Switching to renewable energies – thought experiment (part 1 out of 3)

Switching to renewable energies – thought experiment (part 1 out of 3)

  • Posted by Gerhard Pramhas
  • On 3. August 2022


In times like these, one topic is omnipresent: the switch to renewable or green energies. Many private individuals as well as entrepreneurs are committed to this idea. However, does it pay off? Here is a thought experiment.

First of all, an example:

  • one family house with 4 people: electricity consumption incl. two electric cars: 12,000 kWh per year
  • photovoltaic system on the roof: power 13 kWp, area: about 60 m2, electricity storage, 22 kWh of energy

So far, so good. In Austria, an irradiation power of about 1,000 kWh/m2 and year can be expected, which is about 60.000 kWh in total. A photovoltaic module has an efficiency of about 20 %, i.e., about 12,000 kWh per year are generated. This sounds good, but the devil regarding renewable energy is in the details.

Be self-sufficient through renewable energy – in summer and winter?

Photovoltaic works very well in the period of April to September, when solar radiation is high in combination with lots of hours of sunshine. The plant still works reasonably well when the sun shines on cold winter days. But on the cloudy days in autumn and winter there is hardly any electricity generated. This is the reason why the achievable degree of self-sufficiency of our example is around 70-75 %. The remaining 25-30 % must then be bought when needed. However, the surplus energy of a photovoltaic system is usually sold at an unattractive price.

The essential question that remains in our thought experiment: who delivers the 25-30 % that cannot be provided by a photovoltaic system? Are there any other renewable energy sources that could deliver the rest? Hydropower, wind power, biomass?

Will this calculation work out? What is your opinion? Please share your thoughts with me in the contact form or contact me via LinkedIn. Stay tuned! – Part 2 and 3 regarding switching to renewable energies will follow.