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What size inverter do I require?


CatEyes

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We have three households on the property and I would like to find out what size inverter would be recommended to be able to handle the peak consumption during load-shedding or as a completely off-grid system?


The system will be grid-tied but unfortunately during load-shedding the inverter won't be able to boost the output by pulling electricity from the grid so it needs to be able to supply 100% of the peak consumption even if only for a short while.

Household 1: House with 4 people
Household 2: House with 4 people
Household 3: Flat-let with 2 people

The stoves are gas and the geysers will run either on-grid or from solar if there is excess power available.
There are no air-conditioners or large pumps.

The current maximum household consumption bursts are as following
Household 1: 7000W (Kettle, Microwave & Hair dryer)
Household 2: 4300W (Kettle & Washing machine)
Household 3: 3500W (Kettle & Microwave)
But all of the households will obviously not be consuming their maximum at the same time but they might also add something extra to the mix.

By my guestimate (75% of the peak) we would require 12kW to be able to handle the peak consumption even if only for a short while but that is where my question lies.
Will 2x 5.5kVA SunSynk inverters suffice or should I rather consider 3x 5.5kVA or 2x 8kVA units?

16 kVA is a lot of power and might be a bit excessive.

Thanks

Edited by CatEyes
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Hi,

So in essence you are asking for households  as example be able to draw 11kw:

 

Uhmmmm that on a 48V battery backup is a combined 241Amps current.

Let us assume you install one battery backup, and need it to at least keep them up for 2 hrs, at those required will mean you need in the region of R250k just for that.

Unless you sit down and work out a precise plan.

I would go seperate system for each, with clear guide lines, like no kettle during loadshedding, or hairdrying or something. Problem is the moment you cater for Anything that heats, it escalates the battery costs through the roof.

Example we are a household of 4 and manage with a single 100Ah battery, only using like 20% capacity during 4 hrs loadshedding.

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It will only be 12kW peak for a few minutes, not the total daily consumption.

The average daily consumption is quite low at 9kW per day for household 1 which includes a geyser.
A large portion of this minus the geyser will obviously be supplied directly by the solar panels and won't need to come from the batteries since you will only run the washing machine and other heavy appliances during sunny days.

Unfortunately the current layout of the buildings don't allow for separate units and if 2x 5.5kVA units will suffice then why buy three inverters?
This also causes the problem of excess energy being available but at the wrong place (PV / batteries).
But this is not the question here.

Maybe I should rephrase my question.
Considering the aforementioned peak household consumption.
If it is a bright and sunny day and I have more than enough PV but no grid supply; what size inverter would I require to enable me to use all of my PV without the inverter tripping since it can't boost from the grid?

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Yes off course for only a couple minutes, but even for one second drawing those numbers means a 240+ Amp draw.

Thats why it is not preferred to run a 1000W microwave off a 100AH 24V battery.

1400W (cause yes it uses more) / 220V = 6.3A on AC current but on a battery,

1400W / 12V = 116A

1400W / 24V = 58A

1400W / 48 V = 29A

A normal 100AH battery has a max current of 100A or there about for the recent types.

Now if you want to cater for a pull even for a second for 12kw you would pull,

12000W / 48V = 250A and doing this you would now need to add at least 300AH, which at least should be able to draw 250A.

So thats 75K just to be able cater for the 12kw, now you need to start thinking off uptime. Since every minute adds up.

Which brings me to the make a solid plan of what is required vs really needed.

In loadshedding we can make some sacrifices, in order to save money, if money is not an issue, sure go wild and put in what is needed.

 

Okay so now to the PV. The sun is pretty crappy now and through winter. To ensure 12kw, then check with members on their outputs, but from what I have seen is that a 5000w PV system (good panels), will hit maybe 3kw, but let that sun dip behind a cloud and it will fall way down, making in loadshedding the inverter seeking battery assistance. So now it becomes a real catch 22, do you cater for both now? Well you have to, cause one rainy day and you will get nothing of true value from the Solar, etc.

