Should we solar panel the Sahara?

If you read newspapers often, it's likely you've come across Betteridge's law of headlines. Therefore, you wouldn't have to listen to this entire BBC World Service broadcast to find the answer to the question should we solar panel the Sahara? Still, you should do so anyway, or at least read the accompanying article.

The premise is simple. A back of the envelope calculation (page 2) finds that, combined, the world's deserts receive something on the order of 60 million terrawatt hours solar radiation per year — nearly 600 times the global energy consumption in 2012 (104426 TWh). If even a small fraction of this free and renewable source of energy could be harnessed by solar panels spread over the vast Saharan expanse, it could provide an important supply of power to Africa, Europe and the Middle East which doesn't contribute to global warming. This is what the renewable energy consortium Desertec are looking to achieve.

"Hey trees, stop hogging all the good sunlight"

Obviously there may be some technological issues in such a plan. To start with, as you might have noticed, the sun tends to hide at night. Temporal variability of power generation is one of the traditional issues with solar energy, and it's something I've personally experienced. At the EURENSSA conference I participated in this summer (I did say I'd bring this up again), it took a while for the solar geyser to get going, so I was shocked by the cold water the first time I went for a crack-of-dawn shower. However, advancements in thermal storage – in effect storing this energy by heating molten salt – provide a way for this power to be supplied as demand dictates.

The radio broadcast provides interesting discussion of the geopolitical implications of European companies buying African land in order to generate energy which will largely go back north. Similarly, the social and economic aspects of solar energy as a renewable resource are well covered. However, there is one thing that I'm left wondering, from a modelling perspective. The image below is taken from an EMIC experiment I carried out which simulated the plantation of forests in the Sahel region. It shows that the effects of this on global climate would be very drastic — the changes in pressure at mid/high latitudes are of a greater magnitude than the largest pressure drops recorded in hurricanes. By lowering the albedo of the Sahel's grid cells (to simulate the land's change from savannah to forest), the area became a stronger source of both latent and sensible heat, resulting in a cascade of changes to the atmospheric circulation system.

The pressure anomaly between a control simulation and a green Sahel experiment 

 It should be noted that the limited complexity of the atmosphere model used means that any conclusions drawn from these results should be taken with a very conservative pinch of salt. Nevertheless, this experiment showed me the importance of considering the possible effect of any change in one region on other parts of the world, and such large-scale atmospheric teleconnections are being increasingly found by modelling experiments. One study found that during the transition out of the African Humid Period, attenuation of meridional heat transport was initiated by the aridification (therefore albedo increase) of the Sahara, leading to a strong cooling over the Arctic; while another found a similar mechanism occurring with 65 Ma boundary conditions. Solar panels are dark in colour to absorb as much radiation as possible, however they do re-emit much of this energy. If you consider the construction of huge solar arrays in the Sahara as analogous to afforestation in terms of change in albedo, you should be able to see why modelling should not be neglected when assessing the possible implications of such an ambitious scheme.