Which inverters can be used with this system?

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  • Eric LEric L Solar Expert Posts: 262 ✭✭
    Re: Which inverters can be used with this system?
    The system would be a PV/Wind system that uses the grid as the support AC power for a battery bank (instead of a normal diesel/gasoline generator). This would be similar to a "battery back-up system" except for the fact that the batteries are used as first choice power supply, until their voltage drops below a certain level, and then the grid will kick-in to supply power to the house and charge the batteries. The concept is to use the minimum minimum amount of electricity from the grid (if at all). I hope this is clear.

    I'm sorry if this was discussed and I missed it, but the bold part of this makes no sense to me. Why have the grid charge the batteries here? So let's say the sun is shining brightly (wind is blowing), the battery voltage has dropped below the pre-set level, the inverter has flipped to grid power and is powering the house and charging the batteries, and the PV/Wind system is, what? Sitting idle?

    If your goal is minimum grid power use, I'd think you'd want the battery charge to come from the PV/Wind once the batteries are below the voltage preset, and then you wait (using grid power) until the renewable energy source brings their voltage back up to full. So no grid charge of the batteries at all. Charging batteries from the grid is likely to result in more net grid power use (due to battery inefficiency), not less.
  • Eric LEric L Solar Expert Posts: 262 ✭✭
    Re: Which inverters can be used with this system?

    By the way, if what I say above is what you are after, then some of the Outback inverters can do it with the right controller. I copied the following from the "Mate 3" manual:
    In High Battery Transfer (HBX) mode, the system is connected to an AC source such as the utility grid; however, it will use battery power as the first priority. The AC source is locked out until needed.
    In this mode, the system runs on battery-supplied power for as long as the batteries can be sustained. It is expected that the batteries will also be charged from renewable sources such as PV power. When the batteries become depleted, the system reconnects to the AC source to operate the loads.
    The batteries may be recharged during this time using the renewable source. When the batteries are recharged to a high enough voltage, the system transfers back to the batteries as the primary source (hence the name High Battery Transfer). Note: For best operation, the inverter’s charger should be turned off when HBX mode is in use. HBX mode is intended for systems that rely primarily on the renewable energy source for charging.
  • BB.BB. Super Moderators, Administrators Posts: 32,314 admin
    Re: Which inverters can be used with this system?

    A couple of typical reasons to charge from grid...
    • Live in an area with unreliable power (afternoon outages, etc.). Very common to run on grid/charging when power available. Then power goes out for 8 hours in the afternoon/evening, supply home/business off-grid power until it returns. Very common system for many places (even average home). Basically a whole home UPS. No wind/solar panels needed, use backup genset for longer outages (after hurricane, etc.).
    • For places with Time of Use power... High charges in the afternoon, low charges overnight. Basically time shifted power usage. In theory, works fine. In practice, the cost of the system+batteries is (very roughly) around $0.45 per kWH. Add losses from charging/discharging cycle (~30% or so more energy used to time shift power)--You need almost $0.60 per kWH difference between Peak/Off Peak energy charges to break even. So--usually does not make economic sense. And some countries actually outlaw Hybrid installations (GT+Battery Inverters) to prevent time shifting of power (buy off peak, sell at peak).
    Anyway my 2 cents worth of guesses.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • lazzalazza Solar Expert Posts: 336 ✭✭✭
    Re: Which inverters can be used with this system?

    HI. Yes you're probably right, it doesnt make much sense charging the batteries from the grid once the grid is connected- better to wait for the renewables to charge the batteries and once the cut-in setting is reached to switch to battery power. The inverter must be in "by-pass" mode when the batteries are low therefore.

    Oversight on my part- so I have Outback, SMA, Xantrex.... any other inverters do all this for you?

    Some replies have mentioned that any inverter with generator back-up system will do the same, but i am not sure- if a signal has to go to the "auto generator start-up", and the inverter does not see a generator to start up, will it connect to the grid automatically or not?

    cheers
    Larry
  • BB.BB. Super Moderators, Administrators Posts: 32,314 admin
    Re: Which inverters can be used with this system?

    I am out of the US--So I don't see much from the Spanish/European market. Perhaps somebody here can give you some "local" suggestions.

    Reading programming manuals for "fun" is not something I do very often. ;)

    My suggestion, find a couple of vendors/manufacturers that will support you well, then download their manuals for the details.

