Grid tie inverter that does NOT feed into the grid

mi_cin
mi_cin Registered Users Posts: 8
Hi guys,

I have another solar question, I'm new to the topic and I appreciate your patience.

In my country we still don't have new regulations on solar power systems. So right now selling energy (or feeding into the grid) is illegal with out a problematic procedure no one would like to go through. But I still have some house devices that are connected to the grid and consume power.

Let say I would like to have a 1kWp solar generator on the roof and a grid-tie inverter. If there is a cloudy day and I'm home the energy produced will be consumed by devices immediately and nothing goes out of the house. But if I'm out of home the devices consume less energy and there are some leftovers that would go to the grid (in my case illegally - I don't have a permission to do it and the way to get it is too complicated).

Is there a way to "keep all the power home"? Some kind of a device like DC diode but for AC? I want to use as much as I can for my devices but I don't want to send leftovers to the grid. What's more: I would like that system to be easy upgradeable to work with feed-in-tariff when it finally comes.
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Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Grid tie inverter that does NOT feed into the grid

    No easy/cheap way of doing it... There are "hybrid" AC inverters which operate as both Grid Tied (when utility power is up) and Off Grid (when utility power has failed). And they (in theory) can be programmed not to backfeed the AC meter.

    In practice, the programming has been complex and problematic (right firmware, right things programmed in the right places, and no details in the manuals).

    If you need/want battery backed AC power anyway--Then it is a possibility.

    Otherwise, at this point, I am not aware of any pure GT Inverter system (panels+GT inverter, no battery bank) that can do this (not that I am a big expert--just have seen the question asked lots of times and few workable answers).

    In the US, newer power meters can be programmed by the utility to only spin "forward" -- and in many cases, will spin forward if the customer produces excess power to the grid (was designed for "people" that plug meters upside down for 2 weeks a month to steal power).

    Also, the newer networked power meters can report when "strange things" are happening on the power line, such as the customer producing more power than they use, or possibly even the signature of an unregistered/approved GT inverter.

    In the end--The best bet is to start with "extreme" conservation. For some folks that have never worked at conservation before, they can reduce their power usage by 25% to 50% pretty easily (insulation, LED/CFL bulbs, picking appliances that are very efficient, heat pump based heating/hot water, turning off DVR's/Computers/etc. when in standby/not being used, etc.). And, usually, for less cost than installing solar power.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Grid tie inverter that does NOT feed into the grid

    Actually you can use a battery-based Grid Tie inverter and just set it so it doesn't sell to the grid.
    But you will run in to the off-gridder's problem of potential power not being harvested if there's no place for it to go (i.e. no loads running).
  • mtdoc
    mtdoc Solar Expert Posts: 600 ✭✭
    Re: Grid tie inverter that does NOT feed into the grid

    Yep. Any of the Outback "G" inverters will do what you are asking. You simply turn off the "Sell RE" function (easy to do).
  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    Re: Grid tie inverter that does NOT feed into the grid

    There's a very new all-in-one product on the market that's designed to optimise energy for self use, and from what I can make out in the very limited documentation, you can also prevent it from exporting to the grid while still using the grid as backup. http://powerrouter.com/products/powerrouter-solar-inverter

    You should note the two items I mentioned above, which are exactly the things you don't really want to see for a device that's going to be supplying and controlling your power: It's new. And there doesn't seem to be a detailed manual available- just a few pages of installation guidelines. But it could be worthwhile contacting them for more details.
  • boB
    boB Solar Expert Posts: 1,030 ✭✭✭✭
    Re: Grid tie inverter that does NOT feed into the grid

    What you are talking about is a grid tie inverter that uses a current transformer on the main power panel to back the inverters'
    power off output when it is about to generate more power than your house is using.

    I don't know if powerrouter that Stephen posted the link to does this but it very well may.

    I believe there may be another inverter out there that does this but I'm not positive.

    We talked about doing this 10 years ago and called it "Legal Gorilla mode"

    boB
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Grid tie inverter that does NOT feed into the grid

    In California, even adding a large off grid system to a utility connected home is technically illegal unless home owner pays a "stranding" charge to the utility (who took out 20-40 year loans/contracts to supply power to the homeowner in the first place). There is currently an exemption for small solar/RE power systems (10kW maximum?) in the state regulations--and I am not sure how much it is enforced--But it is there.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • boB
    boB Solar Expert Posts: 1,030 ✭✭✭✭
    Re: Grid tie inverter that does NOT feed into the grid
    BB. wrote: »
    In California, even adding a large off grid system to a utility connected home is technically illegal unless home owner pays a "stranding" charge to the utility (who took out 20-40 year loans/contracts to supply power to the homeowner in the first place). There is currently an exemption for small solar/RE power systems (10kW maximum?) in the state regulations--and I am not sure how much it is enforced--But it is there.

