Grid connected 4.5kW system - take off grid?

My system has been operational for last 4 months. I have 24 Evergreen ES-190 panels, and Fronius IG5100 inverter. I was wondering if this system is totally useless in the event of a power outage - grid goes down.

Would it be possible in the event of a power outage to turn off main breaker (isolating my home from the grid), connect a gas powered generator, and then connect my PV system?

I know the inverter requires a "grid" to sync with - would it turn on and supply power to my home in parallel with the generator?

thanks for your help,
- Mark -

Comments

  • Solar GuppySolar Guppy ✭✭✭ Solar Expert Posts: 1,962 ✭✭✭
    Re: Grid connected 4.5kW system - take off grid?

    won't work, if you search this forum, you will find this exact question has been answered a few times as to why
  • BB.BB. admin Super Moderators, Administrators Posts: 29,629 admin
    Re: Grid connected 4.5kW system - take off grid?

    As Solar Guppy says--this is the "weakness" of the Grid Tied system. It will not function during an power outage.

    Usually, your best option is a fuel powered generator on a transfer switch.

    If you have lots of AC Mains failures (storms, bad grid, etc.)--then there are options--but usually, it would mean re-wiring your panels to a different voltage and using either a full off-grid system, or a "Hybrid" system that can do both Grid Tied and Off-Grid (behind a transfer switch)...

    There is a third way--having an off-grid system behind a transfer switch--and connecting your GT inverter to this off-grid system--but there are some severe issues with doing this (back driving the off-grid inverter and actually charging--or overcharging your battery bank).

    Sort of depends how far down this road you wish to go--with enough information, time, and money--most anything (within reason) can be accomplished.

    Unfortunately, at this time, there is usually no simple way of using your solar array of your GT system and connecting it to your battery system... GT inverters typically are 200-600 VDC, and off-grid systems are 17-140 VDC. It is possible to wire for both, and use configuration jumpers--but this is not straight forward to do safely and can lead to problems if done wrong (or the switch over is done incorrectly).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • wmwinnwmwinn Registered Users Posts: 4
    Re: Grid connected 4.5kW system - take off grid?

    OK - I believe the experts... no way (or very difficult/expensive) to use my GT system during a power outage.

    But, I really want to understand WHY. The GT inverter will only operate if a proper AC signal is present on its output, and then syncs up with that signal. How would it know whether the signal is generated by the utility grid - or by my gas powered generator?

    You're telling me that it just won't work if my house is powered by a generator (not attached to the grid). Something must be different in the generator power versus the utility power that makes the inverter work in one case, but not the other.

    thanks for your quick replies! :D
    - Mark -
  • nielniel ✭✭✭✭ Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Grid connected 4.5kW system - take off grid?

    simply, the generator is not able to sink the higher voltages and power put out by the gt inverter to operate in a safe overall voltage range and most of the non-inverter type generators will not be a stable enough sinewave that'll operate within frequency tolerances of the gt inverter.
    it may be possible for you to tap a few pvs and run them into a controller and batteries, but what kept the batteries charged in the first place as that power during normal operations is being sent to the grid? you could set up a backups type of a deal and keep some batteries charged with an inverter charger in the event of an outage. not as efficient and some of the power you are producing would then go the the backups and it would still be the same circumstance with no power being delivered by your pv array during an outage. alternative is to use a grid tie inverter capable of battery operations.
  • BB.BB. admin Super Moderators, Administrators Posts: 29,629 admin
    Re: Grid connected 4.5kW system - take off grid?

    As Neil says--the generator frequency control is not accurate enough... And if it was (like an inverter style generator--such as the Honda euX000i family)--the generator is not designed to "absorb" power from the GT Inverter if the load is less than the GT Inverter's output...

    The GT inverter is looking very closely at the incoming AC wave form (and line to neutral voltage too). If anything is out of the "ordinary" (voltage, frequency, wave form not sinusoidal, probably bad power factor, etc.)--the GT inverter must shut down for 5 minutes before trying to connect again... This is to protect utility equipment and workers from being damaged, injured, or killed by improper charging of the utility lines.

    The GT inverter actually does not regulate its voltage/frequency output--it just follows the AC utility feed (within tight limits). The GT inverter only controls the output current ("power") based on the solar panel energy available and its own design power/current limits.

    The Utility is what "regulates" your local voltage and frequency.

    If you meet #1, and your load is always greater than the output of the GT inverter (say your 4.5 kW GT inverter--that means you need a 4.5+ kW load to avoid back driving the generator).

