Renewable Energy Systems

Abstract

In this research paper, we examined renewable energy systems with the goal of maximizing efficiency. In particular, we studied wind energy, biogas, and hydropower. Our design project presents a hypothetical problem with an idealized hydropower system where we must design a piping system that optimizes energy production and minimizes cost. We then designed a functional hydropower piping system for a case study in which a consumer wanted to switch to alternative energy. This design process showed the minimal requirements that a system needs to generate enough energy for a family. Introduction Recent changes in both international and domestic politics combined with renewed interest in the environment demand changes in the way people consume energy. The age of abundance that followed the US Victory in World War II greatly changed the way people lived, but the most significant change is in the way people consume. While this mass consumption has helped to fuel one of the richest economies in the world, these policies can no longer go on. In the International Energy Outlook 2007, it is projected that global electricity production will increase by 2.4 percent each year between 2004 and 2030 (7). The increasing demand for energy cannot be met with a decreasing supply of fossil fuels. If this trend continues, the world will only run out of energy sooner and possibly create a situation where scientist and engineers will run out of time to create a new way to power the world that will allow the inhabitants of earth to burn through resources as they currently do. This situation is setting up a new field that is about to become a major part of how people live. Electricity generation from renewable energy sources is by no means a new concept. What are now considered renewable energy sources were once used exclusively as means of power for performing tasks that ancient civilizations needed in order to flourish. As the environmental movement grew, so did interest in alternative energy. Along with this interest from citizens, the government is also trying to foster change through financial incentives. The use of these clean sources is expected to increase at an average annual rate of 1.7 percent (7). If the right geographic conditions can be met, small-scale generation of electricity from wind, biogas, or hydropower can be an effective alternative to reduce or completely replace energy from conventional sources. In the near future, it is foreseen that these electricity generating techniques will become common due to the sheer demand and desire for new renewable energy technology (8). Although wind and hydropower involve the mechanical (or kinetic) energy of wind and water, respectively, the true utilization of these technologies involves the production of electricity. Electricity is a high-quality form of energy. This means that we can use electricity to run a number of systems, even when the systems differ in nature. This characteristic of electricity makes it very useful and valuable in everyday life. In order to be more energyefficient, it is necessary to match the quality of the energy with the task that needs to be done. This way, highquality energy is not wasted on a job that does not require it. For instance, heating water is one task that does not require a particularly high quality of energy. Instead, energy-efficiency can be maximized using solar power or methane. Electricity use can be limited in this manner, and renewable energy can replace the need for excessive amounts of electricity (8). Considering the importance of efficient and renewable energy sources, we designed a cost-efficient small-scale hydropower system to provide power for a home. To do this, we calculated the energy needed, as well as the flow and head of the stream. This is critical in making hydropower systems efficient and appealing to homeowners. Wind Background In a wind turbine system, the kinetic energy found in wind can be harnessed and turned into mechanical energy. This mechanical energy can be used to power machinery or to generate electricity. Wind turbines can help to capture this energy and convert it to a more useful form to be able to perform work in a home or business. The amount of energy that a turbine can produce depends on its size, as well as the area in which it is built. One should always strive to build a turbine in an area where the wind speeds are optimal for the specific turbine. Calculating the “capacity factor” of a turbine can be a key element in determining its productivity. The “capacity factor” is a percentage that compares the turbine’s actual energy yield with the amount of energy that could be produced over the same period of time, provided the turbine was running at full capacity. Normal wind turbine systems often have a capacity factor between fortyand eighty-percent. The amount of energy that a wind turbine can produce depends on the height and size of the turbine (11). Biogas Background Biogas is a good form of renewable energy for people with excess manure or farm waste. Agricultural and animal waste is anaerobically digested, producing a mixture of carbon dioxide and methane gas. This gas is then used either to generate electricity from combustion engines or for direct combustion in cooking or lighting appliances. The waste needs to be stored in a special container while being digested, since the digestion must be anaerobic. Any small-scale farmer owning more than ten pigs that do not graze or more than three dairy cows could potentially reap the economic and environmental benefits of this type of energy system. However, the biogas unit must be planned, constructed, operated, and maintained properly; otherwise, the energy yield may not be as high. Biogas plants also need a large amount of water to be kept in good condition. When designing a biodigester, it is important to consider the size of the family, the daily lighting and cooking requirements, the amount of waste available for digestion, and the material available for construction of the digester. Using these factors, the correct digester type, the proper volume for the digester, and the retention time can be established (2). Renewable energy systems are constantly evolving and changing to meet the demand of the consumers involving both electricity and the environment. As people become increasingly willing to help the environment by making these types of investments, it is, in turn, becoming easier and more practical to implement these systems. Although there are many other forms of renewable energy technology, wind power, biogas, and hydropower are more carefully examined, due to their small-scale benefits. Specifically, it is important for people to understand the benefits of designing a renewable energy system. Motivated by a desire to better understand and make recommendations for specific hydropower systems, we studied a particular hydropower model, and made it cost-effective and energyefficient to suit the homeowner’s needs. Hydropower background Unlike wind power or biogas, hydropower requires some pressure difference on either side of the turbine, which will in turn move a mechanical component. The spinning turbine converts the potential energy of the water into kinetic energy. Due to its predictability and continuous availability, hydropower is a popular energy source for people with access to moving water. For our purposes, hydropower, specifically micro hydropower, may be defined as a system producing less than 500 kilowatts of energy. This definition varies among the international community; China, for example, defines “small” hydropower as being any system below 25 megawatts. Hydropower is very clean, and uses only the pressure of the water, not the water itself, to yield energy. Knowledge of both the flow in a river and the available head, or the vertical difference the water falls down, are essential when determining how much energy can ultimately be produced from this type of energy supplier. Other considerations involved when designing a hydropower turbine should include maintaining the wildlife of the animals in and around the area of the river. To avoid any major detrimental effects on the river and its surroundings, one can generally assume that one-third of the flow is the largest amount that can be put to use in a hydropower system. (9) Micro hydro turbines can take many forms, but the most recognizable is the water wheel, which had formerly been used to grind up grain until this century. While water wheels can be used today for work that does not require a fast-spinning turbine, other types of turbines have since become more common. Turbines may be classified as either impulse turbines or reaction turbines. In impulse turbines, water is pushed at a high speed out of a nozzle. This action, consequently, turns the turbine wheel. Typically, impulse turbines can be found in situations where the head is relatively high. Reaction turbines, conversely, convert only part of the available head into kinetic energy; the rest remains as pressure head. These types of turbines work best where there is a low to medium head installation. Generally, the type of turbine that should be used is dependent on the flow and head, or the distance that the water drops. The Pelton wheel is the most common of the newer turbines, made up of a series of cups attached to a hub. When water enters the cups, it makes the turbine spin. A Pelton wheel generally has an efficiency of close to eighty percent, in some cases even reaching up to the low nineties. (6) Figure 1: A Pelton Wheel (12) Some people would like to use hydropower, but do not have access to a head high enough to generate substantial power. Daniel J. Schneider designed a hydropower plant for a low head to harness power from the United States’ water flow without building dams that had the potential to flood and cause damage. His design involved a careful examination of fluid dynamics, similar to the