    -Bill


    Bill, how would they know if you did not export to their grid ??

    They don't want you reducing your power bill by too much of course cuz it's bad for their business.

    I'm surprised that utilities even sometimes help with higher efficiency lighting like flourescent lighting.
    Especially low power factor lighting which is not as good for the utility.


    boB
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Grid tie inverter that does NOT feed into the grid

    We had one poster here that was taking data to figure out if GT inverters where connected... My guess--the simplest way would be poor power factor (aka MSW) wave from from a "non-legal" / cheap plug in GT inverter.

    I agree with you about using CFL's with extremely poor power factor (on average something like 0.50 to 0.60 PF or so)... They may "save" on kWH used by reducing billing by 75%, but with 0.50 PF, the utility "sees" only a 50% reduction in current flow.

    And the current flow for CFL bulbs is a non-linear wave form--something that they cannot easily (and cheaply) correct with pole mounted transformer banks (as I understand, they will switch the capacitor banks "on" during summer to make up for all of the motor loads/low PF due to Air Conditioning and Water Pumping loads in the central valley of California).

    Like many government "sponsored" projects--The results are frequently underwhelming for their costs.

    Nothing is "free":

    FirstEnergy to give away 3.75 million low-energy light bulbs:
    FirstEnergy Corp. is getting ready to leave two high-efficiency light bulbs on your doorstep. But they're not a gift.

    The utility will charge average users 60 cents a month extra on their electric bills for the next three years -- $21.60 all together. That covers the cost of the bulbs ($3.50 each), their delivery and the delivery of the power consumers would have used if they didn't have them.

    The good news: These compact fluorescent bulbs will reduce your electricity use. If you replace two 100-watt incandescent bulbs with these 23-watt, warm-white CFLs, you'll save $60 by the time they burn out in five to seven years, according to FirstEnergy.
    And you'll pay for the bulbs whether you use them or not, so it makes sense to use them.

    FirstEnergy is distributing the 3.75 million bulbs to comply in part with an energy law enacted in Ohio last year. The law requires utilities to cut their customers' energy use by 22 percent by 2025. The law also mandates that utilities use solar, wind turbines and other renewable energy sources. The Public Utilities Commission of Ohio approved the light bulb distribution and the extra charge on your bill.
    Two CFL's for $21.60??? I can buy CFL bulbs for $1 each all day long... So, instead of 20 CFL bulbs for the whole home--the people only get two for the same amount of money. Sounds really nice.

    And, at least from the article (may have been poorly written); "...covers the cost of...delivery of the power consumers would have used if they didn't have them..." It looks like the utility is getting paid by the customers (tax/fee required by law) for not delivering the power the CFL program is saving... :roll:

    I am sure the people in Ohio are happy the government is watching out for them.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • boB
    boB Solar Expert Posts: 1,030 ✭✭✭✭
    Re: Grid tie inverter that does NOT feed into the grid
    BB. wrote: »

    FirstEnergy to give away 3.75 million low-energy light bulbs:

    Two CFL's for $21.60??? I can buy CFL bulbs for $1 each all day long... So, instead of 20 CFL bulbs for the whole home--the people only get two for the same amount of money. Sounds really nice.


    -Bill


    I remember here when the utility was sponsoring CFls for 19 cents and 49 cents each at the local drug stores !! Small and larger ones. I bought a bunch of them and am still using
    some of them when one breaks. Reminds me that I have to replace the one on our front porch. Last one ran for at least a year I think.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Grid tie inverter that does NOT feed into the grid
    stephendv wrote: »
    There's a very new all-in-one product on the market that's designed to optimise energy for self use, and from what I can make out in the very limited documentation, you can also prevent it from exporting to the grid while still using the grid as backup. http://powerrouter.com/products/powerrouter-solar-inverter

    Stephen, you've posted here a few times about a product called 'EMMA' which sounds like it could do the job. Is there some reason you have not mentioned it in this thread?

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    Re: Grid tie inverter that does NOT feed into the grid
    vtmaps wrote: »
    Stephen, you've posted here a few times about a product called 'EMMA' which sounds like it could do the job. Is there some reason you have not mentioned it in this thread?

