SMA grid tie with backup

Hello all,

I'm quite new to SMA products, and have voraciously been reading any and all information about them. Here are some questions, starting with what we're planning to install.

Plans:
1. 45 x Evergreen ES-E 205wp panels
2. 3 x Sunny Mini Central 8000Wp (more solar panels will be added in the next 2 years)
3. 3 phase

Questions:
1. For some reason the Sunny Island 3348 cannot be used for 3 phase operation? Is that right? Why is that
2. can we install 3 x sunny island 5048 into a single battery bank for 3 phase operation?
3. I think 3 x sunny Island may be too much money and too big in capacity for the backup
4. Can we use 3 x 2224 Sunny Island with the above Sunny Mini Central? Someone told me that there's too much power, and that they recommend only 2 x larger grid tied inverter/solar PV installed. I would think that the problem would come from not having enough grid tied inverter/solar PV to charge the battery system, not having "too much".

Thanks!

Comments

  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    Re: SMA grid tie with backup

    Hi,

    I assume you're not in the US, because neither of those products are available there. Would be good to know where this installation will be, because each country has different rules about backup systems and grid tie.
    rabbit_39 wrote: »
    1. 45 x Evergreen ES-E 205wp panels
    2. 3 x Sunny Mini Central 8000Wp (more solar panels will be added in the next 2 years)
    3. 3 phase

    You also have the option of using a single tripower inverter.
    rabbit_39 wrote: »
    Questions:
    1. For some reason the Sunny Island 3348 cannot be used for 3 phase operation? Is that right? Why is that

    Can't answer this one. The 3024 and 4248 are relatively old compared to the 2k,5k and 6kW versions- so it could very well be that they can't be used in 3-phase setups.
    rabbit_39 wrote: »
    2. can we install 3 x sunny island 5048 into a single battery bank for 3 phase operation?

    Yep that's the standard way to do it. 1 battery and multiple inverters.
    rabbit_39 wrote: »
    3. I think 3 x sunny Island may be too much money and too big in capacity for the backup
    4. Can we use 3 x 2224 Sunny Island with the above Sunny Mini Central? Someone told me that there's too much power, and that they recommend only 2 x larger grid tied inverter/solar PV installed. I would think that the problem would come from not having enough grid tied inverter/solar PV to charge the battery system, not having "too much".

    Chapter and verse about this limitation here: http://files.sma.de/dl/7910/SB-OffGrid-TI-UEN111620.pdf
    Basically, if you're going to be grid feeding through the sunny island itself (which is illegal in Germany and I'm guessing other EU countries, but legal in the US) then the twice as much PV as battery inverter rule holds.
    But if you're using the sunny backup system, which includes it's own transfer switch then the amount of PV is limited by the transfer switch, not the inverter. So from the above document, it seems to me that you could do a 3 x 2224 installation if you're using the Sunny Backup, but not if you're using a plain Sunny Island.

    SMA have a response tech support team who can help you out with these questions. The guys in Germany all speak English so if your country's branch can't help you out you can phone them directly.
  • rabbit_39
    rabbit_39 Solar Expert Posts: 43
    Re: SMA grid tie with backup

    Spot on, I'm in Indonesia at the moment. Hardly any codes and regulations here. So I'm using the NFPA 70 as a basis and guideline, applying it with some judgement against cost and safety and practical application here.

    "SMA have a response tech support team who can help you out with these questions. The guys in Germany all speak English so if your country's branch can't help you out you can phone them directly."
    *Polite way to tell me: call the darn support guys? ;) I know, I was just double checking.

    And the document you gave me gave the limit, but not the why. I was just curious why, but I think I have a guess. The Sunny Island has a built in transfer switch that's only rated for twice its own power, I think. So that's why the Sunny Backup which needs to use the AS box is only limited to the size of the box I use. I wonder if I can convince the SMA guys to sell me the Sunny Backup, currently they're not allowing me to buy it for the Indonesian market.

    While I ask those guys at SMA, is there a different way for me to do battery backup for this system? The SI 5048 x 3 is too expensive...but it may be the only way? Aside from the Sunny Backup that is, because currently SMA doesn't want to sell the Sunny Backup in Indonesia.

