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ReadiesCards

Multiple independent AC inverters

21 posts in this topic

Following on from:

 

As I'm building offgrid I've gone heavy on the solar PV (30 Solarworld 285W installed on two roofs). As per the above question I've 5 of the panels connected to 3 charge controller/batteries/inverters powering various temporary circuits during the build.

 

I'm wondering if I can use that concept in the final solution, so having a number of mid-power battery bank & inverters systems connected to a number of consumer control units rather than one big inverter and one big battery bank connected to one consumer control unit.  So say the lights, downstairs ring mains, upstairs ring main, security cameras, fridge freezer are all totally independently powered (the circuit tails are all in place to do this).

 

There are various reasons why I want to do this but firstly CAN it be done?  While I can ensure a common earth for the inverters, I've no idea if the inverter AC sides need to be 'tied' or as long as I never connect anything from one circuit it will work without danger and if there are any specific precautions I must take.

 

Thanks

 

 

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ID: 2   Posted (edited)

you can use individual inverters, but you cannot connect the outputs together unless your inverters are capable of synchronsing with the others or you may end up with some smoke escaping and no way to get it back in...

 

you also seem to be working a bit backwards. instead of trying to go to 230v for everything, it would probably be easier to get 12v lights and anything else you can

Edited by Andy™
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40 minutes ago, ReadiesCards said:

Following on from:

 

As I'm building offgrid I've gone heavy on the solar PV (30 Solarworld 285W installed on two roofs). As per the above question I've 5 of the panels connected to 3 charge controller/batteries/inverters powering various temporary circuits during the build.

 

I'm wondering if I can use that concept in the final solution, so having a number of mid-power battery bank & inverters systems connected to a number of consumer control units rather than one big inverter and one big battery bank connected to one consumer control unit.  So say the lights, downstairs ring mains, upstairs ring main, security cameras, fridge freezer are all totally independently powered (the circuit tails are all in place to do this).

 

There are various reasons why I want to do this but firstly CAN it be done?  While I can ensure a common earth for the inverters, I've no idea if the inverter AC sides need to be 'tied' or as long as I never connect anything from one circuit it will work without danger and if there are any specific precautions I must take.

 

Thanks

 

 

 

This is a totally different scenario to your other question on routers, you did not give this information there, ow if you have totally different a.c. supplies from different origins, then I would not be prepared to even contemplate what could happen.

 

Why did you not describe this scenario in your other question, because whilst the ethernet comms side is isolated the earth side is not, so, you would be commoning up earth paths in your comms system.

 

You need to take a more holistic view of this first.

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firstly you need off grid inverters - no needs for mains coupling. There's no harm in having multiple systems, but then there's nothing to stop you having multiple charge controllers connected to single bank of batteries either, to which you could also connect a generator or other power source such as a wind turbine.

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This is the rough concept. The capacity of each of the 3 systems would be different so I can fine tune the battery bank capacities as I live in the property.  Larger for those house circuits needed to get through the night.

 

10 hours ago, binky said:

firstly you need off grid inverters - no needs for mains coupling. There's no harm in having multiple systems, but then there's nothing to stop you having multiple charge controllers connected to single bank of batteries either, to which you could also connect a generator or other power source such as a wind turbine.

 

Generator sitting in barn waiting to be added into system (and the site is pretty windy so am also considering a wind turbine but want to live there a year first before going down that route because of the associated servicing).

 

I'm considering the proposed layout becuase:

* it gives me some resilience (I swap systems around if any element fails)

* it allows me to have a flexibly system I can grow as needed

* the mini-charger controllers should give better management of each battery

* potentially it is cheaper to start up

* each house circuit can be optimized e.g. I don't need a massive battery bank and big invertor sitting there just in case we decide to run the washing machine at 3am in the dark

 

Daft idea/downsides?

FieldCottage-Multiple-Invertors.png

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No earthing on the ac side for ADS, unless the ac side earth is common to the dc side -ve.

I would caution you to be sure that the system is done correctly if you are not going to earth the ac, not as easy as it may seem.

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5 hours ago, ReadiesCards said:

This is the rough concept.

 

3 systems supplying a single circuit?

 

3 hours ago, Sidewinder said:

No earthing on the ac side for ADS, unless the ac side earth is common to the dc side -ve.

 

DC side -ve is earthed in the drawing.

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dont forget many inverters are internally wired as IT

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9 minutes ago, Lurch said:

...

DC side -ve is earthed in the drawing.

 

I saw that, but, is the ac side earth connected through to the dc side -ve?

If not, then the ac side is unearthed.

Personally my gut feeling is that there would be separation, though this would obviously need checking.

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2 minutes ago, Sidewinder said:

I saw that, but, is the ac side earth connected through to the dc side -ve?

 

I'm guessing we're just interpreting this drawing differently. I would say that drawing is saying that the AC side earth is connected to the DC side -ve. I suppose technically we could have DC ground and mains ground with no interconnection, which is what you are getting at?

