Renewable Energies

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Energy is always required, whether it be for the production of goods, the supplying of services, or for transportation. Can we reduce our emissions by turning to clean sources of energy? If so, why haven't we already?

Big Ideas: 
  • There are many ways of generating clean energy from a variety of sources
  • Clean energy sources can help greatly reduce carbon emissions
  • While the technology exists there are challenges associated with adopting clean energy sources

Electric cars: zero gas, zero emissions. Right? Well, that depends. We often hear that replacing traditional cars with electric vehicles greatly reduces greenhouse gas emissions, but we must consider where this electricity comes from. For this electrification to be truly effective, the electricity should be obtained from renewable and low carbon sources. If the electricity used in these electric vehicles comes from a zero carbon source, it is only then that the emissions involved in operating the vehicle can be nearly zero.

A large portion of the world's electrical demand is met by the burning of fossil fuels, and we have enough low-cost fossil fuels available to last for the next while. However, with the negative impact of fossil fuels and their resulting greenhouse gas emissions, we turn to other sources of energy such as solar, wind, and hydro power which are infinitely renewable. Biomass fuels also have the potential to be renewable with careful management. Each type of renewable energy has its own advantages, as well as challenges.

Solar.- Solar power is the generation of electricity from sunlight. This can be done in two ways: through photovoltaic panels or through the collection of the Sun's energy as heat. The former directly converts sunlight into electricity while the latter uses the captured heat to produce steam and run a turbine. In either case, the presence of the Sun to provide this power is intermittent but easily predictable.

Solar energy is an extremely promising energy source, and photovoltaic solar panels in particular are the fastest growing source of renewable energy today, but some challenges remain. For example, solar panels cannot provide power during the night or on cloudy days. In order to remedy this issue, inexpensive and effective power storage technologies are needed, something better and cheaper than the batteries of today. Alternatively, storing the Sun's energy in the form of heat throughout the day and continuing to produce steam with the stored heat at night may be a viable option. (As an example, a solar power plant in Seville tackles this issues by using molten salt as the heat storing medium1.)

Wind.- While photovoltaics are a fairly recent development2, wind, created by pressure differences in the Earth's atmosphere (which in turn are caused by uneven heating of the Earth's surface by the Sun), has been used to produce mechanical work for ages. Since as early as 500 AD, windmills have been used to transport goods, crush grains, and pump water3. Since then, advances to the efficiency of wind turbines have allowed the production of electricity. Wind power is now only second to hydro power in terms of its contribution to the amount of renewable energy being produced worldwide. Thanks to the minimal amount of greenhouse gas emissions associated with constructing the turbine, carbon emissions from wind power are almost zero.

Like solar, wind also suffers from intermittent power but is even more unpredictable. Strong and consistent winds are required for cost effective power generation but it is difficult to guarantee. However, there is a solution to this: the variability in power can be made up for by using sources of renewable energy that can be stored and released on demand. Hydro power provides such a solution as hydro dams store water to be run through the dam's turbines to create electricity. This water can be released during times of low winds to supplement power demands and be closed off when wind is sufficient to meet the demand. This combination of renewable energy technologies has been called a "marriage made in energy heaven".

Hydro.-4Like wind power, people have been harnessing the power of water for millennia, and improvements in turbine efficiencies have allowed us to now use this power to generate electricity. Using water to turn a turbine, whether it be from the kinetic motion of a river or of water stored in a dam, is referred to as "hydropower". It taps into the natural water cycle as water evaporates from the Sun's heat, comes down as rain and flows back via rivers into the sea. As of 2010, hydropower accounted for roughly 16% of the world's electricity production. Hydropower dams can serve alternate purposes, built also for flood control or water storage.

Hydropower is stable, adaptable, and can be a nice complement to solar or wind power as energy can be stored in the form of dams (potential energy). However, it is not without its drawbacks. Large-scale hydro projects can cause the displacement of many people from their land and may effect water quality and water ecosystems around the dams or turbines, if not well planned or maintained. Nevertheless, it is a low-carbon source of electricity, and small-scale projects have the potential to empower many local communities.

There is also the potential to use the general motion of tides (caused by gravity and the moon) as well as surface ocean waves (mainly caused by wind) to generate electricity. Tides and underwater currents are especially reliable, and harnessing them does not have the drawbacks of hydropower (e.g., danger to fish is minimal because blades turn fairly slowly). Rotors have been developed in recent years to harness energy from underwater currents, and the challenge is now to build reliable and durable equipment that can run for many years in seawater. On the other hand, capturing surface wave power is largely unexplored; making the equipment withstand powerful and violent sea conditions and still remain economically feasible is a substantial challenge.

Biomass.- Older than all of the above, biomass has been as a source of energy since humanity's earliest days in the form of burning wood for warmth and light. Today, it is still used to meet 15% of the global energy demand. It should be noted, however, that the use of biomass is not intrinsically renewable or sustainable. The use of biomass is made renewable only by the careful management of the resource so that carbon released by plants burned are taken back in by plants which are planted to grow in the place of those burned. More recently uses of biomass have begun to include the use of vegetable fats, plant wastes, and fermented sugar products tor concentrated sources of fuel. Biofuels such as ethanol are created by breaking down cellulose in plants using enzymes and then fermenting bacteria with the resulting sugars. This ethanol is close to traditional gasoline and can be used directly or as a gasoline additive. In contrast to the ethanol process, the process to create biodiesel uses a purely chemical process. The resulting biodiesel is very similar to traditional, petroleum based diesel and can be directly used in any vehicle that uses diesel fuel. A third biologically produced fuel is methane gas. While being a greenhouse gas, it is also a good fuel source for heating and power. Methane is produced by bacterial fermentation in the absence of oxygen and occurs in many places such as landfills, manure, and sewage to name a few.

Overall cost and benefits.- So far, the cost of constructing renewable energy sources has been generally more expensive than fossil fuel sources since they generally require higher technologies and skills to construct. This is changing, but financial cost has been one of the biggest shortcomings of renewable energies. Along with financial cost, the energy density of renewable sources is generally less than that of fossil fuel sources. This means that more energy can be created per unit mass or volume by fossil fuels than renewable sources.

Nevertheless, the benefits of switching over to renewable sources often outweigh the challenges and issues involved. Renewable sources can be placed closer to the user, preventing losses in power lines as the electricity is delivered. In addition, renewable sources ensure variety in supply, protecting local areas from energy insecurities and providing opportunity for innovation. And of course, they provide a sustainable way to meet our electricity demands without the high cost of carbon emissions.

To learn more about renewable energies, you can visit the interactive lessons provided by the Pacific Institute for Climate Solutions by clicking on the image below and selecting sections 9-16 on the left side panel:


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