    Thanks for the great answer!
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: SMA grid tie with backup

    Perhaps you could use three Outback inverters instead: http://www.solar-electric.com/oupoinoffgrb.html
    (I'm assuming 50 Hertz here, but either version can be wired for 3-phase.)

    Where I am one Sunny Island costs almost as much as three Outbacks.
  • rabbit_39
    rabbit_39 Solar Expert Posts: 43
    Re: SMA grid tie with backup

    I guess with the Outback I would also need an external switch. I see that the maximum AC input for the Outback is 30 amps. I guess all this time with the Sunny Island I was expecting it to be able to control the SMA GT inverters and throttle it down to match its input limit. Hmmm...Still have to think about this one a little bit. The Outbacks are cheaper for us as well.
  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    Re: SMA grid tie with backup
    rabbit_39 wrote: »
    "SMA have a response tech support team who can help you out with these questions. The guys in Germany all speak English so if your country's branch can't help you out you can phone them directly."
    *Polite way to tell me: call the darn support guys? ;) I know, I was just double checking.

    Hehe, more of a "better check with the experts" comment. Every country has it's own rules and regs for doing grid tie with backup so the support guys will likely be able to give you much better advise about how you can arrange the system.
    rabbit_39 wrote: »
    The Sunny Island has a built in transfer switch that's only rated for twice its own power, I think. So that's why the Sunny Backup which needs to use the AS box is only limited to the size of the box I use.

    If I was a betting man, that's where my money would be.
    rabbit_39 wrote: »
    I wonder if I can convince the SMA guys to sell me the Sunny Backup, currently they're not allowing me to buy it for the Indonesian market.

    The sunny backup is overengineered for most places. The whole thing was designed for the german market which has very strict rules about anti-islanding. The way it's done in the US version is simpler and doesn't need a whole other box to make it work.... but then you run into the internal transfer switch limitation. How important is it that the changeover during a power outtage must be automatic? Remember that the sunny islands will act as a UPS anyway, when the grid goes down, the loads connected to the sunny islands will continue to function without interruption. It's only the PV output that is switched using the transfer switch. It seems to me that you could essentially do what the AS-Box does using a set of manual switches.

    Victron also make a stand-alone automatic switch: http://www.victronenergy.com/upload/documents/Brochure%20-%20Solarswitch%20-%20SAL064122020%20-%2002%20-%201103%20-%20EN_web.pdf but it has a 25A limit so still not ideal for what you're looking for.

    Another option may be to split the array so that only some of it is available when the grid goes down. I.e. 3 x SI2224 with 4kW of PV on each phase =12kW of PV. Then connect the rest of the PV through another grid tie inverter that won't operate when the grid goes down. Another thing to check with SMA support is whether it's even possible to backfeed the grid through the 2224's internal relay, because this is a US-centric concept and since the 2224 isn't sold in the US... it may not even support it!

    3 x outbacks gives you another option: connect 9kW of PV through a charge controller to the batteries, then configure the outbacks to sell to grid; then connect the rest of the PV to grid tied inverters that will go down when the grid goes down.

    More questions than answers I'm afraid ;)
  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    Re: SMA grid tie with backup
    rabbit_39 wrote: »
    I guess all this time with the Sunny Island I was expecting it to be able to control the SMA GT inverters and throttle it down to match its input limit. Hmmm...Still have to think about this one a little bit.

    It does. But not when connected to the grid.
  • rabbit_39
    rabbit_39 Solar Expert Posts: 43
    Re: SMA grid tie with backup

    I'm not trying to sell to the grid at any time, BTW. Even though there is a feed in tarrif of about $0.07 per kWh, the state owned (only one) utility company won't allow us to sell back.

    So all of this is really only for backup purposes, and the customer wants the whole house backed up, hence the "want" for 3-phase backup system.

    I wonder if I can just give him a manual changeover switch to a backup junction box. And his critical loads are hooked up to this junction box also. Just like what stephendv said: " It seems to me that you could essentially do what the AS-Box does using a set of manual switches."

