is excess power from the solar and wind that the batteries do not need for the particular charge stage the controller is in (either absorb or float).  The controller turns on the element which adds load to the system, and keeps the solar panels and wind turbines at full power output instead of "throttling them back" to maintain the charge stage voltage.

When the bottom element in the primary heater gets up to where the stat kicks it out, the power then goes to the top element in the pre-heater, and finally the bottom element in the pre-heater.  When the bottom element in the pre-heater kicks out (which happens quite regularly when we have both good sun and wind), both heaters are up to about 170 degrees and the Classics then throttle the panels and turbines back because there's no place for the power to go anymore.

No matter how you do it, it still takes one BTU to heat one pound of water one degree F.  And there are 3,412.14 BTU/kWh of electricity.
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Chris

 So you use excess S and W power to preheat... Did I understand that correctly?
 
 So honestly, It doesn't even matter. You have excess power that is being used at the moment to it's fullest...

[ChrisOlson]

So you use excess S and W power to preheat... Did I understand that correctly?

I don't know if I'd call it "excess".  I have sort of designed our system to heat water this way, and the solar and wind power is sized to be able to do it.  First priority is battery charging and on a typical day our bank is done with bulk and into absorb by noon.  No water heating gets done until the bank is in the last stages of absorb (which typically takes 2-3 hours) and once it drops into float the pre-heat elements are on constantly until the bank either drops into re-bulk, or the stats kick the elements out.

The elements are 240 volt AC, powered by the inverters.  So every input power source to the batteries (solar wind and generator) can be used to power the water heater elements.

On a typical day around 7 kWh - fully 1/3 of our daily average power consumption - goes into the water heaters.  There has been really good days when the wind blows hard that we have dumped 30+ kWh into the water heaters.  On "bad" days we normally have enough hot water stored up so the always-on element never powers up.  In the winter time when the days are short, and if we don't get decent wind, then the generator keeps that "emergency" ~30 gallons of water in the top of the primary heater up to 125 degrees so we're never completely out of hot water.

Basically the way I look at it is that the only things you need to live off-grid is a good reliable inverter, battery bank and a generator.  All the solar panels and wind turbines do is reduce the amount of fuel that gets burned in the generator.  I know a lot of folks don't look at it that way.  But we're not about to give up any of our creature comforts, or grope around in the dark, just because there's bad days when the wind don't blow and the sun never comes out.

Edit:
I'm going to add some comments here because many folks have a TOTALLY different idea about all this.

I've seen some (the vast majority) of off-grid folks that I know that consider the generator to be a "necessary evil".  They will abuse their batteries, and drastically shorten their life, just to prevent having to run the generator. 

Our system is not like that.  The generator is designed in as an integral part of the system.  Our generator is brought online long before our batteries get abused.  We don't consider the generator a "necessary evil" - it's our friend.  And we're not afraid to run it.  That's what we bought it for.

And like I told Bob the other day, we don't burn a lot fuel in the generator.  But we burn one hell of lot more than most folks who live off-grid.  But most folks use propane for other things like water heater, and we don't - unless it's thru the generator.

But the point is, if you're looking at living off-grid and want a system where the generator is an integral part of the system and totally automatic - you're going to be almost exclusively looking at an inverter from one of the Big Three.  I'm sure some of these other inverters like Exeltech might be good.  But they don't have the features for off-grid system automation that ours got.

It all depends on what you want.
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Chris

[hydrosun]

I agree that a generator is needed for backup long before the batteries are abused. But your system uses the same strategy fo oversizing the solar array for good days to mimimize generator run time on partially sunny days. So necessary evil or best friend the generator is the most expensive way to make power so a good system uses wind, solar, hydro as much as possible first. And excess power for the batteries is used as available. In your case to heat water that is storeing more energy as heat so less needs to come from the generator.
Another Chris

[ChrisOlson]

So necessary evil or best friend the generator is the most expensive way to make power so a good system uses wind, solar, hydro as much as possible first.

Of course.

The point I'm making is that I know basically two types of folks who live off-grid.  There are some who may as well live in a cave and they have the bare minimum to get by.  They probably have a tiny generator like a EU2000 or something that will barely run the 'fridge and freezer at the same time, much less charge batteries.  And they will only run the generator in the most dire circumstances where the batteries have been below 50% SOC for several days and the inverter is ready to give up because the voltage is getting too low.

