To best understand how renewable energy can be integrated into climate change mitigation and adaptation strategies, one must understand the processes and applications related to each source. Read each of the topics below for an overview of renewable energy as well as the pros and cons of each source:
Wind energy has many benefits; it is sustainable in the long-term and, at least to a certain extent, available to almost all regions of the world. However, in order to harness wind energy most effectively, planners must consider the engineering and placement of the turbines.
Pros and cons exist for various design types of wind turbines. Horizontal axis wind turbines (HAWTs), which are most common, catch only lateral winds and can produce more energy from a given amount of wind, but are less effective in turbulent winds. Vertical axis wind turbines (VAWTs) have the ability to harness winds from any direction without repositioning their rotors, but they are not as efficient in energy production. The number, spacing, thickness, and length also alter efficiency of a wind turbine (and the amplitude of noise emitted).
Regardless of type, wind turbines all have a few consistent components. For example, blades capture wind energy. Velocity sensors measure wind speeds and turbulence, so that breaks can slow down the blades. A vertical tower and a power generator help to convert the collected energy into electricity, which is later distributed to homes and businesses.
The power of wind is proportional to the density of the air, the area of the space through which the wind passes, and the wind’s velocity. Wind maps can help planners determine which locations are best suited for wind turbines. Air density changes based on elevation and temperature, so wind energy is often more effective in colder regions and higher elevations. It is also critical to consider the accessibility of turbines to electricity grids as well as vicinity to public areas and urban environments, especially due to the noise pollution they can emit through mechanical noise (produced by equipment) and aerodynamic noise (caused by the contact of the air flow with the blades). Birds and bats that migrate through windy areas are also susceptible to dangers of wind turbines if placed in indiscriminate locations. When deciding whether to place a wind turbine onshore, it is important to note that offshore wind speeds are generally more consistent and strong, although construction is more expensive and difficult.
Solar Energy & Photovoltaics:
Solar energy is directly related to the photovoltaic effect, which involves the creation of electrical currents when light or radiation comes in contact with semiconductor materials. Variability for solar energy production is high because cloud cover and sunlight are not always consistent between days and seasons; moreover, sunlight is low during nighttime hours.
While photovoltaics directly create electricity from solar energy, solar heating is a more indirect process. During active solar heating, a solar collector absorbs solar radiation to heat water, and during passive solar heating, solar energy directly warms a building or water, thus reducing the amount of additional energy needed to heat it.
Solar panels can be arranged and tilted in various formats in order to best absorb solar radiation:
- Parabolic troughs are curved and angled mirrors that angle light rays towards an absorber in their center
- Linear Fresnel reflectors have mirrors that are long and thin to transfer the sun’s rays towards a focal point
- Power towers use flat mirrors that redirect light to a point at the peak of a tower
- Dish/engine systems use a dish-shaped arrangement of mirrors to focus lights towards a central point
Storage methods for solar energy also exist; solar ponds constructed with saltwater can provide a sustainable option for heat and power. While heated water usually rises and evaporates, the salt weighs the water down enough so that it can’t rise. Another benefit of solar-powered systems is that environmental impacts are relatively low with no noise or chemical pollution.
Harnessing energy from biofuels requires the burning of plant material, which leads to high carbon emissions, as well as the emission of nitrogen oxides and methane. Atmospheric emissions are a major concern regarding biomass energy use, but even though biomass is not carbon-neutral, its carbon emissions are lower than those from all types of fossil fuels. Another major concern regarding biofuels is the need for surface area and water to allow for plant growth; land use takes up space and changes soil compositions. However, biochar, a by-product of biofuel production may be capable of re-fertilizing soils.
There are three generations of biofuels:
- First generation biofuels, which consist of food crops, such as corn, wheat, rice, etc.
- Second generation biofuels, which consist of lignocellulosic materials, such as wood
- Third generation biofuels, which consist of biofuels made from algae
Moreover, biofuels can be divided into primary materials that are derived directly from plants and secondary materials, which are waste products from human use, such as forestry residue left behind from logging, animal manure, cooking oils and municipal sewage. Using waste lowers the deposits in landfills, and thus, greenhouse gas emissions resulting from landfills, while simultaneously transforming energy into a useable state for humans. In other cases, humans intentionally grow “energy crops” to be used for the sole purpose of biofuel.
Biofuels are treated through physical, thermochemical, and/or biochemical methods. During physical processing, biofuels are crushed into smaller fragments through grinding, pelleting, or other, similar methods with the ultimate goal of making the materials easier to burn. Thermochemical processing, on the other hand, involves more than just mechanical processes; heat through combustion, pyrolysis, or other methods breaks the plant material down. Alternatively, biochemical processing requires living organisms to play a role in breaking down the material.
Geothermal Energy & Heat Pumps:
Geothermal energy arises due to the heat from Earth’s creation as well as its supply of radioactive isotopes which release heat as they decay. Geothermal resources are high enthalpy, meaning that their temperature per unit mass is high, and the most abundant sources of geothermal energy are located in or nearby geothermal reservoirs, such as volcanoes, hot dry rocks (impermeable rocks beneath Earth’s surface), and hot wet rocks (permeable, fluid-filled rocks beneath Earth’s surface). Cap rocks retain these geothermal sources within an aquifer, and when humans drill into these aquifers, they can collect the energy for anthropogenic use.
Geothermal power plants generate electricity through different forms of geothermal energy technology. While flash steam plants use geothermal hot water to create steam, dry steam plants directly harness steam to move generator turbines. Binary power plants heat a secondary fluid with the original source of hot water, and flash/binary combined power plants integrate multiple methods.
Critiques of geothermal energy assert that drilling costs are high, ideal locations for extracting geothermal energy are uncertain, and connectivity options are limited. Environmental implications, such as noise pollution during drilling, the clearing of space for drilling, and chemical pollutants released must also be taken into consideration. Furthermore, some even believe that it is actually a non-renewable energy source if mined using unsustainable methods.
However, geothermal energy is one of the few renewable energy sources that has low variability; that is, it has the capacity to provide a constant stream of energy regardless of weather and other variables. It is predictable throughout all 24-hours of the day, and with more consistent electricity available on the market, electricity costs could decrease for consumers. And even with high capital costs to create the initial energy harnessing system, geothermal power can pay off economically in the long-term.
Wave energy is variable by season and geographic region; for instance, in northern Europe, there is more wave and wind energy during the winter than during the summer. To best be harnessed for energy, waves should be steady and have little turbulence that could potentially disrupt the energy technology. Wave energy technology includes attenuators, point absorbers, oscillating wave surge converters, oscillating water columns, overtopping devices, and submerged pressure differentials; the most efficient technology sources depending on the amplitude and strength of the waves.
The height of waves depends upon wind speed, fetch, duration, roughness of topography, and tides. Understanding types of waves can also help to better design technology to harness their energy. Storm waves, which are generated by local wind fields, are generally strong and destructive to shorelines; swell waves, in contrast, have travelled long distances from the wind fields where they were generated and are generally weaker and unidirectional.
Wave energy technology results in low environment disturbance because it does not release chemical pollutants or carbon, alter coastal habitats, or disturb humans and other animals through noise.