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Home Forums Technical Discussion Inverter Suggestions for Fully Off-Grid System

This topic contains 6 replies, has 5 voices, and was last updated by  dcpower 6 years, 8 months ago.

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  • #36657

    FastTurtle
    Participant

    Hello,

    We are currently building a home on our tree farm in TN and are looking for suggestions for good pure-sine wave inverters in the 2500 to 5000 watt range for a fully off-the-grid system.

    The inverters will run from a battery bank of at least 4-6 kw-hr capacity, which will be the heart of the sytem. The batteries will be kept charged with wind and solar (and generator when necessary).

    There’s such a huge selection out there for inverters, I don’t know where to begin. I do know that we would like a pure-sine wave type (not modified). Also, I’d like to avoid the types with built-in chargers, since we will be doing minimal charging from AC sources.

    What are you all’s thoughts on this?

    Thanks!

    JP

    Fast Turtle Farm

    #40739

    elnav
    Member

    Fast turtle said: , I’d like to avoid the types with built-in chargers, since we will be doing minimal charging from AC sources.

    Why the aversion to being able to charge from an AC voltage source in a pinch?

    I would assume you have done your homework and realize that combination charger /inverters are simply using the same components but running the current flow in reverse. There is no real savings by having a dedicated inverter only and then having to buy a seperate and inferior charger when you realize the need for some kind of charging after a proponged period of no wind or solar charging.

    Internally the combination device only differs by the inclusion of a transfer relay and the neutral to ground switching required to make it safe. At most the total cost of components amount to maybe $50 worth of parts. Any greater price differential is simply due to markup not real cost. I know because I used to work for an inverter manufacturer. I won’t name names since this is not a sales pitch for any one brand.

    What you should be looking for is the associated feature set each brand comes with.

    For starters why so much power? Who guided you in developing a power budget? My uncle lives off grid and has a jacuzzci hot tub, a 52 in satellite TV plus every kitchen gadget you can imagine. He does this mostly on a 3kW Outback inverter. Because he is a stubborn logger who will not listen to good advice he does need a big diesel genset for his 300 foot deep well submersible pump. However there are technical solutions to overcome the start surge from a submersible well pump. I could show you how to do the same task with a 2 kW genset from costco or Walmart.

    My point being you can save money by starting with a 2500 – 3000 size inverter which can be supplemented by adding multiple units in parallel should you really need the extra power. I design such systems for a living and the majority of clients are quite happy with 3kW.

    Among the desirable feature set of the combi units is the inclusion of a battery monitor that acts like a fuel gage to tell you how much charger remains in the battery bank. Don’t believe the simple voltage bar graphs that really are not that accurate. The battery monitors actually count each watt extracted from the battery or add each watt added from wind or solar charging. In fact it is able to combine the total from multiple sources. Furthermore these combination chargers often have the ability to control the charge rate based in the size of the charging source be it an 800 watt little portable gasoline genset or a 10 kw Diesel generator, They have battery voltage alarms to warn you when its time to start the generator in a pinch. Believe me this does happen. Excessive snow fall, prolonged cloudy periods, and sometimes freezing rain even. I hear you guys really had a lousy winter this year.

    Don’t kid yourself by thinking an automotive type charger is going to bail you out. They are usually constant voltage taper chargers and will take two to three times as long as the smart chargers found inside the combination models. Just think of the time and fuel burn involved.

    On the subject of 230V submersible pumps don’t get sucked into one of the systems that require two inverter each delivering 120V being hooked in tandem to deliver 240V to a big pump. Either use a step up transformer and a soft start module to drive the pump or if your plans include full air conditioning etc. then select a 230V output inverter and use a step down transformer to provide the 120 V for utility outlets. The latter approach is what I now use because the systems of twinning two 120V to deliver 240V is still crippled if one of them has a problem. The result being you have no inverter at all. with my approach if one goes down you still have 50% capacity remaining.

    Since you are just now building I would assume your electrical wiring is done to NEC code which insist on the usual North American NEC dictated center tapped neutral. Its the worst possible system approach but if you are off-grid you have some latitude to work around it. Manufacturers like Outback are committed to supporting this concept but there are other ways that are as safe and has more benefits.

    Don’t make any final purchase decisions before you have completed your entire load budget to the nth degree.

    You are right there are a gazillion inverter companies out there but not all of them will recommend a specific model for your benefit, more often they do so to enhance their own profit margin. And you can bet they are not going to recommend their competitor even if it has a better feature set that more closely meet your needs.

    #41004

    elnav
    Member

    gOLDLEAF you are plagerizing other peoples posts just so you can insert links to advertising. SEO and SEO company are internet marketing companies and have nothing to do with being off grid. GET LOST AND STAY AWAY!

    #41191

    n3ckf
    Participant

    A friend whose system i work on has exactly that situation. Wind, solar, and about a 4KWH battery bank system. The inverter I got for them is the Exeltech XP1100. I got it on a recommendation over in the Arizona Wind & Sun solar forms. Its a true sine-wave inverter and is probably overkill for that application (they could probably easily use the XP600 which is the half-size version of the XP1100).