Then I know some that have fully automated systems.  The fully automated systems are expensive, but they do take better care of the batteries than any human ever will.

The folks I know that live under the first circumstances always have batteries going tits up at 4-6 years and they can't figure it out.  They don't save any money in the long run, and it's a lot more work keeping their system operating because it has to be monitored every day.  They can't even take off and go fishing for a few days without having somebody there to babysit their system to make sure the 'fridge and freezer stay lit.

Living off-grid is terrifically expensive in the first place compared to somebody who just pays the utility bill every month.  And even though a generator is expensive to run, it's a lot cheaper than replacing batteries because the batteries cost more over 5-6 years than it would to just pay the electric bill for the average grid-tied home for the same period of time.

Anybody who thinks living off-grid is a big money saver hasn't put the pencil to it.
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Chris

[bob g]

Chris
it looks like you have accurately defined the two camps
one camp being of the mind to never run the generator no matter what happens to the batteries,,, (only slightly exaggerated by me)
the other camp being of the mind that they want to protect their batteries so they will last for 20 years or more. (again only slightly exaggerated by me)

i would suggest there is a middle camp, (one i heavily promote) that being of the mind one ought to carefully consider the proper charge regime for best charging efficiency of the batteries in use... wherein a balance is reached where the batteries give reasonable service and the generator fuel consumption is at a minimum needed to enable that lifespan.

the camp that wants to maximize their battery life will often fire up the generator when the batteries get down to maybe 80%SOC where amperage needs to be tapered back to keep down gassing, the result being excessively long run times. even though the batteries might last 15-20 years the amount of fuel burned would likely replace the batteries two or three times over the same time span...

the other camp because of their fear of burning fuel will run their batteries down to 20% SOC and then break down and fire of the generator. while the charging efficiency is higher (up till gassing at least) he is faced with replacing the batteries in maybe 5 years or less.

the camp i am firmly in would dictate the 50/80 charge regime, wherein
i would use the batteries down to 50% SOC and then fire up the generator charging from 50-80% where charge current can be very high relatively speaking with resultant higher charging efficiency.. i would do this for 6 days and on the 7th day plan on a full charge to 100%.
the battery bank would live a reasonable lifespan, although not 20 years certainly more than 5 years and i would have spent much less in fuel than the former and probably not much more than the latter example.   when you pencil out the costs all things considered i think my camp comes out the winner.

i suspect that with your solar pv and wind inputs, your actual generator operation puts you somewhere near the middle camp?

the one point you made that all should agree on, is anyone thinking of living offgrid, had better put a pencil to paper and work out the most efficient way to get their power.

currently with nat gas prices are they are, i can produce electrical power very competitive with the utility company provided i use the waste heat recovered from the cogen unit.  and i can provide charging current to the battery bank a bit cheaper than i can from the utility via a separate charger.

can do it easily in the winter months when i can use all the recovered heat. not so easy in the summer months of course, however getting an absorption chiller coupled to the unit would get me there.

[birdhouse]

i'm in the middle camp!  i don't even have a dedicated permanent charging rig set up.  i bought one of those 30A switching power supplies for led, added a resistor to the trim pot so the voltage goes higher, and i couple that to a generac 1800.  my TS-60 turns the rig into a "smart" charger, and i only run this system under heavy load times, 6-8 times a year. probably MAX of 2 gallons a year...  though i don't live there.  it's just a vacation spot. 

adam

[ChrisOlson]

i suspect that with your solar pv and wind inputs, your actual generator operation puts you somewhere near the middle camp?

I would suspect we're somewhere in between the two extremes I illustrated.  We expect to get 10-12 years from our batteries.

There is another nice setup that automatically takes care of your batteries and doesn't require an inverter/charger to do it.  We looked at getting one of these units:
http://www.alten-dc.com/diesel-powered-dc-generators/item/114-24-volt-80-amp-diesel-powered-battery-charger.html

The Duke 2480 was around $6,000 with auto-start.  We decided against it not only because of cost compared to an AC gen, but also the fact that it could not do peak load support, nor provide redundancy in the event of an inverter failure.
--
Chris