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Are you harvesting your own power yet?

The use of solar panel systems has known a steep rise in recent years. Despite the decline in government subsidies in various countries and regions, installing solar panels is still a very good investment. (Photo source: Fotolia)

The bottom line is that you will not have to pay for the energy you are producing yourself for approximately 20 to 25 years. Taking into account the probable increasing prices for electricity for the upcoming decades, your return on investment will only improve with time.

But is your roof fit for solar panels? What do you need to consider before making a decision?

Orientation and inclination

Ideally, your roof is oriented towards the south and has an inclination of 35°. Of course, not every roof matches these conditions. Orientations towards the southeast or southwest are also acceptable, but energy production will decrease to 90%. The inclination can be between 30° and 50°. In case of a flat roof, the panels can be oriented towards the south in most cases. A mounting system ensures the ideal inclination.

Your roof

Since solar panels will be on your roof for an average 20 to 25 years, it is advisable to check the roof’s condition beforehand. It would be a pity if reroofing needs to be carried out in this period forcing the solar panels to be dismantled. Also make sure the roof is well insulated.

In most cases, a roof is able to withstand the additional weight of the solar panels. A solar panel weighs approximately 13 kg/m². When in doubt, consult an expert. In case of a flat roof, the weight of the mounting system needs to be taken into account as well. The wind can also have a significant impact. In situations where high winds can be expected, the mounting system is then equipped with additional ballast in the form of heavy tiles or the mounting system is anchored into the flat roof.


Check whether there is any shade on your roof, caused by trees, poles, higher houses in the vicinity, etc. This includes shade in the morning as well as in the afternoon and in the evening. Mostly, solar panels are connected in series, and this setup will reduce the production of the entire string of panels when one of them is in the shade. This can be avoided by not using a centralized inverter, but opting for decentralized micro-inverters. In the latter case, each solar panel has its own inverter. Shading on one panel will no longer influence the production of the other panels.

With shading, micro-inverters can offer a solution. (Photo source: Enphase)

How many panels?

Each m² of solar panel produces approximately 120 kWh per year. An entire family’s consumption of electricity reaches 3,500 to 4,000 kWh. A 29 to 33 m² surface of solar panels should be more than sufficient. Smaller is also possible, but in that case you will have to use some energy from the public power grid and pay for it.

Excess production is in most cases not rewarded. So, check your annual power consumption beforehand and adjust the number of m² of solar panels accordingly. Additional tip: using electricity more sparingly will enable you to install fewer panels and reduce your investment.

Your electrical installation

Installing solar panels is also a perfect moment to check the condition of your home’s electrical installation. When it is outdated, it is wise to renew it. It will not only enhance the safety, but also the ease of use as well as the flexibility and the functionality of the entire electrical system.

And the yield?

An example: with an 8,000 euro investment you get approximately 30 m² of solar panels. With a price for electricity of 0.21 €/kWh you will save about 735 euros per year. In the event that the price for electricity does not increase in the upcoming years (but you probably don’t believe in fairy tales) you will earn back your investment in eleven years. After twenty years, your investment will have earned you 14,700 euros. In the event that the prices for electricity rise—and you can benefit from certain types of subsidies in the region you are living in—this amount will of course increase. In short, it makes sense to just do it!