Renewable Energy: A Look at the Present and Future

The energy consumed every day comes from the natural resources available on the planet, which can be renewable or non-renewable. Renewable energy sources are those that are considered inexhaustible, such as water (hydroelectric energy), heat from the earth (geothermal energy), wind (wind energy), sun (solar energy), biomass (bioenergy) and ocean energy. The energy sector is one of the main emitters of greenhouse gases due to the use of fossil fuels, which has increased interest worldwide in the integration of renewable energies into the energy matrix. These energies have been promoted through various mechanisms that have helped to reduce their costs and make them competitive with non-renewable sources. This article provides an overview of the different types of renewable energy and their application to supply end users, as well as the state of progress of renewable energy worldwide.

Types of Renewable Energy

The production of electrical energy from renewable sources refers to the production of energy through projects that utilize the energy produced by various renewable sources, such as hydroelectric, geothermal, wind, solar, bioenergy, and ocean energy, which includes the energy of tides, waves, and ocean currents. The following is a detailed explanation of how each of these renewable energy sources is captured and used to generate electricity.

Hydroelectric energy

This form of energy is derived from the energy in motion and the energy stored in the height of rivers and waterfalls. There are two main types of hydropower technology used to generate electricity: run-of-river and reservoir power plants. Reservoir power plants involve the construction of a reservoir to store water, while run-of-river power plants generally use the natural flow of the river. The main difference between the two types of hydroelectric plants is that reservoir plants are dispatchable, meaning that they can be scheduled to produce electricity, while run-of-river plants are not. In both types of power plants, water is directed toward turbines, creating a rotating motion that in turn generates electricity. Run-of-river plants use the kinetic energy of the river water, while reservoir plants use the potential energy of the water stored in the reservoir. To measure the performance of these plants, it is necessary to measure the water flow and the height of the water fall. The water flow measurement is used to determine the kinetic energy, while the water fall height measurement is used to determine the potential energy. To determine the hydroelectric potential, it is necessary to conduct field surveys to determine the available water resources.

Only run-of-river hydropower is considered a renewable energy source because it does not require a reservoir, which has an environmental impact.

Geothermal energy

Geothermal energy is derived from the heat found within the earth’s crust. To harness this energy, a fluid, such as water, is required to capture the thermal heat from within the earth’s crust. Typically, this fluid is found in the Earth’s crust, forming accumulations called reservoirs, which manifest outside the Earth’s crust in the form of geysers, hot springs, etc. By early 2021, available technologies will make it possible to harness the heat from these reservoirs as thermal and electrical energy, which depends on the temperature of the reservoir. The higher the temperature of the fluid, the greater its application in power generation plants. To determine the maximum power output of these plants, it is necessary to measure the temperature that could be reached in the fluid and also to identify the size of the reservoirs.

There are three types of geothermal power plants that can be identified: First, there are flash steam plants, which draw hot water at high pressure from deep within the earth and convert it to steam to drive the generator turbines. Then, as the steam cools, the water is condensed and returned to the well for reuse. Second, there are dry steam plants, which use dry steam to drive turbines and generate electricity through the generator. Finally, there are the binary cycle plants that transfer heat from hot water to another liquid that evaporates to power an electric generator.

To identify areas with geothermal potential, it is necessary to carry out exploration work, which is divided into three phases: geology, geophysics and geochemistry. Each of these phases is important in determining the presence of the geothermal resource and thus reducing the risk of discovering reservoirs that are technically infeasible to exploit. If, after the exploration phase, it is determined that there is geothermal potential, the exploitation phase can proceed, bearing in mind that there is still a risk that the reservoir may not be economically viable.

Wind energy

This form of energy is based on capturing the kinetic energy of the wind. It uses a technology that consists of an electric generator installed on a tower that harnesses the kinetic energy of the wind to produce electricity. The choice of the optimal size of the wind turbine blades and the appropriate height of the tower depends on the wind profile curve (which shows the wind speed as a function of height) and the geography of the terrain. Currently, the technology makes it possible to generate electricity both onshore and offshore. To measure the maximum power of these wind turbines, the wind speed and direction must be measured with an anemometer placed at the desired height.

Wind potential is calculated as a function of wind speed distribution. Wind turbines located at sites where the average wind speed is 8 meters per second at the height of the rotor axis produce between 75% and 100% more electricity than those where the average wind speed is 6 meters per second. A 1.8 MW wind turbine in a good location produces more than 4.7 GWh per year. This is enough to meet the annual electricity needs of more than 1,500 households.

There are three criteria for classifying wind turbines: turbine orientation (horizontal or vertical), installation characteristics (onshore or offshore), and grid connection (connected or unconnected). Horizontal axis wind turbines are the most popular and have an axis of rotation parallel to the ground. Typically, these turbines have three blades and can reach heights similar to a 20-story building. On the other hand, vertical axis wind turbines are less common and have an axis of rotation perpendicular to the ground. Depending on the shape of the turbine, they can be classified as “Darrieus” (2 or 3 arcs), “Panemonas” (4 or more semicircles) or “Sabonius” (2 or more rows of semicircles).

