Multi-system, sharing/grid tie/redundancy ideas requested Sorry for the complicated post

I have much experience now with Xantrex system integration and have been a little disappointed by the bugs and problems with their Xanbus. I am looking for a possible alternative for an expansion that my friend and I are planning for his system.

Currently the systems is as follows:
2 x XW inverters in master/slave mode on two separate battery banks, each bank 16x 250AH 12V AGM.
2 x MPPT60-150 chargers each with their own set of 3200W of panels each charging one of the banks of batteries, switchable between battery banks or parallel charging of each.
1x System Control Panel
2x Battery chargers, 1 each for each bank.
1x 5kW generator with an AGS

The system is a mission critical system and has been setup so that there are many ways of keeping redundancy depending on cloud, cold, lack of fuel, or lack of city power as a backup.

The system supplying power to 12 (soon to be 15) astronomical observatories. The idea for the original expansion of the system was to be able to double the system capacity while not not having to be concerned about mixing old batteries with new, and not to have too many batteries in parallel and all the problems that can cause. Using to inverters running in parallel also meant having redundancy should something go wrong with one half of the system or batteries. The setup also allowed for the two solar chargers to charge one battery bank should it be necessary.

The generator can be connected to the generator inputs on the inverters, or to the chargers which charge the batteries directly. In this way the generator can be used to charge the batteries directly during the night should they get low and without needing to be the source of power directly to the loads. In this way power quality is preserved and there are no switch over glitches. Should there be a need to have the generator power the loads directly and possibly charge the batteries, then the generator can be connected to the AC2/GEN inputs on the inverters. There is also a bypass to have the generator run the loads completely independently should it be necessary.

In addition to this, there is the option to supply the system using an external AC line to the AC1 inputs on the inverters and/or the battery chargers. It is preferred that the external AC line is used only to assist the batteries directly through the chargers as the quality and reliability of the AC power can be very poor. BUT....

The external AC line can also be switched to another solar system which has good quality but lower capacity.

So the preferred operation is as follows.

Normal operation:
1. Run one inverter in master, run the other in slave and have the slave take the biggest share of the load so that if a battery bank is going to go too low it won't be the master.
2. Should the batteries reach a low voltage state, then turn on the external AC line to the battery chargers so that they can prop up the batteries. This charging state from the external source will not shutdown until the panels can take over the demand when the sun finally rises.
3. Should the batteries not receive a charge sufficient to keep them from getting critically low, start up the generator and have inverters do their thing with a qualified AC2/GEN supply. Shut down the generator when reaching absorb or float.

Short period cloudy operation:
1. Run one inverter in master, run the other in slave and have the slave take the biggest share of the load so that if a battery bank is going to go too low it won't be the master.
2. Manually switch the system to generator charging mode should the batteries reach a low voltage state, then turn on the generator to the battery chargers so that they can prop up the batteries. This charging state from the external source will not shutdown until the panels can take over the demand when the sun finally rises or if it does and the batteries reach float. It is not always the case that there are cloudy nights and days, sometimes it will be cloudy all day and clear all night. That is the worst case scenario for an astronomical observatory power usage.

Long period cloudy operation:
1. Turn off all loads except those needed to maintain minimum operation.
2. Run one inverter in master, run the other in slave and have the slave take the biggest share of the load so that if a battery bank is going to go too low it won't be the master.
3. Manually switch the system to generator charging mode should the batteries reach a low voltage state, then turn on the generator to the battery chargers so that they can prop up the batteries. This charging state from the external source will not shutdown until the panels can take over the demand when the sun finally rises or if it does and the batteries reach float.

Half system maintenance mode:
1. Run one inverter in master only. Switch both solar charge controllers to the one operation battery bank.
2. Should the batteries reach a low voltage state, then turn on the external AC line to the battery chargers so that they can prop up the batteries. This charging state from the external source will not shutdown until the panels can take over the demand when the sun finally rises.
3. Should the batteries not receive a charge sufficient to keep them from getting critically low, start up the generator and have inverters do their thing with a qualified AC2/GEN supply. Shut down the generator when reaching absorb or float.

Full maintenance mode:
1. Connect the generator to the loads directly and shut down the solar system.


Now this all seemed possible and "easy" with the Xantrex system and the descriptions of the functions as provided in the manuals. But you guessed it, it doesn't work. For one, it is impossible to get the inverters to agree on voltages, currents, AC line voltages etc... They are just not accurate enough with their metering to get close enough. Well they get close but it feels like performing a ritual instead of implementing calculated settings.

The Xanbus is a bit of a joke IMHO.

