For those caught up in the COCT NRS-97 web that have the Multiplus and Quattro inverters and would like to use these "on-grid" as per COCT definition thereof.

These inverters have been installed in countless locations falling in the COCT region. Most are installed as off-grid solution using the internal transfer switch or are running ESS which is a grid parallel system.

I am one of those.

I started dealing with COCT by extending the system using the Ziehl anti-islanding solution which is punted by Victron as allowing compliance to NRS-097 and indeed, there is no obvious technical reason why not. However a submission was rejected by COCT as the inverter does not appear on the infamous COCT list - however the Ziehl is on the list.

I briefly looked at taking my system off-grid but this would require some rewiring of the house to create a split DB board for essential and non-essential loads. I did not like the idea much and searched for possible alternates.

The Victron inverters are really UPS systems - by themselves they have nothing to do with a solar system. They consist of an A/C to DC charger and a DC to A/C inverter. That is all there is to it. As such they are SANS compliant if used as UPS. The trouble comes in when you connect an external solar charger to the UPS battery - that moment the system becomes a potential SSEG and the rules change.

So the solution is fairly obvious - the Victron must remain a UPS. No more, no less. No solar charger may be connected to its battery directly. However a solar charger connected to its A/C input is fine - that does not change the fact that the Victron is a UPS.

The A/C based solar charger is of course an ordinary grid tie inverter.

It turns out the Victron inverters are quite flexible little beasts. You can install the grid tie either on the Victron input or indeed the Victron output. If you install it on the output - the grid tie keeps working in case of a grid failure as the UPS kicks in and keeps the grid tie alive. Even more - the Victron in this mode is able to regulate a compatible grid ties power output - an essential requirement. This can be done by direct control of most Fronius models (via CCGX) or this can alternatively be achieved by frequency shifting if the grid tie can be controlled that way (CCGX not needed but does not hurt either).

Now, the Fronius is not the lowest of cost inverter. Turns out the Chinese Solis grid ties however are quite affordable and respond to frequency shifting - and of course they are NRS-97 approved so that is a good match.

Having a grid tie means the output of the grid tie inverter must be controlled if you do not want to export to grid. This requires a grid tie limiter. It turns out the low cost Solis single phase inverters have this built in - just connect a current shunt. Nice. For the three phase jobbies (like I need) you need one extra box - Solis makes an external grid tie limiter for three phase.

With all of the above in mind I submitted a new application based on a Solis grid tie on the output of my Victrons and these Victrons configured as UPS with the Grid-tie PV assistant installed (this is only active during grid failure). The assistant takes care of setting the grid-tie output power as needed.

From an operation point of view you still have a number of options available - you can configure the system to run off-grid, partially off-grid, on-grid (grid parallel) and it is quite possible to use the Victrons with ESS as well (They are still just UPS's in this mode - but it may be seen as a gray area). With ESS you could construct a balancing feed-in system (with some losses). However, for the most part, there is likely no advantage of using ESS in such a system so your inverters are dormant for most of the time (that also means a little more power available for your loads).
Compared to the "Victron only" solution you do gain more power available during load shedding as your Victron produced power adds to that of the grid tie output while any excess is used to recharge the batteries. There is a requirement that the Grid tie power delivery may not exceed the capacity of your Victron inverter so be aware of that. Not normally an issue - just be aware.

This has now been approved by COCT so this is a possible, relatively easy way out for those that want to keep their older Victrons alive and effectively grid connected legally. If you want to apply for such a system please ensure that your drawing shows absolutely clearly that the Victron OUTPUT can never be connected to grid so if you have an optional changeover switch on the Victron output (change between UPS and grid)  - please show this switch as compliant with requirements.

Nice loophole.

According to this approach, presumably the system can now double in size, according to the 1:1 rule.

Where the PV inverter is sized to the maximum regulations allow and the UPS is sized 1:1 to match it.

Or is there a regulation that governs the size of a UPS?

