Is it possible to connect a 350w micro inverter to a UPS for using off grid/grid tie ?

maskanimaskani Registered Users Posts: 7
hello, i have a 350w micro inverter (that is grid tie inverter) so i want to have my system on, when network failure. i think i can use a 200 or 300 watt UPS and a battery for this. we have 2 scenario:
1- when grid is on, i connect output of micro inverter to main grid, and main grid to input of UPS, so the ups can charge batteries, and if we have overplus energy, we can feed (sell) it into local grid.
2- when grid is off, Ups is on, so i can connect output of micro inverter to output of ups, if we have load, we have current and our inverter and solar system is on.

so i have a question, if we don't have enough load what will happen? if ups is going down, all of system is going down?
- if we have just 100 watt load, which of this devices provide energy for load? micro inverter? UPS? both of them?
- is it possible to design a kind of wirring, so all of time solar system is on, and provid energy (for load, and for charging batteris)

thanks for all that they want to help me

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Is it possible to connect a 350w micro inverter to a UPS for using off grid/grid tie

    Welcome to the forum.

    Don't do it.
    What you are talking about is called "AC coupling"; in this case the micro-inverter to the UPS unit. Only the UPS is not meant to be connected in this manner. For one thing it may not be a true sine wave output, which means it will not produce proper Voltage & frequency as far as the micro-inverter is concerned. In that case the inverter should not even fire up.

    But if it does the micro-inverter will try to feed whatever power it can get from the panel(s) to the UPS/loads. If there are not enough loads to consume all of that power it still has to go somewhere, such as back-feeding the UPS to the batteries causing them to charge. Since, again, the UPS was not designed for this there may not be any regulation of that charge; the batteries fry.

    The UPS unit basically has no ability to regulate and control the power coming from the inverter. As such something will have to give, and it will likely give up the magic smoke and then none of it will work anymore.
  • jaggedbenjaggedben Solar Expert Posts: 230 ✭✭
    Re: Is it possible to connect a 350w micro inverter to a UPS for using off grid/grid tie
    maskani wrote: »
    1- when grid is on, i connect output of micro inverter to main grid, and main grid to input of UPS, so the ups can charge batteries, and if we have overplus energy, we can feed (sell) it into local grid.
    2- when grid is off, Ups is on, so i can connect output of micro inverter to output of ups, if we have load, we have current and our inverter and solar system is on.

    To clarify Cariboocoot's response, you can do 1, but you cannot do 2.

    What you could possibly do is get a second inverter that is NOT a grid-tie inverter, and use it to recharge the UPS when the grid is down.
    - is it possible to design a kind of wirring, so all of time solar system is on, and provide energy (for load, and for charging batteris)

    I gather you mean automatically? Rather than by unplugging and replugging things, or wiring in manual switches?
    The answer is no for what you currently have, and possibly yes if you get more equipment. But it is not worth doing (in my opinion) if you only have about 350W of solar panel, and you'd be re-inventing a wheel.

    I will refrain from making comments or asking questions about legality, electrical codes, or the quality of the inverter I am guessing you have.
  • maskanimaskani Registered Users Posts: 7
    Re: Is it possible to connect a 350w micro inverter to a UPS for using off grid/grid tie

    First, thanks for your useful comments and replies.

    we have a project that we want to use sunny island, and sunny boy (from SMA Co.) so i know that is what we want, a system that can provide energy in grid tie and off grid condition.
    so we want to design a device like Sunny Island, or designing a wiring that can do like Sunny island.
    furthermore I know, there are some devices like Sunny Island, for example, Xntraxes, or outback or .... (http://www.affordable-solar.com/store/inverter-grid-tie-batteries), but we want to do free from a especial brand or especial model.

    for first scenario, connecting output of microinverter to main grid is regular.
    but in second scenario, i don't know what happen if we connect output of microinverter to input or output of ups. maybe we can design a load meter, and control system with these scenario:
    - if load > power generating from PV, then UPS is On, and load can handle with PV + UPS
    - if load < power generating from PV, then (use a charge controller) switch pv to charge controller and using just UPS, load handle with UPS
    - if load > power generating from PV + UPS, then Load shedding mechanism, or turning off the loads

    did anyone think about this, or try this before ?

