Inverter size

[Rogan]

After researching this highly complex topic for many hours, I am still sitting with the most basic of question.

Really have to think of how to put this question.

Basically, what determines inverter size for an on grid situation?

The way I understand it.

grid on: The inverter, solar supply dependent, will only supply to the max of its rating. Rest comes from grid. No risk of tripping?

grid off: Here is the problem. While there is solar generation, does the inverter supply non essentials? If yes, is the max it can supply its rating? ie A 5KW inverter can only supply 5KW even if I generate 8KW of solar. Does it trip if I ask for more, like putting an aicon on?

So, what determines the size of inverter I must go for?

[Scorp007]

29 minutes ago, Rogan said:

After researching this highly complex topic for many hours, I am still sitting with the most basic of question.

Really have to think of how to put this question.

Basically, what determines inverter size for an on grid situation?

The way I understand it.

grid on: The inverter, solar supply dependent, will only supply to the max of its rating. Rest comes from grid. No risk of tripping?

grid off: Here is the problem. While there is solar generation, does the inverter supply non essentials? If yes, is the max it can supply its rating? ie A 5KW inverter can only supply 5KW even if I generate 8KW of solar. Does it trip if I ask for more, like putting an aicon on?

So, what determines the size of inverter I must go for?

The answer will be totally dependent on the inverter used.

Grid on a Sunsynk / Deye can supply from the grid the maximum bypass current as per specs which does exceed the inverter rating by a big margin.

When talking of a off grid inverter it will normally only supply the loads on the output from any source up to the size of the inverter.

Again the Sunsynk can supply non essentials based on the settings. This will be affected by the PV connected and how you decide what power is used for load, charging batteries etc.

One would normally size it based on the load one wants to supply when grid is on and then when grid is off. Then the batteries come into play as well as different batteries have different max current allowed. This is given as 0.5C or 1C but also in amps.

At times easier to work out if the load is provided and also how batteries will be discharged over a time period.

The above is needed to even venture to assist in this complex topic to have a workable system.

[Rogan]

Thanks

I am between a 5 or 8 Sunsync.

So based on an on grid installation grrrrrrrrrrrrr... confused.

When grid is off (solar on) , can non ess be supplied without the confusing Aux connection? Supposedly to the max of the inverter rating?

Grid on: is my total usage limited by the inverter size? Or is the inverter "bypassed"?

Edited September 4, 2022 by Rogan

[WannabeSolarSparky]

28 minutes ago, Rogan said:

When grid is off (solar on) , can non ess be supplied without the confusing Aux connection?

Yes

[mzezman]

43 minutes ago, Rogan said:

Thanks

I am between a 5 or 8 Sunsync.

So based on an on grid installation grrrrrrrrrrrrr... confused.

When grid is off (solar on) , can non ess be supplied without the confusing Aux connection? Supposedly to the max of the inverter rating?

Grid on: is my total usage limited by the inverter size? Or is the inverter "bypassed"?

Depends how this is wired - if Non ESS is between grid and inverter then NO they wont be powered if there is no grid. My non-Essentials go down during LS

[GreenFields]

42 minutes ago, Rogan said:

Thanks

I am between a 5 or 8 Sunsync.

So based on an on grid installation grrrrrrrrrrrrr... confused.

When grid is off (solar on) , can non ess be supplied without the confusing Aux connection? Supposedly to the max of the inverter rating?

Grid on: is my total usage limited by the inverter size? Or is the inverter "bypassed"?

Non-essential:

- If the grid is off, the non-essential items are also off.

- If grid is on, the ultimate limit for non-essential loads is when your main circuit breaker trips. The inverter can supplement non-essentials up to the rated capacity of the inverter.

 

Essential:

If grid is off, the essential loads are limited to the power rating of the inverter, supplied either from solar or battery.

If grid is on, the essential loads get up to the power rating of the inverter supplied from solar or battery, but it can take additional power from the grid up to a specified Amp limit, which is different depending on the inverter.

 

[Rogan]

19 minutes ago, WannabeSolarSparky said:

Yes

When grid is off (solar on) , can non ess be supplied without the confusing Aux connection.

So thar will be capped by Inv rating?

 

……..