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What would the potential be across the inverters,?

As they aren't sync'd to each other, would the 3m rule be sufficient,? Or how would separation be achieved,? 

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have a look here for info / books

http://info.cat.org.uk/

 

The only DC earthed panels I've seen were the old style 'thin film' type, I don't think this is relevent to todays technology.

 

Couple of things though, water is best heated via thermal panels.

Avoiding converting from DC to AC is a lot more efficient, so would limit AC stuff to machinery that you can only buy as 240V like washing machines. Avoiding all power consuming items that you don't need like CCTV is also a good idea

A wind turbine is definetly a good idea as these can work 24/ 7 if you are in a windy spot

Don't use lorry batteries - wrong technology.

 

I kind of get the impression you are trying to have a 'normal house' and making renewable energy sources fit that expectation - you may get rather disappointed. The nature of renewables is that they are rather variable in output especially during winter months, so a genie is almost certainly a necessity. Reducing loads is essential. A lot can be done with PV / wind etc etc, but there are limits.

 

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4 hours ago, Lurch said:

 

I'm guessing we're just interpreting this drawing differently. I would say that drawing is saying that the AC side earth is connected to the DC side -ve. I suppose technically we could have DC ground and mains ground with no interconnection, which is what you are getting at?


Yeah, looking at this from the opposite way to say a machinery power supply for controls would be separated, so to get ADS, you have to earth the dc -ve at the output of the PSU.

 

The way I am interpreting this is that the dc -ve is earthed, I would expect separation in the dc-ac inverter, thus I am expecting the ac side not to be connected to the dc side directly, thus I would expect that there is no earth path on the ac side as this is drawn.

The data needs to come from the inverter OEM.

I would also be a bit wary of all of these separate supplies, as they would be slightly out of sync and you could get a potential between the lives of different circuits.

I would expect the ac to be earthed, and all the earthing interconnected though.

 

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9 minutes ago, Sidewinder said:

 

I would also be a bit wary of all of these separate supplies, as they would be slightly out of sync and you could get a potential between the lives of different circuits

 

 

I was kinda hoping you were going to answer my post #11   ;)

 

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I'm doing what I can to reduce electrical load (LPG kettle, hob and oven for instance) and the house is being well insulated, I'm trying to reduce the 24*7 power as far as possible (the non-electrical sewage treatment plant being a jolly expensive item I had not considered when starting this journey).  I am expecting to run the genny, especially in the winter months. And the only way I can see to fit a genny into my concept is to have multiple battery chargers driven by it or some massive switch that can switch out all the battery banks and switch in the genny.  Wind Turbine still considering.

 

The diagram in this post was suppose to show the different power banks running different circuits, so yes I expect the lives to be out of sync but does that matter - I can't think of a situation where I might need to connect the lighting circuit and the downstairs ring main together for instance.  As a DIY'er I don't know what ADS is or the 3m rule. So clearly have some research to!

 

For a simpler 1 inverter solution the Victron Quattro is my preferred option but I'll look at SMA again - thanks for the link @binky

 

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@ReadiesCards

The 3 inverters out of synch could end up like some sort of weird 3 phase system, where although each of the 'lives' would be 230v , they could all have a different voltage potential across them, 

It's not really as simple as just having 3 different supplies.

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Victron is good gear.

 

I haven't done much with totally off-grid systems, but basically your battery bank is the 'hub' of the system, every source of energy charges the batteries, then every load is fed via an inverter or direct from the batteries if using low voltage lighting for instance.

 

I've worked on several solar farms, some have lots of 20kW inverters, some have big central inveters. Personally I prefer multiple small inverters as a system - it's easier to install and in my mind, more efficient due to increased number of MPPTs.

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Ok seems one battery bank and one inverter keeps things simpler - I was just not sure that was a truely optimized solution (when cost and future expansion are included in the picture). Thanks for all the useful input.

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would be far easier with 1 inverter and a changeover switch for the generator

 

 

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ID: 21   Posted (edited)

wouldn't need changeover switch, if genie is running charge controller would prevent PV from inputting to batteries, likewise whatever tells genie to start-up due to load/ flat batteries should register input from PV, and from what I've seen of off-grid genies they run according to demand/ autostart. I suspect Victron do an integerated control system for the lot!

 

I understand what ReadiesCards is trying to do with multiple systems, depending on the various roof orientations, I would suggest an inverter per roof space would probably work better and allow access to more MPPTs giving greater optimisation of the system. If shading or trees (leaves from, and where there are trees you get birds and poo) then as much as I like Solarworld, Jinko have just released a panle with MPPTs built into the panel to give optimisation at cell level, which looks very interesting.

 

Jinko is Chinese, but as the panels are heavily regulated by MCS and employ ISO9000 quality standards overlooked by TuV of Germany (they have an office in the far East) I don't have a problem with Chinese panles. Inverters are not regulated in the way panles are, therefore I do have big issues with Chinese products...

Jinko Maxim Commercial Flyer(1).pdf

Edited by binky
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