Panel voltage clarification

[StephenB]

Good day people. I am extremely new to the solar side of stuff and would like some clarification on a few concerns. Obviously going for a a full on system would cost a kidney and a lung. But I would.like to start small and build up the system to be a  5kw  preferably  a 24v system but if I have to have a 48v system then it is what it is. I am currently using a inverex 1200w 24v inverter  and 2 x 12v 200ah gel batteries just to power a few things in the home I would like to install some panels to charge the current set up, but be able to use the  the same solar panels for the final product. I am not sure how to spec the panels as the voltages vary please assist I am really confused on this

 

[Merlin]

"Obviously going for a a full on system would cost a kidney and a lung"

Nope! Both kidneys will unfortunately have to go if you want full on off grid

[Jaco De Jongh]

24 minutes ago, StephenB said:

would like to install some panels to charge the current set up, but be able to use the  the same solar panels for the final product. I am not sure how to spec the panels as the voltages vary please assist I am really confused on this

If this is a medium to long term plan, start with as big panels you can get, they are normally the newest on the market. This will ensure that they are still available in a year or two. If you also chose to invest in the Best. lets say Victron MPPT, that you can afford right now, It will ensure that you can add to its max capability over time. Added value of MPPT is that the voltage would not matter as the MPPT will control it back to the Battery Voltage. 

Choosing the right components now will just help easing the final transition to your permanent system.  

[Guest]

3 hours ago, StephenB said:

Obviously going for a a full on system would cost a kidney and a lung.

Naa, a kidney and a lung. But on a 24v system you can get away with half a kidney, but it is still painful.

Here is an idea:

3 hours ago, StephenB said:

... inverex 1200w 24v inverter ...

Get a Victron MPPT that can charge the batteries with ease. You can later sell it OR get an 2nd smaller one if you add more batteries LATER.

When you are ready the trick will be to find a Victron Multigrid 24v inverter - it is on the NRS list so that little issue is all sorted.

 

3 hours ago, StephenB said:

... 2 x 12v 200ah gel batteries ...

Perfect, use them for as long as they last. What you do is put the batts in "Keep Always Charged" so that they are only used if there is a Eskom failure, then you can oversize the panels a bit easier till you are ready to go lithium batteries much later.

 

3 hours ago, StephenB said:

... 2 x 12v 200ah gel batteries ...

5kva, why?
5kva's grid tied needs a 83amp DB breaker for SANS and NRS regulations can trip you later. Most homes have a 63amp breaker. So keep in the 3.5kw or less inverter range.
NRS and SANS regulations dictate the future of grid tied in SA. 

So a Victron Multigrid 24v 3kva gets you blerrie far down the track ito saving each and very day being grid tied. Been there done that. 

You start with say 2.1kw or maybe 3kw of panels on a 24v system because the inverter can only handle 2.4kw continuous.
Anything bigger and you are wasting panels because you don't have the batteries to store the power in.
And by having first one MPPT, if you later need more panels and the brand or size is not manufactured anymore, simply buy a 2nd MPPT with another brand of panels, if that is the case later.

Buying the parts separately leaves a lot more room to move over time.

 

FYI:
I started with 2.1kw and saved about R1k per month in summer since last year Sept/Oct.
Now I'm going 3.5kw because Cape Town has some issue with clouds in winter see.
The plan from here for much later is that if Eskom does fail us finally, by simply changing my MPPT from a 150/100 to a 250/100, I can add another 10 panels and go 7kw on a 24v system. Note: For THAT to work I need a lot more batts, a LOT, and a 2nd inverter - so lets hope Eskom stays around for a long while still.

Edited July 16, 2019 by Guest

[Jaco De Jongh]

14 hours ago, The Terrible Triplett said:

The plan from here for much later is that if Eskom does fail us finally, by simply changing my MPPT from a 150/100 to a 250/100, I can add another 10 panels and go 7kw on a 24v system.

I have to ask about this, only if it is to learn something new, but looking at the datasheet I can not figure out how you will be able to do this, even if you use 2 of those MPPT's, or am I missing something very important?

[Guest]

2 hours ago, Jaco de Jongh said:

I have to ask about this, only if it is to learn something new, ...

The two core non-negotiable undeniable rules for all controllers are:
NEVER ever exceed the Max volts of the controller.
NEVER ever exceed the Max PV short circuit current of the controller.