[mzezman]

2 minutes ago, Rogan said:

When grid is off (solar on) , can non ess be supplied without the confusing Aux connection.

So thar will be capped by Inv rating?

 

……..

Yes it will. When there is no grid my output (load) is maxxed at inverter max (5kw)

[WannabeSolarSparky]

4 minutes ago, Rogan said:

When grid is off (solar on) , can non ess be supplied without the confusing Aux connection.

So thar will be capped by Inv rating?

Correct, it will use up to the max inverter output.

[Steve87]

This discussion starts to make me think of why on earth would one want a scenario where you have some circuits powered & others not dependent on the grid availability. 

I may be crazy but I totally believe in having a large enough capacity & staggering loads so they never meet each other, especially large loads like geysers & some other large devices. The power is then in your hands when to decide when something is essential or not & can be scheduled or rescheduled around the changing load shedding scenario. 

Staggering loads using smart switches like the CBI Astute. That way even the non-essential circuits can still be used to make benefit of Solar & or battery. 

For residential power the off grid inverter with this setup is great. Commercial energy on the other hand is a whole other ball game. It's different because they have high loads constantly & roof space to match. 

[mzezman]

Budget is a big one - i couldn't afford an 8KW at the time and so have the Geyser and Oven on Non Essentials. When i have excess PV i push it into the Non-Ess. But yes when grid is gone i lose both devices. 

[WannabeSolarSparky]

27 minutes ago, mzezman said:

But yes when grid is gone i lose both devices. 

Use a transfer switch to bring the non-essentials onto your essentials side when the grid is off/down.
That's how I have done it and it works great.
And then use some home automation to ensure everything can only work within the bounds of the available power the inverter has.

Side Note: This solution is not for everyone, you need to have correct rules etc and of-course household who understands the whole setup

Edited September 4, 2022 by WannabeSolarSparky
Clarified Staement

[Steve87]

Totally agree with you both @mzezmanand @WannabeSolarSparky. On budget how do you save, well buying the more affordable option is a good start. The Sunsynk 8kW or even 5kW can be pricey when one considers a 10kW or 8kW sized Voltronics Off grider. So you have now a larger capacity at the same money spent. 

@WannabeSolarSparkythe transfer switch solution works well but yes its for an advanced user. My more primitive option is smart switching. Just dont switch them on all together much the same as not having all the transfer switches taking the load of the AC output of the inverters all at once. (Pool pump, geyser, oven, heat pump)

Then some will say but wait a second, having the larger capacity forces you to have a larger battery bank? Not really, you can have no battery or you can have a smaller than 1vs1 battery in comparison to an inverter. You can program a discharge limit into the inverter and protect that smaller battery and build the battery stack as you are able to in the future. 

With no battery and some solar, well then you only save by day. At night, unfortunately you are on your own rolling the dice with Eskom on when they keep the lights on. 

Its not a brand bash or mine is better than yours discussion but a value discussion. 

What i have noticed over a period of time in the solar industry: Some ppl will think that a Victron & a Sunsynk are the holy grails of all solar. Some ppl still think a Sunsynk, Fusion, Sol-Ark and a Deye are not the same product from the same factory. The Ui and firmware are. Some ppl still believe that above 30kWh of energy the low voltage 48V battery is still a good option. 

Get the best value that you can at the best price level with the most experienced operator of that equipment. Do your homework, this forum is a great place to soak up as much as you can absorb. Try to see through the marketing drive and see what solution best works for you.

 

[TimCam]

4 hours ago, Rogan said:

After researching this highly complex topic for many hours, I am still sitting with the most basic of question.

Really have to think of how to put this question.

Basically, what determines inverter size for an on grid situation?

The way I understand it.

grid on: The inverter, solar supply dependent, will only supply to the max of its rating. Rest comes from grid. No risk of tripping?

grid off: Here is the problem. While there is solar generation, does the inverter supply non essentials? If yes, is the max it can supply its rating? ie A 5KW inverter can only supply 5KW even if I generate 8KW of solar. Does it trip if I ask for more, like putting an aicon on?

So, what determines the size of inverter I must go for?

Like all the other good people have advised, it all depends on your budget, and your loads you want to supply.

I have a SunSynk 8.8 kW inverter, so I'll try and explain it's setup, and it's  5.5 kW "brother".

