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Grid tie basics


Jos
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Hello Guys

Am new to Solar system I could like to learn more about basic information

How do you calculate Solar panel total kw per day in South Africa am based in Mahikeng

If is I want to use 20kwh per day do I need 20kva or 2x10kva inverters, to be clear I still don't understand how to work around inverter total output/capacity teach me basics

I have Eskom 3kva main switch 60A which power Stove/40A plugs/20A  standard Refrige, Deep Refrige, LED TV, kettle, Microwave, fan, Small kitchen appliances, lights/10A 13 LED lights ~ 2 lights runs 15 hours daily #18W each

I was wondering if using grid tied will help or is useless because mostly I use sub 20Kwh on the grid, I understand grid tied means no backup storage but it can be upgraded to off grid when I add batteries

In terms of batteries if I get 3.6 kw can I buy 5x3.6 and combine capacity into one

Do 400W Solar panel really have major difference compare to 365W I understand in theory 400W panel may save number of panels installed on my roof, I recently saw Canadian 400W panel around R2300-R2600 

If is possible give me names of equipment I can get that will help me achieve my goal inverter brand & model, AC disconnect, etc

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@Jos

First you need to do an energy audit. 

Two main things to look at is how much power you need at any one time and secondly how much power you need per day. 

Peak demand or maximum power would be the kW of all appliances that will be on at the same time. This will be used to size your inverter. A geyser alone would pull 3kw depending on the element. Best would be to get an energy meter measuring peak demand on the main supply. 

Total power would be the kWh used in a day. If you have a 3kw element in your geyser and it runs for 3 hours it will use 9kwh. I don't look at kVa but at kW and kWh as it's easier to work with. 

A sunsynk 5kw or 8kw inverter should be sufficient. I have the 8kw sunsynk inverter with 28 x 305w panels producing on average 40kwh per day. 

Batteries can be stacked to have a bigger capacity. Normally only the same size and make batteries can be stacked. I have 3 x 3.5kw pylontech batteries. 

Battery bank can be sized according to how much electricity you need at night. 

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The way I did it was to start small and build up my system over time. It is not always the right way to do it, but it worked for me. Some may argue that getting the biggest and best of everything will cost more now, but save you in the long run. This is not always necessarily true. While buying one big 20kw inverter will mean less wiring, having two 10kw inverters will mean that you can still have 10kw should one of them fail. Having 2 MPPT’s means that I can still use one of them if the other one needs repairs. To me a system running at 50% is better than the whole system being down. I personally prefer to have separate inverters and MPPT’s not the all-in-one setup, but this is just my personal preference. Once again this is because my system can still operate at 50% while the faulty component is being repaired. 

One of the most important things I learned (on this forum) is about the placement of solar panels. For years I had the understanding that panels have to face north for the best production. I was wrong. I learned that if you face your panels not only north, but also some east and some west, you get much better solar production. Granted it is a little more difficult to get the whole system balanced out, but it is well worth it to have solar production from 6:30 until 17:30. 

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34 minutes ago, Solaris said:

The way I did it was to start small and build up my system over time. It is not always the right way to do it, but it worked for me. Some may argue that getting the biggest and best of everything will cost more now, but save you in the long run. This is not always necessarily true. While buying one big 20kw inverter will mean less wiring, having two 10kw inverters will mean that you can still have 10kw should one of them fail. Having 2 MPPT’s means that I can still use one of them if the other one needs repairs. To me a system running at 50% is better than the whole system being down. I personally prefer to have separate inverters and MPPT’s not the all-in-one setup, but this is just my personal preference. Once again this is because my system can still operate at 50% while the faulty component is being repaired. 

One of the most important things I learned (on this forum) is about the placement of solar panels. For years I had the understanding that panels have to face north for the best production. I was wrong. I learned that if you face your panels not only north, but also some east and some west, you get much better solar production. Granted it is a little more difficult to get the whole system balanced out, but it is well worth it to have solar production from 6:30 until 17:30. 

I don't think he needs a 20kw inverter, or even a 10kw inverter. 

He looked at his usage of 20kwh and incorrectly assumed that it means he needs a 20kw inverter. 

Confusing usage (kWh) with peak demand (kW) 

The former is for sizing the solar array and battery bank and the latter for sizing the inverter. He only stipulated his usage and no indication of peak demand but at a daily usage of only 20kwh I highly doubt that his peak demand is more than 5kw.

