Planning an off-grid hybrid solar system

[Encid]

21 hours ago, Crossy said:

Unless you are really tight for space you will likely get more bang-per-buck from the older, smaller (power and size) panels. Do your sums carefully.

I've done another panel layout this time using the smaller 340W panels.

 

This plan involves installing 60 x 340W panels (20.4 kW) as per the sketch below.

Panels 1-12, 18-23, 38-49, and panels 50-55 facing South (total 36 panels).

Panels 13-17, 31-37, and 56-60 facing East (total 17 panels).

Panels 24-30 facing West (total 7 panels).

 

Future additional panels could be mounted on top of the carport if required.

 

 

I am yet to be convinced (but I am willing to listen to reasonably presented logic) that having panels that do not face south are either useless or a waste of money.

I am of the opinion that PV solar panels are the cheapest components of any domestic solar power system, and will have a working life of 25 years+.

The big money is in the inverters and the batteries, which will need to be replaced in time, as I am sure you will all agree on.

I am also of the opinion that not only will the east facing panels help start my power generating day earlier, they will help to hide the south facing panels from the front of the house, thus increasing the "street appeal".

And the west facing panels will help to extend my power generating day later.

Don't forget... ALL of the panels will receive solar radiation during the peak production period of say 10am to 2pm. 

 

Thoughts?

[Encid]

Using the smaller (power and size) panels comes with a significant cost savings too...

 

40 x 540W = 21.6kW @ 228,000 baht.

60 x 340W = 20.4kW @ 197,400 baht

 

I like it! 

[Crossy]

16 minutes ago, Encid said:

Thoughts?

 

I have no problem with your thoughts ???? 

 

Your next problem is how to arrange your strings, if at all possible, avoid shading one or two panels in a string, the total output will get slugged pretty badly. Bypass diodes do help a bit (and most panels have them as standard now) but careful planning is better ????  

 

Any idea which inverters you are going to use? Separate charge-controllers or all-in-one inverters? (or even a combination of the two)

[Encid]

3 minutes ago, Crossy said:

Any idea which inverters you are going to use? Separate charge-controllers or all-in-one inverters?

Sofar, Solax, and Growatt are the three main inverter manufacturers I am looking at currently... as all have integrated MPPT charge controllers, but I am open to suggestions for others.

 

8 minutes ago, Crossy said:

Your next problem is how to arrange your strings, if at all possible, avoid shading one or two panels in a string, the total output will get slugged pretty badly.

Yes... it is possible that panels 50 and 51 will be shaded by the elevated central roof section in the late afternoon, but if they are on the same string as the west facing panels, then the bypass diodes should help shouldn't they?

 

13 minutes ago, Crossy said:

careful planning is better ???? 

That is exactly why I have started this topic now... before our house is even built. 

Who knows...? In 6-12 months time from now there may be some breakthroughs in technology that may change the specifics of the system we are discussing here.

I have much to learn, and do not want to be conned into buying and installing a system that will not suit our needs.

 

[Bandersnatch]

39 minutes ago, Encid said:

I am yet to be convinced (but I am willing to listen to reasonably presented logic) that having panels that do not face south are either useless or a waste of money.

 

Solar in the tropics is not the same as solar “back home” I think real examples from Thailand is what you should be looking at. 
 

Above is a graph from one of my inverters here in Thailand.

[Rintarah2]

Interesting series of mails, we also will be considering solar array soon.

JBChiangRai would you be interested in offsite mail correspondence this and similar topics ?

We recently entered property market, presently in UK replenishing funds !

<email removed per forum rules. Please PM>

Edited January 21, 2023 by Crossy

[JBChiangRai]

8 minutes ago, Rintarah2 said:

Interesting series of mails, we also will be considering solar array soon.

JBChiangRai would you be interested in offsite mail correspondence this and similar topics ?

We recently entered property market, presently in UK replenishing funds !

<email removed per forum rules. Please PM>

email sent

Edited January 21, 2023 by Crossy

[JBChiangRai]

6 minutes ago, Bandersnatch said:

 

 

What you are experiencing at 11am is kind of why I added in Grid-Tied inverters, I didn't want the power of the sun going to waste, I wanted to squeeze as much efficiency as I could out of my system.