 

First, your mains AC supply comes in from Eskom, through your MCB (Main Circuit Breaker) to your meter.

Just after your meter is the inverter CT (Current Transformer) coil, which is connected to the inverter, and measures the amount of power coming into or out of (Export) your house.

Now, between the CT coil and the inverter you can have Non-Essential loads wired like geysers, stoves, etc, which will not be powered by solar or battery if Eskom is Off.

Not withstanding @WannabeSolarSparky transfer switch method.

When Eskom is On, these loads can be "back-fed" by the inverter with excess solar / battery power, and save you on your Eskom bill. The Max you can "back-feed" to these Non-Essential loads is the rating of the inverter. On a SunSynk 8.8 kW this will be +- 8 kW, on a 5.5 kW it'll be +- 5 kW. If these loads require more power than the inverter can give, the power will be supplemented from Eskom through the MCB and your meter, up to the rating of your MCB. This is possible because the SunSynk is a bi-directional machine, which can take power in from Eskom, or push power back towards Eskom. Using the CT coil, the power can be stopped at the CT coil, (No Export) or even pushed back into the Eskom grid (Export), and supply your neighbors.

 

Then the inverter has an output called UPS (Uninterruptible Power Supply), this is the Essential loads you want to always have power no-matter what Eskom does.

When Eskom is On, these loads will be fed by solar, battery, Eskom, depending on the "System Mode" Timer settings. Normally most people use the solar to charge the batteries, power the Essential loads, and if loads are high, draw some power from Eskom. The SunSynk 5.5 kW can power an Essential load of +- 8 kW by combining Solar / Battery and Eskom. The SunSynk 8.8 kW can power an Essential load of +- 12 kW by combining Solar / Battery and Eskom. If Eskom is Off, (load-shedding) the inverter will only be able to supply an Essential load equal to its rating, i.e. 5 kW or 8 kW.

After all this waffling, I have my entire house wired through the inverter, on the Essential load, as I wish to choose which loads are required during load-shedding or power failures.

Hope you soon join the power independent gang.

[Rogan]

Last one.

So anything connected before the inverter, such as geyser / tumble drier, does not affect the size of the inverter needed. Or put differently, inverter size is determined by your essential load only. 

[Scorp007]

34 minutes ago, Rogan said:

Last one.

So anything connected before the inverter, such as geyser / tumble drier, does not affect the size of the inverter needed. Or put differently, inverter size is determined by your essential load only. 

Mostly correct. My 2c is if you want to use more PV to supply these heavy loads before the inverter then it does affect the size of the inverter. Maximum saving provided you can use this power during day time. Refer to the 5kw for 5.5kw and 8kw for 8.8kw mentioned under the non-essential side. So using a higher rating for more self use daily consumption does increase the essential side as well.

The inverter size does not limit what loads are thus before the inverter as it is mostly fed directly from the grid.

 

[Leonb]

On 2022/09/05 at 12:47 AM, TimCam said:

Like all the other good people have advised, it all depends on your budget, and your loads you want to supply.

I have a SunSynk 8.8 kW inverter, so I'll try and explain it's setup, and it's  5.5 kW "brother".

 

First, your mains AC supply comes in from Eskom, through your MCB (Main Circuit Breaker) to your meter.

Just after your meter is the inverter CT (Current Transformer) coil, which is connected to the inverter, and measures the amount of power coming into or out of (Export) your house.

Now, between the CT coil and the inverter you can have Non-Essential loads wired like geysers, stoves, etc, which will not be powered by solar or battery if Eskom is Off.

Not withstanding @WannabeSolarSparky transfer switch method.

When Eskom is On, these loads can be "back-fed" by the inverter with excess solar / battery power, and save you on your Eskom bill. The Max you can "back-feed" to these Non-Essential loads is the rating of the inverter. On a SunSynk 8.8 kW this will be +- 8 kW, on a 5.5 kW it'll be +- 5 kW. If these loads require more power than the inverter can give, the power will be supplemented from Eskom through the MCB and your meter, up to the rating of your MCB. This is possible because the SunSynk is a bi-directional machine, which can take power in from Eskom, or push power back towards Eskom. Using the CT coil, the power can be stopped at the CT coil, (No Export) or even pushed back into the Eskom grid (Export), and supply your neighbors.