    we have an engineer here that try first scenario and system work correctly, but he didn't try second and third condition.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Is it possible to connect a 350w micro inverter to a UPS for using off grid/grid tie
    maskani wrote: »
    but we want to do free from a especial brand or especial model.
    ...
    did anyone think about this, or try this before ?
    ...
    we have an engineer here that try first scenario and system work correctly, but he didn't try second and third condition.

    The heart of the problem is that the off-grid inverter and the grid-tie inverter function need to work seamlessly together so that neither one damages the other and both are safe.
    This means that you either build both functions into one unit, as with the Xantrex or Outback Hybrid Invertersor
    you design the two separate inverters in separate boxes to communicate with each other, as with the Sunny Boy/Sunny Island combination.

    Anything else but using units designed and certified for that application will not be safe or legal.
    SMA SB 3000, old BP panels.
  • maskanimaskani Registered Users Posts: 7
    Re: Is it possible to connect a 350w micro inverter to a UPS for using off grid/grid tie

    inetdog, you are true, but as you know sunny island , or ... is a bidirectional inverter, (DC to Ac and AC to DC), I think UPS is doning like this, (AC to DC and DC to AC) is it true ? I think we can doing some changes in UPS and changing it to a bidirectional inverter.

    there are some problem about SMA or othere brand, they limit us to select all of system component from them, for example if you want use sunny island, you must use sunny boy or sunny mini central !

    i didn't force to use one device for off grid and grid tie, but if we could gather two inverter in one device , its so fantastic !!!

    you can read this artilce " Photovoltaic Power System with Battery Backup with Grid Connection and Islanded Operation Capabilities, David Velasco, César Trujillo, Gabriel Garcerá, Member, IEEE, Emilio Figueres, Senior Member, IEEE, Rubén Ortega" in IEEE. i think they build a device that we talking about, so if they can do, we can do, too !
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Is it possible to connect a 350w micro inverter to a UPS for using off grid/grid tie

    There is a big difference between a battery-based inverter such as the Sunny Island that is meant to be AC coupled to grid tie inverters such as the Sunny Boy and a standard battery-based inverter or UPS unit.

    UPS units and most off-grid inverters are NOT designed to have AC powered applied to their output. They will not work this way, or will work dangerously this way.

    Do not confused having AC applied to the AC INPUT of a battery-based inverter-charger with applying AC to its output. They do not function the same.

    There is a very good reason why SMA equipment costs the money it does; it is the best for AC coupling in this manner. You can not get this performance on the cheap.

    If you do not understand how these things work do not try to get them to work in a manner other than they were designed to do. It is dangerous to do so.
  • jaggedbenjaggedben Solar Expert Posts: 230 ✭✭
    Re: Is it possible to connect a 350w micro inverter to a UPS for using off grid/grid tie
    maskani wrote: »
    inetdog, you are true, but as you know sunny island , or ... is a bidirectional inverter, (DC to Ac and AC to DC), I think UPS is doning like this, (AC to DC and DC to AC) is it true ? I think we can doing some changes in UPS and changing it to a bidirectional inverter.

    There is no such thing as a bidirectional inverter. Only the part that converts DC to AC is an inverter.

    Your UPS contains both an inverter and a charge controller. Other than being both connected to the battery, they have nothing to do with each other.
    there are some problem about SMA or othere brand, they limit us to select all of system component from them, for example if you want use sunny island, you must use sunny boy or sunny mini central !

    And using a UPS limits your choices in other ways. For example, you can't really choose the amount of batteries, and you can only input AC to it. And it may not meet your power needs. Trying to modify it will probably cost you as much time and money as buying a real product.