    The EMMA is designed to optimise energy that you produce yourself in a normal grid tied setup, but it in no way guarantees that you won't be selling anything back to the grid. So I don't think it's a 100% suitable solution here. If its current measurement is out a bit, or if it lags when turning loads on then you could be feeding into the grid.

    A normal off-grid setup as others have suggested, or perhaps the power router seem more appropriate because you can control grid selling more deliberately.
  • mi_cin
    mi_cin Registered Users Posts: 8
    Re: Grid tie inverter that does NOT feed into the grid

    Hi guys, thanks for your replies.

    Actually I was thinking about some kind of external device. Like DC diode or something through what a current can flow only one way. Maybe any kind of a electric meter, just for 1 phase?
  • XRinger
    XRinger Solar Expert Posts: 529 ✭✭✭
    Re: Grid tie inverter that does NOT feed into the grid
    mi_cin wrote: »
    Hi guys, thanks for your replies.

    Actually I was thinking about some kind of external device. Like DC diode or something through what a current can flow only one way. Maybe any kind of a electric meter, just for 1 phase?

    There isn't any diode device that can do what you want. But, if you were handy, you could build a smart controller that could monitor a few of your circuit breakers that are connected to the larger loads in your home. (Washers, HVAC & Etc).
    When those devices were using their normal power, signals from (1)current sensors could be fed into a (2)controller,
    (1) http://ecorenovator.org/forum/appliances-gadgets/1490-diy-230vac-adjustable-power-limiter.html
    (2)http://ecorenovator.org/forum/appliances-gadgets/1871-webcontrol-universal-industrial-controller.html

    and the controller program would add up the watts needed and connect your GTIs to your
    in-house 'grid' using SSRs. (Depending on how much power you needed at that point).

    A poor man's version would just use (3)current sensors ANDed together (or N.O. sensors in series)
    (3) www.ebay.com/itm/261108782153
    and connect the output (AKA heavy load signal) to one big *SSR that connects your jumbo GTI to the load..
    (The GTI AC connection to the grid would require an SSR that's rated for the max amps your GTI will deliver).
    (Many common SSRs run 25A which would be able to handle 2.5 kw at 120vac and twice that at 230vac).
    http://www.ebay.com/itm/180842481825
    *A small DC supply 9 to 12vdc would be needed for the sensor switches to turn on the SSR.

    I've been thinking about this idea, because I have the parts to build a 'guerrilla' GTI controller on my bench.
    But, my electric company meter has a 'back-flow' detection flag, and my circuit can't work instantaneously.
    So, any law breaking might be detected and I would be sent off to some horrible prison island.. :cry:
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Grid tie inverter that does NOT feed into the grid
    XRinger wrote: »
    So, any law breaking might be detected and I would be sent off to some horrible prison island.. :cry:
    Without POCO power.

    Is that why they refer to anti-islanding circuitry?
    SMA SB 3000, old BP panels.
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Grid tie inverter that does NOT feed into the grid
    mi_cin wrote: »
    Hi guys, thanks for your replies.

    Actually I was thinking about some kind of external device. Like DC diode or something through what a current can flow only one way. Maybe any kind of a electric meter, just for 1 phase?
    Unfortunately there is no cheap and simple way to control the direction of current flow in AC.
  • XRinger
    XRinger Solar Expert Posts: 529 ✭✭✭
    Re: Grid tie inverter that does NOT feed into the grid
    ggunn wrote: »
    Unfortunately there is no cheap and simple way to control the direction of current flow in AC.

    Would you consider under $50 cheap? :) I think that I could control a single GTI, so it only came on when your HVAC
    was drawing high power, with a relatively simple circuit.
    ACBQ.jpg
    (Get rid of the transistor and feed the +5VDC into the SSR control inputs via the N.O. current sensor).

    You can buy an adjustable AC current sensor on Ebay for 15 to 20 USDs.
    SSRs (Solid State Relay) can be found for cheap, if you shop for a while. (I found a lot of 6 for $25).


    The line feeding your HVAC is monitored by the current sensor, when the HVAC is pulling XX amps,
    the sensor contact closes, turns on the SSRs, which connect your GTI to your main house wiring. Very simple.
    When the HVAC shuts off, the 5VDC is removed from the SSR control lines.
    The GTI will be disconnected from the grid when the AC crosses Zero phase.


    On my sensors, I had to use loops to make them work down at 10A (@240vac).
    Here's one I used to limit a Mini Split/heat pump to 10A max..
    afterBH.jpg
    This one actually triggers at 9.9 Amps. Very reliable.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Grid tie inverter that does NOT feed into the grid
    XRinger wrote: »
    Would you consider under $50 cheap? :) I think that I could control a single GTI, so it only came on when your HVAC
    was drawing high power, with a relatively simple circuit.