 

Then the inverter has an output called UPS (Uninterruptible Power Supply), this is the Essential loads you want to always have power no-matter what Eskom does.

When Eskom is On, these loads will be fed by solar, battery, Eskom, depending on the "System Mode" Timer settings. Normally most people use the solar to charge the batteries, power the Essential loads, and if loads are high, draw some power from Eskom. The SunSynk 5.5 kW can power an Essential load of +- 8 kW by combining Solar / Battery and Eskom. The SunSynk 8.8 kW can power an Essential load of +- 12 kW by combining Solar / Battery and Eskom. If Eskom is Off, (load-shedding) the inverter will only be able to supply an Essential load equal to its rating, i.e. 5 kW or 8 kW.

After all this waffling, I have my entire house wired through the inverter, on the Essential load, as I wish to choose which loads are required during load-shedding or power failures.

Hope you soon join the power independent gang.

Thanks for this explanation. I think this is the first time I properly understand the workings of essential vs non-essential.

So what is the benefit then of using the AUX output to power some non-essentials? I.e. how is this different from leaving a particular non-essential between the CT coil and inverter? Thanks

[mzezman]

10 minutes ago, Leonb said:

Thanks for this explanation. I think this is the first time I properly understand the workings of essential vs non-essential.

So what is the benefit then of using the AUX output to power some non-essentials? I.e. how is this different from leaving a particular non-essential between the CT coil and inverter? Thanks

I believe difference between Aux and Non-Essential is that Aux is available when there is no Eskom while Non-Essentials is not

[P1000]

15 minutes ago, Leonb said:

So what is the benefit then of using the AUX output to power some non-essentials? I.e. how is this different from leaving a particular non-essential between the CT coil and inverter? Thanks

For the Aux port you are also limited by the passthrough current (the outputs are summed together). But you have some other interesting features - like you can switch the output off if the battery is below a certain SoC or PV drops below a threshold. And it can be on when the grid is off.

Edited September 21, 2022 by P1000

[Leonb]

On 2022/09/21 at 11:12 AM, P1000 said:

For the Aux port you are also limited by the passthrough current (the outputs are summed together). But you have some other interesting features - like you can switch the output off if the battery is below a certain SoC or PV drops below a threshold. And it can be on when the grid is off.

OK thanks.

It would have been nice to have a option to cut the "smart loads" if the inverter output exceeds max (5kw/8kw) to prevent it from tripping during loadshedding, i.e. having two levels of essential loads. 

[Leonb]

What would be the best way to prevent "non-essential" equipment from exceeding the max inverter load, other than manual intervention. Is there an automated way of cutting loads to prevent the inverter from tripping? 

[Scorp007]

On 2022/09/22 at 4:54 PM, Leonb said:

OK thanks.

It would have been nice to have a option to cut the "smart loads" if the inverter output exceeds max (5kw/8kw) to prevent it from tripping during loadshedding, i.e. having two levels of essential loads. 

Normally if you are drawing close to the tripping level from batteries and you use say SOC 100 down to 80% for the smart load as well as essential the smart load will not have a long time to be used. It is meant for more short time use. It is already a plus to be able to use the smart load during LS where other on grid systems will not be able to provide this load.

[Rogan]

On 2022/09/30 at 1:16 PM, Leonb said:

What would be the best way to prevent "non-essential" equipment from exceeding the max inverter load, other than manual intervention. Is there an automated way of cutting loads to prevent the inverter from tripping? 

Don't understand this question, but discussing it will help me with my own confusion. The way I understand it is that there is NO limit on non-essential size. Inverter will supply up to its rating and rest from grid. Is my understanding correct? 

[Leonb]

45 minutes ago, Rogan said:

Don't understand this question, but discussing it will help me with my own confusion. The way I understand it is that there is NO limit on non-essential size. Inverter will supply up to its rating and rest from grid. Is my understanding correct? 

During load shedding, i.e. how to limit the essential power draw to 5kw during period where there are no power from grid. For example where the wife and kids use hairdryer, microwave and kettle at same this in this period.

[PsyWulf]

Either disable the possible big loads alltogether with smart-plugs or a smart-breaker to cut that load side if it breaches the limit