    Let me think about that...So the AC out of the Sunny Island 5048 will go to a separate junction box, that needs to be manually switched over so the critical loads will disconnect from the grid into the output of the SI 5048. Possible...possible...I'll have to see if the client will go for that. :D But would the frequency control still work? The GridTied inverters are looking for the frequency control from the output of the SI 5048 right?
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: SMA grid tie with backup
    rabbit_39 wrote: »
    I'm not trying to sell to the grid at any time, BTW. Even though there is a feed in tarrif of about $0.07 per kWh, the state owned (only one) utility company won't allow us to sell back.

    So all of this is really only for backup purposes, and the customer wants the whole house backed up, hence the "want" for 3-phase backup system.
    If this were a simple GT system, how would you implement it so that it never pushes power onto the grid when the PV is running full tilt and the household loads are low?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: SMA grid tie with backup
    ggunn wrote: »
    If this were a simple GT system, how would you implement it so that it never pushes power onto the grid when the PV is running full tilt and the household loads are low?

    Haven't we seen that problem before? :D (A Xantrex with "SELL" turned off maybe.)

    Based on info I gleaned from his posts I suggested the Outbacks: grid when available would charge batteries and power loads, when not available loads run off batteries, charging can be supplemented by solar, and they can be configured for 3-phase. That's what I thought he was going for anyway.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: SMA grid tie with backup
    Haven't we seen that problem before?

    Just in case the OP hasn't seen that problem discussed here:

    http://forum.solar-electric.com/showthread.php?16309
    http://forum.solar-electric.com/showthread.php?16619

    Both of these threads are long, and at times off on tangents. But a good read with some interesting links. The second thread has a link to EMMA by coolpowerproducts.com which looks like a solution. --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: SMA grid tie with backup

    If you're not selling to the grid and the system isn't distributed over a big area, then there's not a good reason to go for the Sunny island + sunny boy solution. It would be cheaper to just install 3 battery based inverters and use charge controllers to charge the batteries as cariboocoot suggested.
  • rabbit_39
    rabbit_39 Solar Expert Posts: 43
    Re: SMA grid tie with backup

    I figured it would be cheaper to use GT inverters because there is quite a bit of electric usage during the day. The batteries would just be there to back up some critical systems. He would like the batteries to supplement at night also (instead of just a backup), which is probably why I would use the Outback in HBX mode.

    Also, the meters are one way, so even if I had extra energy, it can't be pushed to the grid. That's what I was thinking anyway.

    Thank you for the discussion, I'm learning a lot from you guys. And hopefully some day I can help others like you guys are helping me. :D
  • rabbit_39
    rabbit_39 Solar Expert Posts: 43
    Re: SMA grid tie with backup

    I have an SMA engineer coming in from Germany tomorrow to train us on the products and installation. I've had a chat with him and it seems that the Sunny Island/Sunny Boy (or other SMA GT inverters) will work together on making sure the system works without producing too much and pushes the energy to the grid. The Sunny Island will alter its frequency as a signal for the GT inverters to reduce its output all the way down to 0% if necessary...

    We have had several outback systems installed, a few in HBX mode with the charger turned off (in the inverter/charger unit) so that the grid never charges the batteries. Whatever the solar PV panels can gather for that day, that's what's used by the home. Easy to figure out the savings of the system.

    Then we have a truly off grid system with Outback that has a genset hooked up as back up. When (if) the batteries are low, then the genset comes on. We designed it so that the system rarely ever uses the genset. 12kWp system (average input to the batteries 36-43kWh on a sunny day) when the usage is 27kWh/day. I know this is a bit less than the 50% rule, but because this is a commercial system, we have to worry about the financial also. We had put in 15kWp initially but it proved to be too much (several hours of floating even on cloudy days). With 12kWp, and 30 days monitoring the batteries get filled to 100% (floating at least 1 hour) at least once a week even during extended cloudy and rainy days. We're on our 3rd 30 day monitoring cycle and it's still doing pretty good. Will have to see what happens during the rainy season.
  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    Re: SMA grid tie with backup

    I'd be very interested to hear his opinions on:
    - What is the maximum ratio of PV panel to battery inverter if you're not going to be selling to the grid through the SI?
    - What is the minimum battery capacity to PV ratio?

    EDIT:
    and if I can add one more: If you had load controls on the consumer side could you change any of the above ratios? E.g. if you had a 20kW PV plant, a 2kW Sunny Island and you had an AC load controller that could dump 18kW based on frequency, could the setup work?