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Decarbonizing the energy mix via renewables

Renewables are energy sources with greenhouse gas emissions of or close to zero. The most promising are solar and wind power.

by Giuseppe Sammarco
10 March 2020
6 min read
byGiuseppe Sammarco
10 March 2020
6 min read

The type of mitigation interventions that reduce greenhouse gas emissions by changing the mix of energy sources used, replacing those with a greater impact on global warming with sources with little or no impact, is very considerable. For each of these sources with little or no impact, there are multiple technological options by which humans can use the energy, and many more are still being researched. It would be unhelpful to attempt to review them all here, so we will only mention a few of them, without purporting to be exhaustive. In addition, the various sources and related technological options are currently at different stages of development. Therefore, there are various obstacles to their full commercial maturity and broad dissemination, which have a greater or lesser effect on a case-by-case basis. 

The limits of lower impact sources

In general, their weaknesses relate to: high cost; the reliability of the technologies; inability to plan for production (if it depends on weather conditions); the cost or complexity of the storage systems of the energy vector produced; the impacts of different types over the life cycle not only of the source but also of the systems needed to produce or use it; the generation of other forms of pollution; social acceptability; low ‘power density’ (i.e. the amount of energy that a plant producing or using a specific source makes available at one time per unit of occupied area); and finally low ‘energy density’ (i.e. the amount of energy contained in one unit of weight or volume of the primary source, energy vector or storage system). We will not go into all the weaknesses of every source in detail, also because it would not be useful to do so here, and will limit ourselves to recalling the main weaknesses from time to time, while keeping in mind that these can be more or less significant depending on the various technology options available. 

Energy from the sun and wind

The first option to decarbonize the energy mix is renewable sources, the level of greenhouse gas emissions from which are at or close to zero. The best-known and most promising of these sources are solar and wind power. Energy can be produced from sunlight, using different technologies that turn it into electricity. The best-known and most common of these is inorganic photovoltaics, the ‘classic’ rigid solar panels that mainly use silicon as their inorganic material. There is then organic photovoltaics. More recently introduced, this uses organic material, meaning it can be fixed on flexible and light supporting structures. Finally, we should mention concentrated solar power, an ancient yet innovative technology. How it works is simple: a parabolic mirror concentrates the sun's rays in a single place, known as ‘fire’, generating a temperature of around 550°C. At the same time, a tube passes through that point, with a fluid flowing through it that can store heat, which is then used via an exchanger to generate steam for industrial use or to spin a turbine and produce electricity. Using a fluid to capture the sun's energy means that it can be stored in special tanks and used to produce energy in the required form (steam or electricity), including at night. Wind can also be used to produce energy for use by humans. 

Modern windmills are wind turbines, capable of generating electricity from the wind. Wind power can be ‘onshore’ (i.e. installed on land) or ‘offshore’ (i.e. installed in the surface of the sea or a lake), where the wind is usually more suitable. 

Costs, planning and land

Different technologies are available to produce energy from the sun or wind, each of which is at a different stage of research and development. The common theme is that their dissemination to a level of having a significant impact on the energy mix is not as simple as it might seem. The first hurdle is the cost of generating kilowatt/hours of electricity. It must be noted that this cost has fallen in recent years, a trend that may continue in the future, but at present, in areas where the climate is characterized by lower intensity of solar radiation or wind – in turn reflected in low annual production, the cost of wind and photovoltaics remains higher than that of fossil fuels. The second obstacle is the inability to plan for these sources, the operation of which depends on weather conditions at any given time. However, to function properly and avoid damage in an electricity grid, there must always be a perfect balance between demand and energy availability. 

If the proportion of unplannable renewable sources increases in the energy mix, backup systems must be provided (e.g. electric batteries), to quickly compensate for the lower electrical production due to adverse weather conditions. More generally, the dissemination of solar and wind power requires concurrent adaptation of the electricity system (backup and other ‘flexibility’ measures), the cost of which must be added to that of installing the plants to generate the power in the first place. 

Finally, solar or wind power plants often have a low ‘power density’ and therefore require the occupancy of large surface areas to produce the power and electricity needed. To provide the same power (calculated as an annual average) of a modern 1000 MW natural gas power plant occupying an area of about 0.22 km2, a photovoltaic power station would need to cover an area around 400 times larger (88 km2). This is also an average figure as the precise value depends on multiple factors, including the intensity of solar radiation where the panels are installed. The land requirements would be even greater for wind farms (there must be an exact distance between turbines to avoid turbulence), although in this case the land on which the wind farm stands could be earmarked for agricultural purposes.
To overcome these obstacles and to disseminate these sources more widely, the process of technological innovation – fueled by continuous research and development in industry and academia – has long since been put into action. Eni is also actively contributing to this process. To learn more about solar and wind power, or about Eni's extensive commitment in this field, see this website. 

 

The author: Giuseppe Sammarco

Energy Sector Integrated Technical Studies Eni, Development, Operations & Technology.