Home solar - inverter configuration?

Forums › Home Workshop DIY › Home solar - inverter configuration?

Sparky42

3 posts

Wannabe Geek

#315789 15-Aug-2024 20:29

I'm looking at installing a grid tied solar system at my home in Wellington.

My house has two phases available for grid connection. Each phase has a similar load (max 5KW on each phase). I am considering using either two 5KW single phase hybrid inverters (one on each phase) or one three phase 10KW hybrid inverter.

Can anyone please offer advice or experience on the benefits of using two single phase inverters or alternatively a three phase inverter.

I will have 4 strings of solar panels and intend to add approximately 10KW of batteries at a later date.

Any advice or experiences welcome.

Thanks

SomeoneSomewhere

1734 posts

Uber Geek

Lifetime subscriber

#3272257 15-Aug-2024 20:56

I'm not sure that a three phase inverter will happily start with one phase missing; I'd expect an immediate fault. Certainly it would be limited to 2/3 capacity.

At present each phase is metered as effectively a separate connection so if you are generating on one phase and importing on another, you are charged retail rate for the imported power but only paid (much lower) export rates for the exported power.

There is therefore some argument to moving as much load as possible to one phase and putting all the solar on that phase; the so-called 'solar phase' option.

Samsung

Shop now on Samsung (affiliate link).

billgates

4704 posts

Uber Geek

Trusted

#3272264 15-Aug-2024 21:26

I have 2 phase at home with Solar PV with a string inverter connected to each phase. My journey along with many others is covered in link below. Benefit of string inverter on each phase in 2 phase is that you can run more things in the house with load spread evenly across 2 phase. You gain more MPPT's to have multiple panel directions setup on the roof with 2 x string inverters. It also provides redundancy atleast to one of your phases for Solar PV generation and battery backup incase one of the string inverters faults. You can export up to 10kW in total (in most networks) as limit is usually 5kW export per phase. I would recommend a hybrid inverter on each phase. Downside is cost as you will need to buy 2 sets of batteries to cover each phase.

Solar options for home in 2022. (geekzone.co.nz)

Do whatever you want to do man.

Sparky42

3 posts

Wannabe Geek

#3273630 19-Aug-2024 22:40

Thanks for the helpful replies and links.

My next questions are around inverter limits. My proposed inverters (one on each phase) are Deye SUN-6K-SGO4LP1-AU and my panels DAS Solar 440W N-Type Black.

I'm planning on two stings on each of my two inverters. The inverter each have two MPPTs that can appearenty take two strings each. I will putting only one string on each MPPT.

My proposed array configurations will have 18 panels on each inverter. 8 on one MPPT and 10 panels on the other MPPT of each inverter.

Panel specifications are:

Panel Open circuit Voltage Voc = 38.82V

Temp coefficient = - 0.25

Min temperature (Wellington) - 2.5 degrees

Max voltage per panel calculated as 41.0V so my max string of 10 panels in series will be 410V

The short circuit current Isc is 14.63A

The operating current Imp of 13.7IA.

The inverter specifications are:

The rated inverter PV input voltage is stated as: 370V (125 - 500)

The startup voltage is 125V and the MPPT voltage range is 150 - 425V

Full Load PV voltage range is 300 - 425

PV input current is 13A

Max PV Isc is 19.5A

So, if my strings of panels have a maximum voltage of 410V, is this an acceptable voltage the 370V (125-500) rating and max voltage 150 - 425V MPPT rating? Have I got enough voltage headroom to suit my inverters?

Plus, the panels are rated at short circuit current Isc of 14.63A, operating current Imp of 13.7IA. This is slightly higher than the inverter PV input current rating of 13A but below the inverter maximum PV Isc of 19.5A. Do I have a problem of the current being too high?

The different voltage and current specifications are confusing me. Any advice would be most welcome please. Thanks in advance.

SomeoneSomewhere

1734 posts

Uber Geek

Lifetime subscriber

#3273633 19-Aug-2024 23:39

It looks like there's a few different contradictory datasheets floating around for those.

A max operating PV current of 13+13A I think implies that while you can connect up to the short-circuit rating of 19.5+19.5A, it cannot draw more than 13A. This might limit your output power under some conditions.

Your system is already slightly over-subscribed (7.9kW of panel for 6kW inverter) so we expect that when both strings are fully lit, it will clip - that's fine. However, the 13A limit means that if you do something clever like aim one string for morning sun and one for evening sun, the fully lit string could still hit the 13A limit and clip even though the inverter has not hit 6kW.

As far as maximum voltage though, you're fine. The full load PV range simply means that it might not be able to extract full power above 425V. It's still safe and approved up to 500V, and the voltage will sag under load to at/near the Vmp figure, not the Voc figure.

Sparky42

3 posts

Wannabe Geek

#3274014 20-Aug-2024 22:07

Thanks again for the comprehensive reply. As said the specifications are confusing. It's a shame they are not more specific about capabilities and limits.

Looking at the specifications again below, I see that the max DC Input Power is 9000W.

Can I assume if I connect up my 18 panels to one inverter with max load of (nominal 440W panels x 18 = 7,920W) then they will be within the max DC input power limits and warranty limits? An alternative calculation is 13A (PV input current) x 369V (max 41V x 9 panels in series) = 4,797W x two MPPTs (18 panels) = 9,594W - a little higher than the 9000W max DC input power?

While understanding that clipping will occur at some point, i'm not sure I understand at what level this will occur? 6000W? I'm expecting the two MPPTs to have equal strings in morning and afternoon locations so likely never full sun and DC output on all connected panels.

Model: SUN-6K-SG04LP1-AU
Battery Input Data
Battery Type: Lead-acid or Li-lon
Battery Voltage Range (V): 40-60
Max. Charging Current (A): 135
Max. Discharging Current (A): 135
Charging Curve: 3 Stages / Equalization
Charging Strategy for Li-Ion Battery: Self-adaption to BMS

PV String Input Data
Max. DC Input Power (W): 9000
Rated PV Input Voltage (V): 370 (125-500)
MPPT Voltage Range (V): 150-425
Start-up Voltage (V): 125
Full Load DC Voltage Range (V): 300-425
PV Input Current (A): 13+13
Number of MPPT / Strings per MPPT: 2/1+1

AC Output Data
Rated AC Output Active Power (W): 6000
Max AC Output Active Power (W): 6600
Peak Power (off grid): 2 times of rated power, 10 S
AC Output Rated Current (A): 26.1
Max. AC Output Current (A): 26.1
Grid Type: Single Phase

SomeoneSomewhere

1734 posts

Uber Geek

Lifetime subscriber

#3274018 21-Aug-2024 00:19

The Australian datasheet specifies a 'max PV access power' of 12kW. I think that implies that you can connect up to 12kW of panels to it (warranty/safety), but it can only use 9kW at any time. I don't think it can physically dissipate 3kW of losses, so I suspect you might be able to inject 6kW into the grid and ~2.5kW into the batteries, plus some losses? Otherwise the 9kW number seems redundant.

This would make some level of sense as I would assume the basic design is 2x ~5kW PV boost converters, a 6kW isolated converter for the battery, and a 6kW inverter sharing a common DC bus.

I am slightly concerned that you may not be able to quite get maximum power out of a fully lit string due to the 13.7A > 13A issue, but this should be a minimal loss. It shouldn't even be the 5.1% you would naively assume as the voltage will rise slightly with the lower current.