Manzanares solar chimney. Feasibility of technology and operational necessities

Solar Wind Energy Tower

Maybe you’ve heard of a solar updraft tower, a tall, hollow cylindrical tower where sunlight heats the air at the base of the tower and creates a chimney effect, causing air to rapidly shoot upward and exit the top. Wind turbines placed at the bottom convert wind energy to electricity.

Although the concept was first proposed over a century ago, it wasn’t until the early 1980s that a prototype was built near Manzanares, Spain. That experiment came to halt in 1989 when the guy wires failed and strong winds toppled the tower. Since then, a handful of experimental solar updraft towers have been built, but none seem to hold much promise as a significant player in renewable energy. Efficiency is a function of tower height, and increasing height causes more stability issues and higher manufacturing costs. That’s probably why we don’t see solar updraft towers all over the planet.

The First of Its Kind

The company will begin building its first commercial Solar Wind Energy Tower (SWET) near San Luis, Arizona. The site was chosen after two years of evaluating the conditions at various locations. The tower’s dimensions are custom-tailored to the site and its microclimate. The company is not yet revealing the dimensions of this tower, but they expect it to produce about 18 megawatts on average. The project was approved on April 23, 2014. No word yet on a tentative completion date.

Whether the tower itself proves to be cost-effective, reliable, and durable remains to be seen, but the project includes patented technology that could potentially be used in other areas of renewable energy production. For example, each wind tunnel at the base of the tower includes three turbines in series, as shown below. The turbines don’t generate electricity directly. they convert wind power to hydraulic power. The hydraulic to electric converters (HECs) operate most efficiently when there is a large pressure differential. A computer system turns HECs on or off depending on hydraulic pressure caused by varying wind conditions. The system ensures optimal pressure for the HECs that are operating, as opposed to giving a little pressure to all HECs.

Image: Solar Wind Energy Tower US patent application US 8120191 B1

I’ve seen wave systems that convert wave power to hydraulic power, which is then used either to generate electricity or to desalinate seawater through a reverse-osmosis unit. It’s possible that this hydraulic control system could be used in that application as well.

Manzanares solar chimney

This blog specifically focuses on Matlab and Simulink applications for Electrical and Electronics Engineers.