    An elegant system for only turning on the PV when a high load is present, and I do consider that cheap!
    But not quite the ticket for backing off the output of a GTI to hold it just short of feeding power back into the grid. As was mentioned earlier, that is a standard function for battery-backed hybrid GTIs, but I have not seen it in a straight GTI because most people want to sell back.

    The "integrated power management systems" that I have seen advertised also seem to take the route of turning on opportunity loads when necessary to keep from selling back rather than throttling the GTI itself. Getting into the control circuitry of the GTI is unfortunately not a DIY project.

    (Apparently there is a somewhat paradoxical Feed In Tariff situation in GB in which you get paid more for power you produce which you also immediately use locally than for power which you feed back into the grid. That actually makes it more economical to waste the excess power than to sell it back!)
    SMA SB 3000, old BP panels.
  • XRinger
    XRinger Solar Expert Posts: 529 ✭✭✭
    Re: Grid tie inverter that does NOT feed into the grid

    If your HVAC (or other load) uses more power than your GTI can make with it's PV array, then my hack would fill the requirement,
    Is there a way to "keep all the power home"? made in post #1 above.

    Yes, it has limitations. But if you happen to be using a setup like Enphase GTIs, each with a 200w panel,
    the idea could still work. Just by duplicating the hack on the circuits where the load is regularly higher than 200 Watts. (42" Plasma TV) :p

    The current sensor can easily be set to trigger at 200W. They can be set to trigger between 1 and 135 amps.
    So, as use falls off, the GTIs would fall off-line, in 200W steps.. :roll:
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Grid tie inverter that does NOT feed into the grid
    XRinger wrote: »
    If your HVAC (or other load) uses more power than your GTI can make with it's PV array, then my hack would fill the requirement,
    Is there a way to "keep all the power home"? made in post #1 above.

    Yes, it has limitations. But if you happen to be using a setup like Enphase GTIs, each with a 200w panel,
    the idea could still work. Just by duplicating the hack on the circuits where the load is regularly higher than 200 Watts. (42" Plasma TV) :p

    The current sensor can easily be set to trigger at 200W. They can be set to trigger between 1 and 135 amps.
    So, as use falls off, the GTIs would fall off-line, in 200W steps.. :roll:

    So how would you suggest controlling individual micro inverters without hacking into the AC connecting harness? Just switching the DC from the panel? (Obviously using a relay rather than an SCR. :-) )
    SMA SB 3000, old BP panels.
  • XRinger
    XRinger Solar Expert Posts: 529 ✭✭✭
    Re: Grid tie inverter that does NOT feed into the grid
    inetdog wrote: »
    So how would you suggest controlling individual micro inverters without hacking into the AC connecting harness? Just switching the DC from the panel? (Obviously using a relay rather than an SCR. :-) )

    The AC power I/O of the GTI is the best place to connect (and disconnect) solar power to the grid.
    Especially when using individual micro inverters (like Enphase).
    Because of my experience with inverters, I would be reluctant to install DC relays in the PV DC lines.
    Plus, when a PV panel is left without a load, the Open Circuit voltage really climbs.
    Might cause a bit of wear on the relay's contact pads. (One of my arrays runs 144Vdc under load).

    But, the contacts in the current sensors that I've used, can easily power a DC relay, to switch PV DC voltage from PV.
    I'm pretty sure that 20A 240AC SSRs (from Ebay) are cheaper than mechanical DC relays at the same power rating..
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Grid tie inverter that does NOT feed into the grid
    XRinger wrote: »
    The AC power I/O of the GTI is the best place to connect (and disconnect) solar power to the grid.
    Especially when using individual micro inverters (like Enphase).

    My concern with that is that I understand that the Enphase uses a proprietary wiring harness to connect directly to the output jack of each micro inverter. That means cutting into the wiring harness to install a shutoff relay. Or is there also a control input somewhere than can turn it on and off with a switch closure?
    SMA SB 3000, old BP panels.
  • XRinger
    XRinger Solar Expert Posts: 529 ✭✭✭
    Re: Grid tie inverter that does NOT feed into the grid

    The last time I looked at the Enphase manual, they were installed daisy chain style.
    Because of the cost of the required junction box on the end of chain is already kinda high,
    buying another one for each panel would be outta $igh..

    So, doing the DC relays on each panel would be the way to go.
    The connectors (MC4) to wire in the relays aren't too costly.