 

I have mono-crystalline panels and decided to use the extra power I was generating in running all the air-cons and keeping the whole house cool, even have air conditioning in the entrance hallway and the garage to keep my BEV cool.

[Elkski]

1 hour ago, Encid said:

I've done another panel layout this time using the smaller 340W panels.

 

This plan involves installing 60 x 340W panels (20.4 kW) as per the sketch below.

Panels 1-12, 18-23, 38-49, and panels 50-55 facing South (total 36 panels).

Panels 13-17, 31-37, and 56-60 facing East (total 17 panels).

Panels 24-30 facing West (total 7 panels).

 

Future additional panels could be mounted on top of the carport if required.

 

 

I am yet to be convinced (but I am willing to listen to reasonably presented logic) that having panels that do not face south are either useless or a waste of money.

I am of the opinion that PV solar panels are the cheapest components of any domestic solar power system, and will have a working life of 25 years+.

The big money is in the inverters and the batteries, which will need to be replaced in time, as I am sure you will all agree on.

I am also of the opinion that not only will the east facing panels help start my power generating day earlier, they will help to hide the south facing panels from the front of the house, thus increasing the "street appeal".

And the west facing panels will help to extend my power generating day later.

Don't forget... ALL of the panels will receive solar radiation during the peak production period of say 10am to 2pm. 

 

Thoughts?

Wouldn't you have to do an analysis of the power produced calculations using the angle of incidence effeciency for the panels.  Maybe need to add design time for different mounting angle bracket needed for 4 surfaces. I thought panel 10 and was it 28  on the first layout needed deleted for access to the big! panel corners. 

[Muhendis]

21 hours ago, Bandersnatch said:

The best compromise angle for winter/summer sun is 15 degrees

That is true up to a point.

Trouble is it doesn't take into account the loss of power from the sun in the winter when it is lower in the sky. In these circumstances the light has a bit more atmosphere to get through and is attenuated before it reaches the solar panels. To compensate for this the angle of 15º is changed by 2º to 17º thus giving better power when the sun shine is weaker.

[JBChiangRai]

I think a lot depends on how you use your power.  The cheapest battery you will ever get is the PEA Grid if you go Grid-Tied.  My battery is only used for power cuts and the other thing about batteries here is the warranty.  I made my own and I'd rather buy a diesel generator than strip the whole thing down if a cell fails.  How good is the warranty on your battery? Do you really trust them? Is it a household name? Supplied by a global household name who will stand behind their warranty?

 

The batteries are usually the most expensive part of a system, if you're cycling them every day they won't last more than 7-8 years.

 

I spin my meter back 30-50 KwHrs every daytime and draw it back every nighttime.  I got my battery cheap from a now deceased friend though his Chinese wife.  I paid 80k THB for 28.8 KwHrs, I would need double that if not Grid-Tied.

[Muhendis]

3 hours ago, Encid said:

ALL of the panels will receive solar radiation during the peak production period of say 10am to 2pm.

You are planning on having 4 inverters but only three PV sources.

I can't think how you are going to achieve connecting three into four. 

If this is done by splitting each of the PV arrays into the right number of strings for each inverter then are you sure you won't be overloading the PV input maximum power?

What are the input limits of the inverters?

[Bandersnatch]

3 hours ago, Muhendis said:

That is true up to a point.

Trouble is it doesn't take into account the loss of power from the sun in the winter when it is lower in the sky. In these circumstances the light has a bit more atmosphere to get through and is attenuated before it reaches the solar panels. To compensate for this the angle of 15º is changed by 2º to 17º thus giving better power when the sun shine is weaker.

Having had off-grid solar for 4 years now in Thailand I would say that there are only 2 seasons as far as solar is concerned: rainy season and dry season.

 

In the video I posted yesterday in this discussion was a drone shot of all my solar panels taken at 7am on the winter solstice last year. All but the west facing panels were in full sun.

 

The easiest way to fit solar is to use your latitude as the angle but if want to change that I would suggest trying to maximize solar gain for the rainy season months.  

 

 

[Encid]

13 hours ago, Muhendis said:

You are planning on having 4 inverters but only three PV sources.

I can't think how you are going to achieve connecting three into four. 

If this is done by splitting each of the PV arrays into the right number of strings for each inverter then are you sure you won't be overloading the PV input maximum power?

What are the input limits of the inverters?