It seems all very daunting, but make it a journey.

Inverter related, again, same story, it would need to cater for that single pull 12kw, single is fine, if it is big enough, wil multi mppts.

Two in parallel also good I guess, gives more redundancy etc.

Size wise I guess 15kva 15000w at least to be safe?

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30 minutes ago, CatEyes said:

Considering the aforementioned peak household consumption.
If it is a bright and sunny day and I have more than enough PV but no grid supply; what size inverter would I require to enable me to use all of my PV without the inverter tripping since it can't boost from the grid?

You haven't mentioned batteries. Without those you are not going to get through a load shed. The inverter will not supply any grid power, no matter how sunny it is.

So there's a second question: How much battery? Well, if you can supply average daily consumption for each household, or (second prize) for the property, then that's a good basis for sizing the battery.

I think you need to consider multiple smaller systems. Simpler wiring. Lighter wiring. And a fault or excessive usage in one household will not affect the other two. You can go for one system for the whole property of course, but at least think about individual systems.

Different brands of inverters have different things going for them. 

My Goodwe can supply PV to the non-essential loads when the grid is up. When the grid is down they get nothing at all, no matter how sunny it is and no matter the state of charge of the battery.

But a Deye or a Sunsynk has a programmable auxiliary output. You can put some loads on there with a rule that says that if there's PV and if the battery has at least X% charge then you can supply the loads on that port. It's more flexible.

OTOH the Goodwe is very, very quiet. The Deye and the Sunsynk have fans that some folks find annoying. That may be a deal breaker for some folks.

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I haven't mentioned batteries since I only wanted to find out about the inverter sizing.

Adding additional batteries and panels later is always an option since someone will find a use for the extra capacity but having to buy an additional inverter just because you spec'd the system 1kW too small for every time grandma makes a cup of tea is going to be expensive.

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Hi CatEyes, welcom to the club.

Taking in account the simultaneous factor (not all families do the same thing at the same time) you do not have to add up the full peak power. Give it 80%. That's the advantage of one system for them all.

Second, consider at least 2 parallel units for redundancy. I would rather go for 3. In case one fails you would still have 2/3 of power available. That's the other advantage of one system for them all. It's part of your liability to the dwellers for reliable service. I.E. 3 4kW or 3 5kW units.

And of course, as mentioned by others - batteries, batteries, batteries! If you conceive only as UPS for LS you may get away with 20kWh (400Ah). If you think of getting off grid with solar, then you would need lots more.

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1 hour ago, frivan said:

Put up a three phase 12kW Deye inverter and give each house its own phase. On battery these inverters can supply 6kW per phase. If the village requires other services, you have three phase power available.

Never thought about that.

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57 minutes ago, frivan said:

Put up a three phase 12kW Deye inverter and give each house its own phase. On battery these inverters can supply 6kW per phase. If the village requires other services, you have three phase power available.

This. And 2 x Greenrich 1.5C batteries. And get lower Watt appliances. Much cheaper to give each house a 1.5kW kettle, etc. than to provide more inverter power.

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33 minutes ago, Superfly said:

Never understood the sense of 3Ph in domestic, but anyway... 3x parallel would be the way I'd go based on individual consumption for the scenario.. IMHO.

3x5kW? How would three inverters make sense? You could do 2x8kW if you really want contingency, you could do 16kW single phase also. The more inverters, the higher the cost and complexity.

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9 hours ago, CatEyes said:

We have three households on the property and I would like to find out what size inverter would be recommended to be able to handle the peak consumption during load-shedding or as a completely off-grid system?


The system will be grid-tied but unfortunately during load-shedding the inverter won't be able to boost the output by pulling electricity from the grid so it needs to be able to supply 100% of the peak consumption even if only for a short while.