I think the wording and descriptions of an application would have to be very detail specific, do you mind sharing?

 

13 minutes ago, The Bulldog said:

This can be done by direct control of most Fronius models (via CCGX) or this can alternatively be achieved by frequency shifting if the grid tie can be controlled that way (CCGX not needed but does not hurt either).

For info, when the grid goes down the CCGX stops controlling the PV inverter. It sets the power limit to the maximum and lets frequency shifting do its job. The modbus control is only used while it is on the grid to prevent feeding into the grid. There was a bug in this that was only fixed in 2.23: It used to shut down the PV inverters (all of them) if the grid went out.

18 minutes ago, The Bulldog said:

likely no advantage of using ESS in such a system so your inverters are dormant for most of the time

I disagree. If you have an energy meter installed, the ESS control loop can "see" the power from your non-supported PV inverter flowing outwards towards the grid. ESS will always attempt to keep the grid meter at zero (or whatever you set the grid setpoint to), and this works in both directions, so when there is a shortage of PV, it will automatically supplement from the batteries. When there is power flowing out towards the grid, it will again try to zero it by charging the batteries. In other words, it works the same way it did with the solar chargers on the DC side, the Multi is just doing the charging.

The only problem with using the Solis is that it cannot be grid limited. I would gladly help someone to add this feature, but the first thing we need to do is check if the modbus-rtu connection 1) has sunspec support, 2) has model 123, and 3) whether it actually works to limit power. Presently dbus-fronius has no RTU support, but maybe one can arrange for it to be added, or it can be done as a separate project too (which will probably be easier).

But... if you get the expensive bi-directional meter and move to the SSEG tariff, then you don't have to limit the PV inverter.

13 minutes ago, phil.g00 said:

According to this approach, presumably the system can now double in size, according to the 1:1 rule.

Indeed. You could have both the PV inverter running at max and the Multi running at 80%, so in theory you could have 180% of the regulated size for at least as long as the batteries last.

It is unclear to me if you can keep the batteries charged with this setup, with the Solis grid-tied inverter on the Victron output - in case of load shedding or a power outage?  It does not seem obviously possible to me, but perhaps there is some kind of Victron magic involved 😄

 

4 minutes ago, plonkster said:

modbus-rtu

Now that I think about it, some inverters come with "gateway" addons that can make them modbus-tcp capable. Adding such a thing might well get you modbus-tcp support. The grid-limiter support is specifically coded to only Fronius and ABB at the moment. Sadly one cannot just make it generic (ie if you see model 123, use it), because unfortunately not all PV inverters implement this model properly. That's why limiting for SMA and SolarEdge is not supported for example. SMA made the register write-only (which complicates things) and SolarEdge doesn't implement model 123 at all.

 

3 minutes ago, admiral said:

It is unclear to me if you can keep the batteries charged with this setup, with the Solis grid-tied inverter on the Victron output - in case of load shedding or a power outage?  It does not seem obviously possible to me, but perhaps there is some kind of Victron magic involved 😄

Oh it is bleedingly simple. So simple I almost could not believe it. It simply controls the frequency based on how close the battery voltage is to the required charge voltage. Because it's a low-frequency inverter, it essentially becomes a battery charger with a large toroidal transformer and synchronous rectification. The more power flows in from the PV inverter, the higher the battery voltage rises, so all you need to do is push the frequency up proportionally to the battery voltage.

14 minutes ago, plonkster said:

 

I disagree. If you have an energy meter installed, the ESS control loop can "see" the power from your non-supported PV inverter flowing outwards towards the grid. ESS will always attempt to keep the grid meter at zero (or whatever you set the grid setpoint to), and this works in both directions, so when there is a shortage of PV, it will automatically supplement from the batteries. When there is power flowing out towards the grid, it will again try to zero it by charging the batteries. In other words, it works the same way it did with the solar chargers on the DC side, the Multi is just doing the charging.

