Does a DC switch on a timer exist to automatically break a parallel GTI connection?

MO-NHMO-NH Registered Users Posts: 9
I've got a solar array grid tied as well as a small wind turbine grid tied using 24v Sun GTI's. What I'm looking to do is utilize some capacity of the wind GTI during the day so the solar units don't have to work as hard, run cooler and are therefore a bit more efficient. When all the GTI's are all in parallel they work well together. I do this manually each day currently, but want to make it automatic. What I want to do is set up a switch between GTI's the 4awg parallel connection between the solar and wind GTI's to open at daybreak and close in the evening - in effect disconnecting the parallel connection. Sometimes at night we get some nasty wind storms - especially in winter and I don't want the overflow power from the turbine flowing into the solar GTI's, but rather dumped via dump load.

Does such a DC automatic switch exist of sufficient durability for this task?

Info that may be needed: The solar GTI bank is three 600w SUN-600 GTI's stacked on a bank of ten 230w 24v panels and the panels max out at 70amps at 29 to 30 volts. The wind GTI that's in parallel is a SUN-1000 wind GTI with dump load and the dump load is a 3ohm resistor.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,924 admin
    Re: Does a DC switch on a timer exist to automatically break a parallel GTI connection?

    I am kind of lost here...

    GTI for us normally means Grid Tied Inverter--I.e., you connect a power source (solar panels to GTI) and the output of the GTI is connected to the utility grid (usually--no dump controller/loads or battery bank) or an off grid AC inverter+battery bank (not standard, but becoming a bit more common).

    Do you have the second setup (GTI+Off Grid Inverter+Battery bank)?

    Why do you have issues with the solar power and want to "unload it". A dump (shunt) type charge controller used would be used with wind turbines (for DC connected turbines) or as a dump load for some GTI+OG+Battery bank setups.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Does a DC switch on a timer exist to automatically break a parallel GTI connection?

    I can only ask "why?"

    A grid tie inverter is designed to operate at capacity. There's no point in cutting them back. If they won't do it, get rid of them. Most of the time people "over panel" GTI's because panel output averages less than rated Watts all day and they want to keep production up.

    If you don't want your inverters running at peak, take some panel off them. In looking at your specs you have three 600 Watt inverter (1800 Watt total capacity) and 2300 Watts of panel. That's about right as that much panel will average just under 1800 Watts in output under typical conditions. You have a separate GTI for the wind turbine, which is as it should be.
    I don't want the overflow power from the turbine flowing into the solar GTI's, but rather dumped via dump load.

    There is no reason this would happen. There's no reason there would be a dump load on a wind-driven GTI. When connected to the grid there is always a place for the current to go (unless the grid goes down).

    I do not understand why you think you should change anything at all. Is there a terminology problem here? Are batteries involved in some way? Am I having a "thick day"?
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Does a DC switch on a timer exist to automatically break a parallel GTI connection?
    MO-NH wrote: »
    What I'm looking to do is utilize some capacity of the wind GTI during the day so the solar units don't have to work as hard, run cooler and are therefore a bit more efficient.

    PV inverters run most efficiently when they are running flat out. Also, if your wind and PV inverters are all grid tied, how hard one is working has no effect on the others.
  • MO-NHMO-NH Registered Users Posts: 9
    Re: Does a DC switch on a timer exist to automatically break a parallel GTI connection?

    To clarify - the GTI's are all stacked in parallel during the day when it's not particularly windy - both the three 600w inverters for the solar panels and the 1000w wind inverter. As a result the 1000w wind inverter is handling a few hundred watts of the solar power. The units all balance out pretty well. What I want to avoid is the three 600w solar inverters getting fed the turbulent power during an overly windy night when I'm asleep and won't be there to manually separate them. The inverters will try to balance the load and since I've heard that it's not a good idea to hook solar inverters to a turbine I'm worried that it would harm the three 600w solar inverters.

    That's why I was asking about a DC breaker or switch of sorts that ran on a timer. I could then set that breaker between the wind inverter and the three solar inverters and it would automatically connect at say 7am and disconnect at say 7pm. This way the solar and wind inverters would stay separated at night which is when we tend to get the nasty strong wind and I'm not awake to separate the GTI's.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Does a DC switch on a timer exist to automatically break a parallel GTI connection?
    MO-NH wrote: »
    To clarify - the GTI's are all stacked in parallel during the day when it's not particularly windy - both the three 600w inverters for the solar panels and the 1000w wind inverter. As a result the 1000w wind inverter is handling a few hundred watts of the solar power. The units all balance out pretty well. What I want to avoid is the three 600w solar inverters getting fed the turbulent power during an overly windy night when I'm asleep and won't be there to manually separate them. The inverters will try to balance the load and since I've heard that it's not a good idea to hook solar inverters to a turbine I'm worried that it would harm the three 600w solar inverters.

