Renewable Energy Electricity Technologies:


Wind energy systems convert the kinetic energy of moving air into electricity or mechanical power. They can be used to provide power to central grids or isolated grids, or to serve as a remote power supply or for water pumping. Wind turbines are commercially available in a vast range of sizes. The turbines used to charge batteries and pump water off-grid tend to be small, ranging from as small as 50 W up to 10kW. For isolated grid applications, the turbines are typically larger, ranging from about 10 to 200kW.
As of 2005, the largest turbines are installed on central grids and are generally rated between 1 and 2 MW, but prototypes designed for use in shallow waters offshore have capacities of up to 5 MW.

A good wind resource is critical to the success of a commercial wind energy project. The energy available from the wind increases in proportion to the cube of the wind speed, which typically increases with height above the ground. At minimum, the annual average wind speed for a wind energy project should exceed 4 m/s at a height of 10m above the ground. Certain topographical features tend to accelerate the wind, and wind turbines are often located along these features. These include the crests of long, gradual slopes (but not cliffs), passes between mountains or hills, and valleys that channel winds. In addition, areas that present
few obstructions to winds, such as the sea surface adjacent to coastal regions and flat, grassy plains, may have a good wind resource. Since the early 1990s, wind energy technology has emerged as the fastest growing electricity generation technology in the world. This reflects the steady decline in the cost of wind energy production that has accompanied the maturing of the technology and industry: where a good wind resource and the central grid intersect, wind energy can be among the lowest cost provider of electricity, similar in cost to natural gas combined-cycle electricity generation.

Small Hydro Systems:

Small hydro systems convert the potential and kinetic energy of moving water into electricity, by using a turbine that drives a generator. As water moves from a higher to lower elevation, such as in rivers and waterfalls, it carries energy with it; this energy can be harnessed by small hydro systems. Used for over one hundred years, small hydro systems are a reliable and well-understood technology that can be used to provide power to a central grid, an isolated grid or an off-grid load, and may be either run-of-river systems or include a water storage reservoir.

Most of the world’s hydroelectricity comes from large hydro projects of up to several GW that usually involve storage of vast volumes of water behind a dam. Small hydro projects, while benefiting from the knowledge and experience gleaned from the construction of their larger siblings, are much more modest in scale with installed capacities of less than 50 MW. They seldom require the construction of a large dam, except for some isolated locations where the value of the electricity is very high due to few competing power options. Small hydro projects can even be less than 1 kW in capacity for small off-grid applications.

An appreciable, constant flow of water is critical to the success of a commercial small hydro project. The energy available from a hydro turbine is proportional to the quantity of water passing through the turbine per unit of time (i.e. the flow), and the vertical difference between the turbine and the surface of the water at the water inlet (i.e. the head). Since the majority of the cost of a small hydro project stems from up front expenses in construction and equipment purchase, a hydro project can generate large quantities of electricity with very low operating costs and modest maintenance expenditures for 50 years or longer.
In many parts of the world, the opportunities for further large hydro developments are dwindling and smaller sites are being examined as alternatives giving significant growth potential for the small hydro market (e.g. China).


(i) Photo-Voltaic: Photo-voltaic systems convert energy from the sun directly into electricity. They are composed of photo-voltaic cells, usually a thin wafer or strip of semi-conductor material, that generates a small current when sunlight strikes them. Multiple cells can be assembled into modules that can be wired in an array of any size. Small photo-voltaic arrays are found in wristwatches and calculators; the largest arrays have capacities in excess of 
5 MW.

Photo-voltaic systems are cost-effective in small off-grid applications, providing power, for example, to rural homes in developing countries, off-grid cottages and motor homes in industrialized countries, and remote tele-communications, monitoring and control systems worldwide. Water pumping is also a notable off-grid application of photo-voltaic systems that are used for domestic water supplies, agriculture and, in developing countries, provision of water to villages. These power systems are
relatively simple, modular, and highly reliable due to the lack of moving parts.
Photo-voltaic systems can be combined with fossil fuel-driven generators in applications having higher energy demands or in climates characterized by extended periods of little sunshine (e.g. winter at high latitudes) to form hybrid systems.