    If you will insist on piecing together a system out of individual parts, you could probably do this:
    - get a grid-tie inverter
    - get an off-grid inverter
    - get a DC charge controller designed to charge batteries from solar panels
    - get an AC powered charge controller designed to charge batteries from the grid
    - hook both charge controllers to the batteries, and hook the off-grid inverter to the batteries
    - when the grid loses power, switch the solar panels from being connected to the grid-tie inverter to being connected to the solar charge controller

    I am making it sound much simpler than it actually is. Also, when you purchase all this, you don't necessarily save that much money, and certainly not any time.
    you can read this artilce " Photovoltaic Power System with Battery Backup with Grid Connection and Islanded Operation Capabilities, David Velasco, César Trujillo, Gabriel Garcerá, Member, IEEE, Emilio Figueres, Senior Member, IEEE, Rubén Ortega" in IEEE. i think they build a device that we talking about, so if they can do, we can do, too !

    I read the abstract. It is funny.
    It is funny that such an article should be dated 2013 when Outback and some other companies have been selling products that do this for years.
    Note that they refer to an inverter that switches between two modes (current source and voltage source) for grid-tie and off-grid use. This is not something you can design yourself. (If you could, you wouldn't be asking basic questions on this forum.)
  • maskanimaskani Registered Users Posts: 7
    Re: Is it possible to connect a 350w micro inverter to a UPS for using off grid/grid tie
    jaggedben wrote: »
    It is funny that such an article should be dated 2013 when Outback and some other companies have been selling products that do this for years.
    Note that they refer to an inverter that switches between two modes (current source and voltage source) for grid-tie and off-grid use. This is not something you can design yourself. (If you could, you wouldn't be asking basic questions on this forum.)

    This is not funny ! SMA and other brands use 2 inverter, 1 off grid inverter, 1 grid tie inverter. for example 1 sunny island can't work grid tie action alone, and need a sunny boy or sunny mini central. but in this article they build just one inverter that can do these action.

    as I said before, we are connecting a 200 watt UPS to a 350 watt microinverter. but in that system we have a 400 watt continuous load. it is bigger than power produced by microinverter all time. so all the time UPS is on. we didn't see any damage, yet.

    so we have some problem in that project, first we can't sell power to grid, if we want. second, we can't charge battery with PV or peak shaving action.

    about my ability, I'm a group manager in R&D office, I don't have enough experience about inverter but i can hire some expert about this. for example I have two friend that they are design and build some microinverter before, and now a factory produce inverter based on their design, i can hire them or other.

    now i must ensure about building this device, if i ensure about this, i can start this project and supply some financial for this.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Is it possible to connect a 350w micro inverter to a UPS for using off grid/grid tie

    Language barrier problem: jaggedben's use of the word "funny" in this instance is not meant to indicate humour but rather peculiarity in that the article is dated so recent when the equipment has already been around for a while now.

    The Xantrex XW can function this way: it is a hybrid inverter capable of being either an off-grid system or a grid-tie system and in either mode can support AC coupling, regulating the input by means of frequency shifting to drop the GTI when its power is not needed.

    SMA's Sunny Island & Sunny Boy combination is the most seamless application of this type because the two units can communicate, but the SI can also work with non SMA GTI's in the same manner as the XW.

    Likewise certain Outback inverters can function in this manner.

    If you or your company are trying to duplicate this sort of function on your own you will need some very talented electrical engineers to help you as it is not a simple thing to do. You can not simply take any existing OG inverter or UPS unit and back-feed it from a GTI of whatever capacity and have it work.

    It is outside of the venue of this forum to design complex electronic circuits for companies or even individuals. As it is the members here give away thousands of dollars worth of engineering consultation daily. You can not expect anyone to do an elaborate piece of design work for nothing.
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Is it possible to connect a 350w micro inverter to a UPS for using off grid/grid tie
    maskani wrote: »
    This is not funny ! SMA and other brands use 2 inverter, 1 off grid inverter, 1 grid tie inverter. for example 1 sunny island can't work grid tie action alone, and need a sunny boy or sunny mini central. but in this article they build just one inverter that can do these action.