 

I am getting the Solis grid limiter anyway but may experiment with the ESS - it is not clear to me how far ESS will take the regulation as docs are a bit thin on the subject. In any case this is not going to work if you are on-grid - the Victrons may be good but they are not good enough to shift grid frequency with grid connected. So the ESS regulating a grid-tie is limited to Fronius via CCGX. Or any other grid-tie that can be regulated by the CCGX without fiddling with grid frequency.

For my application the Solis grid limiter is a must. Even though I am going on the SSEG feed-in tariff with the AMI meter I still want to be able to control feed-in.  

There is a protocol document for the Solis grid ties floating around on the internet I found (for the RS485 modbus). From Dr.B.A.Coghlan - final release December 2018 so "newish". Looks like it contains about all that is needed. Might play with this if I am feeling strong. Using the doc and hacking into the RS485 feed I should be able to see what exactly the Solis grid-tie is doing.

Will probably take a few weeks to get all installed and running. Once I gain a bit of experience with the good, bad and ugly of this solution I'll report of course.

But for the moment - it appears the cleanest and lowest cost solution for me to keep my Victrons. 

48 minutes ago, plonkster said:

I would gladly help someone to add this feature, but the first thing we need to do is check if the modbus-rtu connection 1) has sunspec support, 2) has model 123, and 3) whether it actually works to limit power

I recall we having this chat last year. As i said back then, it would be so cool if somehow Solis also becomes "part of the family" as the Fronius and ABB inverters are.

Nothing I read on the Solis inverters gave me any points of concern. 

Would be good if between @The Bulldog and @plonkster this could become a reality. Would save a lot of Victron installs in SA as Bulldog points out ... AND ... a lot of 2nd hand MPPT's could be coming on the market for the rest whom opt to go for the Multiplus II route. Win win if you ask me.

EDIT: As a matter of fact. If CoCT gave me any more grief going grid tied, and they did not, I would have gone Solis route myself.

Edited May 21, 20197 yr by Guest

7 minutes ago, The Bulldog said:

Dr.B.A.Coghlan

I know that guy! He's from Trinity College in Dublin. Writes these long emails that's hard to get through in a hurry... 🙂

9 minutes ago, The Bulldog said:

Solis grid limiter

There might even be a way to make it work. Set the grid setpoint for the Victrons  a bit higher than the grid limiter of the Solis, so they end up fighting each other.

Eg, the Solis wants to limit to 20W but the Victron wants to limit to 100W. Solis increases power to get the grid to 20W... Victron notices the power is less than 100W and starts charging the batteries (or supplies loads) to get it back up to 100W. Repeat until max power.

When the batteries fill up, the Victron system cannot import all the power anymore, and the power level drifts down to where the solis limiter stops the PV-inverter.

39 minutes ago, plonkster said:

I know that guy! He's from Trinity College in Dublin. Writes these long emails that's hard to get through in a hurry... 🙂

There might even be a way to make it work. Set the grid setpoint for the Victrons  a bit higher than the grid limiter of the Solis, so they end up fighting each other.

Eg, the Solis wants to limit to 20W but the Victron wants to limit to 100W. Solis increases power to get the grid to 20W... Victron notices the power is less than 100W and starts charging the batteries (or supplies loads) to get it back up to 100W. Repeat until max power.

When the batteries fill up, the Victron system cannot import all the power anymore, and the power level drifts down to where the solis limiter stops the PV-inverter.

It will not work.

As long as the Victron is connected to the grid (with ESS) it is not able to regulate the Solis via frequency shift. It can only do so if it is disconnected (transfer switch open).

This is why I need the Solis grid-tie. 

Of course, if the ESS is able to control the Solis grid-tie directly without frequency shift then the Solis grid tie limiter is not needed. The doc I mentioned should suffice.

But it might largely be a mute subject - most of the single phase Solis grid-ties have the limiter included so you have one anyway.