    SMA and Victron are both very good European manufacturers. I think there are a couple more out of Germany that may be worth looking at too (sorry, don't remember their names).

    In the end, this all is going to be pretty expensive. You have already done a lot of conservation? Almost always a much better "investment" to conserve a watt than to generate a watt.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Which inverters can be used with this system?
    lazza wrote: »
    HI. Yes you're probably right, it doesnt make much sense charging the batteries from the grid once the grid is connected- better to wait for the renewables to charge the batteries and once the cut-in setting is reached to switch to battery power. The inverter must be in "by-pass" mode when the batteries are low therefore.

    Oversight on my part- so I have Outback, SMA, Xantrex.... any other inverters do all this for you?

    Some replies have mentioned that any inverter with generator back-up system will do the same, but i am not sure- if a signal has to go to the "auto generator start-up", and the inverter does not see a generator to start up, will it connect to the grid automatically or not?

    cheers
    Larry

    The auto gen start is used to trigger a transfer relay that applies power from the grid to AC IN on the inverter. Once that is present the inverter will switch to charger mode and pass the loads to the gen. That's the way the inverter "sees" a generator; by detecting AC at its input.

    Otherwise, what Bill said; download and read the manuals for any product that looks like it would suit. Research can take an arduous amount of time. Finding a suitable relay that can handle the current will be another issue.
  • lazzalazza Solar Expert Posts: 336 ✭✭✭
    Re: Which inverters can be used with this system?

    Ok, i'll see what my research reveals, and if ever such an installation takes shape- i'll let the forum know the results

    thanks for all your inputs

    Larry
  • Eric LEric L Solar Expert Posts: 262 ✭✭
    Re: Which inverters can be used with this system?

    Larry,

    I seem to remember reading that the Magnum Energy MS-series inverters can do this too with their battery monitor and controller, although I was just now looking at their "ARC" controller manual and couldn't confirm it on a quick read-through.

    But, that's another one to consider and their inverters can be ordered for 50Hz.


    By the way, I'm in a situation similar to you in Alabama. Alabama Power has a 'net metering' plan that won't pay you more than wholesale even for the kwh you use at home (sordid plan details here). To their credit, the Alabama PUC called them on this and 'recommended' that they offer full net metering for customer's used kWh, but Alabama Power never instituted the recommendation. So we sell to them at or below wholesale, and must buy back at retail. Makes it hard to sign on.
  • solarvicsolarvic Solar Expert Posts: 1,061 ✭✭✭✭
    Re: Which inverters can be used with this system?

    i mentioned the magnum before and he didn,t seem interested. The magnum can pass power thru from the grid for battery charging or to pass power thru to your service panel. The way I am setting mine up with using a forktruck battery. I figure if I don,t need power from grid all I need to do is throw the breaker. With the http://www.interlockkit.com/ use of a generator interlock kit I can either use grid power or inverter power. :Dsolarvic:D
  • lazzalazza Solar Expert Posts: 336 ✭✭✭
    Re: Which inverters can be used with this system?

    HI, Good to hear Eric, that we're not the only ones feeling hard done by :roll:

    The main reason I havent investigated the Magnum is that i've never actually heard of it before and I reckon you cant get hold of it here in Europe. But I do appreciate the info solarvic and will continue looking into it, Thanks
  • solarvicsolarvic Solar Expert Posts: 1,061 ✭✭✭✭
    Re: Which inverters can be used with this system?

    Here is a link to our forum sponser. You can download a manual and read it. The pae models suport ac coupleing http://www.solar-electric.com/maensiwainac.html
    . I wishI had the pae model but I got a good buy on the one I got used,. solarvic
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Which inverters can be used with this system?
    Eric L wrote: »
    I'm sorry if this was discussed and I missed it, but the bold part of this makes no sense to me. Why have the grid charge the batteries here? So let's say the sun is shining brightly (wind is blowing), the battery voltage has dropped below the pre-set level, the inverter has flipped to grid power and is powering the house and charging the batteries, and the PV/Wind system is, what? Sitting idle?