    They had had a couple of “cheap” inverters beforehand and they kept dying. You get what you pay for. The Exeltech is also used for medical equipment (becuase its true sine wave you can operate anything within its power rating off it).

    Make sure you use sufficient wire guage to your batteries (at 1100, its drawing 80 amps or so. That means *big* wire, like #4 or #2). In this particular case, its hooked up with #6 but its a really short run. Probably sufficient since all their electrical loads are < 50 amps @ 12 volts into the inverter.

    #41193

    DCPL
    Participant

    There are a lot of good since wave inverters available for off-grid use. When picking one, of designing any off-grid power system, everything starts with the load – both the peak load and the average load. I can send you a .xls worksheet that will size a residential system for you if you know your peak sun exposure. Once you know your load and decide your battery system voltage, you can calculate the battery reserve capacity for 24 hours 48 hours, etc. When you have the battery sized, you then can calculate the size of your battery charger – be it solar, hydro, diesel generator, whatever.

    Off grid power is battery power unless you’re working with a fairly large microhydro system that can handle peak loading. It’s not a solar powered home, it is a battery powered home.

    I am partial to Outback Power Systems, though Magnum makes a nice single box 240VAC unit. Outback requires the use of two inverters at 120VAC to make split phase 240 VAC, or the use of a toroidal transformer if you only need 240 for a well pump occasionally. Exeltech builds good product as well, though I use them mostly for commercial and industrial power systems; at communications sites that don’t require positive ground, mostly.

    Life on batteries requires some diligence in design and in lifestyle choices. A 52 inch TV lifestyle with a hot tub – run primarily by a diesel or propane generator – is NOT off-grid at all, since diesel is provided by a very large grid called global oil production and distribution. Global conventional oil production peaked in 2005-2006 per the EIA and IEA and supplies will not be cheap or reliable over the life, or even warranty, of a new solar power system. Mismatched lifestyle to battery to charger designs inevitably lead to premature battery failure, and lead is NOT inexpensive anymore.

    Finally, AC charging is highly efficient, since 1. backup generators that produce AC very dirt cheap and 2. off-grid inverter/chargers such as the Outback product can provide the multi-state charging the batteries need while unloading them during recharge by switching all loads to the generator, which minimizes the time the gennie runs (and that you have to listen to it.)

    Cheers,

    Bill

    #41208

    elnav
    Member

    “Life on batteries requires some diligence in design and in lifestyle choices. A 52 inch TV lifestyle with a hot tub – run primarily by a diesel or propane generator – is NOT off-grid at all, since diesel is provided by a very large grid called global oil production and distribution”

    Here we go again with the definitions. Taken to its ultimate logical end no one here on this forum who acesses the internet is truly off grid because they rely on the global grid of internet providers and the linking communications network.

    I know a lot of people who are living off grid but they bring in a tankful of propane every year and theer are also those who rely primarily on solar but who must resort to a genset when cloudy winter weather blocks the su for a week on end. Are we going to insult and denigrade these people for not being politically correct and a purist about being off grid.

    If a home is not tied into municipal services; primarily electric power or piped in natural gas and plumbed for municipal sewers then we could in all fairness call it off grid. These homes are for the most part self reliant in that they somehow generate their own power by some means, supply their own water from a well and dispose of their sewage in some manner.

    Talk of being a purist and politically correct does nothing for encouraging more people. If you want the movement towards off-grid living to grow you need to appeal to ordinary middle class people and somehow make off grid living seem comfortable to the average family of two adults and two or three children. Yes I do know some people who have done itin cramped quarters but they are the exception not the rule. Living jammed up in a tiny caravan or trailer is not conducive to family life unless everyone can get their own personal private space. Living on a 37 foot sailboat while gradually circling the globe sounds wonderful until you try it yourself. Personally I found my 48 foot boat cramped and my 37 foot RV was only bearable because I built a big shed next to it for a shop and had a 30 foot gazebo for a sundeck area in summer.

    #41229

    dcpower
    Participant

    Sorry to disagree, but “ordinary middle class people” live lifestyles that encompass luxury beyond that available to royalty before the oil era. I’m not being a purist or PC … I teach energy, which is the powered needed to perform work over time, by definition. Get a calculator and run the numbers – an “average” 1000kW/hr per month electric energy useage costs about $100/mo for the ordinary consumer. Since humans can perform about 100 Watts of work per hour over 24 hours, a human can deliver 2.4kW/hrs of work per day. To get the same work from humans per day, 33.33kW/hrs, requires a daily staff of 14 people at 2.4kW/hrs per day per person. At minimum wage, $7.75 an hour, your energy cost would be $2600 a day. Think $4.00 per gallon gasoline is expensive? Go push an ordinary middle class American car about 15 miles.

    “Ordinary” middle class life has been based on basically free energy for 100 years. That era of nearly free, reliable energy is drawing to a close right now. Ordinary middle class people who expect to continue living in a society based on free energy simply won’t be able to cope with such a rapid change en masse, and nobody’s remotely preparing them for the changes that will take place within the next generation. I don’t think it can be done, actually. People who get it are planning to take care of themselves, their families and their local communities when everyone finds themselves “off-grid.”

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