Using Victron's Calculator, one can do this:
1 and 2 is ok for that is under peak conditions, full power drawn from array, and in Cape Town winter I don't see that ever a problem.
Rest of the time it would be interesting to see it drawing the full potential of the array to make it clip the Max current.

[Guest]

If it all comes to play, it is done so for the newbies - but I must say, I also need to go 48v inverter!
1) First array - 3.5kw = 10 x 350w set as 2 in series / 5 parallel with 6mm2 wire and 5 x double pole 16amp NoArk breakers - no fuses required.
2) Upgrade - IF needed - add another 10 x 350w = 20 panels in total - and no change to combiner box, just upgrade the 150/100 to a 250/100 MPPT.

IF I cannot find 350w or 355w panels at that time, then simply another 150/100 and 10 panels, and stay on 24v.

[Jaco De Jongh]

58 minutes ago, The Terrible Triplett said:

Rest of the time it would be interesting to see it drawing the full potential of the array to make it clip the Max current.

Please be careful not to fall in this trap while designing your system. The following pictures will show you why. The aim is to have everything green. Yellow means that the output is been limited and adding more strings will hold  absolutely no benefit for you. Although you add more to the input, the Mppt wont allow out more than its output rating, in this case its 100 Amps. (No benefit except for early morning, late afternoon and cloudy days, but in the middle of a perfect sunny day, your array will be in idling mode) 

At the bottom of the data sheet, point  1A, you will see the logic's behind it. 

Now look at an example using panel supplied by the app itself. 

1. Start with one string of 4. All green (Total PV = 1320 Watt) 
2. (Total PV = 2640 watt) Add 1 string. Cold whether output gets clipped, note we are getting closer to Nominal  PV power on a 24Volt system as per Datasheet 2 posts up (2900).
3. (Total PV = 3960 watt )Adding one string more.  Now Cold and hot weather output gets clipped. Everything you add after this point will not contribute to the output under normal sunny conditions and will only come into play during low light or cloudy conditions. 
4. (Total PV = 9240 watt ) I can add another 4 strings, without adding 1 amp to the output and still have an "Accepted" Green at the bottom. 
5. (Total PV = 10560) Only when I add string number 8, the app tells me "NOT accepted"

Although the app allowed me to add 4 more strings I had absolutely no benefit on the output side, that is why it is best to design your system toe the Nominal PV Power for your system voltage on the Data sheet, and if you have some extra money, add 30% to that, to help in low light conditions. Anything more than that will be a total waste of money for most parts of the year. 

 

[Guest]

47 minutes ago, Jaco de Jongh said:

Yellow means that the output is been limited and adding more strings will hold  absolutely no benefit for you.

Correct.

Ps. Interestingly on a 24v the 150/100 reaches "More than 30% ... " "differently" than the 250/100, see pic below. 400w panels gave their own challenges.

Ok, first point: Inverter can use a max 2.4kw max continuous, anything more ito paneling and one better have more batteries.
Note 1: I run the old bank "Keep fully charged" ... for now.
Note 2: I can swap the inverter at a drop of a hat with a 48v unit, re-registration but a minor inconvenience.

It all started because in watching the data the last few months, I saw that the 2.1 kw array easily runs out of steam being kinda "pure" grid tied, more so now that I have another geyser (2kw elements) on the system. And being winter it gets even more interesting. I need the 2.4kw from about 11ish to 5pm-ish.
That is for a +-500w average load and 3 x 2kw heating elements - all on timers.

So I sat down and "played" around asking: What combination can I put up one time that:
1) leaves room to maneuver,
2) AND can provide the 2.4kw I want for longer,
3) AND can double up IF I want to really push the envelope next level?

Answer: 3.5kw array.
Theoretically I should get 2.4kw easier from a 3.5 kw array as the MPPT cannot draw more from the panels than what the inverter can use. So the Yellow is a non-issue.
But I can get to 2.4kw earlier and also for longer in the day = better average of getting that max of 2.4kw spread over the entire day.

And WHEN I add more batteries then I suspect I could be pushing the Yellow limits right? So, I simply sell the 24v unit and get a 48v unit. See 2nd pic below.

So, with the goal of getting 2.4kw from the array as consistently and for as long as possible in a day,  I recon I got it covered on all sides and bases ... or am I still missing something?
And remember, I have a "escape" route planned IF I need to push the 3.5kw array to it's max with more batts.
 

