Any inverter that can run without grid/battery?

I am planning a 3 to 4 KV PV system for my home. One thing I'd like to accomplish is to have some capability to generate AC when the grid is down. The standard approach is to add batteries but this seems to add five to ten thousand to the system cost. Is there a lower-cost alternative that will allow me to get some power in an extended grid outage? It seems like there should be some inverter that will come up with the grid down without a full battery backup system. Are there any inverters that have this capability?

Comments

  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Any inverter that can run without grid/battery?

    short answer, no. Because your AC loads can vary quite a lot (fridge starts/stops) the batteries act as a "surge buffer" to keep the DC input voltage from collapse when you have a heavy draw that momentarlly exceeds the PV array capacity. Or a bird's shadow or cloud could easily shut the system down for 5 seconds, and i'll let you imagine how fun that will be.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

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  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    Re: Any inverter that can run without grid/battery?

    WolfgangStiler . Why do you think all systems use expensive batteries if there was something else that was cheaper and required less often replacement ??
    There is just no other cheap and effective way as yet around the problem.
  • System2
    System2 Posts: 6,290 admin
    Re: Any inverter that can run without grid/battery?
    john p wrote: »
    WolfgangStiler . Why do you think all systems use expensive batteries if there was something else that was cheaper and required less often replacement ??

    There's clearly no perfect solution but I am looking for something that would be used only in an emergency. I would shut down all but criticial loads which in my case would be all but the gas furnace in the winter or the refrigerator in the summer. At this point the PV system may be enough to provide some needed heating or cooling. Well, that was what lead to my question anyway.
  • mikeo
    mikeo Solar Expert Posts: 386 ✭✭✭
    Re: Any inverter that can run without grid/battery?
    At this point the PV system may be enough to provide some needed heating or cooling.
    Probably not, just take to much solar to heat and cool. Look into a generator for emergency backup.
  • System2
    System2 Posts: 6,290 admin
    Re: Any inverter that can run without grid/battery?
    mikeo wrote: »
    Probably not, just take to much solar to heat and cool. Look into a generator for emergency backup.

    I am not hoping to heat with solar but just run the igniter, control circuitry, and fan on a gas furnace. The cooling is a refrigerator (assuming a summer outage only).
  • Brock
    Brock Solar Expert Posts: 639 ✭✭✭✭
    Re: Any inverter that can run without grid/battery?

    You could get a Xantrex XW inverter. If I remember the smallest battery bank to even out the solar input is about 100amp minimum. So you could get by with about $400 in batteries and most of the time use it as grid tie. You would also need a solar charge controller so another $600. That is about the only way to make it work.
    3kw solar PV, 4 LiFePO4 100a, xw 6048, Honda eu2000i, iota DLS-54-13, Tesla 3, Leaf, Volt, 4 ton horizontal geothermal, grid tied - Green Bay, WI
  • mikeo
    mikeo Solar Expert Posts: 386 ✭✭✭
    Re: Any inverter that can run without grid/battery?
    I am not hoping to heat with solar but just run the igniter, control circuitry, and fan on a gas furnace. The cooling is a refrigerator (assuming a summer outage only)
    .
    If this is all plus a few lights, you may get by with 4 L16 batteries, 4KW Hybrid inverter and around 2 KW of solar panels. The batteries would cost around 1000 dollars. This would run an 18 cu ftEnerty Star fridge, your fan blower and a few lights The fridge would draw about 1KW / day. Assuming 3 good sun hours a day you would be generating around 3kw per day. You would only have about 1 and 1/2 days reserve before needing to crank up a generator to recharge the batteries in an extended outage with no sun.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Any inverter that can run without grid/battery?

    remember that you can only drain the batteries down to about halfway as deeper discharging will be detrimental to the battery life. use it if you have to (aka emergency), but just don't expect a minimal battery setup to power things for too long. example 100ah 48v bank can use 50ah at 48v for a total of 2400wh and may not accommodate high wattage loads without bogging down the batteries. there aren't easy cheap answers unfortunately.
  • RWB
    RWB Solar Expert Posts: 168 ✭✭✭✭✭
    Re: Any inverter that can run without grid/battery?

    Or you can use LFP Batteries and drain down to 80% or 100% during emergencies.

    You will get the full rated capacity even with Constant 1C loads. My 160AH LFP Battery gives me 200Ah's Consistently so thats a plus also.

    So instead of buying 2 sets of Lead Acid Batteries that you can or should only drain down to 50% you can buy a LFP Battery that you can drain 80-90-100% during Emergencies and the battery is rated to last you 3000 Cycles with consistent 80% DOD, 5000 with 70% DOD.

    My 200 Ah LFP Battery powered my Fridge the other day for 29 hours before the inverter started beeping from the battery being below 11V. I had the fridge set on its highest cold setting. The electricity went out so I plugged in the fridge, Microwave, Wireless Router & Modem, TV to various portable solar power systems.

    Just add a small amount of battery storage now and add more later if you want.
  • AntronX
    AntronX Solar Expert Posts: 462 ✭✭
    Re: Any inverter that can run without grid/battery?
    RWB wrote: »
    Or you can use LFP Batteries...