Solar energy

Solar energy is derived from the sun’s electromagnetic radiation. There are several ways to harness this energy, such as photovoltaic solar, which produces electricity, concentrating solar power, which also produces electricity, and solar thermal for domestic hot water, which produces heat. In photovoltaic solar technology, cells act as semiconductors that produce a physicochemical reaction that releases electrical energy in the form of direct current. Photovoltaic panels, which contain these cells with semiconductor material, are characteristic of this technology. There are several photovoltaic panel technologies on the market, with polycrystalline silicon cells being the most common due to their efficiency.

Concentrating solar thermal power technology works by using the reflection of the sun’s rays on mirrors to concentrate them on a fluid that is heated by absorbing the thermal energy generated by the sun’s rays. This thermal energy is then transferred to another fluid, usually water, which is turned into steam by the increase in temperature and drives a turbine to generate electricity. These systems operate at high temperatures, ranging from 400°C to 600°C. The most common concentrating solar thermal technologies are the concentrating tower, parabolic trough, and linear Fresnel reflector.

Finally, solar thermal technology for domestic hot water consists of a system that includes a tank and a solar panel containing a circuit through which water flows that absorbs the thermal energy provided by solar radiation, energy that is used in homes. These systems are designed to operate at low temperatures (up to 180°C) and are used for applications such as water heating, heating and swimming pools.

The efficiency of power generation in each of these technologies depends on climatic conditions such as cloud cover and the tilt of the sun’s rays relative to the Earth. To measure the maximum output of these systems, it is necessary to measure solar radiation, which is done using an instrument known as a pyranometer or solar meter.

Biomass energy (bioenergy)

Bioenergy is derived from biomass, which includes sustainable organic matter such as energy crops, agricultural and forestry wastes, animal wastes, and municipal and water treatment wastes. Biomass has multiple uses, such as fuel for combined heat and power, liquid biofuel production, and biogas production. The potential of biomass as a fuel and biofuel can be measured using satellite technology and cropland analysis. Biogas is produced by the biological decomposition of organic matter and can be recovered from landfills and wastewater treatment plants. Measuring biogas potential requires information on the amount and type of waste at production sites.

Ocean energy

There are several ways to extract energy from the oceans, such as tidal energy from the tides, wave energy from the waves, energy from ocean currents, and energy from the thermal gradient. Different technologies are available for each of these types of energy.
Although technologies are being developed to harness these forms of energy, they are still in the experimental phase due to their high development costs and the complexity of the marine environment. However, if cost-effective technologies can be developed to harness them, ocean energy could become an important source of renewable energy, helping to reduce greenhouse gas emissions and mitigate climate change.

The state of renewable energy in the world

Each year, more electricity is generated from renewable sources than the year before. By the end of 2021, installed renewable energy capacity was sufficient to provide approximately 28.3% of global electricity generation. However, projects continued to be impacted by supply chain issues, delivery delays, and rising global commodity prices. Below is the estimated global renewable energy capacity by type at the end of 2021 (Source: International Renewable Energy Agency’s Renewables 2021 Global Status Report):

Hydroelectric capacity includes only run-of-river power plants and excludes reservoir power plants, which are not considered renewable energy. The following figure shows the graph of the data from the previous table.

From the above table, it can be seen that hydropower remains the largest renewable energy source in terms of installed capacity, accounting for almost half of the total global renewable energy capacity by the end of 2021. However, wind and solar PV have also experienced significant growth in recent years and together account for more than 50% of total global renewable energy capacity. Bioenergy, geothermal and ocean energy are still a much smaller part of the renewable energy mix, but are expected to experience significant growth in the coming years as technologies continue to improve and costs continue to fall. Overall, the steady growth in global renewable energy capacity indicates a positive trend towards a transition to more sustainable energy sources and greater climate change mitigation.

Conclusion

In general, renewable energy is an increasingly important alternative to traditional energy sources that use fossil fuels and contribute significantly to climate change and pollution. Renewable energy, such as solar, wind, hydro, geothermal, and ocean power, uses inexhaustible and clean energy sources that do not emit greenhouse gases or other toxic pollutants.

The development and expansion of renewable energy has been driven by increased awareness and concern about climate change and the need to reduce greenhouse gas emissions to limit their impact on the environment. In addition, the declining cost of technologies such as solar panels, wind turbines, and batteries has made renewable energy increasingly cost-competitive with conventional energy sources.

Reference

[1] Environment, U. N. (2022, junio 16). Renewables 2022 Global Status Report. UNEP – UN Environment Programme. https://www.unep.org/resources/report/renewables-2022-global-status-report

[2] Carta González, José Antonio. Centrales de energías renovables : generación eléctrica con energías renovables, Madrid ES Pearson Educación 2013.