    If your goal is minimum grid power use, I'd think you'd want the battery charge to come from the PV/Wind once the batteries are below the voltage preset, and then you wait (using grid power) until the renewable energy source brings their voltage back up to full. So no grid charge of the batteries at all. Charging batteries from the grid is likely to result in more net grid power use (due to battery inefficiency), not less.
    You may be able to turn the battery charger off when the grid is up, but functionally I don't think it makes any difference. The battery charger does not know or care whether the AC it is getting is coming from the grid or from the PV inverter, or both. But consider this: if the battery SOC has triggered connection to the grid, the PV is not producing enough to power your loads, anyway. There is only one AC bus, and your PV inverter and the grid are both attached to it. You cannot route the power from your inverter only to the battery charger and the grid only to the loads, but it doesn't make any difference, the net flow will be from the grid until the batteries are charged.
  • Eric LEric L Solar Expert Posts: 262 ✭✭
    Re: Which inverters can be used with this system?

    ggunn,

    The way I see it, the point is to use the grid support to maximize use of the solar power while minimizing the stress on the batteries (and the size of the battery bank).

    So imagine a solar power array and a suitably-sized battery bank for that array. If purely off-grid, with no grid support, you must have average daily loads that are small enough not to draw the batteries down too deeply.

    With the grid-support system, you can have the same sized array and battery bank but larger average daily loads on the system, because you know that you can set the system to switch to grid-support at, say, a 20% depth-of-discharge, or whatever else you want in order to preserve the batteries.

    So consequently, you might be able to put a larger daily load on the grid-supported solar system without stressing the batteries, thus increasing the kwh average load the system is able to carry, relative to the off-grid only system. For instance, while the off-grid system might be done charging by 11:00 a.m. on a typical sunny day, the grid-supported system might have a heavier load connected to it and consequently continue charging the batteries longer into the afternoon. So there's more power being generated by the solar system in the grid-supported situation. The fact that it will flip to grid early on cloudy days might offset this gain if cloudy days are the norm, but shouldn't do so otherwise.

    So the OP's idea makes sense, given his desires and situation relative to the availability of grid-tie. It's not about whether the charge is coming from the grid or the charge controller, it's about how efficiently the system could be used while still prolonging battery life.

    Another thing: even if the above considerations where somehow irrelevant, I can't see how it would make no difference whether or not you charge from grid, if you have the option of passing through grid power directly and charging from the array. Charging from grid forces you to lose power due to the battery inefficiencies and AC/DC conversion losses, even when you normally have the option not to (because you could pass the grid straight through). Charging from the charge controller also involves those losses, but there's no option not to in this case -- it's the only way.

    So unless you have unreliable power or want to load-shift like BB suggested above, I can't see how it would make sense to charge batteries from the grid. But I can see how it would make sense to charge them from the solar array if the goal is to maximize efficiency.
  • BB.BB. Super Moderators, Administrators Posts: 32,314 admin
    Re: Which inverters can be used with this system?

    One other issue for people with grid/off grid operation--Remember that the grid frequency, on average, is very exact.

    Off grid inverters, even with fairly accurate frequency standards will still make clocks and timers that use line frequency as a reference, almost useless because the time will drift way too much:
    • 24 hours per day * 60 min/hour * 60 seconds per min * 0.1% (0.001) clock error = 86.4 seconds per day drift
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 9,511 ✭✭✭✭✭
    Re: Which inverters can be used with this system?
    BB. wrote: »
    ...
    Off grid inverters, even with fairly accurate frequency standards will still make clocks and timers that use line frequency as a reference, almost useless because the time will drift way too much:
    • 24 hours per day * 60 min/hour * 60 seconds per min * 0.1% (0.001) clock error = 86.4 seconds per day drift
    -Bill

    And I wish they would fix this. It's NOT hard to use a TV colorburst crystal (3MHz) and get a stable clock out of it. And that's in every TV sold, and cost is in the pennies.
    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

    solar: http://tinyurl.com/LMR-Solar
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  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Which inverters can be used with this system?
    Eric L wrote: »
    So unless you have unreliable power or want to load-shift like BB suggested above, I can't see how it would make sense to charge batteries from the grid. But I can see how it would make sense to charge them from the solar array if the goal is to maximize efficiency.

    With an SMA system (Sunny Island) there is only one AC bus, which is either connected to the protected loads panel (along with any SB GT inverter(s)), or both the protected loads panel and the grid. It charges the batteries off that bus and has no way of knowing how much power comes from where. I still do not see that it makes any difference.

    With a Xantrex system, the PV array is always connected only to the batteries through a charge controller. You can tell the Xantrex whether or not to charge the batteries from the AC bus (in parallel with the charge controller) when the grid is connected, I believe.

    I know you can configure the SMA system to behave like the OP wants, but I am not sure about the Xantrex gear.
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