For my three phase system I am currently tending not to go with ESS as the three active inverters do add a fairly noticable power draw which is a fair percentage of my base load. Since I will be feeding in most of my solar production I am using the grid as a battery (with the feed in tariffs one can compare it to a battery with really poor charge efficiency but indefinite charge cycles). To make the numbers work I am installing as many panels as I can fit on the roof. About 10KWp - perhaps a tad more. I have a few more roofs that could take panels so perhaps that could be a future extension. It appears COCT have granted me 30KVA feed-in (I was expecting a max of 17.7KVA as per COCT regs but I am not complaining).

Anyway - for me it makes more sense now to simply use the Victrons as "smart" UPS in case of grid fail and preserve my batteries which are still in excellent state after 4 years of use.

However, I am more than willing to work with Plonkster to use my system as development platform for any extension to the excellent ESS system. Since it appears he is not far from where I stay...

 

1 hour ago, The Bulldog said:

It will not work.

I think we are talking about different things. The Solis has its own current transformer attachment, and if you connect that it will do its own grid-limiting (iow I am not talking about frequency shifting, fully aware that you can't shift the whole grid 🙂 ). My proposition is to use both this CT for the Solis AND an energy meter for the Victron setup. Then tell the Victron setup to maintain a slightly higher setpoint than the Solis. The effect should be that they fight each other, causing the Victron inverter to import all surplus power for battery charging and loads (on its output) while the Solis still has the benefit of being limited -- just not by the CCGX.

Edited May 21, 20197 yr by plonkster

Just now, plonkster said:

I think we are talking about different things. The Solis has its own current transformer attachment, and if you connect that it will do its own grid-limiting (iow I am not talking about frequency shifting, fully aware that you can't shift the whole grid 🙂 ). My proposition is to use both this CT for the Solis AND an energy meter for the Victron setup. Then tell the Victron setup to maintain a slightly higher setpoint than the Solis. The effect should be that they fight each other, causing the Victron inverter to import all surplus power for battery charging and loads (on its output) while the Solis still has the benefit of being limited -- just not by the CCGX.

Ah OK, that sounds plausible. 

Would depend on how the CT is connected internally.in the Solis - if A/C coupled, potential free (most likely) then sharing it with something else should be quite possible. 

Interesting idea...

3 minutes ago, The Bulldog said:

sharing it with something else

Separate energy meters. Don't know if you use an external energy meter (Carlo Gavazzi) or not, but the idea is to clamp he Solis's CT right before/after the point where your Victron system measures its grid power (ie at the Carlo Gavazzi meter, or on the input of the Multi(s)). So they are completely independent systems but with the exception of a small bit of calibration difference they will get the same power reading. Then simply tell the Victron to hold at 100W... every time the Solis pushes it down to zero the Victron will attempt to pull it back up.

OK, so not sharing the CT then - not impossible of course, I was just concerned as some metering systems will send a small DC current through the CT in order to detect if it is connected or not.

I do not have an external energy meter at the moment but could install one - was thinking along those lines anyway as I really need something to do some easily accessible accounting.

Were is a good place to get one of those ?

 

3 hours ago, The Bulldog said:

Were is a good place to get one of those ?

Any place that sells Victron stuff should stock it.

On 2019/05/21 at 10:31 AM, The Bulldog said:

F If you want to apply for such a system please ensure that your drawing shows absolutely clearly that the Victron OUTPUT can never be connected to grid so if you have an optional changeover switch on the Victron output (change between UPS and grid)  - please show this switch as compliant with requirements.

I dont quite understand the how the change over switch is connected to prevent the output of the Victron backfeeding into grid - so my understanding is the common point of the change-over is the house load and the two inputs are either the grid or the Multiplus ( UPS ) .  What is the AC input to the Multiplus connected too ? IF the Multiplus is connected to load   and the AC input to grid then the internal transfer switch of the multi also connects the the inverter out to load as well as to grid .  How do you get around that issue ?