9 hours ago, The Terrible Triplett said:

We are working A case sample here, sharing the LOGIC we apply to get this sample working so that the next person can apply the same LOGIC where they live, catering with confidence for Harrismith versus London versus Cape Town.

I disagree, we are using logic in how to develop our purchase decisions, but in real life my scheme is coincidentally with 40km of Harrismith. So I must object to the Cape Town -centric viewpoint choice of equipment and be a voice for the "elsewhere" man nationally. 

If the recipe is going to be 72 cell, fair enough  but follow on decisions have to consider the consequences of previous choices, and I can't, like a lot of SA rely on the temperate effect of living besides the sea. So a consequence of your choice should not be personal to you, but technically considerate of the consequences to others.

The consequence of a 72 cell panel choice is, I have back-off 1 entire panel to ensure MPPT voltage compliance. This was pointed out  by myself and @plonkster prior to this choice.

Basing your decisions on a "it sucks to be you" basis, will result in a scheme that will be specific to you, and we already know your scheme choices.  

It wont be much of an example scheme for people nationally if they have to take a fork in the road before we leave the driveway.

 

 

34 minutes ago, NigelL said:

I opted for the external current sensor, but this required some extra effort with the mains cabling.

 

I usually find that the reverse is true. Using the current sensor helps you avoid a bunch of rewiring. Here is the thing... if you put the non-essential loads on AC-Out two, then you have to size the cabling for the whole house. So you got to have a cable going to AC-In that is thick enough to carry the whole 60A-80A. Then you got to have TWO cables coming back from the AC outputs, again sizing at least one of them for the large loads (stove, geyser, pool pump). If you use the CT (just slide it on the red wire after the main switch), that's an additional R500 bucks that avoids a whole bunch of heavy cabling to your Multi. Those cables now only needs sizing to the backup loads, which is usually a mere 25A or so, meaning you can get away with 4mm^2 cabling.

Additionally, your non-essential loads don't go down when you turn the inverter off (for maintenance or so). Yes, there is a changeover switch, and you might think it is not a big deal... but you'd be amazed how upset the wife gets when you kick out a "non-essential" load for a few seconds... 🙂

12 minutes ago, phil.g00 said:

The consequence of a 72 cell panel choice is, I have back-off 1 entire panel to ensure MPPT voltage compliance. This was pointed out  by myself and @plonkster prior to this choice. 

My opinion about this (at the moment) is to stick a small asterisk next to it, because it is just one of those things that you have to decide on a case-by-case basis. Sticking 60-cell panels on houses where you could have done 72 seems like a bad idea. Conversely, having it blow up in a cold climate is also a poor option. It's like the old direct/indirect solar water heater thing, it's just a box the end user will have to tick. So pick a base setup, and stick an asterisk next to it. It is not that big a diversion, and has little cost implications.

4 minutes ago, plonkster said:

and has little cost implications.

I think it will affect the choice of MPPT,  number of strings, cabling and number of termination devices so I think it is not cost neutral.

10 minutes ago, plonkster said:

So pick a base setup, and stick an asterisk next to it.

On the other hand the price/watt of the 60 cell option and the 72 cell option were identical, so lets do that.

Lets decide on the watt size of the array, and we can evaluate the cost consequence of this choice at a later stage.

So @plonkster, I have indicated what I think Mr Average will want of his system, what is your opinion?

So we can move on to sizing the array.

1 minute ago, phil.g00 said:

I think it will affect the choice of MPPT,  number of strings, cabling and number of termination devices so I think it is not cost neutral.

No, the MPPT stays the same, at least in terms of open circuit voltage, it remains a largish unit with 150V max input. The Asterisk simply says "If you live in a  cold climate (below Freezing) then we recommend <insert alternative arrangement here>". Done.

3 minutes ago, phil.g00 said:

On the other hand the price/watt of the 60 cell option and the 72 cell option were identical, so lets do that.

That is the second half of my "little cost implications" argument. Per watt it is not going to differ much.

3 minutes ago, phil.g00 said:

So we can move on to sizing the array.

A few posts ago someone (might have been you) spoke about how the first 2.5 hours load-shedding cover is by far the most valuable. But you can do that without adding a PV array... so I am unsure if that really matters. What I can tell you from personal experience is that really small systems (less than 500W PV on the roof, less than 4kwh storage) is such a toy of a system that the minimum has to be larger than this, I'd say 1KWp on the roof and minimum 4KWH storage. TTT wants to go Lead Acid (I would not, but he is the boss). Why am I talking about batteries already... cause sizing the array sorta depends on that. In my opinion Mr. Average woud not need more than 3KWP on the roof (and in some jurisdictions that borders on the max anyway). So we're talking in the range 1KWp to 3KWp. TTT has already drawn it with 3 arrays of roughly 1KWp each, which is at the high end.