This is the sort of thing that I am seeking advice on... with the new proposal using 60 x 340W panels (total 20.4kW).

Three inverters or four?

The jury is out on that one at the moment but as it was originally suggested by @Crossy I thought I'd follow suit.

 

I have not selected inverters yet, but if I go with the Growatt SPF500ES off-grid hybrid inverters they are (each) designed for 6000W maximum PV array power with a maximum solar charge current of 100A.

 

"Splitting each of the PV arrays into the right number of strings for each inverter" is something that I am having difficulty understanding... can you explain more please? (in layman's terms).

[Encid]

16 hours ago, JBChiangRai said:

I spin my meter back 30-50 KwHrs every daytime and draw it back every nighttime.

Technically that is illegal, chaimai? 

You would not want to get caught and have your current spinning disk meter replaced by a new electronic one-way only meter.

[Encid]

12 hours ago, Bandersnatch said:

The easiest way to fit solar is to use your latitude as the angle but if want to change that I would suggest trying to maximize solar gain for the rainy season months. 

That is where I think that the east facing panels will come into play more... they won't help much in the event of a 3-5 day tropical storm, but typically during the rainy season the storms arrive in the afternoon. 

[Pink7]

14 minutes ago, Encid said:

This is the sort of thing that I am seeking advice on... with the new proposal using 60 x 340W panels (total 20.4kW).

Three inverters or four?

The jury is out on that one at the moment but as it was originally suggested by @Crossy I thought I'd follow suit.

 

I have not selected inverters yet, but if I go with the Growatt SPF500ES off-grid hybrid inverters they are (each) designed for 6000W maximum PV array power with a maximum solar charge current of 100A.

 

"Splitting each of the PV arrays into the right number of strings for each inverter" is something that I am having difficulty understanding... can you explain more please? (in layman's terms).

Growatt SPF500ES now support 21A, who is perfect for most 330-350 watt panels with  around 10A Current. That way you can set up for example 7+7 or 8+8 panels with parallel connector and then a more medium voltage level. In this example you get around 20 Amp and 400v and 5k watt panels. Then parallel inverters up to needed capacity.

 

Edit: Its smart not push the V limit..

 

Pink

Edited January 22, 2023 by Pink7

[Crossy]

56 minutes ago, Pink7 said:

Edit: Its smart not push the V limit..

This ^^^.

 

The sum of you Voc (Open Circuit Voltage) of your panels in series MUST NEVER exceed the maximum input voltage of your MPPT.

 

The better inverters will simply turn themselves off with an error, the not so good (or if you go way over) will turn themselves off with the exit of the Magic Smoke.

 

It's not likely to be an issue here, but the Voc goes up with decreasing temperature (it's specified at 25C), so in places where it gets really chilly you could actually over-volt your MPPT even if the sums say you are OK.

[Encid]

25 minutes ago, Pink7 said:

Growatt SPF500ES now support 21A

Sorry, but I do not understand this.

See attached datasheet - it states a maximum solar charge current of 100A.

 

Growatt SPF 3500-5000 ES Datasheet.pdf

[Pink7]

11 minutes ago, Encid said:

Sorry, but I do not understand this.

See attached datasheet - it states a maximum solar charge current of 100A.

 

Growatt SPF 3500-5000 ES Datasheet.pdf 7.98 MB · 1 download

If you able to connect 2 strings in parallel the voltage is half compared to all panels in serial. Growatt now handle 21A. V limit 450VDC. So v limit will get you around max 10 panels if all in one string. 2 string in parallel you can have 16 panels.

 

Pink

 

 

Edited January 22, 2023 by Pink7

[Encid]

13 minutes ago, Crossy said:

The sum of you Voc (Open Circuit Voltage) of your panels in series MUST NEVER exceed the maximum input voltage of your MPPT.

The MPPT range at operating voltage for the Growatt SPF500ES is 120VDC - 430VDC according to the datasheet I attached in my previous post.

 

Does this look OK?

 

Funny you should mention decreasing temperature... this morning it was a chilly 18⁰C on the farm... and on Wednesday it is forecast to go as low as 15⁰C. 

[Pink7]

3 minutes ago, Encid said:

The MPPT range at operating voltage for the Growatt SPF500ES is 120VDC - 430VDC according to the datasheet I attached in my previous post.