Household 1: House with 4 people
Household 2: House with 4 people
Household 3: Flat-let with 2 people

The stoves are gas and the geysers will run either on-grid or from solar if there is excess power available.
There are no air-conditioners or large pumps.

The current maximum household consumption bursts are as following
Household 1: 7000W (Kettle, Microwave & Hair dryer)
Household 2: 4300W (Kettle & Washing machine)
Household 3: 3500W (Kettle & Microwave)
But all of the households will obviously not be consuming their maximum at the same time but they might also add something extra to the mix.

By my guestimate (75% of the peak) we would require 12kW to be able to handle the peak consumption even if only for a short while but that is where my question lies.
Will 2x 5.5kVA SunSynk inverters suffice or should I rather consider 3x 5.5kVA or 2x 8kVA units?

16 kVA is a lot of power and might be a bit excessive.

Thanks

Pocket not being a problem, I would suggest 3 x Inverters, preferably Deye/Sunsynk as their user interface and firmware provides for quite a lot of flexibility. My reason for three separate units is so that in the event one household pulls too much energy from the system, the other two households remain unaffected as only one system will go down during loadshedding. Next important issue would be to split the DB (Distribution Board) into essential and non-essential loads so no one puts a kettle or iron on an essential phase during loadshedding or even later on someone adding a washing machine. Minimum I would recommend therefore is 8Kva systems and batteries to match loads but all systems to have a minimum of 3 batteries if you are going to go with Pylontech UP5000. It's going to be a hefty bill but the most important part is discipline on the part of all system users or households. The other two households with lower consumption may even begin with 2 batteries or you could go for 2 x BSL Lithium Ion 48v-135Ah-7kWh batteries.

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As @Beat mentioned one of the reasons for building one system is the redundancy. If one inverter goes everyone still has some electricity albeit less but no-one is sitting in the dark. The other advantage is that the main house has a huge North facing roof whilst the rest have East and West facing.

@GreenFields I will definitely have a look at the Greenrich 1.5C batteries

This is for three households so at least there are three pockets to pay for all of this.

@Moffat I was leaning towards the BSL batteries but I am also considering the Pylontech, Greenrich and FreedomWon batteries and will add more as time goes on.

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2 hours ago, Superfly said:

Edit: How can a parallel system be complex?  

Possible problems with running a generator as backup through the AUX port.

 

If I had this choice, I'd get a 16 kW inverter with a load of batteries and panels, and keep all loads on essential.

When I last looked, 2x 8 kW inverters cost more than 1x 16kW inverter.

Less problems and expenses with DB re-wiring, and less chance of equipment failure.

 

Welcome to the forum, and enjoy your expensive new solar hobby. :)

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7 hours ago, Superfly said:

What? They need 15KW what's wrong with 3x 5Kw?

 

Edit: How can a parallel system be complex?  

I already mentioned the cost but yes, more cabling. Another big one is that you can blow up parallel inverters if you don't set them up correctly.

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6 hours ago, CatEyes said:


@Moffat I was leaning towards the BSL batteries but I am also considering the Pylontech, Greenrich and FreedomWon batteries and will add more as time goes on.

All those batteries sound relatively premium. I have BSL, I had Pylontech. I know some ranges of Pylontech had issues. I don't know why the 1.5C batteries would be beneficial. With load shedding the energy requirement will probably mean that 1C batteries will be fine. Try to stick to common batteries so that in future you can buy or sell the same. Perhaps Shoto and Hubble are more common.

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47 minutes ago, frivan said:

I don't know why the 1.5C batteries would be beneficial. With load shedding the energy requirement will probably mean that 1C batteries will be fine.

Unrelated to the brands, the reason I suggested the 1.5C batteries is because of the high discharge rate of up to 250A (that may be required for short periods for 3 families to survive loadshedding), while at the same time considering that the total energy consumption is moderate. Especially if non-essentials are excluded from batttery requirements and run from the daytime on solar, I think one can try to get away with initially just 10kWh of storage as an absolute minimum.