Again, from personal experience I can tell you that even 1KWp is worth its weight in gold during prolonged outages... so shall we perhaps argue it down from 3KWp? Or leave it as it is? I am inclined to say argue it down, that will make the battery bank cheaper when we get to that! 🙂

43 minutes ago, plonkster said:

I usually find that the reverse is true. Using the current sensor helps you avoid a bunch of rewiring. Here is the thing... if you put the non-essential loads on AC-Out two, then you have to size the cabling for the whole house. So you got to have a cable going to AC-In that is thick enough to carry the whole 60A-80A. Then you got to have TWO cables coming back from the AC outputs, again sizing at least one of them for the large loads (stove, geyser, pool pump). If you use the CT (just slide it on the red wire after the main switch), that's an additional R500 bucks that avoids a whole bunch of heavy cabling to your Multi. Those cables now only needs sizing to the backup loads, which is usually a mere 25A or so, meaning you can get away with 4mm^2 cabling.

The "extra effort" was mainly due to the Inverter being mounted some distance away from the Main DB, rather than the choice of wiring scheme.

It was certainly "extra effort" 🙂 . I ended up installing three 10mm^2 cables between the two DBs. I had to drill holes through thick hard-brick walls, route conduit through an existing cupboard into the roof space. All of this done during the December heat!

EDIT: The choice of 10mm^2 cables was for future-proofing. I really did not want to have to re-do any of this work again!

Edited February 23, 20197 yr by NigelL

7 minutes ago, plonkster said:

In my opinion Mr. Average woud not need more than 3KWP on the roof

We are in agreement that covering a load-shedding window is Mr Average's minimum requirement.

We must also Mr Average's 2.4kW inverter choice is what he considers he needs, and that he has made the correct choice.

Mr Average will also try to use as much of that 2.4kW capability continuously while the sun is shining to minimize his bill and maximize his ROI.

Does your idea of Mr Average fulfill these assumptions?

56 minutes ago, phil.g00 said:

Mr Average will also try to use as much of that 2.4kW capability continuously while the sun is shining to minimize his bill and maximize his ROI. 

Well, I do not know if I resemble Mr. Average that well, but in my experience a continuous 2.4KW is not something you're going to do. I don't have a pool though. Lots of "average" people who put up PV have pools. Such people might want to run pool pumps during the day. My personal opinion is that a 2.4KW is much more of a peak requirement than "as much as possible", which means I really want to size this PV array at around 2KWp.

From an off-grid perspective we're going about this completely the wrong way. From that perspective you would first determine how much this person really needs... but I think we've already determined that all he "needs" is to get through load shedding. The rest is gravy. With 2KWp, there should already be plenty of gravy.

Also keep in mind that Mr. TTT wants to use lead acid batteries... so surplus PV has to be used in the day time... preferably not stored for night time. This necessarily means sizing the array to the daytime loads plus a little bit of charging. So again I contend that a 3KWp array is larger than an average person really "needs".

It would not have mattered what panel or MPPT I have chosen, people fundamentally would have disagreed with any choice I made, derailing the thread over and over, for people can argue but what about options like Axperts, ABB, Solis, Lead Crystal ... but they don't. Thank you for that.

The goal I am trying to drive towards is that from ANY MAKE of panels to MPPT to Inverter to batts to what you power has a few bare bones not negotiable rules that no-one can circumvent, no matter WHAT you buy or use. Like at the level we are now at, the rule is never exceed a MPPT's max Volts / Amps and note carefully the effect of temp on that.

From that baseline the next person can make a very simple yet extremely informed decision, without analysis paralysis.

Ps. Have not had a inkling to form a thought to think "it sucks to be you" ... I will say that out load, not hint it. 😋

 

@plonkster and @phil.g00 we are going to end up with a very very long thread that people are going to ignore - read - wasting our time.

I vote that we ask Energy to change the thread heading to : Discussion on setting up a Victron grid tied setup from scratch

Then we have a second thread: Victron Grid Tied Setup
On this thread there are rules:
1) We only post in it the conclusions we have reached and agreed on in this Discussion thread.
2) No other comments are allowed, unless approved by someone, to keep the core information clear and neat.

What say you guys?

NOTE - I said this before (in other words): Once we have the core thrashed out, lithium batts ARE the next discussion, like so guys and gals, that was lead acid case, here is the case for lithium batts for the system specced.

