Renewable energy technologies produce sustainable, clean energy from renewable sources such as the sun, the wind, plants, and water. Renewable energy technologies have the potential to strengthen our nation's energy security, improve environmental quality, and contribute to a strong energy economy.
Mankind is been using biomass for thousands of years. Biomass is any organic material that has stored sunlight in the form of chemical energy. Wood is a well-known example of biomass: it can be burned for heat or shaped into building materials. There are many additional types of biomass that can be used to derive fuels, chemicals, and power—such as plants, agricultural and forestry residues, organic components of garbage (municipal solid waste), and algae. This broad diversity of suitable biomass has resulted in increased research and development of technologies to produce fuels, products, and power at an industrial scale. The processes that scientists and engineers use to break down biomass into these products vary based on the type of biomass (or feedstock) and its intended end-use.
Bioenergy is a general term that covers energy derived from a wide variety of material of plant or animal origin. Strictly, this includes fossil fuel s but, generally, the term is used to mean renewable energy sources such as wood and wood residues, agricultural crops and residues, animal fats, and animal and human wastes, all of which can yield useful fuels either directly or after some form of conversion. There are technologies for bioenergy using liquid and gaseous fuel, as well as traditional applications of direct combustion. The conversion process can be physical (for example, drying, size, reduction or densification), thermal (as in carbonization) or chemical (as in biogas production). The end result of the conversion process may be a solid, liquid or gaseous fuel and this flexibility of choice in the physical form of the fuel is one of the advantages of bioenergy over other renewable energy sources. The basis for all these applications is organic matter, in most cases plants and trees. There is a trend towards purposefully planted biomass energy crops, although biomass can also be collected as a by-product and residue from agricultural, forestry, industry and household waste.
Bioenergy can be used for a great variety of energy needs, from heating and transport fuel to power generation. There are numerous s commercially available technologies for the conversion processes and for utilization of the end- products. Although the different types of bioenergy have features in common, they exhibit considerable variation in physical and chemical characteristics which influence their use as fuels. There is such a wide range of bioenergy systems that this module does not aim to cover and describe each one.
The amount of sunlight that strikes the earth's surface in an hour and a half is enough to handle the entire world's energy consumption for a full year !!! Solar energy has amazing potential to power our daily lives and thanks to constantly-improving technologies.
Solar energy systems come in all shapes and sizes. There are two main types of solar energy technologies—photovoltaic (PV) and concentrating solar power (CSP). You're likely most familiar with PV, which is utilized in panels. When the sun shines onto a solar panel, photons from the sunlight are absorbed by the cells in the panel, which creates an electric field across the layers and causes electricity to flow.
The second technology is concentrating solar power, or CSP. It is used primarily in very large power plants and is not appropriate for residential use. This technology uses mirrors to reflect and concentrate sunlight onto receivers that collect solar energy and convert it to heat, which can then be used to produce electricity.
Photovoltaic (PV) materials and devices convert sunlight into electrical energy. A single PV device is known as a cell. An individual PV cell is usually small, typically producing about 1 or 2 watts of power. To boost the power output of PV cells, they are connected together in chains to form larger units known as modules or panels. Modules can be used individually, or several can be connected to form arrays.
One or more arrays is then connected to the electrical grid as part of a complete PV system. Because of this modular structure, PV systems can be built to meet almost any electric power need, small or large.
Commonly known as solar cells, individual PV cells are electricity-producing devices made of different semiconductor materials. PV cells come in many sizes and shapes, from smaller than a postage stamp to several inches across. Solar cells are often less than the thickness of four human hairs. In order to withstand the outdoors for many years, cells are sandwiched between protective materials in a combination of glass and/or plastics to make a PV module.
The amount of energy that can be produced is directly dependent on the sunshine intensity. Thu s, for example, PV devices are capable of producing electricity even in winter and even during cloudy weather albeit at a reduced rate. Natural cycles in the con text of PV systems thus have three dimension s. As with many other renewable energy technologies, PV has a seasonal variation in potential electricity production with the peak in summer although in principle PV devices operating along the equator have an almost constant exploitable potential throughout the year. Secondly, electricity production varies on a diurnal basis from dawn to dusk peaking during mid- day. Finally, short-term fluctuation of weather conditions, including clouds and rain fall, imp act on the inter hourly amount of electricity that can be harvested. PV devices use the chemical-electrical interaction between light radiation and a semiconductor to obtain DC electricity. The base material used to make most types of solar cell is silicon (approx.87 percent). The main technologies in use today are: Mono-crystalline silicon cells are made of silicon wafers cut from one homogenous crystal in which all silicon atoms are arranged in the same direction. These have a conversion efficiency of 12-15 per cent); Poly-crystalline silicon cells are poured and are cheaper and simpler to make than mono-crystalline silicon and the efficiency is lower than that of mono-crystalline cells (conversion efficiency 11- 14 per cent).
Thin film solar cells are constructed by depositing extremely thin layer of photovoltaic material s on a low- cost backing such as glass , stainless steel or plastic (conversion efficiency 5- 12 percent). Multiple junction cells use two or three layers of different material s in order to improve the efficiency of the module by trying to us e a wider spectrum of radiation (conversion efficiency 20- 30 per cent). The building block of a PV system is a PV cell. Many PV cells are encapsulated together to form a PV pane l or module. A PV array, which is the complete power-generating unit, consists of any number of PV modules/panels. Depending on their application, the system will also require major components such as a battery bank and battery controller, DC -AC power inverter, auxiliary energy source etc. Individual PV cells typically have a capacity between 5 and 300 W but system s may have a total installed capacity ranging from 10 W to 100 MW. The very modular nature of PV panels as building blocks to a PV system gives the sizing of systems an important flexibility.