The solar updraft tower (SUT) is a renewable-energy power plant for generating electricity from solar power. Sunshine heats the air beneath a very wide greenhouse-like roofed collector structure surrounding the central base of a very tall chimney tower. The resulting convection causes a hot air updraft in the tower by the chimney effect. This airflow drives wind turbines placed in the chimney updraft or around the chimney base to produce electricity. Plans for scaled-up versions of demonstration models will allow significant power generation, and may allow development of other applications, such as water extraction or distillation, and agriculture or horticulture. As a solar chimney power plant (SCPP) proposal for electrical power generation, commercial investment is discouraged by the high initial cost of building a very large novel structure, and by the risk of investment in a feasible but unproven application of even proven component technology for long-term returns on investment—especially when compared to the proven and demonstrated greater short-term returns on lesser investment in coal-fired or nuclear power plants Power output depends primarily on two factors: collector area and chimney height. A larger area collects and warms a greater volume of air to flow up the chimney; collector areas as large as 7 kilometres (4.3 Mi) in diameter have been discussed. A larger chimney height increases the pressure difference via the stack effect; chimneys as tall as 1,000 metres (3,281 ft) have been discussed. Heat can be stored inside the collector area. The ground beneath the solar collector, water in bags or tubes, or a saltwater thermal sink in the collector could add thermal capacity and inertia to the collector. Humidity of the updraft and condensation in the chimney could increase the energy flux of the system. Turbines with a horizontal axis can be installed in a ring around the base of the tower, as once planned for an Australian project and seen in the diagram above; or—as in the prototype in Spain—a single vertical axis turbine can be installed inside the chimney. Carbon dioxide is emitted only negligibly as part of operations. Manufacturing and construction require substantial power, particularly to produce cement. Net energy payback is estimated to be 2–3 years. Since solar collectors occupy significant amounts of land, deserts and other low-value sites are most likely. A small-scale solar updraft tower may be an attractive option for remote regions in developing countries. The relatively low-tech approach could allow local resources and labour to be used for construction and maintenance. Locating a tower at high latitudes could produce up to 85 per cent of the output of a similar plant located closer to the equator, if the collection area is sloped significantly toward the equator. The sloped collector field, which also functions as a chimney, is built on suitable mountainsides, with a short vertical chimney on the mountaintop to accommodate the vertical axis air turbine. The results showed that solar chimney power plants at high latitudes may have satisfactory thermal performance. Solar updraft towers can be combined with other technologies to increase output. Solar thermal collectors or photovoltaics can be arranged inside the collector greenhouse. This could further be combined with agriculture The solar updraft tower has a power conversion rate considerably lower than many other designs in the (high temperature) solar thermal group of collectors. The low conversion rate is balanced to some extent by the lower cost per square metre of solar collection. Model calculations estimate that a 100 MW plant would require a 1,000 m tower and a greenhouse of 20 square kilometres (7.7 sq Mi). A 200 MW tower with the same tower would require a collector 7 kilometres in diameter (total area of about 38 km²). One 200MW power station will provide enough electricity for around 200,000 typical households and will abate over 900,000 tons of greenhouse producing gases from entering the environment annually. The collector area is expected to extract about 0.5 percent, or 5 W/m² of 1 kW/m², of the solar energy that falls upon it. Concentrating thermal (CSP) or photovoltaic (CPV) solar power plants range between 20% to 31.25% efficiency (dish Stirling). Overall CSP/CPV efficiency is reduced because collectors do not cover the entire footprint. Without further tests, the accuracy of these calculations is uncertain. Most of the projections of efficiency, costs and yields are calculated theoretically, rather than empirically derived from demonstrations, and are seen in comparison with other collector or solar heat transducing technologies. The performance of an updraft tower may be degraded by factors such as atmospheric winds, by drag induced by the bracings used for supporting the chimney, and by reflection off the top of the greenhouse canopy. At present, a number of energy sources are utilized on a large scale such as: coil, oil, gas and nuclear. Continuation of the use of fossil fuels is set to face multiple challenges namely: depletion of fossil fuels reserves, global warming and other environmental concerns and continuing fuel price rise. For these reasons, the existing sources of conventional energy may not be adequate to meet the ever increasing energy demands. Consequently sincere and untiring efforts shall have to be made by the scientists and engineers in exploring the possibilities of harnessing energy from several non-conventional energy sources (solar, biomass, tidal, hydrogen, wind and geothermal energy) which they are seen as possible solution to the growing energy challenges. According to energy experts, unconventional energy sources can be used for electric power generation which receives a great attention. Power generating technology based on green resources would help many countries improve their balance of payments. Being the most abundant and well distributed form of renewable energy, solar energy constitutes a big asset for arid and semi-arid regions. A range of solar technologies are used throughout the world to harvest the sun‘s energy. In the last years, an exciting innovation has been introduced by researchers called ―solar chimney‖. It is a solar thermal driven electrical power generation plant which converts the solar thermal energy into electrical power in a complex heat transfer process. The implementation of this project is of great significance for the development of new energy resources and the commercialization of power generating systems of this type and will help developing countries to promote the Rapid development of the solar hot air-flows power generation. The basic physical principles of centralized electricity generation with solar chimney power plants (SCPP‘s) were described by Haaf et al. in 1982. After the pilot plant in Manzanares had gone into operation in June 1982, the first experimental results confirmed the main assumptions of the original physical model. Later, on the basis of experimental data from July 1983 to January 1984, a semi-empirical, parametrical model was proposed for predicting the monthly mean electrical power output of the pilot plant as a function of solar irradiation. The model predictions agreed reasonably with the experimental data for the exceptionally dry months July- October 1983, but the model failed to simulate the wet months following heavy rainfall in winter and spring 1984. It was realized, that natural precipitation entering the collector has a fundamental influence on the collector performance via evaporation, plant growth and infrared absorption in the collector air. A refined parametrical model was therefore proposed, which includes at least the long term, seasonally varying effect on rainwater on the plants performance and allows the simulation of large plants in climates similar to the climate in Manzanares. Solar chimney power plants are an interesting alternative to centralized electricity generation power plants. It is an ideally adapted technology for countries that lack a sophisticated technical infrastructure, where simplicity and uncritical operation of the installation is of crucial importance. A detailed literature survey of this system was performed. The review discusses the principles and characteristics of such a system, its requirements, its construction and its operation. It gives also a brief overview of the present state of research at the solar chimney power plant and future prospects for large-scale plants.

1 comment:

Guy gets almost killed for revealing how to generate electricity from Earth’s Magnetic CoreLadies and gentlemen you won’t believe what just happened:

This crazy guy has discovered how to transform Earth’s Magnetic Core Energy into electricity.

The beauty is that he figured out a clever way (yet dump simple) on how to power your home for 21 hours without interruption.

