grid powered solar panel usless in blackout. Alternative use to charge battery?

st2288st2288 Registered Users Posts: 9
Thanks to Hurricane Sandy, we were out of power for 7 days. Meanwhile I have 9KW grid tie system tie to the LIPA,which became totally useless..Of the 9kw system , I have a sting of 5 200watt panels (each with micro-inverters) which I can access quite easily. (The string of 5 micro-inverter is isolated from the rest of the system) They are tie into a circuit breaker to my main circuit panel.
My question:
Can I put a Y-cable on the 200 watt panels (one feeding the micro-inverter, and the other one wired parallel with other solar panels) I will use the parallel wired panels to hook up a solar charger to charges a bank of deep cycle marine batteries. I will then attach the a pure sine wave inverter to feed my transfer switch.

I have a shut off breaker for the micro-inverters which will be off when I need to use the panels to charge the battery bank.

Will this work?

Thanks
Thanks

Comments

  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: grid powered solar panel usless in blackout. Alternative use to charge battery?
    st2288 wrote: »
    Thanks to Hurricane Sandy, we were out of power for 7 days. Meanwhile I have 9KW grid tie system tie to the LIPA,which became totally useless..Of the 9kw system , I have a sting of 5 200watt panels (each with micro-inverters) which I can access quite easily. (The string of 5 micro-inverter is isolated from the rest of the system) They are tie into a circuit breaker to my main circuit panel.
    My question:
    Can I put a Y-cable on the 200 watt panels (one feeding the micro-inverter, and the other one wired parallel with other solar panels) I will use the parallel wired panels to hook up a solar charger to charges a bank of deep cycle marine batteries. I will then attach the a pure sine wave inverter to feed my transfer switch.

    I have a shut off breaker for the micro-inverters which will be off when I need to use the panels to charge the battery bank.

    Will this work?

    Thanks
    Thanks
    I have contemplated the same question, but never tried it. I wondered if the non functioning inverter would short the output of the panel. It could be done with a Latching Relay where you just took the inverter out of the equation.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: grid powered solar panel usless in blackout. Alternative use to charge battery?
    I wondered if the non functioning inverter would short the output of the panel. It could be done with a Latching Relay where you just took the inverter out of the equation.

    The one thing which you want to avoid is to have two different MPPT type devices connected to the panels at the same time. They will fight over who gets the power, creating an unstable situation. But the inverter or charge controller which is switched off should not present any load to the panels (except maybe a trivial amount to power the inverter's controls.)
    SMA SB 3000, old BP panels.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: grid powered solar panel usless in blackout. Alternative use to charge battery?
    inetdog wrote: »
    The one thing which you want to avoid is to have two different MPPT type devices connected to the panels at the same time. They will fight over who gets the power, creating an unstable situation. But the inverter or charge controller which is switched off should not present any load to the panels (except maybe a trivial amount to power the inverter's controls.)

    no fight involved with no grid power being present. i believe the question might be one of how the gt inverter circuits would react if the pvs were paralleled. to me i don't think the gt inverters would know the difference, but this is a circumstance when the grid is up of having a common pv source to separate inverters and then back to a common load. i'm not real sure if the same rules would apply to these gt inverters as they would to controllers and would be a question that would warrant an answer from some of the inverter manufacturers if there would be any problems in doing this. if it is a problem then i would say you could still be able to wire them in parallel with the main entrance breaker to the grid to remain off and the physical access of connecting/disconnecting of the paralleled pvs to be done at the pvs that would need to be changed over each time depending on if the grid is desired or not at the time.

    st2288,
    what would you have done with the paralleled pv outputs if you had it at the time? do you have a large battery bank and cc to run off of the pvs, plus an inverter for key ac appliances and if so then what would be maintaining the batteries when you are grid tied as those pvs would now be disconnected from the battery bank(if said to not be viable in being connected to the cc while grid tied)? people that opt for gt for its higher efficiency take the chance of a long term outage occurring that would also make the system useless
  • st2288st2288 Registered Users Posts: 9
    Re: grid powered solar panel usless in blackout. Alternative use to charge battery?

    this is what i have in mind.. I just got a APC UTS6H Universal Transfer Switch. The beauty of this switch is it has dual input (Generator or UPS) in case there is a blackout. I will connect a Xantrex prowatt pure sinewave inverter to the UPS input and attach 2 deep cycle marine batteries. (I may buy two more later on) And then attach a MPPT charge controller to the batteries.
    Turn the breaker off the micro-inverter. Use the Y-cable for 2 or 3 panels and tie them parallel to the charge controller. This way I can use the solar during daytime (I average about 4kw hr during the blackout), and use a honda su2000i inverter generator at night. My panels are 200 w each.
    Once the gird comes back on, the transfer switch will auto switch back to grid. then I can shut down the inverter and charge controller. (using a boat battery switch) . Power the micro-inverter breaker back on.
  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: grid powered solar panel usless in blackout. Alternative use to charge battery?

    I guess it'll always be a roll of the dice as to whether your PV's are involved in the disaster in some way. The one time in 30 years I could have used the PV.s they were covered with 3" of ice for 10 days. I opted for the Inverter and a bank of 4 GC-2's and a 75 Amp charger for my Honda. A couple gallons of gas I am good to go. It looked like in Sandy if you didn't have the Inverter mounted on the roof you were out of luck.
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: grid powered solar panel usless in blackout. Alternative use to charge battery?