For example,none of the controllers or inverters can see the actual state of the batteries from an aggregate of the the information. When one charging system sees that the charging current has dropped below the 2% threshold to switch to float mode, from its perspective only, it does so whether or not the total charge current going to the batteries is far more than that or not. Yes I know it says so in the manuals. This can result in the remaining chargers not having sufficient charge current to finish the charge. None of the Xantrex devices with AUX relays have state change criteria of bulk, absorb or float states. The slave inverter MUST have the master online or it too goes offline..... There also seems to be so much buss traffic it overloads sometimes.

So in the plans of the next doubling of capacity I have been given the enviable task of trying to sort out a system that will be a bit different. First of all I am going to split the double system we have now to two systems and split the loads. Then I want to investigate a masterless grid sharing system that automatically start grabbing power from the remaining systems should a system go down. The philosophy here is to have a fully redundant system made up of four system blocks, each with the capability to start the generator and charge their individual battery banks, or steal from another outside source as the current system can.

Can this be done with any available inverter or system? If not totally possible using the built in capabilities of the inverters or accessories, are there any inverters that will grid share without a master and that can be controlled using some kind of buss and an external custom controller or computer? The base capabilities of the XW series is what I wanted, but I have very little confidence that I can make them dance the way I want even with an external controller. That is especially with little or no information from SE/Xantrex on the control protocols. Maybe I just haven't found it yet.

Thank you to anyone who takes the time to read and try to comprehend my convoluted question.

Comments

  • Eric L
    Eric L Solar Expert Posts: 262 ✭✭
    Re: Multi-system, sharing/grid tie/redundancy ideas requested Sorry for the complicated
    So in the plans of the next doubling of capacity I have been given the enviable task of trying to sort out a system that will be a bit different. First of all I am going to split the double system we have now to two systems and split the loads. Then I want to investigate a masterless grid sharing system that automatically start grabbing power from the remaining systems should a system go down. The philosophy here is to have a fully redundant system made up of four system blocks, each with the capability to start the generator and charge their individual battery banks, or steal from another outside source as the current system can.

    I'm hardly an expert with anything this complicated, but since no one else has piped in I'll offer a hunch: it's probably not possible to do this using off-the-shelf equipment given that you want it to be masterless. Something has to provide a reference for the various connected sources to sync to for frequency, phase, a reference system voltage, and so on. If there is no master, what do you think will do this?

    I'm not sure why you want this set up to be "masterless". Is it that you think it will offer greater redundancy? How about if the system had a master inverter for reference but the hierarchy was 'flat' otherwise, in the sense that any element could be swapped out while the system continued working? Would that be enough? If so, the SMA Sunny Island might work. It can do most of the rest of what you seem to want. NAWS has a link the the North American model's manual here, under the "details" tab:

    http://www.solar-electric.com/suis5050waba.html
  • Les Nagy
    Les Nagy Solar Expert Posts: 121 ✭✭
    Re: Multi-system, sharing/grid tie/redundancy ideas requested Sorry for the complicated

    Yes I know a masterless system is a bit of a dream, but it should be possible in principle. The first inverter on the "grid" if it sees no AC waveform it just does its own thing. The next one to come online, and all subsequent ones, if they see an AC waveform on the grid, they just follow the signal they see. An "automaster" if you wish.


    I know I am unlikely to find such an inverter. What I would really like to know is if there is a grid tie/stand alone inverter that has a good communication buss that doesn't overflow or saturate and can be commanded by a computer or other external controller. The Xantrex Xanbus seems very unstable and there is no published way to control the inverters except through their XWConfig program which does not have external API that I can see.

    I guess if I have to make a dedicated external transfer/switching/sharing panel, I guess that is what I will need to do.
  • Eric L
    Eric L Solar Expert Posts: 262 ✭✭
    Re: Multi-system, sharing/grid tie/redundancy ideas requested Sorry for the complicated

    Given that you and whoever is paying for this are going to be replacing a lot of very expensive equipment with a lot of very expensive equipment, I think you have a reasonable claim on the time of one of the representatives of the few companies that might be able to help design something like this (SMA and Outback come to mind). You're paying their salary, after all.

    SMA inverters (and disclaimer: I have zero first hand experience with them) seem like they can do what you basically want: they can be arranged in a "multicluster" with each inverter or inverter cluster assigned to its own battery bank while all are networked into a single grid, they are designed for multiple redundancy with grid support, gen support, etc., they are designed to make increasing the system size easy (allegedly), and so on.
  • Les Nagy
    Les Nagy Solar Expert Posts: 121 ✭✭
    Re: Multi-system, sharing/grid tie/redundancy ideas requested Sorry for the complicated

    Thanks for the replies. I will email the manufacturers and see what they have to say.