    There are some products commercially available which are all-one-devices, so you plug the panels, grid, batteries and loads into 1 device, e.g.:
    http://powerrouter.com/products/powerrouter-solar-battery-self-use
    and
    http://www.tab.com.es/ENG/vx1.aspx
  • BB.BB. Super Moderators, Administrators Posts: 28,994 admin
    Re: Is it possible to connect a 350w micro inverter to a UPS for using off grid/grid tie

    What is it you are trying to do again?

    There are two basic configuration that you can do with a GT Inverter...

    One is connect the GT Inverter to the Utility Grid. Normal setup for most people.

    The other is connecting a GT inverter to an Off Grid Inverter... The off grid inverter behaves like the utility grid (sets frequency and voltage for "local" grid -- Off Grid Inverter is a "voltage source"). The GT inverter then is connected to the OG Inverter's AC ouput. The GT Inverter (current source) then qualify's the local grid for frequency/voltage (and probably sine wave output vs MSW -- Modified Square Wave output for some OG inverters).

    Once the GT Inverter has qualified the local grid output from the OG Inverter, the GT inverter will output as much current/power as it can (solar array input power).

    Normally, the OG Inverter will do what it takes to keep the local grid voltage to specification... If the loads are greater than the GT Inverter's output power, the OG Inverter will add some additional power to keep the load running (and local grid in specification). If the load is less than the GT Inverter's output power, many TSW inverters will "absorb" the extra power and transfer it to the battery bank (think synchronous rectification). The "standard" OG Inverter will run "backwards", but does not have any way of regulating the battery's charging current and can over charge the battery bank.

    To keep the batteries from being over charged, some folks have added a "dump" controller and load to the battery bank... If the battery bank is "full", the Dump Controller will turn on and dump excess power to a resistor (heater) bank.

    Another way to do this is to measure the battery bank's state of charge, and then use the "full battery" signal to turn off a relay inline with the GT inverter--causing it to "fault" for ~5 minutes. In the US, because of the safety issues involved, there are "two" different circuits required to turn off / dump charging current (in case one fails).

    We some more recent OG Inverters, they have the ability to monitor the battery bank's state of charge. And when the battery bank is full, the OG Inverter will take the 50/60 Hz grid frequency +/- 1 Hz (high or low, or even alternate to keep AC clocks accurate)--This will cause the GT Inverter to shut down for ~5 minutes (the SMA sunny island compatible GT inverter will vary its AC output power as the AC local grid frequency goes farther and farther from "spec".

    Note, in all cases, the assumption is that the OG Inverter is equal to, or larger than, the GT inverter... The OG Inverter has to be able to accept all current/power from the GT inverter if there is no AC load... Plus the OG inverter needs to be able to operate all AC loads (surge current, running current, etc.)--Or there is a good chance that the AC loads (such as a water pump) would never start (it would fault both the GT and OG Inverters).

    Now, with a Hybrid AC inverter--It can behave both like a GT inverter and push power to the grid, or it can disconnect from the utility power (i.e., if the utility power fails) and run off grid and support the local AC loads (like a UPS). This is the function that is not something that can be "converted"--Switching a single AC inverter from "GT" to "OG" mode (behind a transfer switch).

    What you can do is take a "UPS" type inverter (AC Utility power -> AC Transfer Switch (AC utility one side, OG inverter other side) -> AC load on a protected circuit). This is the "normal" UPS function.

    You can take a UPS type function (AC mains -> transfer switch -> protected load) and connect the GT inverter to the protected load circuit too... That way, when the grid is up, the GT Inverter can back feed the utility power when the utility power is working, and if the utility power fails the transfer switch will connect to the off grid inverter and support the loads+OG Inverter+battery charging (with the above limits).

