To protect against all overloads caused by running a geyser combined with any other high draw devices you just install a CBI ECU unit on your inverter output and the ECU controled circuit goes to the geyser.

This device monitor the total current consumption and when it goes over a pre-determined Amp, it switch off the geyser. This type of device is also known as a LCR (load contol relay). Works very well on heating circuits but I don't think the wife would like it if you switch off her oven for a while while the load goes too high. 

Interesting , this type of required load management for off grid inverters (i'm assuming you have off-grid) , is where the grid-tie owners will justify the performance of grid-tied inverters . Its actually magic in the way that the grid-tie pushes what it has available against the grid , even if the grid load demand is very high.

 

BUT .... there is also a flip-side to the coin.  It is of little value if the load demand is say 7Kw , but the grid-tie inverter can only push 2.5kW at a given instance  . It would also be opportune under these circumstances to provide for some load distribution , load balancing like switching the geysers off at times , in order to  convert as much solar energy to load energy as possible. Not the mention  how and when to charge a flat battery , without giving up on load energy .

For these reasons , I for one will still need to do a lot of homework if i need to buy my next inverter. To grid-tie or to not grid-tie. 

But I must admit that if one is looking for a one-size-fits-all  , then a grid-tie , eg. SunSynk, is looking very attractive . If you know exactly what you doing , you know the load profile of an installation ,you know how to scale the off-grid inverter, then you can create great and awarding results with an off-grid. 

Edited May 28, 20224 yr by BritishRacingGreen
Correction

40 minutes ago, Vaal said:

To protect against all overloads caused by running a geyser combined with any other high draw devices you just install a CBI ECU unit on your inverter output and the ECU controled circuit goes to the geyser.

This device monitor the total current consumption and when it goes over a pre-determined Amp, it switch off the geyser. This type of device is also known as a LCR (load contol relay). Works very well on heating circuits but I don't think the wife would like it if you switch off her oven for a while while the load goes too high. 

@Vaal  Thank you , I was not aware of this type of product. What is the ballpark cost off such unit.?

1 hour ago, BritishRacingGreen said:

@Vaal  Thank you , I was not aware of this type of product. What is the ballpark cost off such unit.?

Looks like around R649.

4 hours ago, BritishRacingGreen said:

BUT .... there is also a flip-side to the coin.  It is of little value if the load demand is say 7Kw , but the grid-tie inverter can only push 2.5kW at a given instance  .

? Why can't the grid tie inverter push its 2.5 kW, with the balance of 4.5 kW taken up by the grid? If the grid drops out, then the inverter trips with overload.

5 hours ago, Coulomb said:

? Why can't the grid tie inverter push its 2.5 kW, with the balance of 4.5 kW taken up by the grid? If the grid drops out, then the inverter trips with overload.

Your 2.5 and 4.5 values are spot on. When the grid drops out the grid tied would actually just switch off and it MUST switch off as to not energise the dead grid from solar. Some grid tied don't even have an overload or switch to switch on/off. When no PV in the evenings it would just switch off. This is for a pure grid tied. Not units with batteries like the true hybrids.

Great units and simple installation due to no splitting of DB and best ROI.

@Coulomb  @Scorp007 yes , of course the 2.5kw will be contributed from solar . What I meant is the 4.5kw doesn't , which is high .  So I am saying that load staggering may as be crucial to grid-tie as is with off-grid . Say the 3kw geyser was switched off during that time , then the grid import would have only been 1.5kw.  Then switch on geyser at a stage when the load demand is much smaller than 7kw . So we can keep grid import as low as we can , or in other words , leverage the available solar energy as much as we can.

Edited May 29, 20224 yr by BritishRacingGreen
Correction

On 2022/05/28 at 9:21 AM, BritishRacingGreen said:

Interesting , this type of required load management for off grid inverters (i'm assuming you have off-grid) , is where the grid-tie owners will justify the performance of grid-tied inverters

There seems to be some misunderstanding. An off-grid installation does not mean that there is no grid connection. It only means that there cannot be any back-feeding into the grid. The classic off-grid installation uses the grid as a backup for recharging the batteries when there is need but no sun (UPS function). Also - important - if the inverter suffers from overload it switches to "utility (grid) bypass", therefor protecting the inverter. One must only make sure that the inverter feeding breaker in the DB is sized to support the overload and ev. the battery charging altogether. However, a CBI ECU unit can help to prevent such situation.

Edited May 29, 20224 yr by Beat

1 hour ago, Beat said:

There seems to be some misunderstanding. An off-grid installation does not mean that there is no grid connection. It only means that there cannot be any back-feeding into the grid. The classic off-grid installation uses the grid as a backup for recharging the batteries when there is need but no sun (UPS function). Also - important - if the inverter suffers from overload it switches to "utility (grid) bypass", therefor protecting the inverter. One must only make sure that the inverter feeding breaker in the DB is sized to support the overload and ev. the battery charging altogether. However, a CBI ECU unit can help to prevent such situation.

Hi @Beat, ok , I think I didn't make my point clear enough. I was merely comparing a non-grid-tie inverter  with a grid-tie inverter configured for no export outside the local db board.  For both the inverters I assume the availability of grid .  My argument is the grid-tie will not trip outside it's rating , but the off-grid will . The grid-tie merely 'pushes' what it can , whereas the offgrid will trip.

