Recommended spacing between ground mount array rows

[drcarrera]

Hi

 

We're looking to install a ground mount system probably comprising 24 375W panels. As we'll need to install in two or three rows, is there a recommended distance between each to minimise shading?

I appreciate there's bound to be some when the sun's very low (unless we lay them all flat!) but for 1.7m high panels at, say 40^o , would a 1m gap between front of row and back of one in front be enough to avoid too much loss?  We're in the south of England, by the way.
Also, would it make sense for each row to be on a separate inverter?

 

Any pointers gratefully received!

[Dillsue]

Get a couple of panels or the same size sheets of wood, prop them up one in front of the other and see where the shadows fall at different times of the day. At a guess, 1 metre will be no where near enough to give year round generation from the rear rows. Setting the panels in landscape orientation will allow them to be closer but make the rows longer. If youve got the option to raise the rear rows, that would allow the rows to be closer together

 

PVGIS will give you hourly generation figures so you can see how much an unshaded array should be generating at different times of the day throughout the year. You can then decide when and how much you want to generate and set your panels so there is no shading when youve chase to generate.

 

Unless youve got the rows spaced far enough that theres no shading, It's almost certain that you want the front row on its own MPPT input and the rest of the panels on a separate input(s). Alternatively you can use optimisers or micro inverters which will both help maximise generation when theres some shading.

[Iceverge]

The sun it at about 6 deg elevation the Sun - Interactive Sky Chart | TheSkyLive.com  from this website at 9am on the 21st of December. 

 

Sketching it out to scale  it appears that you would need to have 14m spacing to ensure that the rearmost panels are not shaded by the first. 

 

 

 

You need to decide if your goal is maximum self use of the electricity or maximum annual production. The economics depend on your feed in tariff, the capacity you have to self use the power and your cost of  bought in electricity.

 

For maximum production 35deg works well in SE England, this enables closer spacing (especially on south facing slopes). Also an azimuth of true South is optimal. This is what commercial solar farms do. 

 

 

 

For domestic self use the equation changes somewhat. 

An angle of 35 would give 9.2MWh annually but only 338kWh in January. 

 

 

An Angle of 70deg would drop annual production to 8.3MWh but the January output would be 424kWh.

 

 

 

Similar juggling can be done on a daily basis by splitting the array East/West giving more power in the house at times you will use it at the cost of total production. Search for  @ProDaves henhouse on here. These daily fluctuations can be buffered somewhat if you have a battery or a load that can be timed from say 11am to 1pm. 

 

My rough guess on this is you'd be best off with a single array of 24 panels in landscape, 2 high at about 60-75 deg pointing due south. 

[drcarrera]

Thanks for the replies.

 

Yes, it's impossible to eliminate shading from a practical point of view with multiple rows. Unfortunately we don't have the space for a single row of 12 panel width so we're looking at two or three rows.  I do wonder whether we should simply reduce the total number of panels so we can have a 2-high single row. 

Also, my gut feeling is that even though we'll be having battery storage, as we'll also have an ASHP we shouldn't just be looking at total annual production and shouldn't maximise that at the cost of lower winter production. 

So many variables! 

[Bramco]

10 minutes ago, drcarrera said:

we shouldn't just be looking at total annual production and shouldn't maximise that at the cost of lower winter production.

 

Do the PVGIS calculations for several angles of incidence.  For us in the midlands, the annual production doesn't vary very much between say 30deg and 45deg but the winter output is far higher the more upright the panels are.   We're expecting to export a lot of our summer output (no battery yet) but want to maximise output in the winter when we won't be exporting - so for us the more vertical the better within the window of roughly similar annual output.  Ours will be a 12 panel array, in line, so no worries about shading between arrays.

 

Simon