Rumor has it that the inventor was about to get killed for this secret as some bad guys wanted to steal his invention and get rich quickly.

Fortunately, he managed to escape and he’s now finally able to reveal his story in the video below:

From what I heard this video can be taken down by the end of the day. so I advice you to watch it right now while you still can. Reply Delete

Description of Solar Chimney Power Plants (SCPP)

2.1. History

Although the first application of solar chimney power plants was in the 1980s, theoretically, the idea was first accepted as the smoke jack designed by Leonardo Da Vinci in the 1450–1500s [5]. However, the idea of generating electricity from solar chimneys was first put forward by Spanish engineer Isidoro Cabanyes in 1903 [5]. By considering the current definition of solar chimney systems, Professor Bernard Dubos designed the idea of solar chimney power plants in 1926 to be built on a mountain slope in North Africa. Besides this, the system’s working principles and elements are included in the Dubos study [5]. Although the researchers carried out different studies in the following process, Robert Lucier made a detailed patent application in 1975, and this application was accepted in 1981 [5]. In 1982, he produced a prototype with a height of 200 m and a maximum power output of 50 kW in Manzanares, Spain, with the German team of Jörg Schlaich [6]. Since the first prototype’s production, researchers’ interest in solar chimney power plants has increased, and there are many such power plants installed in the world nowadays.

2.2. Working Principle

Although solar chimney power plants can be seen as large-scale complex structures, their working principle is based on simple and fundamental physical laws. The system is based on the upward buoyancy of fluids depending on their density difference and movements, which depend on their pressure difference. Due to the semi-permeable feature of the collector, which is the part of the system exposed to the sun, it transfers the solar radiation falling on it. The mechanism starts to function when it is transmitted to the ground. The solar radiation transferred to the system causes the air to heat because the collector acts as a cover. The decrease in the density of the heated air causes the air under the collector to move towards the collector. In addition, the solar radiation reaching the ground from the semi-permeable collector causes an increase in the temperature on the ground due to the opaque structure. Due to the temperature difference on the ground, the system’s air under the collector is exposed to the force of upward buoyancy. These forces push the air below the collector to the center of the collector, where it can only move. The pressure difference occurring at the entrance and exit of a long chimney placed vertically in the center of the collector creates a vacuum effect on the system’s air. It forces the system’s air to be drawn up through the chimney. With all of these effects, an increase occurs in the kinetic energy of the system’s air, the temperature and speed of which increase. There is a turbine in the chimney at a certain height from the ground. The kinetic energy of the system’s air hitting the turbine blades is converted into electrical energy, and power output is obtained from the system. The simplified mechanism of the system is given in Figure 1.

Solar Chimney Components: Construction and Materials

3.1. Tower

Although solar chimney power plants are large-scale structures, they consist of three main parts. These are the collector where the solar radiation is transferred to the system, the high chimney causing the pressure difference, and the turbine that provides the power output. The cylindrical pipe, called a tower or chimney, is positioned in the collector’s center (Figure 2) [7].

The chimney acts as a kind of motor in the system, allowing the system’s air—which heats up in the collector and increases in its kinetic energy—to be evacuated from the system by accelerating upward. It does not need any additional mechanism. There is a difference in height at the entrance and exit of the tower. The pressure difference caused by this height difference creates a vacuum effect in the collector’s center, which is the tower’s entrance, which evacuates the system’s air.

The chimney is the element that creates the pressure difference in the system. The total pressure difference in the chimney is directly proportional to the chimney’s height, and is calculated as follows [6]:

Due to the low-temperature difference in the system, some researchers renew Equation (1) based on the Boussinesq approach [7]:

Schlaich claims that the efficiency of the chimney is directly dependent on the chimney height and the initial temperature, which can be given as follows [6]:

In traditional solar chimneys, the cross-sectional area does not change with the height [9]. Von Backström and Gannon [10] claimed that increasing the chimney’s cross-section area from the chimney inlet to the chimney outlet will improve the system’s power output. Similarly, Motoyama et al. [11] also showed that the system’s power output would increase by increasing the chimney’s cross-sectional area towards the chimney outlet. On the contrary, other researchers examined the effect of designs in which the cross-sectional area decreases towards the chimney outlet on the system’s performance (Figure 3) [12]. When the existing solar chimney power plants are examined, it is seen that they mostly contain a chimney with a fixed cross-sectional area.

