Solar PV - going bigger

ed110220

Hi all, looking for some advice on going bigger with solar PV.

I've been quoted for 12x Hyundai 400 W solar panels + 3.68 Kw inverter due to be installed next month. Since then I've had the roof covering replaced and the ridge to gutter dimension has been increased.

So I think extra panels should fit. Instead of 2 x 6 portrait or 4 x 3 landscape, it looks as though 4 x 3 landscape plus 6 x 2 portrait will fit, for 5.6 kWp.

Just wondering what route I can go down - I'm guessing the 3.68 kW inverter would clip unacceptably as all the panels will be on one SSW facing roof plane?

So either seek DNO approval - is this a long process? Or maybe export limit + battery?

2nd_time_buyer

ed110220 said:

Hi all, looking for some advice on going bigger with solar PV.

I've been quoted for 12x Hyundai 400 W solar panels + 3.68 Kw inverter due to be installed next month. Since then I've had the roof covering replaced and the ridge to gutter dimension has been increased.

So I think extra panels should fit. Instead of 2 x 6 portrait or 4 x 3 landscape, it looks as though 4 x 3 landscape plus 6 x 2 portrait will fit, for 5.6 kWp.

Just wondering what route I can go down - I'm guessing the 3.68 kW inverter would clip unacceptably as all the panels will be on one SSW facing roof plane?

So either seek DNO approval - is this a long process? Or maybe export limit + battery?

Are you sure about the number of panels that will fit 4x3 + 6x2 is 24 panels which is a lot more than 5.6 kwp.

Our DNO approval for 5kw took 1 month we then had to wait a couple of months after install for the new meter to be assigned for export. I believe that some areas can pre approve up to a certain amount. Might be helpful to post where you are in case anyone has specific experience of that location.

I suspect you will regret not getting DNO approval for the higher capacity as it is a 25 year investment. Even with a battery, on a summer's day it could fill up by mid morning and you will then be clipping substantial amounts. 

ed110220

2nd_time_buyer said:

ed110220 said:

Hi all, looking for some advice on going bigger with solar PV.

I've been quoted for 12x Hyundai 400 W solar panels + 3.68 Kw inverter due to be installed next month. Since then I've had the roof covering replaced and the ridge to gutter dimension has been increased.

So I think extra panels should fit. Instead of 2 x 6 portrait or 4 x 3 landscape, it looks as though 4 x 3 landscape plus 6 x 2 portrait will fit, for 5.6 kWp.

Just wondering what route I can go down - I'm guessing the 3.68 kW inverter would clip unacceptably as all the panels will be on one SSW facing roof plane?

So either seek DNO approval - is this a long process? Or maybe export limit + battery?

Are you sure about the number of panels that will fit 4x3 + 6x2 is 24 panels which is a lot more than 5.6 kwp.

Our DNO approval for 5kw took 1 month we then had to wait a couple of months after install for the new meter to be assigned for export. I believe that some areas can pre approve up to a certain amount. Might be helpful to post where you are in case anyone has specific experience of that location.

I suspect you will regret not getting DNO approval for the higher capacity as it is a 25 year investment. Even with a battery, on a summer's day it could fill up by mid morning and you will then be clipping substantial amounts. 

Hi, I'm in Bath so Western Power distribution.

For the number of panels, I've been quoted for 12 (4.8 kWp). They haven't said how they would be arranged - I assume two rows of 6 arranged portrait, but three rows of 4 would be almost exactly the same size. For either the length of the roof gable to join with neighbours is the limiting factor and it would be tight, so perhaps only 10 would fit. Ridge to gutter would allow plenty of space top and bottom.

*But* now the new roof covering has been fitted the ridge to gutter dimension has been increased so I *might* be able to fit more in that way. I'm thinking two rows of 4 panels landscape plus one row of 6 portrait for a total of 14 modules (5.6 kWp). That would  be quite tight in both directions.

Basically because of the roof dimensions being tight both ways for all layouts except the 10 module one, it could be 10 (4 kWp), 12 (4.8 kWp) or 14 (5.6 kWp) modules, but I'm keen to try to squeeze as much electricity out as I can!

ed110220

2nd_time_buyer said:

Are you sure about the number of panels that will fit 4x3 + 6x2 is 24 panels which is a lot more than 5.6 kwp.

Hi sorry that was a typo, it would be 6x2 portrait or 4x3 landscape for 4.8 kWp, not both. Or 4x2 landscape and 6x1 portrait for 5.6 kWp.

Magnitio

As mentioned above, it is worth seeking approval for 5kw and an appropriate inverter. If you have 5.6kWp and a 3.68kw limit with no battery, you will probably have a few hours in the middle of the day for several months where the potential output will be limited.

ed110220

Magnitio said:

As mentioned above, it is worth seeking approval for 5kw and an appropriate inverter. If you have 5.6kWp and a 3.68kw limit with no battery, you will probably have a few hours in the middle of the day for several months where the potential output will be limited.

Does the installer need to do that or can I?

Roofing has been finished today and so I can measure rather than estimate the dimensions: - 7050 mm gable to join with neighbours, 4320 mm gutter to ridge.

