Despite the fact that renewable energies offer a great theoretical potential of energy and that most of them have only a small share of global primary and final consumption (less than 2% of final World energy consumption was provided by wind, solar, geothermal, biomass and biofuels together) , their limits should be carefully analyzed. While other methodologies are based on theoretical efficiencies of renewable energies, generous estimations of effective global surface that could be occupied by the renewable infrastructure and/or ignore the mineral reserve limits, our assessment is based on a top-down methodology (de Castro et al. 2 and 3) that takes into account real present and foreseeable future efficiencies and surface occupation of technologies, land competence and other limits such as mineral reserves.
We have focused here on the net density power (electric averaged watts per square meter, We/m2) and compared our top-down assessment, based on real examples, with other theoretical based assessments; our results show that present and foreseeable future density power of solar infrastructures are much less (4–10 times) than most published studies. This relatively low density implies much bigger land necessities per watt delivered, putting more pressure on Earth than previously thought. On the other hand, mineral reserves of some scarce materials being used will also put pressure on this industry, because there is also a trade-off between solar park efficiencies and mineral limits. Although it is very difficult to give a global limit to the expansion of solar power, an overview of the land and materials needed for large scale implementation show that many of the estimations found in the literature are hardly compatible with the rest of human activities.
Overall, solar could be more limited than supposed from a technological and sustainable point of view: around 60–120 EJ/yr.