    Not without battery management electronics and smart charger. For the price of 160Ah 12V LFP set of batteries only ($ 704) the OP can get almost 900Ah at 12V of golf cart lead acid batteries and no need for custom battery management electronics.
  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    Re: Any inverter that can run without grid/battery?

    RWB I promise you if you take a LFP battery cell below 2.2v you will destroy it even if only done once. As an experiment Idid that and was told in no uncertain terms from the manufacturer that that will certainly happen and NO WARRRANTY.
  • RWB
    RWB Solar Expert Posts: 168 ✭✭✭✭✭
    Re: Any inverter that can run without grid/battery?
    AntronX wrote: »
    Not without battery management electronics and smart charger. For the price of 160Ah 12V LFP set of batteries only ($ 704) the OP can get almost 900Ah at 12V of golf cart lead acid batteries and no need for custom battery management electronics.

    Yea all you need are a Balancing Module for each cell so that it will keep you from over charging each cell and keep the cells balanced, and the same balancing Module has a output so you can hook up a Relay for a Low Voltage Disconnect if any of the cells drops below 2.5V. It simple and cheap, 4 balancing modules will cost you $100, if you want the Low Voltage Disconnect feature then just pick up a relay to cut your batteries output off and it will automatically turn the output back on once all the cells are within the perfect cell voltage range of 2.8-3.6V.

    Just depends on if the OP wants 900 or more pounds of batteries which will take up much more room which may or may not matter. To get the same life span of 3000 cycles you would only want to drain the batteries to 30% or so vs 80% with LFP. So 900AMP Hours x 30% for a 3000 Cycle Life Span = 270Amp Hours of Usable Amp Hours vs 200 with LFP.

    If you want to just let those 900Ah of Lead Acid Batteries just sit there and only use them for emergency situations and then drain them to 80% during a emergency situation then that would work good. But my partner has thrown away 15 Lead Acid Batteries that were quality and he kept them charged every month or 2 to maintain them, they were AGM and they all went bad over a 1-1.5 year time span. So from our experience these AGM batteries do not last very long when you let them sit there and not get used. Maybe if they were all hooked up to a Solar Charge Controller and float charged every day they would have been fine but it basically proves to me that these batteries need to used often or else they risk dying a early death.

    The Thundersky LFP Cells have a 1 year warranty, if a cell dies they will replace it.

    LFP Batter Tech is basically superior in all ways it just cost more up front to buy them, but they are actually cheaper than lead acid batteries over the long haul because you do not have to replace them near as much as you do with Lead Acid type batteries. They are almost 2 completely different animals really.

    If your going to be using the Batteries Daily then a 1000Ah Bank of LFP Cells will give you 800 Amp Hours of Storage Everyday for 8.2 Years, and then you battery bank will drop down to 80% of its initial 1000Ah Capacity, it will not just die on you just slowly drop its total capacity over time. This is draining your battery bank to 80% every day. You can get 13.6 years if you only drain 700Amp Hours per day vs 800 amp hours.

    Now to get a Lead Acid Battery Bank to last 3000 Cycles or 8 years you can only drain it to 20-30% on average everyday. So we would need 2500 Amp Hours of Lead Acid Batteries if you want that bank to last you 8 years with you draining the same 800 Amp Hours every day by discharging 30% of the banks capacity everyday.

    The difference is 1500 Amp Hours between Lead Acid and LFP Batteries. The Weight difference is Crazy too. 1000 Amp Hours of LFP Weigh 64 Pounds per 200Ah 12V Pack so 64x5 packs = 320 Pounds vs 160 Pounds for a AGM 200 AH Battery x 13 to get 2500 Total Amp Hours = 2080 Pounds !

    So that's a 1760 Pound Weight Difference.

    5 200Ah LFP Batteries vs 13 200Ah Lead Acid Batteries to get the same capacity and life span. That's more than 2 times the amount of Lead Acid Batteries vs LFP Batteries to get the same results. The cost of LFP does not look so much more expensive once you start really looking at all the benefits and do the math.

    Also you do not need a Smart Charger, Charging to 14.4V will work just fine. No need to Equalize either. Most Solar Chargers can be programmed easily with your desired bulk and float charges.
  • RWB
    RWB Solar Expert Posts: 168 ✭✭✭✭✭
    Re: Any inverter that can run without grid/battery?
    john p wrote: »
    RWB I promise you if you take a LFP battery cell below 2.2v you will destroy it even if only done once. As an experiment Idid that and was told in no uncertain terms from the manufacturer that that will certainly happen and NO WARRRANTY.

    Yea they are just like Lead Acid Batteries when it comes to Low Voltage killing the battery. You have to use the same caution when draining either battery packs.

    Usually you just need recharge the battery pack once the voltage drops below 11V.

    When the inverter starts screaming its time to recharge. Watch any DC loads carefully that do not have LVD built in to avoid draining the battery below 11-10V.

    Most of the Protection Circuit Boards for LFP will cut the battery output off when any cell drops below 2.5V, and since these smaller 12V battery pack stay pretty closely balanced they are all going to hit that voltage at the same time. Its the High Voltage Car packs with crazy discharge currents is where they can get out of wack quicker from what I have heard.