Photo-voltaic systems can also be tied to isolated or central grids via a specially configured inverter. Unfortunately, without subsidies, on-grid (central grid-tied) applications are rarely cost-effective due to the high price of photo-voltaic modules, even if it has declined steadily since 1985. Due to the minimal maintenance of photo-voltaic systems and the absence of real benefits of economies of scale during construction, distributed generation is the path of choice for future cost-effective on-grid applications. In distributed electricity generation, small photo-voltaic systems would be widely scattered around the grid, mounted on buildings and other structures and thus not incurring the costs of land rent or purchase. Such applications have been facilitated by the development of technologies and practices for the integration of
photo-voltaic systems into the building envelope, which offset the cost of conventional material and/or labour costs that would have otherwise been spent.

Photo-voltaic systems have seen the same explosive growth rates as wind turbines, but starting from a much smaller installed base. For example, the worldwide installed photo-voltaic capacity in 2003 was around 3,000 MW, which represents less than one-tenth
that of wind, but yet is growing rapidly and is significant to the photo-voltaic industry.

(ii) Solar-thermal power:

Several large-scale solar thermal power projects, which generate electricity from solar energy via mechanical processes, have been in operation for over two decades. Some of the most successful have been based on arrays of mirrored parabolic troughs. Through the 1980’s, nine such commercial systems were built in the Mohave Desert of California, in the United States. The parabolic troughs focus sunlight on a collector tube, heating the heat transfer fluid in the collector to 390ºC (734ºF). The heated fluid is used to generate steam that drives a turbine.
The combined electric capacity of the nine plants is around 350 MW, and their average output is over 100 MW. The systems have functioned reliably and the most recently constructed plants generate power at a cost of around $0.10/kWh.
Several studies have identified possible cost reductions.

Another approach to solar thermal power is based on a large field of relatively small mirrors that track the sun, focussing its rays on a receiver tower in the centre of the field. The concentrated sunlight heats the receiver to a high temperature (e.g., up to 1,000ºC, or 1,800ºF), which generates steam for a turbine. Prototype plants with electrical capacities of up to 10 MW have been built in the United States, the Ukraine (as part of the former
USSR), Israel, Spain, Italy, and France.

A third solar thermal power technology combines a Stirling cycle heat engine with a parabolic dish. Solar energy, concentrated by the parabolic dish, supplies heat to the engine at temperatures of around 600ºC. Prototype systems have achieved high efficiency.

All three of the above technologies can also be co-fired by natural gas or other fossil fuels, which gives them a firm capacity and permits them to be used as peak power providers. This makes them more attractive to utilities, and gives them an advantage over photo-voltaic, which cannot necessarily provide power whenever it is required.
On the other hand, they utilize only that portion of sunlight that is direct beam and require much dedicated land area. Solar thermal power is still at the development stage: the costs of the technology should be reduced together with the associated risks, and experience under real operating conditions should be a further gain.





Ocean-thermal power:

Electricity can be generated from the ocean in several ways,
as demonstrated by a number of pilot projects around the world. In ocean thermal
electrical conversion (OTEC), a heat engine is driven by the vertical temperature
gradient found in the ocean. In tropical oceans, the solar-heated surface water may
be over 20ºC warmer than the water found a kilometre or so below the surface. This
temperature difference is sufficient to generate low-pressure steam for a turbine.
Pilot plants with a net power output of up to 50 kW have been built in Hawaii
(USA) and Japan. High production costs, possible negative impacts on near-shore
marine ecosystems and a limited number of suitable locations worldwide have so
far limited the development of this technology which needs further demonstration
before commercial deployment.

Tidal power:

Narrow basins experiencing very high tides can be dammed such that water flowing into and out of the basin with the changing tides is forced through a turbine. Such “barrage” developments
have been constructed in eastern Canada, Russia, and France, where a 240 MW project has been operating since 1966. While technically feasible, the initial costs are high and environmental
impacts may include sedimentation of the basin, flooding of the nearby coastline and difficult to-predict changes in the local ecosystems. Tidal power technology raises many technical questions (e.g.configuration, reliability, safe deployment and recovery, grid connection, operation and maintenance) and market barriers that limit the deployment of this technology.

