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Sarebbe possibile trasformare il deserto in un parco solare in grado di dare energia a tutto il mondo? Al di là della complessità dei fattori tecnici, il dato finale sulle potenzialità dell’energia solare è sorprendente. Secondo Mehran Moalem, esperto di energia citato da <anchor>Forbes</anchor>, basterebbe l'energia solare catturata in un'area poco più ampia dell'1 per cento del deserto del Sahara per coprire il fabbisogno mondiale.
We Could Power The Entire World By Harnessing Solar Energy From 1% Of The Sahara
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# We Could Power The Entire World By Harnessing Solar Energy From 1% Of The Sahara

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Opinions expressed by Forbes Contributors are their own.

Sep 22, 2016,12:32pm EDT

Updated Jun 30, 2021, 12:38pm EDT

This article is more than 7 years old.

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(Photo credit should read SVEN HOPPE/AFP/Getty Images)

Answer by Mehran Moalem, PhD, UC Berkeley, Professor, Expert on Nuclear Materials and Nuclear Fuel Cycle, on Quora:

I have taught courses in Nuclear Engineering and a few seminar courses in alternative energies. I also worked for two years starting up six solar factories around the globe. In spite of my personal like for nuclear engineering, I have to admit it is hard to argue for it. Here is the simplified math behind it.

The total world energy usage (coal+oil+hydroelectric+nuclear+renewable) in 2015 was 13,000 Million Ton Oil Equivalent (13,000 MTOE) - see World Energy Consumption & Stats. This translates to 17.3 Terawatts continuous power during the year.

Now, if we cover an area of the Earth 335 kilometers by 335 kilometers with solar panels, even with moderate efficiencies achievable easily today, it will provide more than 17,4 TW power. This area is 43,000 square miles. The Great Saharan Desert in Africa is 3.6 million square miles and is prime for solar power (more than twelve hours per day). That means 1.2% of the Sahara desert is sufficient to cover all of the energy needs of the world in solar energy. There is no way coal, oil, wind, geothermal or nuclear can compete with this. The cost of the project will be about five trillion dollars, one time cost at today's prices without any economy of scale savings. That is less than the bail out cost of banks by Obama in the last recession. Easier to imagine the cost is 1/4 of US national debt, and equal to 10% of world one year GDP. So this cost is rather small compared to other spending in the world. There is no future in other energy forms. In twenty to thirty years solar will replace everything. There will still be need for liquid fuels but likely it will be hydrogen produced by the electrolysis of water and that powered by solar. Then tankers and pipelines will haul that hydrogen around the world. One can also envision zirconium or titanium batteries that store large quantities of hydrogen.

By the way, note that the cost of a 1 GWe (Gigawatt electric) nuclear plant is about three billion dollars. the cost of 17.3 TW nuclear power will be fifty-two trillion dollars or ten times that of solar even if all the other issues with safety and uranium supply are resolved.

All that said, there is a niche application for nuclear power. It has the highest power density of any generation and lasts longest without refueling. So where the space is limited or like in space far from the sun, or in submarines nuclear power makes sense.

Additional notes:

There has been a notable interest in this subject and some vey good questions have been asked. It is only fair to present the questions and replies here.

Question: What required to achieve the solar capacity factors discussed in this proposal?

Answer: You might have heard a capacity factor of 25% mentioned for solar panels. The 25% factor essentially means that a two hundred Watt panel only produces fifty Watts when averaged over twenty-four hours. In fact this low number is an artificial byproduct of the choice of installation site. Most small installations are done on roof tops in Europe (Germany in particular) and United States. The distribution of solar flux has a strong dependence on Latitude. In the equatorisk region (latitude around zero) the sun shines near normal and the power density can be as high as fourteen hundred Watts per square meter. At a latitude of forty-five degrees the power density drops by at least a factor of two. Major cities in United States are around thirty-seven North Latitude and Europe is even higher. On top of that, in these regions, a significant portion of the year has cloudy and rainy days further reducing net available power. It is conceivable a major undertaking in solar industrial-scale production will take advantage of vast available equatorial lands. The site proposed here as an example in African Sahara is on the Equator and there are very few if any cloudy days per year. The Saharan desert land is inexpensive and mostly unused and as such readily available for utilization. In this proposal, an average annual power density of one hundred and fifty-five Watts per square meter is assumed that compared to peak values of one thousand three hundred and fifty to one thousand three hundred and seventy Watts/m2 represents a mere 11% capacity factor. Given twelve hour days at Sahara and current efficiencies of greater than 22% for solar panels, this average value is certainly achievable.

