→ Within 6 hours the world’s deserts receive more energy from the sun than humankind consumes within a year. This means that sufficient clean power can be generated from the world’s deserts to supply mankind with enough electricity on a sustainable basis. The DESERTEC Concept promotes the large-scale production of solar and wind power in the desert regions of the world, combined with a smart mix of photovoltaics, hydropower, biomass and geothermal energy.
The Technology behind Desert Energy
In contrast to nuclear fusion, super batteries or other technology said to save the world, desert energy is already in the phase of commercial use. Of course improvements are still possible and happening, but the current state of the technology is ready for large scale use. The key concepts, Solarthermal-Plants, Photovoltaics and Direct Current Transmission, have been in application for decades.
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The desert offers several options to supply energy. These options include traditional PV-Systems and Wind-Power, either to supply the local market or to export it as peak demand energy to Europe.
The most attractive for the European Electricity Market is solarthermal energy as it can be provided 24 hours a day, 7 days per week. It offers power in the range of Gigawatts (like big nuclear power plants) and thanks to several security measures with the same reliability as a conventional power plant.
Even the basic concept is the same as a conventional power plant. The only difference is that instead of fossil fuels it is the sun that produces the steam to run the turbines. To reach the necessary temperatures the sunlight is concentrated with mirrors. Therefor these power plants are called CSP-Plants (CSP = Concentrated Solar Power).
If one would build one giant CSP-Plant to cover the energy-consumption of the entire world it would cover less than 1% of the area of the Sahara.
Concentrated Solar Power
To concentrate the sunlight, either parabolic mirrors or mirrors aligned towards a central tower are used. The sunlight heats up a special oil (or other mediums to transport the heat) that can produce high pressure steam in a thermal exchanger. Some concepts produce steam directly. Due to the huge mass of the turbine, it spins at a controllable rate with rapid change of load not causing a major disruption.
Just like the turbines in gas- or coal-plants this moment of inertia buffers against short disruptions in the energy grid. With a traditional generator being used, providing 50 Hz alternating current for the North African or European Grid is always accomplished.
Finally Green Basline Energy
Some of the heating oil can be directed into storage tanks with either salt or other storage mediums. These store the heat for producing energy during the night. Although cloudy days are extremely rare in the desert, this system solves that problem as well as providing an opportunity to run the power plant even during maintenance work on the collectors.
In extreme cases a traditional boiler can boost or replace the power of the sun. This boiler could run on hydrogen or biogas to ensure 100% green energy.
Contrary to popular imagination, the Sahara is mostly not covered in sand. Most of it is bare rocks. For that reason sand dunes and wandering dunes are no problem for the power plants. In case of a sandstorm the mirrors can be moved into a protective position.
Waste Product: Water
Running a power plant with high water consumption is not a problem in the desert. The steam can either be cooled with air or seawater. This way the steam condensates and that forms a closed water system. The seawater would evaporate quite fast and when condensated can be used as drinking water. The waste product of the solarthermal plant is therefore another valuable resource: water in the desert.
Development of CSP-Plants
These plants had a rapid development over the past 20 years. Components are now cheaper and more efficient, the software to operate the mirrors has improved and the overall design has been perfected. The plants can roughly be divided in four generations of development:
First Generation: These scientific prototypes had less than 50 MW of peak power and were usually integrated into conventional gas-plants, just to boost their power and check the potential of CSP-Technology.
Second Generation: These pilot-projects (like Al Noor) reach several hundred MW. These plants are almost competitive without subsidies. However a few technical issues remained like the high water demand as well as low storage capacity that made additional gas firing necessary for the night.
Third Generation: These are the projects that went online recently or are currently under construction/in planning. Even without subsidies these plants can compete with other power plants and are significantly cheaper and more efficient than the previous generation. Water usage has been cut to a minimum and storage capacity has been increased massively.
Fourth Generation: These plants are currently in development. The goal is to achieve higher temperatures by focusing the light more accurately. That will improve efficiency and storage capacity. New materials and designs are tested for the thermal storage. Whether the conduct of high temperature industrial processes directly powered by the sun is possible, is the focus of the current research. Solarthermal-Plants can already power low temperature thermal applications.
For long transmission distances direct current transmission is superior to alternating current. Alternating current has high losses due to capacitive and inductive resistance, which do not occur in direct current transmission. With that technology a 3000 km line (for example Cairo to Munich) has losses lower than 10%.
For this reason direct current transmission is already used to connect islands to the mainland or to connect the Scandinavian grid to the Central-European grid.
But why is that technology not used everywhere? Historically it was difficult to produce a lot of high voltage direct current and even more difficult to invert it to alternating current. And we need high voltage to transmit with lower losses and transformers only work with alternating current. Today inverters can convert Direct and Alternating Current, but the whole system is set up on AC and many applications prefer AC anyway.
Is there any possibility to use the advantages of both worlds?
Luckily due to the retiring of coal and nuclear plants many electric substations are freed up. We can lay direct transmission lines to those sites and invert the direct current to alternating current. The technology of the required inverters has improved drastically.
So called VSC-Systems or similar inverter-systems can bring the benefits of CSP-Plants (baseline power, stable frequency) to Europe.
This way we can use direct current for low transmission losses on the way to Europe and still use alternating current in our daily life.
The hydrogen myth
Hydrogen is a versatile fuel. In contrast to many myths, hydrogen is neither dangerous nor futuristic. It is already used in many applications ranging from rockets, submarines, planes to cars, power plants, and even heating.
Especially the chemical industry uses a lot of hydrogen to produce fertilizer since World War One.
The fact that the hydrogen atom is the smallest atom in the periodic table doesn’t mean that hydrogen gas (H2) can magically go through barriers. All of the applications above have no problem not losing hydrogen to the environment.
Many fear hydrogen explosions. But no one fears explosion from the liters of gasoline in their cars or the gas pipes in their house, despite these fuels having a comparable energy density. The required mixture of 33,33 % Oxygen and 66,6 % Hydrogen for the famous hydrogen explosions we all loved in chemistry class is impossible to achieve in an atmosphere that only contains 21 % Oxygen, to begin with. Although explosions can occur besides the ideal ratio, the strength of the explosion is far weaker than the reaction of the pure chemicals.
The pressurized tanks for hydrogen have been tested in car crashes with lorries, fires and even tests with gunfire have been made. All security tests proved the concept to be very secure and even superior to gasoline tanks as the hydrogen can be released into the atmosphere and no flammable liquids spill all over the accident site.
For all the applications above the products have met the official security standards and have been approved by the respective authorities in many countries.
Until now most of the hydrogen is produced by steam reformation of natural gas. Many carbohydrates can be used for the process but methane, the main component of natural gas, shall be used as an example.
Methane and Water (CH4 and H20) are heated and under high pressure they react to form carbon monoxide and hydrogen (CO and H2). Carbon monoxide is used as the fuel to heat the reaction and burned with oxygen. This way pure hydrogen is produced (which is mostly needed for the chemical industry), but no CO2 is saved.
A different process is an electrolysis: Two metallic rods put into water are enough to produce hydrogen. With cheap desert energy that process is ideal to supply green hydrogen without any harmful byproducts (the only byproduct is pure oxygen).
This green hydrogen can then be shipped around the world to be used in the chemical industry, as fuel for transportation, heating or local power production.
At the moment different processes are developed to use heat directly to split water into hydrogen and oxygen making the process much more efficient.