Renewable Energy - Wind (Part 2)

Wind energy basically involves converting airflow into electricity by using wind turbines. A wind turbine is a device that converts kinetic energy from the wind into mechanical energy and the mechanical energy is used to produce electricity. There are two types of wind turbines, based on their rotation axis; wind turbines can rotate about either a horizontal or a vertical axis. Interestingly, wind power always been integrated with solar power in hybrid renewable energy system due to the both system simplicity and operation independent.

1) Horizontal Axis

Horizontal-axis wind turbines (HAWT) have the main rotor shaft and electrical generator at the top of a tower, and must be pointed into the wind. Small turbines are pointed by a simple wind vane, while large turbines generally use a wind sensor coupled with a servo motor. Most have a gearbox, which turns the slow rotation of the blades into a quicker rotation that is more suitable to drive an electrical generator.

Since a tower produces turbulence behind it, the turbine is usually positioned upwind of its supporting tower. Turbine blades are made stiff to prevent the blades from being pushed into the tower by high winds. Additionally, the blades are placed in a distance in front of the tower and are sometimes tilted forward into the wind a little. Most HAWTs are of upwind design and most commonly used between the two types.

2) Vertical Axis

Vertical-axis wind turbines (VAWT) have the main rotor shaft arranged vertically. Key advantages of this arrangement are that the turbine does not need to be pointed into the wind to be effective. This is an advantage on sites where the wind direction is highly variable. The key disadvantages of VAWT include the low rotational speed, the inherently lower power coefficient, the pulsating torque generated and the difficulty of modelling the wind flow accurately.

In VAWT configuration, the generator and gearbox can be placed near the ground, using a direct drive from the rotor assembly to the ground-based gearbox, hence improving accessibility for maintenance. When this turbine is mounted on a rooftop, the building generally redirects wind over the roof and these can double the wind speed at the turbine. This type of wind turbine is suitable in urban areas because wind speeds within the built environment are generally much lower than at exposed rural sites.

Other than wind, maybe we can directly harness the electricity from the skies, lightning...

... maybe not, but still, it's a good possibility... (if we can find a way to harness 1.21 gigawatts from a lightning bolt that is 5 times hotter than the surface of the sun!)

Renewable Energy - Wind (Part 1)

Wind comes from atmospheric changes; changes in temperature and pressure makes the air move or flow around the surface of the earth. Wind energy involves converting these airflow into electricity by using wind turbines. Besides from generating electricity, other wind energy usage like windmills for mechanical power for grinding grain, windpumps for water pumping or drainage, or sails to propel ships. Wind energy is a clean energy source that can be relied on for the long-term future. A wind turbine creates reliable, cost-effective, pollution free energy. It is affordable, clean and sustainable. One wind turbine can be sufficient to generate enough electrical energy for a household.

Offshore wind power can harness the better wind speeds that are available offshore compared to on land, so offshore wind power’s contribution in terms of electricity supplied is higher. Technically, wind energy is considered a secondary or indirect solar energy because the sun is the main source of wind, warming the air, creating different temperature and pressure to make the air flowing.

In Malaysia, wind energy conversion is a serious consideration. In present technology, wind energy in Malaysia is not suitable to generate electricity commercially or wind is not particularly good in Malaysia as compared to the UK or Denmark, but islands like Perhentian Island can definitely gain a lot of power. A more recent research in 2005, a 150 kW wind turbine in Terumbu Layang-Layang was demonstrated with some success by a team from UKM. However, the availability of wind resource varies with location.

The potential of wind energy for Malaysia is level 1 which is the velocity of wind is less than 5.9 m/s. The mean wind speed over the sea surface around the sea surrounding Malaysia is generally below 5 m/s. Researchers observed that the highest wind speed is in east peninsular Malaysia, Sarawak and Sabah. Wind speed at these locations reach above 5m/s during the northeast monsoon season and for the rest of the year wind speed is low. The direction of the wind is from the northeast and east quadrant during the northeast monsoon season, and south and southwest quadrant during the southwest monsoon season. These mean that the wind energy in Malaysia is available all year round but in the opposite direction for different monsoon season.

The stronger the wind, the better...

... but lets hope it's not too strong.

Renewable Energy - Hydro

Hydro energy is energy harnessed and used from large water resources like rivers, lakes and even ocean. Since water is about 800 times denser than air, even a slow flowing stream of water, or moderate sea swell, can yield considerable amounts of energy. It is a cheap, reliable and non-polluting source of energy. There are many forms of water energy technologies depending on their capacity and designs:-

1) Hydroelectric is a term usually referred to generation of electricity by hydroelectric dams. Hydroelectric dams use the gravitational force of falling or flowing water (collected by the dam) to produce electrical power through the turbines. It is the most widely used form of renewable energy.

