Google DIY Solar Australia: Design and Location

Monday, February 27, 2012

Design and Location

The size of the Solar System you desire and the location of it are dependent upon each other.  Firstly the place to position your system should ideally be both north facing and without shading for more than 90% of the daylight hours.

Lets consider the fundamentals, just a little.  A (photo-voltaic) Solar System produces electricity from light energy.  Whilst I don't want to bore you with details of the theory,  this is the most important fact and so it is important that your Solar System is exposed to the maximum amount of light energy available. This also means that the panels should face the suns rays directly for the best result.

Keeping this in mind, take a look at your home. 
  • Do you have any north facing roof slopes?
  • If so, are they shaded at any point of the day?
Ideally a home with a roof pitched east-west, i.e. sloping to the north (and South) is the best.  If you don't have this, don't sweat it, there are still several options to take.

As to shading, it will really depend on the area shaded and for what length of the day.  You must also consider winter time shading vs. summer as the shadows from an obstruction are longer (bigger) during the winter due to the low angle of the sun.  There are various calculations to determine the difference in shading, this can be difficult for all but the most mathematics savvy people.  So if you are at the summer end of the year or in the middle when you do this it can be difficult to judge.  I will get into the calculations of this a bit later, but for now a bit of visual inspection may suffice. Take a look to the north, north-east and north-west of the place you might use.  Are there any trees or buildings higher than the lowest point of the roof in question? If so, how far away.  A general rule of thumb is in winter, the shadow will be up to about 2 times as long as the object is tall at midday. This depends on where you live: Brisbane the shadow is as long and the object and in Hobart 2.2 times longer than the object is tall.  Take into consideration the height of the roof, so consider objects twice as high as lowest part of the roof in question.

Keep in mind the shadows are longer near sunset and sunrise so this must also be considered.  In all, unless you have large trees like (gum trees) close to the house, this shouldn't be an issue.  Normally, buildings on adjacent properties are not allowed to "overshadow" so this should not be an issue also.  Various parts of your own buildings and the effect they have on your potential location are more likely to be a problem.  As I mentioned, the calculations, if you are in doubt will be covered later.

Your roof is flat, near flat or doesn't have a north facing surface?  Don't worry yet, there are still ways to do it!  For a flat or near flat roof, there are elevating brackets available, these can also be used to some extent on a pitched roof if needed.

The area of available roof to fit panels will detemine the amount of power you can generate.  A typical 180 Watt panel is approximately 1.6m high by 0.8m wide. So you can detemine from this approximately how many panels will fit the area.  For example a 1.6kW system requires 9 panels of this size and so will need 1.6 x 0.8 x 9 sqm = 11 square metres of roof area.

Look out or more details in the next post.  I shall discuss problematic, less than ideal roof areas and other topics.

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