1 hour ago, The Terrible Triplett said:

I vote that we ask Energy to change the thread heading to : Discussion on setting up a Victron grid tied setup from scratch

Then we have a second thread: Victron Grid Tied Setup

This looks good to me.

Another topic for consideration is the type of Municipal Energy Meter that you have installed. A grid-tied setup, using the Multigrid/Multiplus-II, has the potential to push back energy to the grid, even if only for a brief moment when a large AC load turns off.

Pushing excess power back to the grid is not economically feasible for this discussion, so lets assume we do not get any compensation for any power "backfeed" to the grid.  However, pushing energy back to the grid has different effects on different types of Energy Meters:

1. Some old "analogue" Energy Meters will spin backwards and reduce your total units used. Lucky you if you have one of these 😉 , but I know someone who was caught out when they did an unscheduled reading and found that the new meter reading was less than the old reading!
2. Some meters to go into "Tamper Mode" as soon as they detect any reverse power flow. One then has to pay a significant penalty fee to reset the meter.  Not so lucky if you have one of these!
3. Some meters will treat "backfeed" power the same as normal power usage, and charge you as though you were using this power.

Upgrading the energy meter is expensive, so best factor this into your overall budget if you need to change it.

I have the Landis & Gyr "CUI3" 3-Phase Meter, which conveniently does not go into tamper mode if there is a brief power backfeed. This is however a programmable option, so maybe I was just lucky when they installed it.  FYI the manual states "A significant reverse power condition will be flagged when there has been a continuous
reverse power measurement equivalent to 50Wh."

The bottom line is that I can now setup the Multigrid-II to operate with an average net inflow of just 20W (on the one phase).

Edited February 23, 20197 yr by NigelL

4 hours ago, NigelL said:

Cons:

• You need to purchase an extra current sensor (about R500).
• The current sensor has a 1m lead, so the Multi-II must be physically close to the current sensing point where the Assisted Loads combine with the AC-IN to the Multi. Victron states that one cannot extend the current sensor lead without running into problems (noise coupling into the low-level current-sensing signal).

Carlo with a 5 meter RS485 to USB interface cable looking at wot, about R1500 - much cheaper than re-wiring.

Or save a 100 or two and get a shorter RS485 to USB cable and use a spare UTP cable lying around, cut off the ends, use wire pairs, and extend it.

And as you said you now can read the whole DB current in and out because the Carlo is mounted immediately after main DB breaker, before anything else.

In my mind that is one huge Pro, with very little if any Con's bar the R1500 price tag. But the R1500 becomes mute when it is compared to feed the entire DB board with grid tied savings.

Edited February 23, 20197 yr by Guest

So, for Mr Average, to save on costs of re-wring coupled with the limitations of the max total inverter amps available to feed all, a Carlo is a very good option to add to the mix.

14 minutes ago, NigelL said:

... has the potential to push back energy to the grid, even if only for a brief moment when a large AC load turns off.

Not potential, it does that all the time. 🙂

The CoCT LTron meter they fitted free  of charge, they ran a months special for that, meter has no problem with the feedback, even when I set the ESS to export all surplus power to test it.

I look at it like this. The total seconds it does feed back over a day adds up to a few cents, maybe a unit if it is a rough day or some such I guess.

Versus the fact that if we can go with 154 units the rest of the month, we will be on R600 for the months Eskom use: ("vat so" CoCT and Eskom!!!)
- and that is on a 2.1kw array that does not run at full tilt all the time
- and with 6 people home at night using computerS / TV'S.

And we have three geysers:
1 x 200l  on EV tubes
1 x 200l heating only between 13h00 - 15h00 - because array is slightly North West.
1 x 50l

11am the dishswasher is switched on.

Simple free easy lifestyle changes.

And it makes for a compelling confirmation of Plonks point of view that ...

2 hours ago, plonkster said:

... a 2.4KW is much more of a peak requirement than "as much as possible", which means I really want to size this PV array at around 2KWp.

I want to add 2 more panels - 2.8kw ... but that would be a WANT.

Ps. And the wife and rest of the family is never upset about anything power related ... I'm of a larger circumference than any of them see. 🙂 

OK, I'll sit out for a bit, and see where this goes in the interest of progress.

 

48 minutes ago, phil.g00 said:

OK, I'll sit out for a bit, and see where this goes in the interest of progress.

 

No, you ARE the reason for progress. 👍

Alright, I'll try again, I am not saying we won't come to the same answer, but the engineer in me needs a more logical rationale to determine the solar array size than a guesstimate of what should be good enough.

And we have to let the problem dictate the answer, not fit the answer to the problem.