    If you replace the generator with a 5+kW Off-Grid battery based TSW inverter (behind a transfer switch such that you don't back drive the AC mains out to the street)--it turns out that an Off-Grid TSW inverter, when back driven by a GT inverter will actually charge the battery bank with the excess power available from the GT inverter. And, they will share the AC loads very nicely--from 0 watt load to Off-Grid inverter maximum load without human interaction. The Off-Grid inverter will regulate the voltage/frequency of the shared AC circuit with the GT inverter.

    Works well-but you have the issue of 4.5 kWatts being driven into the battery bank with no regulation/battery charger control--so you can ruin the battery bank or even boil it dry and catch it on fire.

    If you are an electrical engineer--you should be able to work up some sort of redundant GT charge controller / Dump Load controller to prevent the battery bank over charging--it is an interesting engineering problem.

    However, if this is your first major electrical project--it is not something I would recommend for a first time user to play with.

    Solar Guppy has actually tried this on his own home setup (thread somewhere around here) and found that the basic idea works well. I think he also pointed to a paper about this too.

    And an Outback TSW has been tested this way too by SkyStream for their "Off Grid" application using their GT only wind turbine--I am not sure anybody has one up up and running yet.

    If you still want to try this--it can be done... But you will need to define your application and work with the people here to understand how to connect everything together--and you will probably need somebody local to help (if this is beyond what you want to be responsible for).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • wmwinnwmwinn Registered Users Posts: 4
    Re: Grid connected 4.5kW system - take off grid?

    WOW - excellent information here. I believe I now understand the WHY, thanks to your help and explanations.

    This board rocks! 8)
  • BB.BB. admin Super Moderators, Administrators Posts: 29,629 admin
    Re: Grid connected 4.5kW system - take off grid?

    wmwinn,

    I have thought long and hard about the 3.5kW of GT connected solar panels on my roof... And, in my area, no way I can justify the costs. Power outages don't don't happen often, or more than a couple hours in our area--the last multi-day outage I lived through was 50+ years ago--and the real danger was running out of water (hillside tanks running empty). Candles and natural gas worked fine (at least as far as a few year old kid was concerned ;) ).

    For me, a good quality, small gasoline generator, 20 gallons of stabilized fuel (changed once per year), and a siphon hose is enough.

    Personally, I am a big proponent of the Honda eu2000i inverter/generator... Very fuel efficient with small loads (~15 hours on 1.1 gallons of fuel running a 400 watt load). Fridge/freezer, a few lights, and radio/TV should be enough. Also wired in a manual transfer switch that can run the central heat (natural gas) if needed.

    The big 3-5kW noise makers just drink the fuel when running at light loads.

    If you have big loads that are needed a couple times a day (such as a well pump)--run it on the 5kW unit for 15 minutes, and the rest of your loads on a smaller inverter/generator.

    Since we have natural gas--I have also looked at the smallest "home" emergency systems (~10kW)--and they still such natural gas at ~$1.00 per hour--and my average loads are quite small--again, just hard to justify. And for me, an earthquake will probably be my "emergency"--and I cannot guarantee I would have natural gas anyway.

    If you want to see a nice "state of the art" Hybrid Grid Tied / Off-Grid capable system which will accept solar and generator inputs--Take a look at the Xantrex XW system. I would like--but still does not make sense for my home.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • boBboB ✭✭✭✭ Solar Expert Posts: 965 ✭✭✭✭
    Re: Grid connected 4.5kW system - take off grid?
    wmwinn wrote: »
    I know the inverter requires a "grid" to sync with - would it turn on and supply power to my home in parallel with the generator?
    - Mark -

    I don't know about everybody else's grid, but my grid voltage comes from a generator... Actually, lots of generators in parallel.
    Coal, gas, hydro, nuclear powered. All of those. So, it ~can~ (and does) work of course.

    Just depends on the generator and loads and regulation methods.

    boB :D
  • nielniel ✭✭✭✭ Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Grid connected 4.5kW system - take off grid?

    this is what i was trying to say as the generators in home usage are not going to be big enough to sink very much of the solar gt. might work with a small pv on one of those enphase inverters and a fairly good sized generator that is loaded down. that's a far cry from what the op had in mind to do.
  • autoxsteveautoxsteve ✭✭✭✭ Solar Expert Posts: 114 ✭✭✭✭
    Re: Grid connected 4.5kW system - take off grid?

    there are devices such as load controllers that dump the excess power being provided by a source ( me thinks these were referenced in wind turbines). A generator that produces a clean sinewave might work in conjunction with a load / dump controller....
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