2) Micro hydro systems (or also known as mini-hydro) are hydroelectric power installations that typically produce up to 100 kW of power. They are often used in water rich areas as a remote-area power supply and usually stand alone power systems. Unlike the hydroelectric, this mini-hydro does not need dam to create falling or flowing water but converting the flow of water (like rivers) into electrical energy.

3) Run-of-the-river (ROR) hydroelectricity systems are a type of hydroelectric generation whereby a considerably smaller water storage called pondage is used to supply a power station but some ROR system doesn’t use pondage. The ROR systems derive kinetic energy from rivers and oceans without using a dam.

Hydro energy is the oldest and most exploited renewable energy in Malaysia, so this type of renewable energy is already have a good reputation and contribute 5% (in 2008) of total Malaysian power grid. The Bakum dam in Sarawak, one of the largest dams in South-East Asia, is expected to finally complete by 2010 with a capacity of 2400 MW. But hydroelectric have the most impact on the environment than all other renewable energies, ecosystem damage, loss of land and siltation due to the dam. For this project, a micro hydro system is suitable approach for the usage of hydro power.

Micro hydro systems are hydroelectric power installations that typically produce up to 100 kW of power. They are often used in water rich areas as a remote-area power supply and usually stand alone power systems. All hydro power plants have similar operation in generating electricity which is flow in water from water source to turn the turbine and generating electricity. Unlike the hydroelectric, this mini-hydro does not need dam to create falling or flowing water but converting the flow of water (like rivers) into electrical energy. So, this type of hydro power system has very little impact to the environment, unlike their hydroelectric dam cousin.

Typical Mini Hydro Diagram

Micro hydro systems are the complement photovoltaic solar energy systems because in many areas, the water flow (and thus available hydro power) is highest in the winter when solar energy is at a minimum. Micro hydro is frequently accomplished with a pelton wheel for high head, low flow water supply. The installation is often just a small dammed pool, at the top of a waterfall, with several hundred feet of pipe leading to a small generator housing.

Renewable Energy - Hydrogen Fuel Cell

Being the most abundant element on earth, hydrogen has been identified as one of the most viable and long term renewable alternatives to fossil fuel after solar. A fuel cell is an electrochemical cell which captures the electrical energy of a chemical reaction between fuels, through chemical reactions from hydrogen and air (oxygen), without the production of greenhouse gasses. In principle, although a fuel cell operates like a normal battery, it does not run out nor requires charging as long as fuel is supplied to it.

Fuel cells are not commercially available yet, and remain very expensive. They are used as power sources in remote areas. Fuel cells cannot store energy like batteries. Even if the energy delivered from fuel cells is stored, their electrical efficiency is not nearly as high as a battery's efficiency which also happens to be a much cheaper option.

At the moment, research and development is being carried out to harness hydrogen to be used in fuel cells for transportation purposes. Hydrogen and fuel cells are identified as priority research by the Ministry of Science, Technology and Innovation (MOSTI) after solar, as applications of fuel cells are viewed as one of the more important energy conversion devices in the future.

A fuel cell is a device that converts the chemical energy from a fuel into electricity through a chemical reaction with oxygen or another oxidizing agent. Hydrogen is the most common fuel, in the form of hydrocarbons such as natural gas and alcohols like methanol. Fuel cells are different from batteries in that they require a constant source of fuel and oxygen to run, but they can produce electricity continually for as long as these inputs are supplied.

Fuel cells are consists of an anode (negative side), a cathode (positive side) and an electrolyte (in this case, Hydrogen) that allows charges to move between the two sides of the fuel cell. Electrons are drawn from the anode to the cathode through an external circuit, producing direct current (DC) electricity. Individual fuel cells produce very small amounts of electricity, about 0.7 volts, so cells are "stacked", or placed in series or parallel circuits, to increase the voltage and current output to meet an application’s power generation requirements.

In addition to electricity, hydrogen fuel cells produce water and heat. The energy efficiency of a fuel cell is generally between 40-60%, or up to 85% efficient if waste heat is captured for use. Although fuel cell is technically not a renewable energy source but fuel cells can play an important role in the design of hybrid renewable energy system. Renewable energy sources, like the sun and wind, can't produce energy all the time, like at night. Fuel cells can be used as the primary power source during that period. The renewable energy system can produce electric energy and hydrogen for the fuel cell, which can be stored until it's needed.