Using Three Approaches To Determine Whether Renewable Energy Sources Have Replaced Fossil Fuel

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The exploitation of wind and solar sources has transformed the electricity production systems, allowing for a diversified, endogenous, and green mix of electricity sources. It would be expected that the penetration of renewable electricity sources (RES), such as wind power, solar photovoltaic (PV), bioenergy, geothermal, and hydropower would substitute fossil fuel sources. In the meantime, one expects to reduce carbon dioxide emissions and energy dependence. Usually, the benefits of RES have been taken for granted, but have the RES really seen those expected benefits? Have they been preserving the environment through the decreasing of burning fossil fuels to produce electricity?


There is a notorious worldwide trend of countries shifting their energy systems to use more electricity instead of fossil fuels to power all economic activities. However, if the shift towards electrification is sustained by electricity production through fossil fuels, the advantages are canceled out.

RES, specifically wind power and solar PV, are characterized by their intermittent generation, i.e., their generation depends on the availability of wind and sun, respectively. For example, if wind exists in the right conditions, the wind turbines could produce electricity, but if no wind exists, they cannot produce electricity. So, when the wind turbines do not produce, i.e., they have the capacity to produce but not exists resources, this capacity is known as “idle.”

To overcome this phenomenon, electricity systems have maintained or increased the installed capacity of fossil fuels to generate electricity when RES do not fulfill the community’s demands. This work contributes to clarify whether RES have been effectively decreasing fossil fuel usage. Additionally, the research studies the impacts of electrification of economies and peaks of consumption in fossil fuel preservation. To do that, three approaches were used: namely the capacity, generation, and demand approaches.

The combined use of the three approaches embodies the difficulties and barriers that electricity production systems have encountered to effectively match electricity supply with demand. The capacity approach, represented by the wind power and solar PV installed capacity, analyzes whether their growth leads to a decreased use of fossil fuels. The generation approach, represented by the share of electricity production from RES, clarifies whether they reduce electricity production through fossil fuels. Lastly, the demand approach aims to ascertain the fossil fuels use through the electricity demand characteristics, namely intensity of electricity consumption in the economy and peaks of demand.


The installed capacity of solar PV has been grown over time by major players and by consumers who have become producers (prosumers). These prosumers have scheduled their consumption to periods with the availability of sun. So they have removed the load from the entire electricity grid during these periods, which has been helpful. This work proved that the increase of solar PV capacity has decreased the amount of fossil fuel burned to produce electricity.

Regarding wind power, this source is still very unpredictable and volatile, which has put pressure on electricity production management. As is well known, the electricity supply must be continuous to avoid shortages. Accordingly, electricity production systems have stipulated in advance the production of the other sources based on wind power generation predictions. Furthermore, because wind power can also cause an excess of electricity on the grid, the hydropower and the large hydro dams have been used to store this excess to use when the electricity market is not a solution. As such, for instance, when an excess of electricity exists on the grid because of high wind power production, that excess is used to return the water from the lower reservoir to the upper reservoir. Afterward, when it is needed, the water from the upper reservoir is used to produce electricity again, working as a kind of storage for a deferred generation in time.

The generation approach reveals that hydropower and other renewable sources have been decreasing fossil fuels usage. However, this work corroborates that the intermittent production of RES has required the use of natural gas, which translates to flexible power plants. However, the bioenergy has similar characteristics to natural gas plants, which could constitute a key renewable energy to substitute them. The paper has proven that the advantages of bioenergy have not been taken, but if they have been taken they could also create new diversified streams of employment and income, as well as the reutilization of firewood from forestry, industrial waste, and municipal wastes.

The demand approach highlights that electrification has maintained and increased the need for fossil fuels to satisfy them, which is an outcome of concern. As such, much of the RES advantages could have been aborted. The outcome of large concern suggests that periods of high consumption have been a barrier to RES effectiveness. Thus, it has also emphasized the need to preserve fossil fuels. Therefore, policymakers and mainly consumers have to cut off peak consumption, but little has been done to do that. In fact, the energy transition will require an effort from consumers to smooth the electricity demand curve, or even adapt the electricity consumption needs to the availability of natural resources. In such a way, one expects everyone mobilized to the need for measures on the Demand Side Management (DSM).

These findings are described in the article entitled Have fossil fuels been substituted by renewables? An empirical assessment for 10 European countries, recently published in the journal Energy Policy. A preliminary version was presented at the V International Academic Symposium: Challenges for the Energy Sector at IEB, Barcelona. This work was carried out by António Cardoso Marques, José A. Fuinhas, and Diogo A. Pereira from the University of Beira Interior.

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Cite this article as:
António Cardoso Marques, Diogo A. Pereira & José A. Fuinhas. Using Three Approaches To Determine Whether Renewable Energy Sources Have Replaced Fossil Fuel, Science Trends, 2018. Available at:
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