 

If I go 48v one day, same 3.5kw. Not boxed in in other words - and I can THEN add more panels and start the dance again.

 

[Jaco De Jongh]

1 hour ago, The Terrible Triplett said:

Answer: 3.5kw array.

Now that I can agree with......

[Guest]

2 hours ago, Jaco de Jongh said:

Now that I can agree with......

... then you are halfway there.  

Because on a 48v system the exact same logic I used for justifying a 3.5kw array on a 24v system, will apply "as is" to doubling the array to a 7kw array on a 48v system.

The ONLY caveats being:
1) YOU HAVE THE BATTERIES to store that power.
2) AND / OR you have 2 x 3kva (2.4kw continuous) inverters in parallel = 4.8kw AND THAT YOU CAN USE THAT 4.8kw near continuous.

For me to get to that level, yes the plan is in place, Eskom would have failed us horrendously and therefor ... well, lets just say a whole new set of rules shall be followed.

Let me share how I got to it:
What I did was I loaded a few panels and over a while I mixed and matched the combinations until I felt I had the most watts from the array WITHOUT getting the "Exceeding 30%" warning. That is also where I saw that the 400w panels do not "fit" so nicely.

The i.e. SPP330 panels you used to illustrate your point does not "fit" nicely. They and the 330w Canadians get to 6.6kw before the warning of exceeding 30%, which is at 8.25kw.

On a 48v system with a 250/100 MPPT - the "rule" used is to not get a "Exceeding 30%" warning right?
So a 400w panel gives you up to 6.4kw before exceeding 30% at 8kw. I can get to 7kw with the 350w panels.
FYI. Why I like larger panels: To get to 6.5kw with 400w panels you need 16. I like.
To get to 7kw on the 350's, you need 20 - I suck it up and take the 500w extra.  

And on 24v system, 400w panels gets me to 3.2kw before exceeding 30% at 4kw. I can get to 3.5kw with the 350w panels.
The 330w panels gets me to 3.3kw ...

Edited July 17, 2019 by Guest

[Jaco De Jongh]

12 hours ago, The Terrible Triplett said:

... then you are halfway there.  

Your current "logic" is just telling me what I have already told you above. None of what you are saying explains how you got to your first "logic", (7kw on 24 Volt)

 

On 2019/07/17 at 12:14 AM, The Terrible Triplett said:

I can add another 10 panels and go 7kw on a 24v system.

 But lets leave it there... just glad we could straighten it out before someone follows your "logic" and install 7kw on 24 volt, resulting in almost 2/3 of his array just sitting on the roof not adding value to his setup under normal conditions.  

[StephenB]

On 2019/07/17 at 12:14 AM, The Terrible Triplett said:

Naa, a kidney and a lung. But on a 24v system you can get away with half a kidney, but it is still painful.

Here is an idea:

Get a Victron MPPT that can charge the batteries with ease. You can later sell it OR get an 2nd smaller one if you add more batteries LATER.

When you are ready the trick will be to find a Victron Multigrid 24v inverter - it is on the NRS list so that little issue is all sorted.

 

Perfect, use them for as long as they last. What you do is put the batts in "Keep Always Charged" so that they are only used if there is a Eskom failure, then you can oversize the panels a bit easier till you are ready to go lithium batteries much later.

 

 

5kva, why?
5kva's grid tied needs a 83amp DB breaker for SANS and NRS regulations can trip you later. Most homes have a 63amp breaker. So keep in the 3.5kw or less inverter range.
NRS and SANS regulations dictate the future of grid tied in SA. 

So a Victron Multigrid 24v 3kva gets you blerrie far down the track ito saving each and very day being grid tied. Been there done that. 

You start with say 2.1kw or maybe 3kw of panels on a 24v system because the inverter can only handle 2.4kw continuous.
Anything bigger and you are wasting panels because you don't have the batteries to store the power in.
And by having first one MPPT, if you later need more panels and the brand or size is not manufactured anymore, simply buy a 2nd MPPT with another brand of panels, if that is the case later.

Buying the parts separately leaves a lot more room to move over time.