    Anyway--were these the questions you were asking--Or did I misunderstand?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Is it possible to connect a 350w micro inverter to a UPS for using off grid/grid tie
    maskani wrote: »

    we have a project that we want to use sunny island, and sunny boy (from SMA Co.) so i know that is what we want, a system that can provide energy in grid tie and off grid condition.
    so we want to design a device like Sunny Island, or designing a wiring that can do like Sunny island.
    Why? Why not just get a Sunny Island and Sunny Boy? You're not going to be able to "roll your own" anywhere nearly as easily or as cheaply. The Sunny Island is a pretty sophisticated machine.
  • BB.BB. Super Moderators, Administrators Posts: 28,994 admin
    Re: Is it possible to connect a 350w micro inverter to a UPS for using off grid/grid tie

    I am guessing, but I believe the original poster may live in a country where getting western goods may not be easy.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jaggedbenjaggedben Solar Expert Posts: 230 ✭✭
    Re: Is it possible to connect a 350w micro inverter to a UPS for using off grid/grid tie
    maskani wrote: »
    I don't have enough experience about inverter but i can hire some expert about this. for example I have two friend that they are design and build some microinverter before, and now a factory produce inverter based on their design, i can hire them or other.

    Then that's probably what you should do.
    Language barrier problem: jaggedben's use of the word "funny" in this instance is not meant to indicate humour but rather peculiarity in that the article is dated so recent when the equipment has already been around for a while now.

    Well, I did mean to indicate that I was amused... 8)
  • maskanimaskani Registered Users Posts: 7
    Re: Is it possible to connect a 350w micro inverter to a UPS for using off grid/grid tie
    stephendv wrote: »

    lol this device work as grid tie inverter in normally condition, and work as a UPS in off-grid condition !!! just UPS (not solar inverter) !!!

    http://www.tab.com.es/Documentos/InversoresCargadores/Inv-Carg/TAB%20VX-1%20brochure%20EN.pdf

    you can see the diagram no. 2 in page 2.
  • VicVic Solar Expert Posts: 2,969 ✭✭✭✭
    Re: Is it possible to connect a 350w micro inverter to a UPS for using off grid/grid tie
    BB. wrote: »
    What is it you are trying to do again? ...

    ... The other is connecting a GT inverter to an Off Grid Inverter... The off grid inverter behaves like the utility grid -Bill

    Thank you BB Bill for the concise synopsis of AC Coupling.

    Have considered this for my OG system, as will be developing some additional roof space, hundreds of feet from the battery bank, but will have a stout AC feeder. Had thought of using have considered Enphase of other micro inverters for some additional early morning power. Time will tell which way we go. Thanks, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • hughnghughng Registered Users Posts: 5
    Re: Is it possible to connect a 350w micro inverter to a UPS for using off grid/grid tie

    Hello all,
    I am newbie to the solar and forum as well.

    I want to do the same thing for my grid tie system as backup just in case the power from the grid is out for extended period of time. Can I remove the connection from the grid and hook it up to something like the Magnum power (MSH4024RE). This Hybrid inverter support the back feed from the grid tie inverter.

    So basically my connection is follow:

    PV --> GridTie Inverter -- Output --> <<-- Output -- MSH4024RE <<-- 24V Battery Bank.


    Thank you very much for all the help.

    Hugh
  • BB.BB. Super Moderators, Administrators Posts: 28,994 admin
    Re: Is it possible to connect a 350w micro inverter to a UPS for using off grid/grid tie

    Probably... What is your array wattage, GT Inverter Rated Output current/voltage, and battery bank AH capacity (at 24 volts?)?

    If the GT inverter is 240 VAC output, the AC inverter needs to have 240 VAC output too.

    And welcome to the forum Hugh.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • hughnghughng Registered Users Posts: 5
    Re: Is it possible to connect a 350w micro inverter to a UPS for using off grid/grid tie

    Thank you Bill. My current system is 5KW with SolarEdge inverter. The system generate around 25KW daily. I am thinking about getting 8-10 12V deep cycle batteries and connect them into the set of 4 or 5 to give me 24V output. Between the batteries and PV, I should be able to run everything including my main AC unit.