The way I see is starting from nothing, we can add panels to the array and  utilize 100% of every watt up to a certain size, then from that point on we can add more panels at a diminishing rate of returns, until we reach a point where there is no practical further benefit because either we cant export, use or store the extra power.

I am saying our array size must be somewhere along this rate of diminishing returns slope.

The limitation by not being able to export is a clear line in the sand.

Our system is a 2.4kW hybrid system, our founding premise is that this choice is absolutely correct and it is the best fit to the usage pattern.

The influence of legalities aside, our mythical man chose a hybrid inverter of this certain size, because as against all other solar options of other sizes because it best fulfilled his needs in terms of standby power and bill reduction.

Therefore his usage pattern is not a movable feast, it isn't your usage profile or my usage profile, it is a usage profile that fits our man's choice.

He chose a hybrid grid-tied inverter, that speaks to knowing his peaks are taken care of, and the size he chose gives an insight into the size of his continuous load requirement while the sun is shining.

He chose hybrid grid-tied inverter, that speaks to his needs to provide a certain amount of backup power for a certain length of time.

The array size must fulfill these requirements.

He is our client, it is his usage profile that we have optimally size the array to, not our own.

 

 

Hi all,

So me as a average Joe started tinkering with Solar power about 4 months back and have been doing my own research along the way, and have been following feeds on this forum for some time now, soaking up all knowledge that i can.

Key notes about my DB board
Municipality MCB (25A) with street-side running meter
Two pre-paid meters attached (House on 1, Flatlet on another) - I am renting the house and the flat is rented out to another party
3KW Geyser
1KW = R2,49

My approach is as detailed

Phase 1: (PURCHASED AND RUNNING)
Items:
- Hoymiles MI-600 (R2500)
- Hoymiles Plastic bits (R250)
- 2 x 80W Panels (R600)
- Cabling and Misc (R500)
Total:  R4450
As a individual who doesn't have capital to go out and buy everything one shot, i started off with a "micro" grid-tied PV system after establishing what my base-load is.
This allowed me to invest in a non-expensive Hoymiles MI-600 and drop 2nd hand panels onto it to cover my base load (2x 80W in Series). My ROI so far works out to be less than 40 months with zero change in lifestyle, thanks to paying R2,49 per unit (and thats the cheap rate!).

Being stuck in a hard place of how do i continue to grow. I have a prepaid meter that does not trip when exporting, but does charge when going backwards (tested this for sanity sake)...

Phase 2:(CURRENTLY TESTING)
So still not having capital to invest in a Axpert or Multiplus II but wanting to reduce my consumption even more. I have been reading about diverting power on Openenergymonitor.org and on Mk2pvrouter.co.uk
Ive built a similar system and have calibrated it successfully and am busy testing the logic on a 1000W Oil Heater using a Solid State Relay.

This Phase of my system will allow me to go from running my base-load off solar to covering my consumption during the day and feeding all excess into the Geyser.
The intention is that i will be able to feed ~400W p/Hr into the Geyser on a good day. Therefore looking at feeding 2KW per day into the Geyser and switching the Geyser on then for maybe 30 minutes a day.
My geyser uses about 4.6KW from ambient to 60deg.

Ideally this is where i would stop as im not worried yet to protect myself from Load Shedding. However this is where this feed peeks my interest.

Phase 3:(CURRENTLY RESEARCHING)
This is where i would now need to look at a Inverter (Axpert or Multiplus II) around 3KW. And the battery system to go along with it.
This is where the capital spend would be around R50k-R60k for just inverter, batteries and electrical work

Phase 4:
Add Solar incrementally in 1KW increments and start using a ESS system to extend on the investment

 

Its a bit of a tangent, but I think it could add to that initial start for the smaller players such as myself. provided of course grid-tie is an option for you

22 minutes ago, PhatWheZ said:

I think it could add to that initial start for the smaller players such as myself.

You may be surprised to know that I started with LED outside lights on a 20w panel - traded 2 of them to Plonkster for 2 Trojan batts a while ago.

Then I bought more and then even more stuff and sometimes I even blew stuff up. 

It was a journey but what I think I have picked up, we can put down here the core non-negotiable fundamentals to help anyone, not matter the size of their system, nor the make ... in a one page document. 🙂 

 

15 hours ago, phil.g00 said:

He is our client, it is his usage profile that we have optimally size the array to, not our own.

Right, Phil, guide us where you want to go next - array size?

Where we are:
We have sound salient points for 60 vs 72 cell panels, and how one must look at it.
And we have the three core fundamentals of MPPT versus panel choice.
(I will make posts as we go along, and summarize at the end again.)