The chimney, which forms the main part of solar chimney power plants, is a large structure due to its height and diameter. Although the chimney’s height causes some structural difficulties, it can be dangerous due to environmental factors after the construction of the system is completed. Although this seemed like a problem in the first prototypes, technological developments allowed the construction of safer high-rise structures. Solar chimneys with a chimney height exceeding 1000 m could be built (Figure 4) [13]. Researchers stated that solar chimneys could be built with strong ring reinforcement such as internal wire, or wirelessly for higher chimneys’ economy, safety, and stability. They can be made reliably without any ring reinforcement up to 500 m in height [13]. The wall thicknesses vary according to the height of the solar chimneys. Von Backström et al. [13] designed a 1000-m high solar chimney for a 200 MW electric power output. The concrete chimney’s diameter was 260 m on the floor, the chimney diameter in the middle of the chimney was 133.4 m, and the diameter at the top of the chimney was 145 m. They designed the chimney with a wall thickness of 0.65 m at the base and 0.25 m at the top. Some researchers have recommended the measurement of different structural wind speeds and wind drag forces before installation [14].

Zhou et al. [15], considering the cost and strength calculations, designed an experimental solar chimney power plant using standard PVC drainage pipes with a diameter of 0.3 m and a height of 8 m as a chimney (Figure 5a). Some researchers used polycarbonate pipes with high temperature and impact resistance in their studies [16]. Ucgul and Koyun [17] used a solar chimney power plant with a height of 15 m and a cross-section of 1.92 m 2 for experimental purposes. The chimney was made of steel, in one piece (Figure 5b).

3.2. Collector

In solar chimney power plants, the collector is the facility’s base part, where the solar radiation is transferred to the system’s air. The air entering the system from the open part of the collector is warmed up by the solar radiation falling on the collector; therefore, the collector acts as a starter. The collector is made of a glass or plastic film (Figure 6a) [18]. These materials are used because they are transparent. The collecting material is positioned at a certain height from the ground [18].

The majority of the solar radiation passes through the collector, and a fraction of the radiation is directly absorbed by the system’s air. The soil and the system’s air emit long-wavelength radiation due to the solar radiation that is absorbed and trapped, and due to the collector, which is almost opaque to this long-wavelength radiation (transmittance 0.01), generating a greenhouse effect. The radiation effect under the collector increases the system temperature (Figure 6b and Figure 7a) [5]. Continuous heat transfer occurs between the collector, the system’s air, and the ground (Figure 7b) [19].

Performance Assessment of SCPP

The first experimental study on SCPP systems was carried out by Haaf [26]. They compared theoretical studies with 24-h experimental results (Figure 10a). They measured the floor temperature during the day, and the temperatures at different depths under the floor (Figure 10b).

They measured the change in the solar radiation and ambient temperature during the day (Figure 10c). Air velocity and temperature changes within the system form part of the 24-h measurement (Figure 10d). The results obtained from the pilot plant in Manzanares shed light on many researchers’ work, and contribute to the development of new theoretical models. Zhou et al. [50] conducted experimental measurements by designing a small-scale SCPP system. A numerical model was generated using the experimental data to calculate the power output of different radiation intensities. They compared the effect of a change in the collector radius and chimney height on the power output at 850 W/m 2 constant radiation intensity with experimental and simulation results (Figure 11a,b). Some researchers carried out radiation, temperature, and velocity measurements at different hours during the day with the small-scale SCPP systems they established [12,15,51,52,53,54,55,56,57]. Atit [58] conducted a detailed experimental study and compared the effect of the fixed diameter chimney and the divergent chimney on the system (Figure 12a,b). Furthermore, the convergent and divergent collector comparison was studied considering a constant chimney entrance height. He compared the experimental results with the CFD model. Some researchers have examined the effect of the system’s speed and temperature by changing the collector inlet height after measuring the temperature and velocity distribution of SCPP systems with an experimental study [16,59]. Bugutekin [60] set up an SCPP facility and measured the change of the temperature–velocity values in the collector and chimney with the energy storage application throughout the day. They also studied the ground temperature change during the day.

He claimed that the temperature increase during the day at the outlet of the collector was 21–26 °C. By establishing experimental SCPP systems, some researchers analyzed the effects of changes in geometric dimensions such as the chimney height, collector radius and collector height on the system using mathematical, CFD and analytical models they developed with the experimental results [61,62,63,64]. Motoyama et al. [11] compared the temperature and velocity values of the SCPP system with a divergent chimney in a laboratory environment compared to the SCPP system with a fixed-diameter chimney. They stated that the SCPP system with a divergent chimney gave five times more power output at a 35 °C temperature difference. They compared the temperature and speed of the turbine and the non-turbine systems. Kalash et al. [65] analyzed the performance of an SCPP system they built on sloping ground (Figure 13a). They measured the temperature and speed within the system for 24 h. They stated that the temperature increase reached 19 °C even in winter, and the upward airflow velocity was 2.9 m/s.