Wave power:

Waves have enormous power, and a range of prototypes harnessing this power have been constructed. These include shore-based and offshore devices, both floating and fixed to land or the ocean floor. Most utilize either turbines, driven with air compressed by the oscillating force of the waves, or the relative motion of linked floats as waves pass under them. Pilot plants with capacities of up to 3 MW have been built; the major barrier to commercialization has been the harsh ocean environment. It is crucial that the current prototypes and demonstration projects are successful to overcome barriers to further deployment.

Ocean current power:

Just as wind flows in the atmosphere, so ocean currents exist in the ocean; ocean currents can also be
generated by tides. It has been proposed that underwater turbines not unlike wind turbines, could be 
used to generate electricity in areas experiencing especially strong currents. Some pilot projects
investigating the feasibility of this concept have been launched.

Renewable energy heating and cooling technologies:

Solar water heating systems:

Solar water heating systems use solar energy to heat water. Depending on the type of solar collector used, the weather conditions, and the hot water demand, the temperature of the water heated can vary from tepid to nearly boiling. Most solar systems are meant to furnish 20 to 85% of the annual demand for hot water, the remainder being met by conventional heating sources, which either raise the temperature of the water further or provide hot water when the solar water heating system cannot meet demand (e.g. at night).

Solar systems can be used wherever moderately hot water is required. Off-the-shelf packages provide hot water to the bathroom and kitchen of a house; custom systems are designed for bigger loads, such as multi-unit apartments, restaurants, hotels, motels, hospitals, and sports facilities. Solar water heating is also used for industrial and commercial processes, such as car washes and laundries.

Worldwide, there are millions of solar collectors in existence, the largest portion installed in China and Europe. The North American market for solar water heating has traditionally been hampered by low conventional energy costs, but a strong demand for swimming pool heating has led unglazed technology to a dominant sales position on the continent. Solar water heating technology has been embraced by a number of developing countries with both strong solar resources and costly or unreliable conventional energy supplies.

Biomass heating systems:

Biomass heating systems burn organic matter—such as wood chips, agricultural residues or even municipal waste—to generate heat for buildings, whole communities, or industrial processes. More sophisticated than conventional woodstoves, they are highly efficient heating systems, achieving near complete combustion of the biomass fuel through control of the fuel and air supply, and often incorporating automatic fuel handling systems.

Biomass heating systems consist of a heating plant, a heat distribution system, and a fuel supply operation. The heating plant typically makes use of multiple heat sources, including a waste heat recovery system, a biomass combustion system, a peak load heating system, and a back-up heating system. The heat distribution system conveys hot water or steam from the heating plant to the loads that may be located within the same building as the heating plant, as in a system for a single institutional or industrial building, or, in the case of a “district heating” system,
clusters of buildings located in the vicinity of the heating plant.

Biomass fuels include a wide range of materials (e.g. wood residues, agricultural residues, municipal solid waste, etc.) that vary in their quality and consistency far more than liquid fossil fuels. Because of this, the fuel supply operation for a biomass
plant takes on a scale and importance beyond that required for most fossil fuels and it can be considered a “component” of the biomass heating system. Biomass heating systems have higher capital costs than conventional boilers and need diligent operators.
Balancing this, they can supply large quantities of heat on demand with very low fuel costs, depending on the provenance of the fuel.

Today, 11% of the world’s Total Primary Energy Supply (TPES) comes from biomass combustion, accounting for over 20,000 MW (68,243 million Btu/h) of installed capacity worldwide [Langcake, 2003]. They are a major source of energy, mainly for cooking and heating, in developing countries, representing, for example, 50%
of the African continent’s TPES [IEA Statistics, 2003].

Solar air heating systems:

Solar air heating systems use solar energy to heat air for building ventilation or industrial processes such as drying. These systems raise the temperature of the outside air by around 5 to 15ºC (41 to 59ºF) on average, and typically supply a portion of the required heat, with the remainder being furnished by conventional heaters.