We are catering for the average client, i.e. 3kva hybrid grid tied inverter knowing peaks are taken care of, size of the continuous load while the sun is shining is catered for, needing to provide a certain amount of backup power for specific dedicated loads for a certain length of time.

Throw the next curve ball.

1 hour ago, The Terrible Triplett said:

We are catering for the average client, i.e. 3kva hybrid grid tied inverter knowing peaks are taken care of, size of the continuous load while the sun is shining is catered for, needing to provide a certain amount of backup power for specific dedicated loads for a certain length of time.

Throw the next curve ball.

That's it really.

Our man is going to load his system to draw the full 2.4 kW during the solar window, and during the same solar window he must put enough back into his batteries to cope with consecutive days of load-shedding.  There is a 30% turnaround loss for LA batteries.

This represents the floor size, but after this our man would have to start increasing battery bank size to benefit from a bigger array, and I think then that the diminishing rate of returns become too small.

This changes for the size of solar widow, but if it was 4.5hrs, and load-shedding was 2hrs that would equal:

(2.4kW X 4.5hrs + (2.4kwX1.3) x 2hrs)/ 4.5 = 3.8kW .. This would be the liberal calculation.

Or if the solar window was 4 hrs, and the load shedding window was 2.5 hrs that would equal:

(2.4kW x 4hrs + (2.4kW x 1.3) x 2.5hrs)/4 = 4.35kW... This would be the conservative calculation.

So splitting the difference a 4 kW array would seem not far off the mark.

 

2 hours ago, PhatWheZ said:

So still not having capital to invest in a Axpert or Multiplus II but wanting to reduce my consumption even more. I have been reading about diverting power on Openenergymonitor.org and on Mk2pvrouter.co.uk
Ive built a similar system and have calibrated it successfully and am busy testing the logic on a 1000W Oil Heater using a Solid State Relay.

This Phase of my system will allow me to go from running my base-load off solar to covering my consumption during the day and feeding all excess into the Geyser.
The intention is that i will be able to feed ~400W p/Hr into the Geyser on a good day. Therefore looking at feeding 2KW per day into the Geyser and switching the Geyser on then for maybe 30 minutes a day.
My geyser uses about 4.6KW from ambient to 60deg.

I envisage load manipulation will become part and parcel of optimizing this system in due course, we are aways off that part yet though.

But stay tuned.

So taking 4kW as a minimum array size, this translates into:

4000/350 = 11.42 panels, rounding up = 12 panels.

3 strings of four in series.

Incidentally, using 60 cell, 280 W panels would yield exactly the same wattage using the same with 3 strings of 5 in series.

At the same cost/watt it would actually make the 60 cell vs 72 cell debate irrelevant.

We could go  for 250/85 MPPT, its specs indicate it is good for 4900kWp

Edited February 24, 20197 yr by phil.g00

At under 1 % losses/run:

Use 6mm2 Cu from panels to combiner box ( 6 x 6mm2 glands)  ( I used a typical 72 cell Vmp and Imp of 10A for calculations)

We assumed the furthest panel was 20m, so 100m roll of 6 mm2 should suffice.

Use 10mm2 from from combiner box to  MPPT   ( 2 x 10mm2  glands )   ( 3 x Imp of 10A combining the 3 strings)

We assumed this was a 10m run so, 20m of 10mm2.

Use 35mm2 from MPPT to battery busbar. ( 4.2kW @  55V = 76A)

I'll let someone else populate the combiner box, with lugs, fuses, surge arresters and whatever it needs to tick all the legal boxes.

 

 

 

32 minutes ago, phil.g00 said:

Use 6mm2 Cu from panels to combiner box

The Panel to Combiner box cabling should be the fancy UV rated solar specific stuff.

I also forgot about the earthing cable.

Edited February 24, 20197 yr by phil.g00

Regarding the earthing the solar array mounting rails there are two main considerations:

Namely: leakage power from down below the roof and lightening from up above.

Some schools of thought about earth conductor sizing:

1. Should be at least capable of carrying the current of the over-current protection device, which would make it quite small. (2mm ish). This is the electrical minimum to prevent electrical shocks from below.

2. Should be at least half of the phase conductor if run in conduit, ( if we replace phase conductor by DC conductor) that would make it 3mm2. 

3. Should be at least 4mm2 for the physical strength requirement. 

4. Should be at least the same size as the phase conductor if run as a separate cable, making it 6mm2 

5. If used to afford a lightening protection element it should be 10mm2,  exceeding the phase conductor size to make the earth the lowest impedance path.