Clean Energy Technologies
Many Aboriginal and northern communities are looking at developing and integrating clean energy projects so that their communities can continue to grow in sustainable and efficient ways while reducing their impacts on the earth. These projects are being implemented in communities at various scales and include clean energy sources such as hydro, wind, solar, biomass, geothermal, and waste heat recovery.
Hydropower converts the natural flow of water in a river, stream or channel into electricity. Energy is produced by the fall or flow of water turning the blades of a water turbine. Two thirds of the electricity produced in Canada comes from hydropower.
Conventional hydroelectric power is derived from hydroelectric dams, which use the potential energy of dammed water to drive water turbines and generators. The dammed water is held in a large reservoir and can be accessed at times of high electricity demand. The amount of potential power depends on the volume of water held by the dam and on the difference in height between the water source and the outflow, called head. A large pipe (called the "penstock") delivers water to the turbine to generate electricity. Generally, projects over a few hundred Megawatts are considered to be large-scale.
Run-of-river hydro does not store large quantities of water behind a dam. It is dependent on the flow of the water in a river and is therefore less predictable than conventional hydro. Run-of-river hydro projects generate power by passing water that is under pressure through turbines. This pressure is generated by using natural drops in elevation.
In run-of-river hydro systems, a small dam or weir (about 1 to 3 meters high) is typically built across a waterway which directs the water in the river toward the intake point. After the water has come through the intake, it is channeled along canals, tunnels or pipelines that run both parallel to and above the river, to a point downstream. At this point the water is allowed to fall through a pipe, or penstock, down to the powerhouse where it spins turbines to generate electricity. The water is then channeled out of the powerhouse so that it can rejoin the river. A three to five meter drop in elevation is generally the minimum required for the smallest run-or-river hydro projects.
The energy of the wind can be harnessed by building a tall tower with a propeller on the top of it. Wind turbines convert the kinetic energy of the wind into mechanical energy, by turning the propeller, which is used to drive a generator that converts this energy into electricity. Wind turbines generally take up very little space, allowing for the land to be used for other purposes such as farming. Small-scale wind turbines are particularly suited to off-grid applications. Most wind energy technologies can be used as stand-alone applications, connected to a power grid, or used in combination with solar PV.
The global solar energy resource is vast and essentially inexhaustible. Opportunities to harness this energy for heating and electricity production are enormous. Solar powered systems are very well suited to off-grid and remote areas.
Solar thermal technology uses a solar collector to absorb the sun's energy and transform it into heat. A solar collector generally consists of a metal box with a glass or plastic cover and black absorber plates inside. Low and medium-temperature collectors are generally used to heat houses and other buildings. Water used in the collector is warmed by the sun and then pumped to heat the building. High-temperature collectors concentrate sunlight using mirrors to obtain higher temperatures. Steam and gas turbines then convert the heat into electricity. Active solar technologies employ electrical or mechanical equipment, such as pumps and fans, to optimize the amount of usable heat in a system.
Solar Photovoltaic (PV)
Solar PV technology converts sunlight directly into electrical energy using PV cells, which are made out of semiconductive materials such as silicon. PV cells are connected to form PV modules that are connected to form larger PV arrays. When light strikes the PV cell, the energy in the light is transferred to the semiconductor. The energy disturbs the electrons in the semiconductor and moves them in a certain direction, creating an electrical current that can be tapped into for our electricity needs. Solar PV systems can often be used in conjunction with other forms of energy production, such as fossil fuel powered generators and wind turbines.
Bioenergy is the conversion of biomass (plant matter or other organic waste material) into useful forms of energy, such as heat and electricity. Burning biomass directly to produce space heating or water heating, or to produce steam to drive a turbine for electricity generation produce much lower greenhouse gas emissions compared to burning fossil fuels. Typically the most economical bioenergy feedstocks can be accessed for free or have negative economic value—such waste wood and mill residues such as bark, sawdust, planer shavings, end cuts, paper sludge etc.
Geothermal technologies use the energy stored in the Earth for heating and cooling purposes. Heat contained underground or underwater represents a significant, and mostly untapped, renewable energy resource. The temperature of the earth at a depth of a few meters stays relatively constant year round at 8°C, and can be used for heating purposes in the winter, or cooling purposes in the summer.
Heat is extracted from the earth through a liquid medium (heat transfer fluid) that runs through a loop of buried tubing, and is pumped through a heat pump. The pump concentrates and extracts the heat, which is then supplied to the building heating system. In the summer the concept works in reverse and air conditioning is supplemented by the relatively cooler earth.
A range of systems exist, such as closed loop systems, which pump a heat transfer fluid through underground coils, or open loop systems, where water is drawn up from a well directly to a heat exchanger. Heat pumps can be used with forced air or hydronic heating systems, and can provide different types of space conditioning, such as heat only (no cooling capability), heating and passive cooling, and heating and active cooling (NRCan, 2002).
Waste Heat Recovery
Waste heat is the by-product of the heat of machines, or heat that is generated as the result of fuel combustion or a chemical reaction, and then released into the environment. Waste heat recovery is a method to recover the large amounts of heat that are lost and use them for space heating, water heating, or to produce electricity. Waste heat recovery can be used with diesel generators so that the fuel is used as efficiently as possible. The heat is channeled through pipes filled with air, water or oil.
Systems that convert waste heat into electricity are referred to as combined heat and power (CHP), or cogeneration systems. In CHP systems, the heat produced from the burning of fossil fuels is captured and used. Many existing power-only systems can be retrofitted to capture the waste heat.
When heat is produced in a central location and piped to different buildings in a community through a network of insulated underground pipes using either water or steam as the transfer medium, it is called district heating.
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