 

FYI:
I started with 2.1kw and saved about R1k per month in summer since last year Sept/Oct.
Now I'm going 3.5kw because Cape Town has some issue with clouds in winter see.
The plan from here for much later is that if Eskom does fail us finally, by simply changing my MPPT from a 150/100 to a 250/100, I can add another 10 panels and go 7kw on a 24v system. Note: For THAT to work I need a lot more batts, a LOT, and a 2nd inverter - so lets hope Eskom stays around for a long while still.

Thanks for the information. The reason for the 5kw option is for the booster pump I use . I want to be able to run freezer fridge adsl and two TVs and approx 20 lights off it. And probably a few little gadgets the the motor is a 1/2 horse. I am actually situated in Zimbabwe and I dont think there will be a issue with the option of 5kw inverter being installed. 

[Guest]

11 minutes ago, StephenB said:

Zimbabwe

Then all the Victron inverters are for there for your perusal.

If you have no access to electricity, only off-grid, you COULD even look at the Phoenix range - the have no chargers - so the MPPT is your only "charger".

[seant]

I believe Zim has just scrapped import duties on solar kit so that should help a bit

[StephenB]

4 hours ago, seant said:

I believe Zim has just scrapped import duties on solar kit so that should help a bit

They have and we been having 18 hour power outages here and i am looking at putting together a system over time. For the sanity of the family and myself we have to look at a decent system  to tie us over till we either off the grid totally or fill the time when we have no power.

[StephenB]

6 hours ago, The Terrible Triplett said:

Then all the Victron inverters are for there for your perusal.

If you have no access to electricity, only off-grid, you COULD even look at the Phoenix range - the have no chargers - so the MPPT is your only "charger".

Will do and will ask questions as I go. It's nice to have some advice on these things.

[Guest]

Just to add more clarity on a 2.4kw inverter and a 3.5kw array - or 5kva (4kw) inverter on a 7kw array.

For me it is all about the average generation from the array over 12 months, from as early to as late as possible per day, than about peak generation.

Being grid-tied, and not off-grid, peaks like i.e. kitchens or what a array can do for a "short period" is of no concern to me when it is the average over 12 months that I need to focus on.

And then there is a side benefit.
After dealing with the average daily 2.4kw loads there should be enough spare to re-charge a larger battery bank to store the excess power during those few peak hours on good days.

So my plan is:
Today I deal with the 2.4kw (inverter max) I want to consistently as possible generate.
Then with the new data I will deal with more batteries ... later.

So @StephenB , you mentioning 24v and wanting to "grow" the system over time, I think we are not that far apart in where I started, and am today, on this journey of generating our own power.

Edited July 20, 2019 by Guest

[StephenB]

On 2019/07/20 at 11:26 AM, The Terrible Triplett said:

Just to add more clarity on a 2.4kw inverter and a 3.5kw array - or 5kva (4kw) inverter on a 7kw array.

For me it is all about the average generation from the array over 12 months, from as early to as late as possible per day, than about peak generation.

Being grid-tied, and not off-grid, peaks like i.e. kitchens or what a array can do for a "short period" is of no concern to me when it is the average over 12 months that I need to focus on.

And then there is a side benefit.
After dealing with the average daily 2.4kw loads there should be enough spare to re-charge a larger battery bank to store the excess power during those few peak hours on good days.

So my plan is:
Today I deal with the 2.4kw (inverter max) I want to consistently as possible generate.
Then with the new data I will deal with more batteries ... later.

So @StephenB , you mentioning 24v and wanting to "grow" the system over time, I think we are not that far apart in where I started, and am today, on this journey of generating our own power.

For me it's about keeping family happy and having power when the supplier is out we currently experiencing 18 hour outages here in zim and I am purchasing my first  two 400w Canadian panels next week with a victron 100 35 charge controller this would be the initial setup to keep people happy. I would definitely like to go bigger on the solar and run more stuff in the future. For now it's about keeping the lights on and TVs. Its trivial but it's a big thing when you dont have power when u awake.

[Guest]

On 2019/07/26 at 6:18 PM, StephenB said:

Its trivial but it's a big thing when you dont have power when u awake.

Nothing is trivial when you don't have power. 

400w panels on a 150/35 is interesting. I see you can get to about 1600w (2S/2P) on 48v and only 2S (800w) on 24v. 

24v gets one quick to the limits of a MPPT and forces creativity ito matching what panels to which MPPT's.

[StephenB]

Cash is a slight issue at the moment. It's a starting point will upgrade bits as time goes what I remove for the upgrade I will use for a aquaponic project on the cards.