Ground mounted solar

[Dmeltd]

Would you know the advised distance between solar frames on a ground mount system

Ie one system directly behind another?

The back of the first system is 1900mm affl and the next system behind this should be 9000mm away to clear sunlight at 12 degrees in decemeber (its in scotchland!)

But that means you need a lot of space to mount a few systems back to back without raising them off the ground.

Anyone else came across this issue?

 

[dansk]

Never done a ground mount, but from what ive read on here a rule of thumb is 3 x height = space between racks.

 

[Markc]

The rule of thumb is a guide but the further North you go the more this needs to be increased. There is an equation to work it all out and I think its in the "Planning and Installing Photovoltaic systems: A Guide for Installers, Architects and Engineers" A Book well worth having.

 

[Dmeltd]

been reading up on it mark and they ( the guide section 3.8 i think it was) take the view that some shading is necessary when you have multiple systems to utilise the space ie a utilisation factor and if this factor is above 50% then you need to look at the distances, ive made mine too close unfortunately and i want to get it right second time around, i knew some shading was going to occur in winter but the system in front has generated 110kwh compared to 48.3 at the back after being switched on since dec 2011.

 

[Earthstore]

Just go and bang a post in the ground at the finished height of the first row, measure the shadow at different times of day, allow a little more space as we are now in January, shadow would be longer if sun was lower...

The best way to see if a roof has shading is to look at it....

Hope this helps

 

[solarfred]

Would you know the advised distance between solar frames on a ground mount system

Ie one system directly behind another?

The back of the first system is 1900mm affl and the next system behind this should be 9000mm away to clear sunlight at 12 degrees in decemeber (its in scotchland!)

But that means you need a lot of space to mount a few systems back to back without raising them off the ground.


Anyone else came across this issue?

Yes, and this is where science works in your favour as the universe is pretty much fixed.
If you get a small amount of shading on a portrait ground mount you will get 0 output as you will kill the panel and any panel in that row/string at the same level. Watch the shadow move down and then bam the thing lights up!! (are you doing single row or double row?).

If you have several rows on a ground mount I assume we are talking cash income? Shading is a cash killer so you need to get it right.
In winter you should aim for 4 hours a day of useful sun. If you can move the panels in the vertical plane then you will increase the potential output but that increases the distance between the rows.
If you are on a flat surface then work out the distances and get it right as a few inches out means no production for an increased period.
If you are on a sloping site then terrace the site and bring the rows closer together.
It is simple trigonometry but critical to get it right but remember the output in winter is limited by the simple fact the sun is weaker and only available for a shorter period.

 

[IronLiver]

PV Sol Expert does the row spacing calculation for you if you specify the dimensions of the frame and select the appropriate panels. From what I could tell their calculations are based on there being no shading on the rear array at 12 noon on the winter solstice (if your array is facing due south). However, If you model this in other software or look at the animation in PV Sol you will notice that either side of 12 noon you will still experience some shading on the lower corners of the rear array as the sun dips towards the horizon.

If you want to be able to visualise this without spending a grand on the software then download Google sketchup, it's free but will take a bit of getting used to. I also think that the images look much more professional that the very basic graphics produced by PV Sol. In Sktchup you can grab your actual location and it displays an accurate angle of the sun's path for a given time of day if you activate shadows. Example is shown below:



The image above shows the angle of the sun at midday on the 21st December for a recent project we completed. I wasn't happy with going with the distances specified by PV Sol due to the shading either side of midday and there was a bit of space to play with so we moved the rear array back a reasonable amount. The diagonal line from the near top corner of the front array is the angle of the sun at noon - the minimum spacing. In fairness I don't know if this will have a massive impact on total output as this is only really an issue during a poor month for generation.

Image below shows same installation again but at 8:50am on 21st and highlights the most significant shading situation, still pretty minimal.



Hope these images enlarge OK.

 

[SpitfireW'sale]

PVSol has a part of the program that puts all of the relavant variables (panel dimensions, array location, pitch etc) into an equation and gives you an optimum row distance. It is a useful tool. We will be happy to help with your system design, get in touch if of interest.

edit: as mentioned above!

 

[Mr Peacock]

PV Sol Expert does the row spacing calculation for you if you specify the dimensions of the frame and select the appropriate panels. From what I could tell their calculations are based on there being no shading on the rear array at 12 noon on the winter solstice (if your array is facing due south). However, If you model this in other software or look at the animation in PV Sol you will notice that either side of 12 noon you will still experience some shading on the lower corners of the rear array as the sun dips towards the horizon.

If you want to be able to visualise this without spending a grand on the software then download Google sketchup, it's free but will take a bit of getting used to. I also think that the images look much more professional that the very basic graphics produced by PV Sol. In Sktchup you can grab your actual location and it displays an accurate angle of the sun's path for a given time of day if you activate shadows. Example is shown below:

View attachment 10190

The image above shows the angle of the sun at midday on the 21st December for a recent project we completed. I wasn't happy with going with the distances specified by PV Sol due to the shading either side of midday and there was a bit of space to play with so we moved the rear array back a reasonable amount. The diagonal line from the near top corner of the front array is the angle of the sun at noon - the minimum spacing. In fairness I don't know if this will have a massive impact on total output as this is only really an issue during a poor month for generation.

Image below shows same installation again but at 8:50am on 21st and highlights the most significant shading situation, still pretty minimal.

View attachment 10191

Hope these images enlarge OK.

Google Sketch up is awesome. I started using it earlier this year and ive found no end of uses. I didnt know you could do this with the shading though, so im gonna have a bash at that now.