Step 2: Your House - The Sun Power >>>

Step 2 - Analyse the orientation of your roof, incline and shading

In step 1 we have calculated the peak power of your PV system. The peak power is expressed in KWp(eak). The more KWp you are able to install on your roof, the more electric energy you can generate.

Apart from the system size, the orientation of your roof, slope of solar panels and shading have significant effect on electricity production. These factors determines how much sun-light your photovoltaic system is able to capture. Learn more ...

a/ Orientation of Your Roof:

For best performance your roof should face to South (on northern hemisphere), but also all direction up to West or East are in many cases still efficient.

Use a compass to measure the direction of your roof. In case you don't have a compass another easy way is to use the free software Google Earth. With the "ruler tool" in Goggle Earth measure easily the orientation of your roof.

In solar the angular measurement is expressed in the so called "azimuth angle". Direction to south means an azimuth angle of "0", East "-90", West "+90".

House PV - Directions

Courtesy: PV*SOL® Expert


House PV - Azimuth Angle

Roof Orientation and Azimuth Angle

b/ Shadow:

You need to consider any shadows on your roof as this has a potential to make your system very inefficient. Consider that the sun and shadow is changing over the year and over the day. A shadow often occurs in morning or afternoon hours or in winter months when the sun path is low.

Of course, an all day shadow for most time of the year on your whole roof is not acceptable and your roof is definitely not suitable for a photovoltaic system.

In contrast, minor shadow on your roof, like a shadow caused from your chimney, from antenna or a shadow from tree in early morning / afternoon for winter months only is okay. For those cases it is important only to arrange the panels in separate strings. Plus, choosing the an appropriate solar power inverter. But this is something to calculate in late stage, once you go into details.

Make sure to take the areas with an "most of the day shadow" off your available roof space. For example, if you have a dormer or a chimney subtract the space itself plus half meter around from your available roof space. If you have an all day shadow from a tree, subtract the space where the shadow occurs from your available roof space. Alternative consider to cut some trees.

Rough calculation for shadow is okay here. In your final calculation you can go into details.

House PV - Directions

Courtesy: PV*SOL® Expert

c/ Tilt Angle:

A fixed angle measured from the horizontal to which a solar array is tilted. The optimal tilt angle varies upon sun path and latitude. As a rule of thumb the tilt angle would be best between 2/3 to 4/5 of the latitude - resulting in angles of 32° to 38° in Middle and Western Europe or 30° to 36° in most of the US.

For instance if you are living on 51 degree of latitude the best fixed tilt angle is ~30° - 40°. The closer to the equator, the smaller the optimal tilt angle. However, the tilt angle may never be less than 10° to ensure that the dirt will be removed from the modules by rain.

But also smaller or larger angles are often still efficient.

For in-roof system the tilt angle is equal to your roof pitch (first picture). At a flat roof, you install freestanding PV modules under the optimal angle (second picture).

If you want to maximize the performance you can consider solar trackers. They aim to achieve best performance by moving the photovoltaic panels to follow the sun. The downside is that these systems are around 30% more expensive and need to be maintained. And they cannot be mounted on a pitch roof.

House PV - Directions

House PV - Tilt Angle

Courtesy: PV*SOL® Expert

d/ The Static of your Roof:

The load of photovoltaic modules including the mounting frame is typically around 15 to 20 kg per sqm (3.0 - 4.5 lb per sq ft).

Installing a PV system on a house in good conditions with a pitched roof (modules are installed parallel to the roof) usually doesn't cause any problem for the roof static. However, If you have any doubts consult a specialist (e.g. structural engineer, technical expert), in order to guarantee the loading
capacity of your roof structure.

If you install your PV system on a flat roof (modules are installed not parallel to the roof, but with a tilt angle) you need to consider additional loading conditions from wind and maybe snow.




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