100% solar and self-sufficient buildings, this was the promise of many project leaders around the world throughout the 2000s. Fifteen years later, where are we? Will the miracle of autonomous buildings be achieved?

A city with buildings covered with solar panels or vegetable gardens that would be self-sufficient in energy and basic vegetable products, what progress it would be!

It is with this belief that hundreds of municipalities and architectural firms, dreaming of inventing the city of tomorrow, have launched innovative urban project, redefining the concept of city itself, all over the world throughout the 2000s. Ecodistricts of Copenhagen, Grenoble or Bordeaux to the new cities of King Abdullah Economic City in Saudi Arabia, Masdar or Songdo in Korea, ecobuildings have arisen in the tens. Are they really self-sufficient?

It is not possible to draw a global picture because the initial philosophies, technologies and concepts of every project were different, but overall, we can see a relative failure. Green buildings are not only less self-sufficient than hoped (they continue to have significant energy needs, but their overall environmental footprint (including construction, maintenance and recycling costs), once their life is over) is also higher than expected.

Faced with this, new approaches, less ideal, but perhaps more realistic in the early 2010s, are explored. The gas-solar combined path seems promising, according to Hassan Hachem, a French-Lebanese building professional. The main limitations of today's photovoltaic energy is, everyone knows, the difficulty of storage. Elson Musk with its super battery start up, promises to solve this problem, but that remains to be solve. Sometimes solar energy is produced when it is needed. Sometimes it is at times when there is no need, nor for heating, nor for air conditioning or the operation of electric appliances. It is therefore necessary to supplement the contributions of the solar energy source if we want to reduce the use of diesel. "The energy best positioned to meet the needs of solar energy is certainly gas," Hassan Hachem says, offering both flexibility and relative energy efficiency.

Facilities combining gaz and photovoltaic solar panels are both complementary in terms of energy, gas taking over solar energy when it produces no energy, than from a technological point of view, says Hassan Hachem.

The situation does not seem static because it remains possible that someday, an electricity storage technology will emerge (that of Elon Musk ?) and partially solve the problem of the lag between the periods of production of solar energy and the periods of consumption, but these technologies will not be available for a reasonable cost in the near future. It will probably be necessary to go through a technological breakthrough in order for these conditions to be met.

Sur une idée originale de Raphael Richard