    My main concern is if I am not using all the power from the PV system during the day, where all those extra power goes. Does it back feed the off grid inverter to charge the battery bank automatically or I have to hook up external charger to charge the battery bank.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Is it possible to connect a 350w micro inverter to a UPS for using off grid/grid tie
    hughng wrote: »
    I am thinking about getting 8-10 12V deep cycle batteries and connect them into the set of 4 or 5 to give me 24V output.

    That will be a mistake. Too many batteries in parallel.
    read: http://forum.solar-electric.com/showthread.php?14674

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • BB.BB. Super Moderators, Administrators Posts: 28,994 admin
    Re: Is it possible to connect a 350w micro inverter to a UPS for using off grid/grid tie

    I would need to read the specifications for the Magnum inverter in more detail--The 50,000 foot view is that the OG (off grid) inverter sets the line voltage and frequency. And supplies power to the loads.

    The GT Inverter "follows" the line voltage/frequency and dumps as much power as it has avialable into the the "local grid". The power then goes to the loads and if there is more GT power than loads, the excess energy goes "backwards" through the OG inverter and charges the battery bank.

    When the battery bank is "full" (as determined by the OG Inverter), the OG inverter will shift the 60 Hz output frequency by + or - ~1+ Hz -- This knocks the GT inverter "off line" for ~5 minutes and the OG inverter supplies the loads.

    5 minutes later, the GT inverter checks the line voltage/frequency--if OK, then starts dumping available energy back into the local grid.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • hughnghughng Registered Users Posts: 5
    Re: Is it possible to connect a 350w micro inverter to a UPS for using off grid/grid tie

    Thank you Bill. Here are the links to the MSH-RE series page and also the PDF for user manual. This is a fairly new inverter from them.

    http://www.magnumenergy.com/Products/MSH-REseries.htm
    http://www.magnumenergy.com/Literature/Manuals/Inverters/64-0059%20Rev%20A%20(MSH-RE%20Series)_Web.pdf
  • hughnghughng Registered Users Posts: 5
    Re: Is it possible to connect a 350w micro inverter to a UPS for using off grid/grid tie
    vtmaps wrote: »
    That will be a mistake. Too many batteries in parallel.
    read: http://forum.solar-electric.com/showthread.php?14674

    --vtMaps

    Thank you for the info. It is very interesting to learn as I am new to this. Great info.
  • richardkgrichardkg Registered Users Posts: 1
    Re: Is it possible to connect a 350w micro inverter to a UPS for using off grid/grid tie

    Using UPS with inverter must depend on the type of inverter you have. Sine wave inverters are good for working of PCs. They won’t cause any issues while working with UPS. There are are some inverters with inbuilt UPS functionalities which eliminates the need of an UPS. But there are some reports of non-sine wave inverters damaging the UPS. Using output power of inverter to charge UPS can be done. I don’t think the other way can be done, I don’t have any personal experience with it, but in theory I think it is true. Anyway I am sure about the sine wave inverters as I am personally using a UPS with the inverter and in some ways it helps as PC won’t be affected by the starting time of inverter when power goes down.
  • syedameralisyedamerali Registered Users Posts: 1
    The reply by Bill, summarising everything so concisely and precisely, is brilliant. I only wish I had read it before blowing up two APC UPS's (a 2700W and 3750W).
    Where I am things like Schneider Grid Tie Inverters and APC UPS's are very cheap as all the stuff auctioned after a bankruptcy lands up here.
    What I was trying to do was to sync the GridTie to the output of a UPS. The first time around battery voltage hit 65V (nominal voltage 48V) when there was excess energy from the sun so I said to myself the power is flowing into the front end of the UPS and getting to the batteries - the solution - simple put a blocking diode so that current from the batteries can only flow in one direction. Not a good idea, this is when the 2nd UPS decided to call it a day.
    Being stupid I will still not give up - I will try and put together an Arduino based system to put initially the GridTie to sleep every time the battery voltage hits 54V and then make the GridTie go online when the battery voltage hits 50V.  Will try this for a few days and see where this takes me.
     If it works then I will try and find suitable sources where I can dump power when I have an excess. This is obviously going to be more complicated and requires a real time assessment of various loads but hopefully will get there eventually.
    Why am I doing this when good well engineered options already exist? Basically cost. I belong to a poor country where power outages are one hour on and one hour off. People are desperate for uninterrupted power but do not have the resources to implement reliable and tested solutions because of cost.
    A pair of 2700W APC UPS's wired in series (and that is another story) give me 5400W. A 5 kW Schneider Grid Tie is paralleled  to the the output of the UPS's - the cost of the three items is US $ 750 .........
  • BB.BB. Super Moderators, Administrators Posts: 28,994 admin
    Syedamerali,

    Your choices of turning off the GT inverter when the battery is "full"--Will work.

    The second choice of using a "dump load" on the battery bank will work too.

    And, for safety, it would not be the worst idea in the world to do both--If one control fails, the second will work as backup (for example, setup dump loads--heating, hot water, water pumping as the "standard" regulation--And use the GT shutdown as the backup--And connect the GT shutdown to a light/alarm to indicate that the primary dump load system has shut down for some reason).

    From a battery's point of view--You are (possibly) adding more cycles to the battery (GT solar on, battery charges, GT solar off, battery discharges). A dump load with PWM dump load control (more or less, keeps the battery at absorb/float voltage when there is excess solar power available) may help give you longer battery life (less stress on the battery bank).

    Otherwise--Unless GT solar really gives you an advantage (such as a long wire run from the solar panels to the battery bank where running at 230 VAC will have lower current/less voltage or power drop)--You might want to go with the "standard" solar array to solar charge controller to battery bank--Usually optimum battery charging and no "bang bang" controls (bang bang controller is an actual engineering term for On/Off type control systems).

    The UPS system should work fine with a properly configured and operating DC solar charge controller tied directly to to the battery bank (in some cases, the UPS chargers are not very good and can cause early battery failures too).

    Also--Picking the right battery (and right size battery) for the job is critical, and having the appropriate charging current to the battery will all help extend battery life (many UPS chargers have very low charging current with respect to the battery bank, especially if you put a large battery bank so you can run the UPS for 1/2 day or more without utility power).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • MarkCMarkC Solar Expert Posts: 175 ✭✭✭

    What I was trying to do was to sync the GridTie to the output of a UPS. The first time around battery voltage hit 65V (nominal voltage 48V) when there was excess energy from the sun so I said to myself the power is flowing into the front end of the UPS and getting to the batteries - the solution - simple put a blocking diode so that current from the batteries can only flow in one direction.
    Syedamerali - this is of great interest to me.  In my location, many high quality APC UPSs (that work fine) are available from 750 watts to 6000 watts - for little cost. 

    Are you suggesting that using the standard APC battery packs (multiple AGMs) that you were successful in connecting the output of your GT inverter to the output of (SU or SUA model??) APC UPS?  And - as you monitored the battery charge voltage of the UPS, it went up to 65 volts when the power usage was less than the GT inverter was producing??  Did you have any auxiliary batteries hooked up to the UPS?  As you probably have experienced, the battery charging system in these UPSs are 1. very limited and 2. "smart", but actually easily fooled and go what we call "brain-dead" and cause problems for the UPS - and have to be reset.  Anyway, I'd certainly like to understand better what you have tried to do and any results of additional testing.
    3850 watts - 14 - 275SW SolarWorld Panels, 4000 TL-US SMA Sunny Boy Grid tied inverter.  2760 Watts - 8 - 345XL Solar World Panels, 3000 TL-US SMA Sunny Boy GT inverter.   3000 watts SMA/SPS power.  PV "switchable" to MidNite Classic 250ks based charging of Golf cart + spare battery array of 8 - 155 AH 12V Trojans with an  APC SMT3000 - 48 volt DC=>120 Volt AC inverter for emergency off-grid.   Also, "PriUPS" backup generator with APC SURT6000/SURT003  => 192 volt DC/240 volt split phase AC inverter.  
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