    If you used a programmable controller, to run the relays, you could control a large Enphase array.
    Then pull the plugs on the relays when you got legal with the power company..
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Grid tie inverter that does NOT feed into the grid
    XRinger wrote: »
    Would you consider under $50 cheap? :) I think that I could control a single GTI, so it only came on when your HVAC
    was drawing high power, with a relatively simple circuit.
    Very nice, but it's not precisely what he was asking about.
  • XRinger
    XRinger Solar Expert Posts: 529 ✭✭✭
    Re: Grid tie inverter that does NOT feed into the grid
    ggunn wrote: »
    Very nice, but it's not precisely what he was asking about.

    Okay, from now on, I'll just read posts and resist the urge to put in my 2 cents worth..
    Besides, a lot of people have no clue about electronics. Why confuse them?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Grid tie inverter that does NOT feed into the grid
    XRinger wrote: »
    Okay, from now on, I'll just read posts and resist the urge to put in my 2 cents worth..
    Besides, a lot of people have no clue about electronics. Why confuse them?

    Don't worry about it: everyone's 2 cents is worth the same around here and we're all guilty of wandering off on a tangent from time to time.
    Why, I remember once when I was looking for a suitable replacement for a 6AU6 and this man came up and wanted to sell me a dead mule: said feeding it would be no problem and it didn't kick. :p
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Grid tie inverter that does NOT feed into the grid
    XRinger wrote: »
    Okay, from now on, I'll just read posts and resist the urge to put in my 2 cents worth..
    Besides, a lot of people have no clue about electronics. Why confuse them?

    One of the beauties of the forum format for me is that you can learn things that are not *exactly* what the OP asked about. Please keep up the contributions, but also keep in mind whether the original question has been answered or not, just in case the whole thread veers off course. In those cases, I see the problem not as off topic information being added b

    By the same token, a lot of people have no clue about Solar PV, but we want to inform them, even if it requires electronics. :-) The easiest way to avoid confusion is to do nothing.
    SMA SB 3000, old BP panels.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Grid tie inverter that does NOT feed into the grid
    ... wanted to sell me a dead mule: said feeding it would be no problem and it didn't kick. :p

    Sounds like some financial derivatives that were sold. :-)
    SMA SB 3000, old BP panels.
  • XRinger
    XRinger Solar Expert Posts: 529 ✭✭✭
    Re: Grid tie inverter that does NOT feed into the grid
    Don't worry about it: everyone's 2 cents is worth the same around here and we're all guilty of wandering off on a tangent from time to time.
    Why, I remember once when I was looking for a suitable replacement for a 6AU6 and this man came up and wanted to sell me a dead mule: said feeding it would be no problem and it didn't kick. :p

    Yeah, for some reason when I read the OP, I got the idea that he wanted to use a GTI (or GTIs),
    but avoid putting any power out to the city grid.
    Hey, when you get old, you get confused too.. :confused:
    I'm really lucky that most of the things I build seem to work pretty well. (It's the experiments that make smoke). :)
    Sadly, all of the lab equipment & instruments that I built on the job, are still working great.
    Since I went into semi-retirement, they never call me back to repair anything. :(
    Maybe I should have used cheaper parts.?. I coulda been rollin in taxpayer bucks$$ ;)
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Grid tie inverter that does NOT feed into the grid
    XRinger wrote: »
    Yeah, for some reason when I read the OP, I got the idea that he wanted to use a GTI (or GTIs),
    but avoid putting any power out of the city grid.
    "Putting any power out of...."
    ?
    A. "Putting any power back into...." or
    B. "Pulling any power out of...."

    I think that A is exactly what he wanted to do. But he wanted to keep the GTI running all the time and just throttle down the output so that he was supplying all of the load from his PV as long as he had the capacity, but never pushing back.
    SMA SB 3000, old BP panels.
  • XRinger
    XRinger Solar Expert Posts: 529 ✭✭✭
    Re: Grid tie inverter that does NOT feed into the grid
    inetdog wrote: »
    ?
    A. "Putting any power back into...." or
    B. "Pulling any power out of...."

    I think that A is exactly what he wanted to do. But he wanted to keep the GTI running all the time and just throttle down the output so that he was supplying all of the load from his PV as long as he had the capacity, but never pushing back.

    A. He didn't want to sent power to the grid.. (Since that would be illegal).
    I missed the part about keeping the GTI running after his house loads dropped off to low usage, and "and just throttle down"..

    That was an idea that I discussed above too, by shutting down one panel at a time..