The sun sends 1,08*10¹⁸ KW/H per year of energy to the earth's surface, which is 10,000 times of the human's primary energy needs. The sun is doing this for some billions years and - after momentary level of knowledge - will do it for some more billion years until the sun will go out of fuel. Therefore 20 squares at 50 km each side distributed at appropriate places over the world would be already sufficient. "already" sounds funny, because all squares counted together correspond to 1/7 of Germany's size.

However - some of the above mentioned KW/H we would like to have to reduce our own primary energy need.

Gas consumption before we started and after we finished our project:

Since I had noted the counts for gas, water and electrical energy each month as a hobby from the day we moved into our house, I can easily compare the old values with the new values now. Additional remark: the winter 2006/07 was relatively warm and April 2007 had many sun hours more than usually.

Solar energy portion of the complete energy need for heating and warm water of our house:

The solar portion for January refers only to the second half of January. Here can easily see that the heating support is rather small. But in March it is already 1/3; we could have had switched off the burner in March for one whole week. The heating and warm water was served by the storage, which was loaded over day by the sun. April offered much sun: The solar portion was greater than 84%; the gas burner was switched off on 23 days; the underfloor heating continued to run, since the temperatures were close to the freezing points at some nights. The average of the minimum temperatures of the April days was with scarcely 8°C.

The months in detail: