Energy Sciences

Renewable Energy

Solar

One of the major sources of renewable energy comes from the sun. On average, the Earth receives 1.73 x 10⁵ TW of solar energy penetrating the atmosphere.³² With this amount of energy available, it would make sense as a good source of energy. However, worldwide, solar energy only makes up about 0.29% of the energy consumed.³³ The way in which solar energy is obtained varies and where one can utilize solar energy also affects its use. First, passive solar heating systems absorb the suns heat which is stored in well insulated structures such as concrete, adobe, brick, or stone. The solar heat in passive systems becomes distributed by the natural flow of heat exchange versus a forced system that involves a blower or pump. Second, there are also active solar heating systems in which the heat from the sun is captured by pumping a heat absorbing fluid through special collectors that are mounted to face the sun. The benefit of using an active solar heating system is the energy can be stored and used as needed. Third, another widely used system is photovoltaic systems. These systems convert sunlight energy into electrical energy. “When light shines on a photovoltaic (PV) cell, it may be reflected, absorbed, or pass right through it. The PV cell is composed of semiconductor material, which combines some properties of metals and some properties of insulators. That makes it uniquely capable of converting light into electricity. When light is absorbed by a semiconductor, photons of light can transfer their energy to electrons, allowing the electrons to flow through the material as electrical current. [The] current flows out of the semiconductor to metal contacts and then makes its way out to power your home and the rest of the electric grid.”³⁴ Solar cells can be enticing for large cities due to their ability to be installed in various locations. Many large cities have parking structures with solar panels which contributes to the overall available energy budget. Finally, solar farms can be installed in areas such as deserts where there is a large percentage of solar exposure in any given day which increases the total collection of solar power.³⁵ A fourth type of solar collector system is a solar thermal plant. Solar thermal plants concentrate solar energy to “produce the high temperature heat needed to generate electricity… [there are] two main components: reflectors (mirrors) that capture and focus sunlight onto a receiver. In most types of systems, a heat-transfer fluid is heated and circulated in the receiver and used to produce steam. The steam is converted into mechanical energy in a turbine, which powers a generator to produce electricity. Solar thermal power systems have tracking systems that keep sunlight focused onto the receiver throughout the day as the sun changes position in the sky.”³⁶

Despite the many positives in solar power, there are negatives from the use thereof. First off, there can be negative impacts on avian species. According to a federal investigation, certain species of birds have been known to fly into the concentrate solar collectors becoming burned when they fly in the line of concentrated light. The panels create a lake effect where some birds view it as a body of water, and they die flying into the panel. Second, there can be health issues that arise for workers building photovoltaic solar farms in southwestern regions of the United States. The California Department of Public Health has received multiple cases of workers contracting Valley Fever. Valley Fever is caused by the inhalation of a soil dwelling fungus called Coccidioides. This fungus becomes air-borne when disturbed and can cause influenza-like symptoms and at times pneumonia.³⁷ Third, there are environmental concerns, but they tend to be site specific. Some examples include visual impacts, routine and accidental release of chemicals, land use, effect on ecosystems and water resources to which all can be minimized with appropriate practices, evaluating appropriate placement, and education.³⁸ In the end, solar powered sources of energy are sustainably safer and provide fewer negatives to the environment than fossil fuel powered sources of energy.

Hydropower

Next is hydropower which makes up about 2.64% of the world's energy consumption.³⁹ Hydropower is created by using the energy in water, specifically, using the kinetic energy generated in water to turn a turbine to generate electricity. There are many different designs that convert the flow of water into available energy. Greeks used water to generate power to grind wheat into flour over 2000 years ago. This concept is still used today but on a more modern scale with the use of motors and turbines. The most common type of facility for hydropower is an impoundment. Dams are utilized where water is stored in reservoir and water is released which turns turbines that generates electricity. Next, gravity can also be utilized in mountainous areas where there are sources of water. In this case, water is free flowing from an area of high elevation to an area of lower elevation which can then turn turbines to generate electricity. In other areas, electricity can be generated in open water. Waves generated by wind travel in open water until they encounter an object. If said object has a turbine, the waves spin the turbine generating electricity.^{40, 41} Another form of hydropower is brought on by tidal waves. Tidal power is generated from the gravitational imbalances between the Earth, sun, and moon. During the new and full moon, the gravitational pull on the Earth’s surface is greater due to the combined pull of the sun and moon. Larger waves or more prominent tides are a result of this pulling effect. Conversely, during the first and third quarter phases of the moon, the gravitational pull between the sun and moon counteract each other and the effect on the Earth’s surface is less prominent. Tidal energy is not a significant source of energy worldwide as the amount of power needed from tides requires a large change in water level from high to low tide. Likewise, the equipment gets worn out due to the corrosive nature of the water and organisms having to be removed from the equipment. Therefore, there are only so many places in the world that this can be taken advantage of. However, there are benefits such as tidal energy is predictable, energy can be stored and delivered on demand, does not require high cost hardware, etc. A major benefit of utilizing hydropower is the fact that there are low emissions of carbon dioxide and other pollutants. On the other hand, there are disadvantages of using hydropower to meet energy needs. The major disadvantage is the impact on natural processes. For instance, hydroelectric dams can prevent flooding in low lying areas until there is catastrophic flooding. Dams are built to withstand multiple days of flooding and have security measures in place to prevent damage to land, home, and life. However, when catastrophic flooding occurs, towns downstream from dams tend to experience catastrophic flooding and loss of land, property, and life. Likewise, hydroelectric dams can affect the environment and health of organisms. For example, soil degradation can occur due to the accumulation of runoff. A change in hydrologic cycle can bring about a change in the spawning patterns of fish, their fattening, and affect their hibernation cycles. Other influences on water that affects the hydropower system include, but are not limited to, earthquakes, karst, landslides, and river erosion.⁴²

Wind

Lastly there is wind power which makes up about 0.73% of the world's energy consumption.⁴³ Wind energy can be generated by windmills and wind turbines. What is the difference? Windmills generate mechanical energy and are mainly used for more primitive activities such as grinding grain or pumping water. Wind turbines are more advanced and modern in which they are complex pieces of machinery that can be used to harness the wind’s energy to generate electricity. From this point forth ‘wind turbine’ will be denoted as turbine. Wind energy is generated by a turbine turning a shaft that is connected to a generator. As can be seen in Figure 5, a turbine functions by wind turning the blades which turn an internal shaft connected to a gearbox. This initiates a generator to spin converting the mechanical energy into electricity. However, we know that wind can vary by speed and by direction. As a result, wind turbines are designed to rotate to face the strongest winds taking advantage of strong winds throughout a greater portion of the day. At the same time, wind blows stronger with an increase in altitude; therefore, turbines are designed to be atop tall towers to take advantage of the greater wind speeds.⁴⁴ Wind turbines are not optimal in all areas as there is a wind speed range. In order to begin generating electricity, the wind speeds need to be in the range of six to nine miles per hour. On the other end, windmills will shut down when the wind speeds begin to top 55 miles per hour.⁴⁵

Figure 5: Diagram showing a wind turbine.⁴⁶

There are many benefits of using wind power: it is free, wind is everywhere, requires no fuel, creates jobs, and has a drastically lower impact on the environment compared to fossil fuels. However, there are potential downsides of wind power in the fact that it can be spontaneous due to the intermittency of wind.⁴⁷ It can be costly to build and maintain wind farms as there is a huge capital investment to be made. Other concerns are the issues with the impact on nature views, disruption of radar systems for air control due to noise, and the number of birds and bats killed due to collisions with wind turbine blades.⁴⁸