Orientation of solar PV panels

[vivienz]

We're getting pretty close to applying for planning permission and so I'm thinking more about our energy supply in the new build.  If the submitted design gets through more or less intact, we will have pitched roof areas that face to all 4 points of the compass and the scope for fitting PV to all/any of the roof surfaces.

 

I've come across a few comments that say although all south facing will give the maximum amount of energy, it gives a day time peak whereas having east/west orientation will give a lower but more useable amount of energy throughout the day.  As our roof will be shaded only by itself, does it make sense to distribute the panels between east, south and west oriented roof areas? Is there anything likely to make this more difficult than just south facing?

[ProDave]

A typical inverter for a typical 4WK system has two inputs that work independently, so lends itself to two banks of panels. So probably one facing south the other either east or west, depending if you think you are likely to self use more in the morning or evening.

 

I think a gable ended house suits solar PV beter. The aesthetics of panels on a hipped roof, which usually means the bottom row of panels is longer than the top tow, does not look as nice. On s gable ended roof you can make them all the same length.

[ragg987]

Number of factors to consider, apart from the aesthetics... (I agree with @ProDave about gable vs. hipped)

 

Shading is a factor - e.g. consider trees and buildings both nearby and further away, and choose an orientation that minimises this. Also roof angle - about 38 degrees is considered optimal in Southern England.

 

South facing will give maximum energy over the course of the year, and power output will tend to be focussed less towards the start and end of the day. East and West facing will give less output overall, but will extend the hours of availability of power. You are looking at a reduction of approx 20% in total energy. Note that in winter the sun tends to be more southerly so benefit of east or west facing is significantly reduced.

 

Now if you are able to make use of the power (e.g. divert it to DHW or run your heat-pump, dishwater, washer etc) during peak generation periods, then you can have-your-cake-and-eat-it as this allows you to maximise consumption and export the minimum. If you do not get a smart meter, you have the option to be paid (FIT) on an assumed 50% export.

 

One other factor is installation cost - you may find it is cheaper to put all the panels in one place compared to split them out over 2 or more locations.

 

My view is to go optimal energy (South).

 

You can model your exact scenario here: http://re.jrc.ec.europa.eu/pvg_tools/en/tools.html

Edited July 31, 2017 by ragg987
typo

[vivienz]

Thanks both, that's really helpful.  The house will have 3 gable ends as it's a sort of stunted L-shape, but there will be some shading on the south facing roof from the other roof axis.

 

That's a really useful widget, @ragg987.  I put in our details and it seems that pretty much the only direction that will receive any sun in December is the southerly aspect.  I suspect a combination of east and south will be most effective for us.

[ragg987]

If you get significant partial shading over the array (e.g. from your roof or chimney), or if you end up with multiple arrays, you may wish to look at power optimizers like Solaredge or Tigo. These permit each panel to operate at the optimal point. Slight increase in cost but might be worth it. I use Solaredge and also like the internet-enabled access it permits to monitor the array, inverter and each panel.

[AliG]

I just went through the same exercise on my house, originally I was going to have south and west facing.

 

Then when I thought about it, any panels not facing south are shaded by the actual house for a substantial portion of the day, thus although I might have got extra output late in the evening this was way more than offset by the fact that the west facing roof would not have received any sun until after 12.

 

Depending on the shape of your roof, a south facing roof likely generates power for the majority of the time that an east or west facing roof will without being overshadowed for part of the day.

 

I would then use a Earthwise Solic 200 or similar to divert excess generation to heat hot water.