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11 minutes ago, Achmat said:

I don't think he needs a 20kw inverter, or even a 10kw inverter. 

Oh, I totally agree. A 5kw inverter should cover his needs quite comfortably.

I was only offering advice on how you don’t need to go for the biggest inverter available as some salesmen might lead you to think. A system can start small and be added to, over time. 

I also agree that peak demand determines the inverter size, while the day/night usage will determine the solar array and battery size. 
 

 

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2 hours ago, Solaris said:

The way I did it was to start small and build up my system over time. It is not always the right way to do it, but it worked for me. Some may argue that getting the biggest and best of everything will cost more now, but save you in the long run. This is not always necessarily true. While buying one big 20kw inverter will mean less wiring, having two 10kw inverters will mean that you can still have 10kw should one of them fail. Having 2 MPPT’s means that I can still use one of them if the other one needs repairs. To me a system running at 50% is better than the whole system being down. I personally prefer to have separate inverters and MPPT’s not the all-in-one setup, but this is just my personal preference. Once again this is because my system can still operate at 50% while the faulty component is being repaired. 

One of the most important things I learned (on this forum) is about the placement of solar panels. For years I had the understanding that panels have to face north for the best production. I was wrong. I learned that if you face your panels not only north, but also some east and some west, you get much better solar production. Granted it is a little more difficult to get the whole system balanced out, but it is well worth it to have solar production from 6:30 until 17:30. 

True about panels directions I also learned that it won't produce decent energy but it balance the equation like you just mentioned

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2 hours ago, Achmat said:

I don't think he needs a 20kw inverter, or even a 10kw inverter. 

He looked at his usage of 20kwh and incorrectly assumed that it means he needs a 20kw inverter. 

Confusing usage (kWh) with peak demand (kW) 

The former is for sizing the solar array and battery bank and the latter for sizing the inverter. He only stipulated his usage and no indication of peak demand but at a daily usage of only 20kwh I highly doubt that his peak demand is more than 5kw.

I get your point but I also indicated that am newbie I don't know if I have to match inverter output with usage output I only see 5kva inverter but no mention of highest energy it can produce per day with grid meter box can just consume energy, I could also like to know how can I measure inverter output capacity

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1 hour ago, Solaris said:

Oh, I totally agree. A 5kw inverter should cover his needs quite comfortably.

I was only offering advice on how you don’t need to go for the biggest inverter available as some salesmen might lead you to think. A system can start small and be added to, over time. 

I also agree that peak demand determines the inverter size, while the day/night usage will determine the solar array and battery size. 
 

 

Thanks for last paragraph I learned something 

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3 hours ago, Solaris said:

The way I did it was to start small and build up my system over time. It is not always the right way to do it, but it worked for me. Some may argue that getting the biggest and best of everything will cost more now, but save you in the long run. This is not always necessarily true. While buying one big 20kw inverter will mean less wiring, having two 10kw inverters will mean that you can still have 10kw should one of them fail. Having 2 MPPT’s means that I can still use one of them if the other one needs repairs. To me a system running at 50% is better than the whole system being down. I personally prefer to have separate inverters and MPPT’s not the all-in-one setup, but this is just my personal preference. Once again this is because my system can still operate at 50% while the faulty component is being repaired. 

One of the most important things I learned (on this forum) is about the placement of solar panels. For years I had the understanding that panels have to face north for the best production. I was wrong. I learned that if you face your panels not only north, but also some east and some west, you get much better solar production. Granted it is a little more difficult to get the whole system balanced out, but it is well worth it to have solar production from 6:30 until 17:30. 

Couldn't agree more.

I started with a 2Kw Growatt direct inverter and 8x250w panels. This allowed me to cut 10kwh per day out of my bill, and learn a ton of lessons. I added a 5Kw Goodwe, 2x2.4Kw Pylons and 22x250w panels. Recently put in a further 4.6Kw Kodak direct inverter and another 12x330w panels. All three systems entirely separate but linked to my mains.

If one or even two go down or need to be decommissioned it's no biggie.

It's not the most economic way to do things, but it worked for me and allowed me to experiment.

 

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1 hour ago, Jos said:

I also learned that it won't produce decent energy

Not so much that it doesn’t produce decent energy, but rather takes away your peaks. Most of us will have a peak charging ability of perhaps 100a for charging (as an example) so instead of peaking at 100a at midday with a north facing array only, rather have a peak of maybe 90a at 9:30am (from east array) then another peak of 90a at midday (from north array) and the last peak of 90a at 15:30 (from west array). Slightly less power but for a much longer time. Your equipment will be happier with not having to work so hard.