 

Does this look OK?

 

Funny you should mention decreasing temperature... this morning it was a chilly 18⁰C on the farm... and on Wednesday it is forecast to go as low as 15⁰C. 

V limit 450VDC. So v limit will get you around max 10 panels if all in one string. 2 string in parallel you can have 16 panels.

 

Pink

[Muhendis]

3 minutes ago, Encid said:

The MPPT range at operating voltage for the Growatt SPF500ES is 120VDC - 430VDC according to the datasheet I attached in my previous post.

 

Does this look OK?

 

Funny you should mention decreasing temperature... this morning it was a chilly 18⁰C on the farm... and on Wednesday it is forecast to go as low as 15⁰C. 

Yes.

As the temperature of the panels goes down their output goes up and conversely as the day goes at the time of most output the panels will be hotter and give less output.

If you derate the output by 10% you will be on the conservative side of about right (this loss can be as much as 20%).

The panels are characterised at 25ºC and with a 1kw sunlight simulator.

[Muhendis]

9 minutes ago, Pink7 said:

V limit 450VDC. So v limit will get you around max 10 panels if all in one string. 2 string in parallel you can have 16 panels.

 

Pink

Note there is only 1 MPPT input per inverter so paralleling needs to be done with a combiner. 

BUT

The East and West arrays could produce 7.82kw each which is above the spec. of 6kw per inverter.

Edited January 22, 2023 by Muhendis

[JBChiangRai]

56 minutes ago, Encid said:

Technically that is illegal, chaimai? 

You would not want to get caught and have your current spinning disk meter replaced by a new electronic one-way only meter.

Illegal? I don't think it's illegal as in "breaking a law", for sure it's against PEA rules because although my equipment is on their approved list, I just use a lot more of it than they like and I had my sparks install it instead of one of their approved installers. Most Grid-Tied installations are like that.  I can think of 6 of my friends off the top of my head who all do the same and I don't know anyone who has an approved installation.  

 

We are all going to end up with one-way meters at some point.  In Chiang Rai all new meter installations appear to be one-way electronic types, if they replace mine I would be no worse off than not exporting from the outset, I'm not so sure I would want to cycle my batteries though, I would need to do the sums on the cost of replacing them vs. the cost saving of cycling them.  I am 40% of the way to generating an ROI on my installation.

 

One of my friends also has a Hybrid system, one of his two batteries failed after 2 years, the supplier isn't interested in honouring the warranty.  I definitely wouldn't go Hybrid again.

[Muhendis]

Another thought about the panel arrangement.

Although the total power capability is over 20 kW you will never get that much with panels pointing in different directions. 

Also the max. power from three 5kw inverters in parallel could be 15 kW but only if all inputs are at good power.

 

[Encid]

17 minutes ago, Pink7 said:

V limit 450VDC. So v limit will get you around max 10 panels if all in one string. 2 string in parallel you can have 16 panels.

 

I'm not sure where you get the V limit of 450VDC... the datasheet gave an "operating range limit" of 430VDC, it makes no mention of a "maximum range limit".

 

According to the 340W panel datasheet the Voc is 46.4V, so wouldn't 10 panels in one string exceed the limit? 464VDC. 

9 panels in one string would be 417.6VDC, which is well within the "operating range limit" of 430VDC.

 

Or am I missing something here?

 

[JBChiangRai]

I'm not sure about systems charging batteries, but if you are Grid-Tied, you can exceed the maximum power in watts of the inverter, but not the VoC.  Exceeding the input power will just flatten the curve and give you more output outside peak sunlight hours (11:00-13:00) and also on poor sunlight days.

 

Your PV will derate by about 15-20% in the first 18 months, certainly mine have, they are mono-crystalline which are supposed to be better than Poly.

[Crossy]

3 minutes ago, Encid said:

I'm not sure where you get the V limit of 450VDC...

 

[Crossy]

If you are using 340W panels then the 6,000W per inverter limit gives you 18 panels per inverter.

 

Arranged as 9S2P you are in the sweet-spot for the MPPT and everyone is happy ????

 

60 panels are going to need 4 inverters.

 

Provided you stay with the 18 panel per inverter and 9 panels in series limits then you can decide how to organise your strings for best performance (look for shading issues at either end of the day).