Are you wondering whether your house is suitable for a photovoltaic system? In this guide, you will learn how to check your location for photovoltaics and whether a PV system is even worthwhile. We will show you what requirements your roof must meet and how you can check these yourself.
1. How high is the global radiation?
The global radiation of the sun largely determines the maximum yield of your photovoltaic system. It consists of the direct and diffuse solar radiation. In Germany, global radiation is generally higher in the south than in the north. The average value is around 1,000 kWh/m² per year.
The German Weather Service has a map of global radiation created where you can check this for your location. In addition to the global radiation, you can also check the diffuse radiation and the direct radiation for your photovoltaic location.
Diffuse radiation occurs when sunlight is scattered due to fog or clouds. It hits the photovoltaic system from different directions. Direct radiation reaches the surface without scattering.
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2. What is the orientation of the roof?
The orientation of the roof is another important factor and contributes to the maximum possible yield of photovoltaics. In Germany you can achieve the highest yields with a south oriented photovoltaics.
When aligned with Southeast or South-West Losses of less than 5% occur compared to the south. These two options are therefore also worthwhile for photovoltaics. With a roof orientation east-west the losses are around 10 to 20%. However, you can cover both sides with solar modules.
An east-west PV system can be more economical than a south-facing photovoltaic system. Most of the electricity production takes place in the morning and evening, when most electricity is consumed. This increases your own consumption and means you don't have to feed in as much solar power (because that's hardly worth it anymore).
You can easily find your roof orientation at Google Maps To do so, enter your address and select the satellite map. Here you can see your roof from above in detail.
You can also use the compass app on your smartphone. Android and Apple devices have this pre-installed. To do this, stand as straight as possible with your back to the wall of the roof area in question. Hold your smartphone horizontally and still. Now you can see the exact degree of orientation of the roof read.
3. What is the pitch of your roof?
The slope of your roof has just as great an influence on the solar yield of your PV system as the roof orientation. They are both connected. You will achieve the best PV system yield when the sun is exactly at an angle of 90° hits the PV modules.
Over the course of the day and year, the radiation angle However, in the winter months The sun is much lower in the sky than in the summer months. In winter, a flat roof angle is therefore advantageous and in summer a steep one. Over the year, the optimal angle of inclination is between 30 and 45°.
Do not forget that the angle of inclination also depends on the orientation of the roof. In Germany, you will achieve the highest yield with south-facing with a inclination of 35°. At a east-west orientation A flatter angle is better because the sun is also lower in the morning and evening.
The exact yields in relation to roof pitch and orientation can be seen in percent in the following table.
To create your own roof pitch To check the suitability of a PV system, you can go to the attic and measure the degree of inclination of the roof beams or a straight roof slope. You can also use your smartphone for this. Download a app for measuring angles like the free iLevel app.
Another method is to calculate angles yourselfTo do this, measure the height (b) from the floor straight up to the roof slope. Then measure the length (a) from your first measuring point on the floor to the roof slope.
Then calculate the following with the calculator: a² + b² = c²
Take the square root of c² to get c.
You can now calculate the angle using c. a / c = sin (ß)
Then type sin-1 (sin ß) and get your angle of inclination.
If your roof pitch is suboptimal, you can install the modules as a roof-mounted installationThe mounting frame of the modules can be easily adjusted in terms of inclination.
4. Will the roof be shaded?
Yes, Photovoltaics also works in the shadeHowever, this will reduce the yield of your PV system. Therefore, check whether there is any shading on your roof. To do this, check it at different times of the day. Also remember that the sun is lower in the sky in winter and the shadows are much longer than in summer.
If a small area of the roof is only shaded for a short period of time, this is not a problem. Modern photovoltaic modules can losses from partial shading with the help of bypass diodes. If there is large and long-term shading, you should not cover the corresponding areas with solar modules. If the shading is caused by trees, bushes or, for example, a satellite dish, these can possibly be removed.
Also think about the shading that the house creates. This can easily be caused by dormer windows or chimneys.
How to calculate the expected yield at your location
To calculate the yield of your PV system, you need to global radiation for your location, the roof orientation and the angle of inclination, as well as the nominal power of the photovoltaics.
The rated power is made up of the total output of the individual PV modules and is given in kWp (kilowatt peak). A typical nominal output for a photovoltaic system on a single-family home is 5-10 kWp.
Example: You have 20 solar modules with an output of 350 Wp (watt peak) -> 20 x 350 = 600 Wp = 6 kWp
Next, find the global radiation for your respective location per month. The map from the German Weather Service very helpful. You then multiply these values by the kWp output of your system. In our example, this is 6.
Our facility is located in Hamburg, has a Orientation of 40° to the southwestt and a roof pitch of 30°. The orientation and inclination reduce the yield by 4%, which means that 96% of the maximum possible power yield is achieved. You can find this value in our "Orientation and inclination angle" table above.
| Month | global radiation kWh/m² | global radiation x 6 kWp | Reduction due to orientation and inclination (x 0.96) |
| January | 18 | 108 | 103,68 |
| February | 43 | 258 | 247,68 |
| March | 78 | 468 | 449,28 |
| April | 128 | 768 | 737,28 |
| May | 128 | 768 | 737,28 |
| June | 178 | 1068 | 1025,28 |
| July | 163 | 978 | 938,88 |
| August | 108 | 648 | 622,08 |
| September | 83 | 498 | 478,08 |
| October | 53 | 318 | 305,28 |
| November | 18 | 108 | 103,68 |
| December | 13 | 78 | 74,88 |
| annual total | 1011 | 6066 | 5823,36 |
Our example system therefore generates 5,823.36 kWh of electricity per year. The months with the lowest yield are November to January. The highest yields are achieved from April to July.
If the effort is too much for you, you can also use solar cadasters. More and more cities and municipalities are offering these on the Internet. Solar cadasters are detailed development maps that show which roof areas are suitable for photovoltaics. All you have to do is enter your address.
Conclusion
Whether a photovoltaic system is worthwhile at your location, you can check for yourself. You need the global radiation, the orientation of your roof and the angle of inclination. You can easily read the radiation on the weather service map. You can find out the reduction in yield due to orientation and inclination in our table. You can also simply make a rough estimate of 1000 kWh per kWp power go out.
