Design Rules

ctlsleh

Just wondering what the design rules are for optimisation of the investment and return.

I have a south, east and west facing roofs 3 strings optimally, but inverters only take 2. What’s the best way to approach asmd what are the considerations and max panels , assuming a standard Jinko 435 as example, that can be deployed efficiently across the 3 spaces.

TIA

10-10-20

As you probably already know, the design rules are in the main defined by the natural aspect of each roof, the export limitation on NC6 and the MPPT capabilities of the inverter.

Your primary aspect in an ideal site is always S as this provides the best returns over the whole year (strength of sun, slope). You would normally size-up S first, then work on whether a W or E install would provide more gains by looking at each array in a modelling tool and with shading added in. Then you need to work out the key element - oversizing the panels for all three aspects by working off the max MPPT input voltage and system max power. It might be that W and E get oversized so that they are producing best while S is still rising. You then choose the optimal configuration based on the export limit of 25A so that your generation profile is at it's max for the longest possible duration over the solar day.

Conceptually you could have E and W strings both on optimisers and fed into the same MPPT input... there could be merit in that.

https://energyd.ie/dc-over-sizing-pv-solar-in-ireland/

A note of caution on the Jinko... they have a high Voc so you can't as easily oversize as they max-out the input voltage quicker.

idc

NOTE: NC6 is not about export limitation, export limitation is actually not allowed under the rules of NC6. NC6 rules dictate the total size of all inverters connected to the grid in your house. NC7 does allow export limitation. Now will ESBN know - who knows.

10-10-20

NC6 is the name of the notification form for microgeneration and it's within the microgeneration policy that the single-phase installed capacity limitation of 25A is stated.

https://www.esbnetworks.ie/docs/default-source/publications/conditions-governing-the-connection-and-operation-of-micro-generation-policy.pdf?sfvrsn=fdcb2515_17

idc

I may of read your point wrong, I see a lot of people on here assume that if they turn on export limitation technology in there >25A inverter to limit it to 25A then they are fine with ESBN rules, that was more the point I was making. A lot of people wrongly assume NC6 is just about the 25A export limit and once you state below that its all fine (using inverter in built export controls). But ESBN don't see it that way. No export limitation devices are allowed. As the doc you pointed out also states

Any installations with inverter capacity greater than Micro-Generation (6/11 kVA) are classified as MiniGeneration (up to 50kVA installed inverter capacity). There are no active Export Limitation Schemes available under the Micro-Generation ‘Inform and Fit’ process, as the inverter capacity itself, which shall be within the allowed Micro-Generation limits, is used to determine the export limits

10-10-20

https://www.boards.ie/discussion/comment/121806314#Comment_121806314

Yeah, it's a complicated affair in that respect. I wish you could just enable a limit and go on from there, that would be nirvana.

idc

Exactly and I expect most hybrid inverters (possibly not all string inverters) include export limitation as a feature in most cases now anyways as other countries have 0 or other limits why can't the ESBN just say the your limited to 25 Amp EXPORT based on an approved inverter. If that happens to be 50Amp cool.

I guess where people start adding 2 or more inverters (be it hybrid/string or battery only) thats where things get messy although some inverters handle that too. With mine, my secondary 1kW inverter is monitored by the primary hybrid inverter. Thus export limitation could be applied to both (well i'm guessing apart from fact it can't stop the 1kW inverter from exporting! but the hybrid inverter can adjust its output -- would test it but don't want to lose any FIT money 🤣)

10-10-20

https://www.boards.ie/discussion/comment/121808317#Comment_121808317

The reason is because they need a fail-safe to protect the local grid as well as maintain some surplus control. In a hypothetical scenario where the export limit setting failed to function on a 5kW inverter, it could only export 5kW anyway; while if the same function failed on three inter-operating 5kW inverters they would push 15kW (65A) onto the grid. Say that all happened over an extra sunny weekend when the grid is already underloaded, then you potentially have a serious grid compromising event (not an issue here now due to the relatively low rate of installations).

ctlsleh

https://www.boards.ie/discussion/comment/121806900#Comment_121806900

https://www.boards.ie/discussion/comment/121808563#Comment_121808563

https://www.boards.ie/discussion/comment/121808317#Comment_121808317

thanks all, this is excellent information

Mr Q

https://www.boards.ie/discussion/comment/121806009#Comment_121806009

Are you sure you need the optimisers for the E/W on one string? Upgrading my own currently and using the SMA design site their inverters will work with 3 orientations according to the software. Once the type and number of panels are the same on the two strings sharing a MPPT.

If that is correct I assume plenty of other brands also will.

10-10-20

https://www.boards.ie/discussion/comment/121820043#Comment_121820043

If it says that it offers that in the inverter then that's wonderful. There is mention of just paralleling the E and W panels into the same MPPT, that could work too; or else go for a large single-MPPT inverter for the S panels and then a smaller dual-MPPT inverter to take care of the E and W groups. It's just a matter of sizing and then deciding where the battery should go (probably S).