17 hours ago, CatEyes said:

It will only be 12kW peak for a few minutes, not the total daily consumption.

The average daily consumption is quite low at 9kW per day for household 1 which includes a geyser.

Just high-level, 2x 1.5C at approx R70K, with 300A max discharge, and I did suggest finding some replacement appliances with lower wattages to stress them less. This would be to try handling peak consumption during loadshedding, supported by solar if that's the main focus, with option to expand.

Otherwise 3x 1C 5kWh batteries like Hubble, FreedomWon, Sunsynk, etc.  at approx R100K-R110K, with 300A max discharge, gives more breathing room from the word go.

To get this type of discharge with 0.5C batteries like Pylontech you need to buy 5 or 6 UP5000's at a cost ballpark of R200,000 if you're more serious about going off-grid.

Just my 2c, somewhat stating the obvious, but for the OP to decide what he's interested in.

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6 hours ago, frivan said:

Another big one is that you can blow up parallel inverters if you don't set them up correctly.

That should be no issue with the instructions coming with the inverters. But yes, some talented people even blow them up with hoking up the battery revers.

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36 minutes ago, Beat said:

That should be no issue with the instructions coming with the inverters. But yes, some talented people even blow them up with hoking up the battery revers.

My BEST experience. We repair a power supply where a staff member of a company reversed the polarity. 20min the same PSU came back with another reverse polarity with the PCB track just burnt more. 

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16 hours ago, GreenFields said:

To get this type of discharge with 0.5C batteries like Pylontech you need to buy 5 or 6 UP5000's at a cost ballpark of R200,000 if you're more serious about going off-grid.

Wasn't aware that Pylontech was 0.5C batteries, well perhaps not all of them.

I'll make sure to check the specifications.

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28 minutes ago, CatEyes said:

Wasn't aware that Pylontech was 0.5C batteries, well perhaps not all of them.

I'll make sure to check the specifications.

0,5C or 1C is really not going to make the difference in reality as it only allows to draw the battery to dead quicker.

I have only one 0,5C battery (paint is still wet on the installation it is that new) and while the wife (and old man) have tripped it twice, the smaller draw limit gets me through load shedding with battery capacity to spare. Have ordered a second 5KW block for the upcoming stage-to-the-moon to get through winter days.

As mentioned there is a mindset change that needs to be done. Three pockets will need to be super deep to keep to old habits. 

I did not see where you are but here in Cape Town I'm only getting 10-20% production on my panels in this overcast weather on a true north-facing roof. Battery storage is far more important than I realised.

Edited by cbrunsdon
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5 hours ago, cbrunsdon said:
5 hours ago, CatEyes said:

Wasn't aware that Pylontech was 0.5C batteries, well perhaps not all of them.

I'll make sure to check the specifications.

0,5C or 1C is really not going to make the difference in reality as it only allows to draw the battery to dead quicker.

You can handle higher brief peaks. You obviously don't want to discharge at that rate continuously. The requirement here is to service three households, so the chances of exceeding 5kW (assuming 10kWh battery) seem a bit higher.

 

It's either going to be 1 pretty large inverter or 2 not exactly small ones. Again increasing the likelihood of a high peak.

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On 2023/04/28 at 6:11 AM, Bobster. said:

You can handle higher brief peaks. You obviously don't want to discharge at that rate continuously. The requirement here is to service three households, so the chances of exceeding 5kW (assuming 10kWh battery) seem a bit higher.

 

It's either going to be 1 pretty large inverter or 2 not exactly small ones. Again increasing the likelihood of a high peak.

Valid point and more correct than my response.

It will be hard to get all three households to work in sync with smaller discharge rates. If I look at how many spanners just one stubborn individual throws into the works in my house,  I would not want multiple. 

Being able to supply peak load through batteries is very important for the OP.

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