Panels are 1140 x 1719 mm so assuming 20 mm spacing and at the edges I'm thinking:-

• 4.8 kWp made up of 6 x 2 portrait, total array 6980 x 3498 mm. This would be tight lengthways but not gutter to ridge.
• 4.8 kWp 4 x 3 landscape, total array 6976 x 3500 mm so basically the same as above.
  
• 5.6 kWp 4 x 2 landscape plus 6 x 1 portrait, total array 6976 x 4079 mm. This would be tight in both dimensions.

2nd_time_buyer

Installer will apply for DNO.

Minimum recommended is normally 200mm from edges (often 300mm). It looks a bit tight lengthways.

Narrower panels?

Boffinboy24

Just as a point of reference - I have a 5.6kwp 14 panel system with 3.68 inverter setup - basically at max size for the inverter rating. It faces SE. I pushed my installer on whether to get a larger inverter and they told me from their analysis I wouldn’t lose that much to clipping as the generation would come in earlier and run later, and perform better on poorly lit days etc - this makes sense as well in terms of “value” unless you have a battery because a small amount of usable energy saving 30p per kWh is worth much more than stuff exported to the grid for 5p. I am still skeptical though, I get a lot of clipping on sunny days right now as it’s quite cool but the installer suggests it may not be quite as dramatic when the panels are hot. See image for my most obviously clipped totally clear day so far. Without seeing the modelling I can’t be sure, but I didn’t expect quite as much clipping. As you can see I do get some generation from around 6AM to nearly 8PM, and the clipping can be there from mid morning to early afternoon (given its SE). Oh well, too late for me now - but may be useful for you to see!

2nd_time_buyer

Out of interest I modelled my system in the Solaredge designer software.

6.72 kw split over SE and SW. The peak DC output from the panels is predicted to be 6.0kw.

With the 5kw inverter that I have, the clipping loss is 0.25% and the inverter efficiency loss is 0.95%. total annual production is 6.85mwh

With a 6kw inverter, the clipping loss is 0% and the inverter efficiency loss is 1.04%. Annual production is 6.63mwh

With a 4kw inverter, the clipping loss is 2.04%, inverter efficiency loss is 0.9%. Annual production is 6.71mwh

So basically it makes surprisingly little difference but it is marginally better to have an inverter slightly undersized compared to peak DC output of the solar panels. Although, you could even argue that the 4kw inverter could be optimum for the reason given above by Boffinboy24 that energy at low power output is more useful.

Boffinboy24

2nd_time_buyer said:

Out of interest I modelled my system in the Solaredge designer software.

6.72 kw split over SE and SW. The peak DC output from the panels is predicted to be 6.0kw.

With the 5kw inverter that I have, the clipping loss is 0.25% and the inverter efficiency loss is 0.95%. total annual production is 6.85mwh

With a 6kw inverter, the clipping loss is 0% and the inverter efficiency loss is 1.04%. Annual production is 6.63mwh

With a 4kw inverter, the clipping loss is 2.04%, inverter efficiency loss is 0.9%. Annual production is 6.71mwh

So basically it makes surprisingly little difference but it is marginally better to have an inverter slightly undersized compared to peak DC output of the solar panels. Although, you could even argue that the 4kw inverter could be optimum for the reason given above by Boffinboy24 that energy at low power output is more useful.

Honestly I can’t thank you enough for sharing that analysis! I should have asked my installer to share theirs, this makes me feel reassured I’m not really throwing away much energy and the smaller inverter is not a disaster!

ed110220

Boffinboy24 said:

Just as a point of reference - I have a 5.6kwp 14 panel system with 3.68 inverter setup - basically at max size for the inverter rating. It faces SE. I pushed my installer on whether to get a larger inverter and they told me from their analysis I wouldn’t lose that much to clipping as the generation would come in earlier and run later, and perform better on poorly lit days etc - this makes sense as well in terms of “value” unless you have a battery because a small amount of usable energy saving 30p per kWh is worth much more than stuff exported to the grid for 5p. I am still skeptical though, I get a lot of clipping on sunny days right now as it’s quite cool but the installer suggests it may not be quite as dramatic when the panels are hot. See image for my most obviously clipped totally clear day so far. Without seeing the modelling I can’t be sure, but I didn’t expect quite as much clipping. As you can see I do get some generation from around 6AM to nearly 8PM, and the clipping can be there from mid morning to early afternoon (given its SE). Oh well, too late for me now - but may be useful for you to see!

Thanks, this would be similar to my potential setup, all facing one way, fairly close to south. It's also what I'm thinking, that the clipped generation will be the least valuable as it will be when you've got plenty anyway.

One more question: does anyone know how the 3.6 kW limit works with a Growatt SPH3600 inverter? I presume the battery can be charged at the same time as exporting, ie say you're generating 5.6 kW you can export up to 3.6 kW and use 2 kW to charge the battery? If you're using electricity in the home is this taken off before or after the limit? Say (potential) generation is 5.6 kW and you're using 5 kW at home, can you only draw 3.6 kW from your PV, or can you draw 5 kW as it only leaves 0.6 kW for export?