    Another option is "AC coupling" to connect the output of your grid tie inverters to the output of certain battery based inverters. Here's a page describing the concept: http://www.wholesalesolar.com/AC-coupling.html

    Caveats:
    - Can only be done with certain battery based inverters, e.g. Xantrex XW, some Magnums, the much bigger outback radian and Sunny Island.
    - The battery inverter must be sized to match the output of the grid tie inverters. You mention a 9kW system with 1kW of that on micros. If you have 2 x 4kW inverters for the rest, then you could tie one of those to a 4kW battery inverter.
    - There is a minimum battery size recommended per kW of connected panels, you'll have to check with the battery inverter manufacturer to confirm.

    For very rare events, this is an expensive solution compared to something like a Honda inverter/generator.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: grid powered solar panel usless in blackout. Alternative use to charge battery?

    yes, i forgot about the backfeeding on inverters. that can be shakey to do if you don't know what you're doing.

    i don't think he had this in mind though as he's seeking a simpler solution in paralleling the pvs for a battery based dc solution for batteries. the fact that all of the pvs would be paralleled while at the same time selling to the grid is the problem. the pvs may need to be auto disconnected when the inverters are feeding the grid. if they feed the grid then they aren't being used to upkeep the batteries in the first place. maybe your real solution is to take some of the gt inverters out of line and have those pvs feed a brand new inverter that can sell to the grid with battery backup without even acknowledging that some of the so called ac panels may backfeed the new inverter adding extra capacity available while the sun shines.
  • st2288st2288 Registered Users Posts: 9
    Re: grid powered solar panel usless in blackout. Alternative use to charge battery?

    Thanks for all the replies. I basically just want the CC, batteries and a pure sine wave inverter as a blackout backup solution along with a honda su2000i generator. The reason i want a solar as a part of the backup was Gasoline was tough to come by during Sandy.

    I guess the easier way is to disconnect a couple of the PV and connect them to the CC when there is a blackout. As for the
    up keep for the batteries, I can get a 50-100 w PV connected to the CC to maintain the batteries. I am also thinking about making a switch at the panel to switch between micro-inverter and the CC.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: grid powered solar panel usless in blackout. Alternative use to charge battery?

    The overriding problem is that a grid tied inverter is a current source. When it's connected to the grid there is a nearly infinite sink for that current to flow into at a clamped voltage, but in a microgrid environment you must have some way of throttling back the inverter's output to match the demands of the load. You cannot draw current on demand at a constant voltage from a GT inverter like you can from a battery inverter. Also, what happens when the demand exceeds the output of the inverter? This is why off-grid systems use batteries, to buffer the output of the inverter and supply current on demand to the loads. These forums are chock full of schemes to fool a GT inverter into thinking the grid is up without using batteries or by using tiny batteries compared to the demands of the load. To date and to my knowledge, none have been successful.

    UL1741 is there to ensure that a GT inverter does not try to energize the grid when the grid is down, but it is in a way just legislating what physics has already decreed. When the grid is down it appears a a virtual dead short to the inverter because of all the loads still on line, and it would require nearly infinite current output to bring the voltage up. UL1741 notwithstanding, you aren't going to power up your city's grid with your puny little 5kW inverter.

    There is a right way to do this, but it ain't cheap.
  • solarixsolarix Solar Expert Posts: 713 ✭✭
    Re: grid powered solar panel usless in blackout. Alternative use to charge battery?

    SMA recently announced a new inverter that has an emergency capability. During an outage you can go flip a switch and it will disconnect from the grid but then turn on a dedicated output that you can connect to 1 outlet and get 10amps of power even without any batteries involved! (only while the sun is shining strong of course) What a great idea! I'm sure it it is inefficient but who cares, probably doesn't even add much to the inverter price. With 10 amps part of the day, most households could survive an outage quite well. I suppose the inverter is slewing around the array power point to match the input power with the output power close enough to be within the internal cap bank's ability to keep stability.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: grid powered solar panel usless in blackout. Alternative use to charge battery?

    is that 10a at 12vdc, 24vdc, 48vdc, 120vac, or 240vac? good to have when there's nothing else in any case.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: grid powered solar panel usless in blackout. Alternative use to charge battery?
    niel wrote: »
    is that 10a at 12vdc, 24vdc, 48vdc, 120vac, or 240vac? good to have when there's nothing else in any case.


    That is 10 amps at 120 volts, I believe. Since the exact same backup output is available from the 3000, 4000 and 5000 models, I do not think it could be 10 amps at 240 volts. The PV you would normally attach to the 3000 just could not handle it.
    SMA SB 3000, old BP panels.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: grid powered solar panel usless in blackout. Alternative use to charge battery?
    inetdog wrote: »
    That is 10 amps at 120 volts, I believe. Since the exact same backup output is available from the 3000, 4000 and 5000 models, I do not think it could be 10 amps at 240 volts. The PV you would normally attach to the 3000 just could not handle it.
    It is a single 120V outlet mounted under the inverter. I saw it at SPI. I don't know if it's available in the States yet.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: grid powered solar panel usless in blackout. Alternative use to charge battery?

    you were at spi in pa?
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: grid powered solar panel usless in blackout. Alternative use to charge battery?
    niel wrote: »
    you were at spi in pa?
    I was at Solar Power International in Orlando in September.
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