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Author Topic: DIY ON grid solar PV battery storage (mainly a question about inverters)  (Read 14394 times)
Ted
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« Reply #45 on: May 05, 2015, 01:19:59 PM »

My interpretation would be the same I think. If there is synchronisation with the grid then it is in parallel.
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« Reply #46 on: May 05, 2015, 01:30:15 PM »

Yep , then propably conecting the FiT harvesting PV  to the AC-In side of a Victron , SMA or Studer is a solution ....., then ....

or direct DC feed the Battery  and  use all AC  trough an Inverter above (that has a  Grid back-up)  (and accept some losses )


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ProDave
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« Reply #47 on: May 05, 2015, 01:34:39 PM »

Here's a picture of what I am wanting to achieve




I still don't see any of the off the shelf solutions doing that as simply as that. They all seem to want to route all power used via the big inverter.

All I want is to store surplus PV to a battery bank. Then when there's no PV generation, use that power to offset some of my usage but making sure i never export any battery power (so inverter power from the batteries is never greater than usage) If there's more excess solar PV than the batteries can accept then that will go to the immersion heater.

And it's the variable power grid tied inverter that has me stumped at the moment.

Perhaps I am confusing you all with the term grid tied?  Whatever the correct term is, whatever inverter(s) I use must synchronise to the incoming mains frequency.

EDIT

apologies for the typo in that drawing semand should be demand.
« Last Edit: May 05, 2015, 01:43:25 PM by ProDave » Logged

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billt
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« Reply #48 on: May 05, 2015, 02:06:34 PM »

my take on it is this, when connected to 'AC2' it does not 'synchronise' so does not need certification, but bear in mind I'm no authority. When the generator starts on any 'off grid' inverter the inverter only acts as a 'transfer switch' and all loads are supplied directly from the generator/grid. This is why so many people have problems with washing machines 'off grid' when their generator is running because the sine wave produced by the inverter is better than any generator.  This is the same as in any UPS system and as far as I'm aware none of those need G83 certification. There is no sharing of loads and the inverter is not 'synchronised' or in parralel with the grid/generator.

Having said all that I would really like to know for sure, not that I ever plan going 'on grid' but it would be nice to know.

Cheers, Paul

The Sunny Islands can be used either as "battery back up systems" or "battery backup systems with increased self consumption" as well as off grid systems, so they can be set up to backfeed power to the grid on the AC2 connection. AFAICS that means they cannot be legally attached to the grid without an expensive add on G59 relay.

Presumably the Victrons et al can't back feed to the grid so they should be OK.
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« Reply #49 on: May 05, 2015, 02:07:55 PM »

Paul, the Marina analogy is a good one & Victron must have it sorted, because that sort of thing is their bread & butter.

Do you get Sunny Islands used in such cases too?

My interpretation would be the same I think. If there is synchronisation with the grid then it is in parallel.
Setting 250.11 AfraEna, is described as "Automatic frequency Disable synchronization (AFRA) Enable (expert mode)" and is considered "relevant for off-grid systems" (page 8, SI30M-44M-60H-80H-BE-en-30 Operating Manual), so turning off synch looks at least a possibility.

However, on page 94, the list of possible states for 132.01 GdStt, described as "Status of the management for the operation on the utility grid (expert mode)" don't seem to include a status that equates to connected but not synchronised, unless maybe the SI simply stays in state 2 (Init (2) Utility grid has been detected.) if  AfraEna has been disabled?

As CM has might say, for details like this the manuals probably make sense to people who've been on the courses and are just using them as a memory jog, but as a means of finding an answer to a question it's not so easy. The obvious  solution is to ask SMA (or maybe a UK dealer)?

[Edit: Cross posted with  billt who seems to share my analysis, i.e. it's either connected & synchronised, or not connected.]
« Last Edit: May 05, 2015, 02:11:21 PM by skyewright » Logged

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David
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« Reply #50 on: May 05, 2015, 02:17:35 PM »

Here's a picture of what I am wanting to achieve
I suspect that in order for the AC from the battery in your system to not count as parallel to the grid there would need to be some sort of relay, so that the immersion was either fed from the grid (via the immersion controller), or fed from the batteries?

That would be pretty much be a variation on the nowty arrangement (he has circuits that have relays controlling whether they are on the utility grid or on his local grid).

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David
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« Reply #51 on: May 05, 2015, 02:24:21 PM »

Here's a picture of what I am wanting to achieve
I suspect that in order for the AC from the battery in your system to not count as parallel to the grid there would need to be some sort of relay, so that the immersion was either fed from the grid (via the immersion controller), or fed from the batteries?

That would be pretty much be a variation on the nowty arrangement (he has circuits that have relays controlling whether they are on the utility grid or on his local grid).



This isn't just about the immersion. It's so that in the evening the batteries can help run the house loads, tv, lighting etc and so reduce import. the immersion is just in the mix so when there's lots of sun and the batteries are full, there's still somewhere to dump excess power to.

I'm not bothered about being 100% "legal" this is a one off experimental system, not something I am going to put into production. The battery system will never be exporting power, just reducing what I use and reducing import.

It still boils down to the puzzle of finding a suitable inverter.
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« Reply #52 on: May 05, 2015, 03:00:28 PM »


Have you considered an EV.  This is the best leveraged up value of PV  and you could then use it to power the house at night.  This is available in Japan i understand but a DIY version with a good electrician must be poss.