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7 hours ago, Solaris said:

Oh, I totally agree. A 5kw inverter should cover his needs quite comfortably.

Just bear in mind that on a 60A breaker if you may go grid-tied with export you still cannot connect more than 3.5kW of generating capacity. (Not sure if this limitation applies to the inverter capacity or to the installed panels).

But even something like a 3.6kW grid-tied hybrid inverter could contribute to covering up to 70-90% of total energy demand with a small measure of emergency backup power for critical circuits if you put in some batteries. You just shouldn't go off-grid with an inverter like that because you likely won't cover your peak demands. Lots of disclaimers in these figures.

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12 hours ago, GreenFields said:

Just bear in mind that on a 60A breaker if you may go grid-tied with export you still cannot connect more than 3.5kW of generating capacity.

Very good point!! I forgot about this. Probably become my system is totally off grid. 😁

Also, another point that one needs to keep in mind is that only certain municipalities allow you to feed into the grid. So wherever Jos lives will also determine if he can actually feed back or not. Where I stay in East London, it is not allowed.  

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18 hours ago, Jos said:

I could also like to know how can I measure inverter output capacity

 To too sure what you mean by this..... 
 

If you are referring to the inverter’s power output, this is usually stated in the spec sheet. In the case of the older Axpert inverters, they were marketed as 5kva which is a little misleading as they were only good for about 4000w. So before buying an inverter look at output wattage, not kva. 
 

If you are referring to how much power it can put out throughout the day, then you take your output in watts and multiply it by how many hours you use it for. So if you can put out 3500w continually for 8 hours in the day then you have an output capacity of 28000w or 28kwh, but if your system has the capability of doing this will also be determined by your solar production and how long your batteries can last.

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  • 2 months later...

There seams to me a lot of whaotwhao between power and energy. I give you a picture: The power of the engine of a car determines how fast you can go uphill with it. But the fuel content in your car is the stored energy and determines how far you can drive. Electric power is measured in Watts (W, kW) whereas energy is measured in  Watt-hours (Wh, kWh). What you buy from your utility is electric energy in kWh. In order to size an alternative electric power system you should look into your electricity bill. The bill lists the amount of kWh you have consumed. Devi-de this amount by the number of days the bill covers and you will get the average daily consumption. That should be the base of your considerations for sizing your system, in particular the battery and the PV panels. Depending on whether you want to be almost totally or only partly independent from grid. Second consideration is the energy the PV panels can yield in kWh. I found on Internet a yearly yield curve for the latitude of the Garden Route. It shows that 3000W of PV panels yield at optimal exposure 10 kWh per day in the months of June and July. In other months its accordingly more. If you are further North you will get more.

The power sizing has been mentioned quite good. It depends on the size of your household and whether you cook electric or with gas. I first sized my system with a 5kW inverter, 3000W of PV panels and 9.6kWh (200Ah, 48V) battery. Pretty soon I added 4.8kWh (100Ah) battery in order to have some reserve for a cloudy day. With electric cooking the cook sometimes managed to overload the inverter. So I decided to parallel it with a second unit. That not only boosts the max power but also reduces the strain on them by sharing the load. And it provides redundancy in case one fails.

A word to units: It is not left to the taste of a writer whether to write units in lower or upper case. There is an International Standard for Units. And the case has a meaning. For example: mm means millimeter whereas MM would mean mega Mile. So the Watts are W, the Watthours are Wh, the current is A, the voltage is V.

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3 hours ago, Beat said:

There seams to me a lot of whaotwhao between power and energy. I give you a picture: The power of the engine of a car determines how fast you can go uphill with it. But the fuel content in your car is the stored energy and determines how far you can drive. Electric power is measured in Watts (W, kW) whereas energy is measured in  Watt-hours (Wh, kWh). What you buy from your utility is electric energy in kWh.

Just to clarify between kW and kVA: If you have a reactive load (motors, transformers etc.) the current is not in phase with the voltage. With a resistive load it is in phase. Most residential properties loads are almost totally resistive so there is no difference between kVA and kW.

The utilities will bill in kVAh since they need to power any reactive load if there is one (which they discourage)

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19 hours ago, Richard Mackay said:

Just to clarify between kW and kVA: If you have a reactive load (motors, transformers etc.) the current is not in phase with the voltage. With a resistive load it is in phase. Most residential properties loads are almost totally resistive so there is no difference between kVA and kW.