Question: What is required to achieve the solar costs discussed in this proposal?

Answer: The current panel costs run about fifty-five cents per Watt. There are additional costs for panel installation and inverters. The inverters are devices that convert the Direct Current (DC) output of panels to Alternating Current (AC) needed for long distance transmission. The total costs currently run about ninety cents to a dollar per Watt installed. In this proposal we have assumed the realistic thirty cents per Watt. There are two main factors that need to be considered in this regard. First the current economy is based on third-party suppliers such as panels made by ChinEde manufacturers. For an utility installing terawatts of power, there is little reason to buy from third parties and enrich the manufacturers. Since the manufacturers make as much as twenty cents in profit per Watt, a large scale production facility will fully benefit from that lower cost if they produce their own panels. If Chinese panel suppliers want to profit from this venture they need to be part investors and supply the panels at cost and make their profits from sale of the power not panels. As far as the inverter costs, note that the main use of fossil energy in the world is not for electricity generation. Fossil fuels are used for running automobiles, heating houses, propulsion and other industrial uses. It is conceivable that the main use of a large scale solar facility such as above that displaces all other generation in the world is in producing environmentally-friendly fuels such as hydrogen. Hydrogen can be produced by electrolysis of water and the solar DC power is readily usable for electrolysis without a need for inverters. Once hydrogen is produced, it can be transported by pipelines and tankers to four corners of the world as fuel for cars, factories, home heating and so on. Large scale reusable batteries can also be made from zirconium and titanium that will store hydrogen in the safe solid:-D form. Finally, any costs such as this are infrastructure costs not energy costs. Currently we do not count the cost of making highways and tankers and high-voltage transmission lines as a part of the cost of the fuel. Those are costs any civilization will bear to bring comfort to its citizens be it the source of power be solar, fossil or nuclear.

Question: Are there any other environmental concerns with the use of either nuclear or solar energy that should be considered alongside global warming?

Answer: There are a few concerns.

- Nuclear power requires heat rejection. The net efficiency of a plant is 30 to 32% due to restrictions with water/steam cycle. HTGRs (High-Temperature Gas Reactors) using CO2 and helium can push this up to 50% but are being frowned on due to other problems. In any case what that means is that for every Watt of electricity produced by nuclear reactors one has to reject two Watts to the environment. With nuclear at 10% of electric grid and 2% of total energy production, this is tolerable. However, if one goes much above that we run out of rejection capacity as it has happened in France. The warm water flowing back from power plant condensers is destructive to ecosystem of oceans and rivers where this heat is rejected to. In the picture of nuclear plant above, the two large stacks you see are not smoke stacks as nuclear plants have no smoke (compared to coal). They are for heat rejection to air. We can not have 17.5 TW nuclear power production since that requires 35 TW heat rejection to environment unless some large-scale new technologies for reject heat recovery are invented and implemented. The warm waters in oceans and rivers enhance parasitic plant life and change normal marine life. They are also detrimental to current fish populations resulting in unnatural selection.
- The production of solar panels is not environmentally benign at the moment. The current production process uses semiconductor manufacturing technology that generates pollution. Again at the current small levels it is not much of an issue but at 17 TW, solutions need to be devised to neutralize those toxins and reduce the pollution. The current solar panel production technology also uses large quantities of energy and that can become a factor to consider for sustainability.

Question: Are there any concerns with damaging the desert ecosystem when using the deserts as solar production farms?

Answer: This is the least concern of all. The proposed project as shown only needs 1.2% of the African Sahara to replace all forms of energy production in the world. That is such a miniscule part compared to the total desert area in the world. Also it will save vast tracts of land that are currently suffering from strip mining for coal and from contamination by acid rain not to say anything about possible radioactive land regions in case of nuclear accidents. Furthermore, the Saharan ecosystem perhaps will flourish better in the shade under the backside of the panels. The current erosion of the deserts result in large sandstorms that contaminate and pollute the air in civilized parts of Africa and Middle East. The PM10 and PM2.5 pollution is at epic levels in much of these growing societies. Solar farms will actually benefit the life by stabilizing the sand. The residents of these regions of the world would probably wish the project was larger and covered more areas.

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