Ken
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« Reply #53 on: May 05, 2015, 03:01:49 PM »

I think the simplest DIY approach to this is as follows:
Install a battery bank with an off grid inverter that allows AC coupling - the much maligned (here) PowerJack low frequency ones are one such product.
Install an automatic changeover switch with the off grid inverter on one side and the mains on the other, house loads and grid tie inverters on the output.
When the batteries are mid charge they will supply loads with the grid tie inverters helping meet the load and recharge the batteries.
Progarm the ATS to change back to mains when the batteries are either at the upper or lower limits of charge with some hysterisis.
This way you will be able to export excess energy when your batteries are full and cut back to grid when your batteries are empty.
Something like the open energy monitor hardware would be ideal to set up a controller to decide when to connect to and drop the grid.
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« Reply #54 on: May 05, 2015, 05:42:15 PM »

.... systems like this are at least 3 -20 years old http://www.navitron.org.uk/forum/index.php/topic,16936.0.html
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1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
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« Reply #55 on: May 05, 2015, 05:54:57 PM »

.... systems like this are at least 3 -20 years old http://www.navitron.org.uk/forum/index.php/topic,16936.0.html
Yes, and that just explains the product does NOT meet my requirement on ONLY charging the batteries when there is surplus solar PV and varying the charge rate appropriately. Neither does it vary the output power when generating from the batteries to match slightly less than the power being consumed in the house to ensure no export.

So I am STILL looking for a solution as nothing off the shelf does what I am trying to design, and I still can't find a variable power inverter (leaving just a switched bank of small inverters as my "variable" generation.
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skyewright
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« Reply #56 on: May 05, 2015, 06:22:22 PM »

So I am STILL looking for a solution as nothing off the shelf does what I am trying to design, and I still can't find a variable power inverter (leaving just a switched bank of small inverters as my "variable" generation.
Have you seen what Forum member chris75sf came up with (in France)?

IIRC that's a system based around a stack of small inverters?

If you check out hos forum profile, that'll take you to his posts, most of which relate to what he's done. He has (or at least had) a website, but as the Mod's have removed the link from his sig I guess I'd better not include it in a message either!
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David
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« Reply #57 on: May 05, 2015, 06:34:56 PM »

Quote
Yes, and that just explains the product does NOT meet my requirement on ONLY charging the batteries when there is surplus solar PV and varying the charge rate appropriately
 NO , you have not understand  the system  the bidirectional off grid inverter will supply the house loads  to 100 %   does not matter if 200 watt or 3000 watt are  used in the house ,  and only the surplus PV   wanders into the battery  or/and   into the thermal store

No , wrong again
Quote
Neither does it vary the output power when generating from the batteries to match slightly less than the power being consumed in the house to ensure no export.
it will exactly match the load  and consumers you are running  in the house @ 50 Hz 230 Volt   = so much cleaner than the Grid


No intention to have to  be right , .... perhaps  Dave   we talk about  total different ideas .....  
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ProDave
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« Reply #58 on: May 05, 2015, 07:29:17 PM »

Quote
Yes, and that just explains the product does NOT meet my requirement on ONLY charging the batteries when there is surplus solar PV and varying the charge rate appropriately
 NO , you have not understand  the system  the bidirectional off grid inverter will supply the house loads  to 100 %   does not matter if 200 watt or 3000 watt are  used in the house ,  and only the surplus PV   wanders into the battery  or/and   into the thermal store

No , wrong again
Quote
Neither does it vary the output power when generating from the batteries to match slightly less than the power being consumed in the house to ensure no export.
it will exactly match the load  and consumers you are running  in the house @ 50 Hz 230 Volt   = so much cleaner than the Grid


No intention to have to  be right , .... perhaps  Dave   we talk about  total different ideas .....  

You may well be right, but that was not how I was reading the thread.

the trouble with that sort of system is the manufacturers do a very poor job of actually describing exactly what it does. I want to be 100% sure it will do exactly what I want, and if I can't be 100% sure then i would rather design my own, at least I then have the ability to reprogram and tweak what it does.

I don't see any current monitoring with that device, so just how can it measure import and export and therefore make the charge rate / discharge rate decisions?
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ProDave
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« Reply #59 on: May 05, 2015, 07:37:10 PM »

So I am STILL looking for a solution as nothing off the shelf does what I am trying to design, and I still can't find a variable power inverter (leaving just a switched bank of small inverters as my "variable" generation.
Have you seen what Forum member chris75sf came up with (in France)?

IIRC that's a system based around a stack of small inverters?

If you check out hos forum profile, that'll take you to his posts, most of which relate to what he's done. He has (or at least had) a website, but as the Mod's have removed the link from his sig I guess I'd better not include it in a message either!
Thank you very much.

at last that's just what I am looking for.

I've found his web page but I won't upset anybody by placing a link to it. but googling DIYESS should find it.

He's doing exactly what I want to, so there is a wealth of information there. Interestingly he's using an Arduino as well.

I will read the spots of his page and I'm sure that will answer all my questions.

He appears to be using six 250W Chinese grid tie inverters. So there's a recommendation of one model that appears to be reliable.  The fact he has chosen the same solution suggests he could not find a variable power solution. So he can switch in anything from 250W to 1500W in 250W steps.

It's good to find someone that has done it already, i knew I wouldn't be the first.
« Last Edit: May 05, 2015, 07:47:40 PM by ProDave » Logged

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