The utilities will bill in kVAh since they need to power any reactive load if there is one (which they discourage)

Thank you for your remarks. The first one is correct.

The second remark surprises me. I have never and nowhere seen billing the apparent power in kVA. As a matter of fact the meters are (must) be designed to meter only the active (resistive) power in kW. In the countries I know it's a legal requirement. The utility companies may however have agreements specially with industrial customers to additionally meter and bill the reactive power. Special meters are required.

Remark: The apparent power is the combination (vectorial sum) of active (resistive) power and reactive (pure inductive) power.

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  • 2 weeks later...
On 2020/10/07 at 5:59 PM, GreenFields said:

Just bear in mind that on a 60A breaker if you may go grid-tied with export you still cannot connect more than 3.5kW of generating capacity. (Not sure if this limitation applies to the inverter capacity or to the installed panels).

But even something like a 3.6kW grid-tied hybrid inverter could contribute to covering up to 70-90% of total energy demand with a small measure of emergency backup power for critical circuits if you put in some batteries. You just shouldn't go off-grid with an inverter like that because you likely won't cover your peak demands. Lots of disclaimers in these figures.

Please help me understand you correctly the 3.4kW is inverter capacity? Or is solar array capacity? Sorry if I use wrong terminologies just bear with me am trying to check if is with it to get Grid-tie/hybrid inverter if is small Eskom power supply "4000W" can I have 10kwh solar array capacity?

Let me say I get 3kW hybrid inverter, 6x410W solar panels, 2x3.5kwh battery plus accessories 

 

 

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On 2020/12/22 at 8:07 PM, Jos said:

Please help me understand you correctly the 3.4kW is inverter capacity? Or is solar array capacity? Sorry if I use wrong terminologies just bear with me am trying to check if is with it to get Grid-tie/hybrid inverter if is small Eskom power supply "4000W" can I have 10kwh solar array capacity?

Let me say I get 3kW hybrid inverter, 6x410W solar panels, 2x3.5kwh battery plus accessories 

Thing is, I don't really know the finer interpretation, and I'm cautious to give any advice other than: speak to your municipality and get it from the horse's mouth. My own experience is from having a pure grid-tied system with export that's safely within all limits.

Generally, if you have a 60A circuit breaker on your house, you may not export more than 3,5kW (3500W) into the municipal grid. But if you have 6x410W array, that's just a 2460W max output, so that shouldn't be a problem. Also, if you have a 3kW hybrid inverter, and I mean a "true" hybrid grid-interactive inverter that exports power to Eskom, and not one of these so-called hybrid Axpert battery inverters with solar inputs, even that 3kW inverter is within the 3.5kW export limit, so that should be safe.

The part I don't know is, if you have a nominal 3kW output grid-tie inverter that allows you to add up to say 4kW of panels on the input side, whether that is allowed. Or if you have a 5kW inverter but you're only connecting 2460W of panels, if that's okay. Or if you've got a grid limiter that keeps the power internal to your premises... ??? If you find out, please let me know.

The 2x3.5kWh battery has nothing to do with it. That's just the amount of "petrol in the tank", not the "size of the engine output"

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8 hours ago, GreenFields said:

Thing is, I don't really know the finer interpretation, and I'm cautious to give any advice other than: speak to your municipality and get it from the horse's mouth. My own experience is from having a pure grid-tied system with export that's safely within all limits.

Generally, if you have a 60A circuit breaker on your house, you may not export more than 3,5kW (3500W) into the municipal grid. But if you have 6x410W array, that's just a 2460W max output, so that shouldn't be a problem. Also, if you have a 3kW hybrid inverter, and I mean a "true" hybrid grid-interactive inverter that exports power to Eskom, and not one of these so-called hybrid Axpert battery inverters with solar inputs, even that 3kW inverter is within the 3.5kW export limit, so that should be safe.

The part I don't know is, if you have a nominal 3kW output grid-tie inverter that allows you to add up to say 4kW of panels on the input side, whether that is allowed. Or if you have a 5kW inverter but you're only connecting 2460W of panels, if that's okay. Or if you've got a grid limiter that keeps the power internal to your premises... ??? If you find out, please let me know.

The 2x3.5kWh battery has nothing to do with it. That's just the amount of "petrol in the tank", not the "size of the engine output"

Thank you very much

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