Energy Mega-Projects that Links Continents
In the global race to stop climate change, ditching fossil fuels as energy source is the number one priority. The European Union plans to cut at least 40% of greenhouse gas emissions by 2030, and 80-95% by 2050. At present, Europe imports 60% of its energy in the form of fossil fuels. If targets are to be met, there is a need to look at large scale renewable energy plants outside the European borders. In recent years, the idea of using the natural resources at the Sahara Desert as sources of power has become stronger. Among various types of renewable energy sources, solar energy is promising due to its large energy potential and clean nature. The solar energy received by the worldwide desert regions within 6 hours is roughly estimated more than the energy consumed by humankind in a year. In other words, by covering just 1% of the Sahara Desert would be enough to supply the world annual energy demand (see Figure 1).Nevertheless the development of solar energy plants in such a harsh climate is not a trivial task. The lack of water, the high temperatures, the remote locations and the interconnections with mainland are some of the challenges facing these projects.
Figure 1 Solar annual direct normal irradiation (DNI) across the world (unit:kWh/m2/year) (SolarGIS ©2015 Geo ModelSolar).
There are currently two major types of solar energy technologies that could be installed in the dessert. Concentrating solar power (CSP) and solar photovoltaic (PV). The former uses mirrors or lenses to focus the energy in sunlight and deploy a heat transfer fluid (HTF). The latter converts directly sunlight into electricity through solar cells.
Assessing the implementation of large solar projects in the Sahara requires a good understanding of the physical conditions in there. The main constraint with PV plants is its efficiency with high ambient temperature (see Figure 2). As ambient temperature increases, the output voltage of the PV panel decreases gradually. Therefore, the performance at very high temperatures of PV panels can reduce up to 20% the power output of the system.
Figure 2. Performance of a PV Panel under different temperatures
In severe climate conditions, CSP systems are proved to perform more efficiently than any other form of solar technology. The high temperature used to for the HTF transports the energy to turbines for power production. Four main types of CSP technologies are developed nowadays (Figure 3). Linear Fresnel reflector (LFR) and parabolic trough collector (PTC) are line-focused technologies where the sunlight is focused on a series of receivers oriented in the north-south direction. Solar power tower (SPT) and Parabolic dish system (PDS) are point-focused technologies redirecting sunlight to where the receiver is located. Even though more than 82% of the current CSP installations are based on PTC, the latest projects are more oriented towards SPT. Solar power tower shows a potential enhancement in efficiency compared to PTC, converting heat into electricity and achieving higher temperatures. CSP has been widely developed by Spain and United States, with more than 80% of the installed capacity in the world in 2017. However, in recent years countries such as Morocco or Saudi Arabia are developing large scale solar projects based on this technology. There is a trend to shift from fossil fuels towards renewable energy generation, even in those countries with high dependence on fossil fuels.
Figure 3. Most common CSP technologies [Source]
The idea of using the Sahara Desert to power Europe is not new. There have been many attempts over the last decade to build large scale solar plants in the Sahara Desert. One of the first was DESERTEC, ua foundation created in 2009 with the initial concept to create a super grid between the European Union and the MENA (Middle East and North Africa) countries. Despite the initial support from countries and organisations, the complexity of the project and huge capital cost has made it unfeasible and no actions were taken after 2013. However, in 2017 TuNur, a small company based in the UK, began actions to build a 2.250 MW CSP solar power tower plant located in Tunisia. The energy will be carried through a 2000MW HVDC transmission line across Tunisia, through the Mediterranean Sea to Italy. The project is currently in a very early stage but if successful, it could launch a series of new projects to interconnect the EU and MENA countries.
Figure 4. Stages of TuNur Project [Source]
To ensure security of supply and improve system stability, there is a need to increase transmission capabilities within market zones and between Europe and North Africa. Currently, the only electrical link between these two regions is via 2 submarine power cables that provide a maximum capacity of 800 MW. To allow large-scale integration of renewable energy into a future European supergrid, several cross-border lines must be reinforced to decrease the actual congestion in the power system. Besides, the construction of HVDC undersea grid connections across the Mediterranean sea would allow a higher penetration of renewables and to maintain system stability. The main challenge is still the growing gap between the dynamics of the development between renewable generation and the reinforcement of construction of transmission infrastructure. The time required to build a transmission line can be twice as long than to complete a solar power plant.
If Europe aims to make a successful transition towards secure, low-carbon and sustainable energy systems there is a need to rethink the future power grid and explore the power potential outside its borders. North Africa has a broad range of benefits that can facilitate and support a successful transition towards low carbon energy systems. The interconnection between the two regions would help to build a European super grid with high penetration of renewable energy using technologies such as CSP that will maintain security of supply of the grid.
Sergio Lamas Casas
Sergio is an Electronic Industrial Engineer and works at Norvento as Project Engineer. Contact Sergio