A solar air heating system currently considered by RETScreen consists of a transpired collector, which is a sheet of steel or aluminium perforated with numerous tiny holes, through which outside air is drawn. Mounted on an equator-facing building wall, the transpired collector absorbs incident sunshine and warms the layer of air adjacent to it. A fan draws this sun-warmed air through the perforations, into the air space behind the collector and then into the ducting within the building, which distributes the heated air through the building or the industrial processes. Controls regulate the temperature of the air in the building by adjusting the mix of recirculated and fresh air or by modulating the output of a conventional heater. When heat is not required, as in summertime, a damper bypasses the collector. The system also provides a measure of insulation, recuperates heat lost through the wall it covers and can reduce stratification, the pooling of hot air
near the ceiling of voluminous buildings. The result is an inexpensive, robust and simple system with virtually no maintenance requirements and efficiencies as high as 80%.

Solar air heating systems tend to be most cost-effective in new construction, when the net cost of the installation of the transpired collector is offset by the cost of the traditional weather cladding it supplants. Also, new-construction gives the designer more latitude in integrating the collector into the building’s ventilation system and aesthetics. Installation of a transpired collector also makes sense as a replacement for aging or used weather cladding.

Given the vast quantities of energy used to heat ventilation air, the use of perforated collectors for solar air heating has immense potential. In general, the market is strongest where the heating season is long, ventilation requirements are high, and conventional
heating fuels are costly. For these reasons, industrial buildings constitute the biggest market, followed by commercial and institutional buildings, multi-unit residential buildings, and schools. Solar air heating also has huge potential in industrial processes which need large volumes of heated air, such as in the drying of agricultural products.

Ground-source heat pumps:

Ground-source heat pumps provide low temperature heat by extracting it from the ground or a body of water and provide cooling by reversing this process. Their principal application is space heating and cooling, though many also supply domestic hot water. They can even be used to maintain the integrity of building foundations in permafrost conditions, by keeping them frozen through the summer.

A ground-source heat pump (GSHP) system has three major components: the earth connection, a heat pump, and the heating or cooling distribution system. The earth connection is where heat transfer occurs. One common type of earth connection comprises tubing buried in horizontal trenches or vertical boreholes, or alternatively, submerged in a lake or pond. An antifreeze mixture, water or another heat-transfer fluid is circulated from the heat pump, through the tubing, and back to the heat pump in a “closed loop.” “Open loop” earth connections draw water from a well or
a body of water, transfer heat to or from the water, and then return it to the ground (e.g. a second well) or the body of water.

Since the energy extracted from the ground exceeds the energy used to run the heat pump, GSHP “efficiencies” can exceed 100%, and routinely average 200 to 500% over a season. Due to the stable, moderate temperature of the ground, GSHP systems are more efficient than air-source heat pumps, which exchange heat with the outside air. GSHP systems are also more efficient than conventional heating and air-conditioning technologies, and typically have lower maintenance costs. They require less space, especially when a liquid building loop replaces voluminous air ducts, and, since the tubing is located underground, are not prone to vandalism like conventional rooftop units. Peak electricity consumption during cooling season is lower than with conventional air-conditioning, so utility demand charges may be reduced.

Heat pumps typically range in cooling capacity from 3.5 to 35 kW (1 to 20 tons of cooling). A single unit in this range is sufficient for a house or small commercial building. Larger commercial and institutional buildings often employ multiple heat pumps (perhaps one for each zone) attached to a single earth connection. This allows for greater occupant control of the conditions in each zone and facilitates the transfer of heat from zones needing cooling to zones needing heating. The heat pump usually generates hot or cold air to be distributed locally by conventional ducts.

Strong markets for GSHP systems exist in many industrialized countries where heating and cooling energy requirements are high. Worldwide, 800,000 units totaling nearly 10,000 MW of thermal capacity (over 843,000 tons of cooling) have been installed so far with an annual growth rate of 10% [Lund, 2003].