1 hour ago, Beat said:

There seems to be some misunderstanding. An off-grid installation does not mean that there is no grid connection. It only means that there cannot be any back-feeding into the grid. The classic off-grid installation uses the grid as a backup for recharging the batteries when there is need but no sun (UPS function). Also - important - if the inverter suffers from overload it switches to "utility (grid) bypass", therefor protecting the inverter. One must only make sure that the inverter feeding breaker in the DB is sized to support the overload and ev. the battery charging altogether. However, a CBI ECU unit can help to prevent such situation.

I don't agree with your definition of off-grid. It seems the rest of the internet also think you are wrong, just google define off-grid inverter.

Quote

Off-grid inverters are designed to work alone and cannot synchronise with the grid.

 

@P1000, my learned friend ,  I was comparing a grid-tie inverter (e.g. Sunsynk) with the non-gridtie , off-grid inverter (eg. Voltronic MKS)   .  My MKS is is labelled off-grid inverter as such  ,  because of , inter alias :

• it is not grid tied , it cannot export any power to the grid side (fundamental design philosophy for offgrid) 
• it can operate without the availability of grid  ((fundamental design philosophy for offgrid) 

It is by definition also a hybrid , because Solar and Battery functionality is combined within the same machine.

I wish not to indulge in  pedantic matters , if you don't understand the point I was making in my first response to OP , then lets abort.

 

 

The purist my argue that the third generation  MKS and upwards use gridtie mechanisms to accomplish blending of ac power , it is by commercial definition off-grid , because the machine does not push back onto the grid outside the borders of the machine , or , it is not suppose to be ( there are reports of Voltronics machines exporting , but that's a failure mode ).

Edited May 29, 20224 yr by BritishRacingGreen
Correction

1 hour ago, P1000 said:

I don't agree with your definition of off-grid. It seems the rest of the internet also think you are wrong, just google define off-grid inverter.

 

I have to agree. One should rather say "with the grid as back-up.

@BritishRacingGreen

You are spot on that one wants to use all the PV available. The grid tied always comes to its own as there is no wasted PV like we will always find when a battery is full. Provided one can export or you always have enough load switched on.

One just have to look at the yields that are mentioned here. Grid tied guys get over 150 x the PV installed per month and the true hybrids around 105 x.

@Beat @Scorp007 @P1000 I do get me stumbling on semantics here ,  I have just been so used to term a non grid tie as off-grid . In my defence , the attached image of my MKS refers.  

 

18 minutes ago, BritishRacingGreen said:

@Beat @Scorp007 @P1000 I do get me stumbling on semantics here ,  I have just been so used to term a non grid tie as off-grid . In my defence , the attached image of my MKS refers.  

 

Great picture for a novice to see what a Kodak looks like.  😀😀😀😀😀Sponsored by Red Bull

Edited May 29, 20224 yr by Scorp007

43 minutes ago, BritishRacingGreen said:

@Beat @Scorp007 @P1000 I do get me stumbling on semantics here ,  I have just been so used to term a non grid tie as off-grid . In my defence , the attached image of my MKS refers.  

 

I would be wary of using terminology from Chinese packaging as reference 🤪.

@P1000well at least the entire internet thinks me AND the Chinese are wrong , that feels a little bit better than me standing alone in the cold🙂 

Using a Sunsynk you don't have to worry about all these other overloading and mixing parameters etc 😀

22 hours ago, BritishRacingGreen said:

The purist my argue that the third generation  MKS and upwards use gridtie mechanisms to accomplish blending of ac power , it is by commercial definition off-grid , because the machine does not push back onto the grid outside the borders of the machine , or , it is not suppose to be ( there are reports of Voltronics machines exporting , but that's a failure mode ).

In my knowledge there are as well grid tied as off-grid models available from Voltronics. My MKS5K definitely are "off-grid", as they cannot back-feed. From their behavior it looks to me that they were originally conceived as powerful UPS. They then added the MPPT with appropriate programming features to sell them as "solar inverter". Sure they can be used as stand alone without grid connection as well as with grid back-up.

 

@Beat yes , I know of the InfiniSolar  and the Axpert King , they are grid-tied by design .  The MKS "off-grid" family as from the MKSIII has a much wider MPPT input DC range , the DC inputs of Solar and Battery ac-dc converter  can 'push' against the input grid , allowing the grid to blend with the  available dc sources . As mentioned before , this is not unlike grid-tie techniques employed , however the machine is not allowed to export ' access solar into the db board .  Coulomb has mentioned that the grid will always import about 100W or so , even though solar may be able to supply everything , the reason being is so the machine can form some stable  grid barrier  in order to prevent inadvertent exports on the grid side. And of course , being 'off-grid' the MKSIII are capable of generating its ac output from solar / battery when input grid is not available.

 

Now , as @P1000has stated correctly that the original meaning of off-grid  is pure off-grid (e.g. it does not sync to any mains input) , the question arises what a machine like MKSIII can to classified as . My view is that the machine conforms to off-grid standards ,  though its my opinion as i've discovered in this thread.

Edited May 30, 20224 yr by BritishRacingGreen
Extra info

19 hours ago, BritishRacingGreen said:

I know of the InfiniSolar  and the Axpert King , they are grid-tied by design .

Actually the King is not grid tied; it's a dual conversion. So it blends AC-in with battery and/or PV differently to all other models. With the King, AC-in is converted to DC, so the power is easily blended at the DC bus level.

As for the classification of Axperts, since Voltronic advertise them as off-grid, I'm happy to go with that.