One or two solis inverters?

[bladerunnerpv]

Simple solis only question. One solis 6kw string inverter or two smaller ones for an East-west system?

Background...

Quote for East West system
West roof 10 panels 4.35kWp maybe 9panels
East roof 10 panels 4.35kWp
Roof ridge line points about 10deg towards East of due South. 29deg pitch

Shading factor is about 0.9 for East and 0.82 for West from using easypv buildings beta

Quote received uses a solis s6-gr1p6k string inverter, (2 x mppts, 120V startup) with requested ac coupled battery.

Seems to me like the 6k inverter is underspecced and will waste energy in summertime which could be reducing the payback time slightly, running future aircon or charging an EV

I could use 2x string inverters, say s6-gr1p4k, one for each roof I thought to myself. ..

Is there anything specific to solis you guys know of which would prevent this approach?
Will it result in more efficient system (less wasteful)

Thanks for taking a look
PS I'm well aware of other brands of inverters, this query is specific to solis.

 

[binky]

6kw inverter on nearly 9kw of panels - don't think so! Solis do an 4.6Kw single phase hybid inverter, which is far more suitable if you want two inverters, you can get 8kw inverter, single phase, but not hybid, awkward size array for single phase. But you could have one inverter for the array and second for the battery only.

 

[bladerunnerpv]

Thanks binky, yes taking the 'max out the roof' approach is proving a bit awkward!

My thoughts were 2 smaller string inverters with an AC coupled hybrid inverter for battery, e.g. givenergy AIO or cough tesla powerwall. Not a cheap system, payback about 10yrs.

Is that what you were saying?

AFAIK solis don't do a string inverter bigger than 6k.

There's a solis EH1P8K which i think is dc coupled hybrid but the mppts are odd, iirc one accepts 12.5A the other 25A, bigger one for two strings in parallel I presume

I have another quote with dc coupled hybrid and pylontech batteries, but suffers the same problem essentially, seems like not enough inverter for the available pv. That's a separate thread though I think.

 

[binky]

the 8kw is a bit of an odd design, but if you want a separate battery inverter, solis do offer a 4 or 4.6kW inverter - you would need to run to sets of DC cables to each roof to take advantage of the dual MPPTs - do check 5 panels will be sufficient for the minimum DC start up voltage of 120V. It's worth using all the MPPTs as this will reduce any losses due to, say, leaves or seagull poo on a panel.

 

[Oldman22]

Ask Solis directly if their inverters will work together, when I inquired in the spring I don't think they had a 2 inverter solution, they did just bring out a new range which I think overcame the problem.

 

[Badger]

Simple solis only question. One solis 6kw string inverter or two smaller ones for an East-west system?

Background...

Quote for East West system
West roof 10 panels 4.35kWp maybe 9panels
East roof 10 panels 4.35kWp
Roof ridge line points about 10deg towards East of due South. 29deg pitch

Shading factor is about 0.9 for East and 0.82 for West from using easypv buildings beta

Quote received uses a solis s6-gr1p6k string inverter, (2 x mppts, 120V startup) with requested ac coupled battery.

Seems to me like the 6k inverter is underspecced and will waste energy in summertime which could be reducing the payback time slightly, running future aircon or charging an EV

I could use 2x string inverters, say s6-gr1p4k, one for each roof I thought to myself. ..

Is there anything specific to solis you guys know of which would prevent this approach?
Will it result in more efficient system (less wasteful)

Thanks for taking a look
PS I'm well aware of other brands of inverters, this query is specific to solis.

Why dont you look at micro inverters from enphase which would.make the system far more efficient and that would mean its not one inverter or invetters to fail and produce a more efficient power generation

 

[Badger]

Image of mine

 

[binky]

Image of mine

the best bit of micros, unless you have a commercial size system to map out on the app .

How much are the Enphase these days, I havn't looked at those for years.

 

[Badger]

the best bit of micros, unless you have a commercial size system to map out on the app .

How much are the Enphase these days, I havn't looked at those for years.

i think the micro inverters are around 100 each plus the panel and about 300-400 for the hub unit.

 

[bladerunnerpv]

Thanks for the suggestion Badger

 

[bladerunnerpv]

OK little bit of free time again at last...

Just posting an example schematic for a 2x inverter E-W setup, using a solix 4.6kw for east and one for west roofs (4.6kW is picked somewhat arbitrarily as I had the details to hand) the startup is 120V

for the worst case string of 4 panels West-facing :
open circuit voltage at -10deg is 171V
MPPT voltage 126V at +40deg and 142V at -10deg

This would work in principle? Am I missing something about the way the PV inverters are connected into the consumer unit that they don't need to know about one another? I can see they should be able to communicate if both were hybrids with battery, but not for just PV inverters?

In case it helps...
Predicted Shading: (from easypv not a site survey)
6 panels West shading 0.92
4 panels West shading 0.82
upper 5 panels East shading 0.93
lower 5 panels East shading 0.91

Performance prediction
Import 1084
Export 3082
Generation 6227
Self consumption 2929

Thanks if anyone has time to take a look

 

[daveg]

Hi I am interested in this setup as I am looking at a similar installation - total of 8kWp split evenly between E & W facing rooves.
From the research I have done it seems the E-W configuration reduces the peak power by about 25% so for my system a 6kW inverter looks ok.

For your 8.7kWp installation this would give a peak output of 6.525kW and depending on the shading maybe a bit lower so a 6kW inverter may not be too far out and only have to clip for a short time around mid-day on the sunniest days.

This is an interesting article about E-W designs:-

https://ratedpower.com/blog/solar-panel-orientation/
Warning - i am new to solar so may be talking rubbish.

 

[bladerunnerpv]

Hello daveg,
some generation curves from easypv you may find interesting, 2x 4.6kW inverters, no shading applied for these. The dips in generation are cloud cover presumably.

Colour coding is green=battery, blue is self consumption, red = export

Over 6kw from approx. 11am til 2pm, peaking approx. 7.5kW, seems there would be quite a bit of 'clipping' if it were using a 6kW inverter. What you get will vary with where you are in the country, this is for my location.

 

[daveg]

Hello bladerunner,
Thanks for that information - perhaps an E-W configuration doesn't reduce the peak output by 25% if your simulation is showing a 7.5kW output. I've lived in Hertfordshire and it does have more sunny days than rainy Wales. I will have a play with easypv and see what it predicts for my proposed installation.

 

[binky]

Hello bladerunner,
Thanks for that information - perhaps an E-W configuration doesn't reduce the peak output by 25% if your simulation is showing a 7.5kW output. I've lived in Hertfordshire and it does have more sunny days than rainy Wales. I will have a play with easypv and see what it predicts for my proposed installation.

Have a look at the SMA portal for similar systems, it will give you real world data. I've fitted a few EW systems and don't recall peak output being down by 25%. Roof pitch will influence that number, a shallow pitch, will drop less than a steep pitch roof.

 

[bladerunnerpv]

You might find pvgis useful too for judging generation, it's less detailed than easy-pv though.

 

[daveg]

I have put an 8.7kWp split 50:50 E-W array, 35 deg roof slope, no shading system for my location into easypv. Total generation is 63176kWh pa. This is the prediction for a very sunny June day. The peak output is well under 6kW. If I change the location to Hertfordshire the peaks are over 7kW so the location makes quite a difference.

 

[bladerunnerpv]

Seems to make sense then, that's good.
Pvgis has a nice irradiance diagram showing variation across uk and europe if you're interested.