    That's why I was asking about a DC breaker or switch of sorts that ran on a timer. I could then set that breaker between the wind inverter and the three solar inverters and it would automatically connect at say 7am and disconnect at say 7pm. This way the solar and wind inverters would stay separated at night which is when we tend to get the nasty strong wind and I'm not awake to separate the GTI's.
    You should never combine the DC outputs of PV and wind into the same input of a single CC or GTI. The actions that the GTI has to take based on input voltage and current and the need to maintain a load on the turbine even when the PV panels are at full output makes that combination unusable. The possibility of the turbine sending a damaging voltage to the panels is a totally separate issue, and although a series diode on the panels would prevent that, it is still NOT a workable setup.
    And if you have three GTIs you should not be paralleling their DC inputs either. That may work with some plug-and-pray inverters (and enough said about them. We do not support them.) But it will not work with most real MPPT input devices such as UL-approved GTIs.

    Paralleling the AC outputs of GTIs is no problem. They are built for that, unlike off-grid inverters when used without interconnects.
    SMA SB 3000, old BP panels.
  • MO-NHMO-NH Registered Users Posts: 9
    Re: Does a DC switch on a timer exist to automatically break a parallel GTI connection?

    So does that mean that you do not know of any DC breakers or switches on a timer?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Does a DC switch on a timer exist to automatically break a parallel GTI connection?
    MO-NH wrote: »
    So does that mean that you do not know of any DC breakers or switches on a timer?

    Well if you want to use a timer to control a DC relay with sufficient contact rating to shut off the PV input to one or more of your inverters, go ahead. There's no commercially available unit to do this because there is no point to doing it.

    I shall refrain from speculating on why you would.
  • mike95490mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Does a DC switch on a timer exist to automatically break a parallel GTI connection?

    You could use a Solid State Relay, controlled by a seperate timer. There are SSR models rated for DC.
    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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  • NorthGuyNorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Does a DC switch on a timer exist to automatically break a parallel GTI connection?

    DC Relays that can handle more than 24V DC are expensive. For example this one. You will need a timer and a power source on top of this.

    If you're concerned about GTIs working too hard, you'd be better off using bigger GTIs.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Does a DC switch on a timer exist to automatically break a parallel GTI connection?
    MO-NH wrote: »
    To clarify - the GTI's are all stacked in parallel during the day when it's not particularly windy - both the three 600w inverters for the solar panels and the 1000w wind inverter. As a result the 1000w wind inverter is handling a few hundred watts of the solar power. The units all balance out pretty well. What I want to avoid is the three 600w solar inverters getting fed the turbulent power during an overly windy night when I'm asleep and won't be there to manually separate them. The inverters will try to balance the load and since I've heard that it's not a good idea to hook solar inverters to a turbine I'm worried that it would harm the three 600w solar inverters.

    That's why I was asking about a DC breaker or switch of sorts that ran on a timer. I could then set that breaker between the wind inverter and the three solar inverters and it would automatically connect at say 7am and disconnect at say 7pm. This way the solar and wind inverters would stay separated at night which is when we tend to get the nasty strong wind and I'm not awake to separate the GTI's.

    I guess I am confused. What is all this about separating/switching DC when you have separate inverters for wind and solar? What is the bit about "...the 1000w wind inverter is handling a few hundred watts of the solar power"? If you have DC from the wind turbine(s) and DC from PV going into the DC side of the same inverter, don't do that.

    If the inverters have contact only on the AC side you don't have to do anything; the PV inverter is never "handling" any power for the wind turbine. You cannot push AC into an inverter and have DC come out the other side. At night the PV inverters are off, anyway, and have taken themselves off the grid. Nothing you do on the AC side is going to affect them.

    It sounds to me as if you are trying to solve a nonexistent problem.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Does a DC switch on a timer exist to automatically break a parallel GTI connection?
    ggunn wrote: »
    It sounds to me as if you are trying to solve a nonexistent problem.
    Or has a much more fundamental problem of not understanding how the pieces fit together. Which is a constant danger with Plug-and-Pray.
    SMA SB 3000, old BP panels.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Does a DC switch on a timer exist to automatically break a parallel GTI connection?
    inetdog wrote: »
    Or has a much more fundamental problem of not understanding how the pieces fit together. Which is a constant danger with Plug-and-Pray.
    I think my way of stating that was a tad more diplomatic. :D
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Does a DC switch on a timer exist to automatically break a parallel GTI connection?
    ggunn wrote: »
    I think my way of stating that was a tad more diplomatic. :D
    One problem with subtlety and diplomacy is that it is not always understood.....
    SMA SB 3000, old BP panels.
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