DC999

https://www.boards.ie/discussion/comment/121820043#Comment_121820043

Does the roof pitch not impact it? I’ve seen an old design whitepaper from Australis (Fronius inverter release it afaik) where they put the E + W on the same string and there was only minor reduction in output. No optimisers. That showed it can work. But…afaik the snag was the roofs needed a very shallow angle, so the sun with be on both at the same time. Maybe Aussie’s roofs are like that, Irish houses roofs aren’t. 

Mr Q

https://www.boards.ie/discussion/comment/121820470#Comment_121820470

The design tool indicated one inverter would cover the three directions even when I changed the angles of the panels. Mine will be vertical.

The SMA inverters have 4 pairs of inputs but only 2 MPPT, the Fronius you mention are similar. So I will have two inverters and 7 strings.

All good in theory but I won't know for sure until it is running.

10-10-20

https://www.boards.ie/discussion/comment/121822430#Comment_121822430

Which tool was this? Can you share it and we'll have a look?

Mr Q

https://www.boards.ie/discussion/comment/121822694#Comment_121822694

SMA Sunny Design.

Punchin A Keyboard

I assume inverters feeding into an inveter drop out of the equation in other words micro inverters ac coupled into the genset/ac port on a hybrid, if it supports it

garciasa

my assumption on this (i was wrong) was if you are using an inverter on grid that is connected to a inverter that manage batteries (ac coupling) and the ongrid inverter it's not able to export more than 5kw, it would be a NC6 compliance, but I've learn that even if one of the inverters is not generating or exporting at all to the grid ESB consider both that can export summing their power so from my point of view is not correct... but of course they make the rules

10-10-20

https://www.boards.ie/discussion/comment/121931262#Comment_121931262

Correct. It's a pig.

garciasa

can anyone give me any opinion in these different options I'm looking at?

in 4/5 weeks the installers will come install the panels, and I've tell them one these options.

The roof of my house is a little bit tricky, so I'm able to fit 10/12 panels East side, 5/6 South and 3/4 West (I could put another 3/4 in the other West part, but not sure)

east face

south face

my options for the solar setup, taking into account certain constraints. Unfortunately, I'm unable to opt for the Fronius/Victron combination without NC7. Here are the options I'm considering:

Option 1 - Solis 5kw inverter

a. 10 panels east (string 1) and 6 south/4 west (string 2, this string all panels will have optimisers)

b. 6 panels south (string2) and 6 south (serie) / 6 east (serie) this two in parallel in string 2. Not optimisers this way.

Solis accept 520v for mppt, so I think those two series in parallel shouldn't be an issue (completely different orientation)

I'm installing a 15kwh battery (weco) that means in winter months I would need to charge the battery in 4 hours, but the Solis inverter after 15 mins around 90/100a will be throttling down around 65a, which is not the best and probably it wont be able to charge the battery in 4 hours.

and also integration with home assistant for real time data via the new dongles is tricky.

Option 2 - Sunsynk 5kw inverter

a. similar as option a) from solis, but this minimum voltage for mppt in this around 150v, which means those 4 panels on West are going to be on the limit. (solis start around 90v)

b. 10 panels east (string1), 6 south (string 2) and 4 panels microinverters connected to the GEN port on this inverter. No need for optimisers.

Sunsynk is also able to keep charge rates around 90/100 for 4 hours, but I'm guessing will be louder that solis (it will be placed in the attic)

also integration with home assistant it's not the smoothest, but via solar assistant (paying the software) it's quite good.

Option 3 - and overthinking too much and leave the installer do whatever they want hahaha the less preferable option :)

Thank you for any feedback.

10-10-20

I think I'd knock the easterly option on the head on the basis of shading from that house to the right.

oaklands

Consider the newer REC Pure-r. They have a higher Voc which should ??? work for the Sunsynk mppt start up. (or similar)

I have a sunsynk 5kW & from what I observe the charge/discharge current is also limited by the 5kW not just the headline charge current of 120A. I get my 15kWh battery charged every night in 3 hours or less depending on initial SoC. There will also be ~10% conversion loss when charging or discharging.

So depending on the actual battery voltage I can see charge currents of ~86A…discharge currents can go up to 106A. This concerned me at first until I figured out the 5kW limit along with the battery voltage.

(I only charge from grid & export remaining after midnight)

garciasa

https://www.boards.ie/discussion/comment/121952610#Comment_121952610

Yes, we are removing the ventilations and put the panels as higher as we can (in the restrictions of 50cm from edges and 20cm from the top I think it is).. probably i could fit not more than 13 in the east side..

garciasa

https://www.boards.ie/discussion/comment/121952720#Comment_121952720

I wouldn't need more that 85/90a but solis it's not even reaching that in 4 hours :(

ctlsleh

I am considering 6 south facing, 4 east facing and 4 west facing panels. I am just wondering what’s the best string setup? And does it make sense to have optimisers on every panel?

looking a Huawei inverter, battery and optimiser together with Jinko panels…

Cheers!

bullit_dodger

https://www.boards.ie/discussion/comment/121999439#Comment_121999439

Unless you have shading in the above configuration you can avoid optimizers.
String1 = Your 6 south facing panels.
String2 = Your 4 East and 4 West facing panels, hooked up in parallel. Need to check voltages/current limitations of your inverter, but you should be alright with a relatively low number of panels on String2.