Eryener et al. [28] claimed that smaller collectors could be used for the same power output with an application that would increase the collector efficiency of SCPP systems. They emphasized that the collector efficiency was increased by covering a part of the collector with polycarbonate (Figure 13b). They measured the effect of a change in the wind flow on the thermal efficiency, and measured the temperature, radiation, and airflow rate throughout the day. They claimed that the collector’s efficiency was between 60% and 80%, and that it was two times more efficient than regular collectors. Ayadi et al. [66] investigated the effect of the collector height on the system by constructing a small-scale model prototype. They compared the temperature and velocity distribution in the collector with the experimental results with the CFD model they developed. They examined the effect of the collector height on the system. They stated that the system’s power output will decrease with the collector height, and that the power output at a 0.005 m collector height is 50% more than the power output at a collector height of 0.02 m.

Collector and Chimney Design Parameters

The collector is where solar radiation is absorbed in SCPP systems. The change in the collector’s geometry and design affects the system’s performance, as it will directly change the thermal energy entering the system. The studies in the literature will be examined separately according to their geometric and design effects. In SCPP systems, the chimney is the element of the structure positioned in the center of the collector; it creates a pressure difference due to its height. Thanks to the pressure difference it creates, it acts as a kind of system engine. The pressure difference is an essential factor because the power output of solar chimneys is directly caused by the system’s volumetric flow rate and pressure difference. The chimney and air velocity cause the pressure difference in the system. However, because the main component of the pressure difference is the chimney, the increase in the chimney’s height directly increases the pressure difference compared to Equation (2). In this section, firstly, studies in the literature will be given regarding the effect of the chimney height on the system. Because the change in the chimney’s diameter will affect the flow rate of the air in the system, the results of the difference in the diameter of the chimney will be included, and then the chimney profile will be continued.

5.1. Collector Radius

In the literature, the effect of the change in the collector radius on the system’s performance parameters, such as temperature, airflow rate, efficiency, and power output, has been repeatedly analyzed by many researchers. Considering the studies conducted, and given that changing the collector radius of the experimentally installed power plant is not allowed in most cases, the researchers mostly calculated the collector radius change’s effect on SCPP systems using mathematical, theoretical, and numerical analyses. Zhou et al. [50] conducted experimental measurements on a small-scale SCPP model with 8-m high and 0.7 m diameter. By changing the collector radius at 850 W/m 2 radiation intensity, they claimed that the power output, which was 2.087 W at a 2-m collector radius, increased by 140% to 5.01 W in a collector with a 5-m radius. Ghalamchi et al. [16] emphasized that the collector diameter increases the power output for the same geometry with their experimental data results. They stated that an SCPP system with a 500-m high chimney could give 468 kW power output with a collector of 420-m diameter. Al-Azawiey et al. [69] experimentally studied an SCPP prototype with a 6.3-m high and 0.32-m diameter chimney, with collector diameters of 3 m and 6 m. They stated that the chimney’s air velocity was 1.56 m/s for a 3-m collector diameter and 806 W/m 2 radiation intensity, and 2.25 m/s at the chimney for a 6-m collector diameter and 808 W/m 2 radiation intensity. Although the radiation intensity is almost the same for both measurements, doubling the chimney’s diameter increases the airflow rate in the chimney by approximately 44.23%. Larbi et al. [77] performed a performance analysis of a possible SCPP system installed in the Adrar region, which has a higher radiation intensity than other areas of Algeria, using a mathematical model. They claimed that the 200-m high, 10-m diameter chimney and a 500-m diameter collector SCPP system would provide between 140 and 200 kW of energy throughout the year. Designed with an 800 W/m 2 constant irradiance value and 30 °C initial temperature, the system gives a power output of approximately 142 kW with a collector diameter of 444 m; if the collector diameter is set to 690 m, the power output will increase by 140% to about 342 kW. Zhou et al. [78] developed a simple mathematical model to analyze the SCPP system’s performance installed on the Qinghai–Tibet plateau. They claimed that a 1000 m high, 80-m diameter chimney and a 5650-m diameter collector system would give 100 MW power output at 800 W/m 2 radiation at 20 °C atmospheric temperature. The system, which has a 1000-m high chimney, gives 10 MW power output with a 1750-m diameter collector under the same conditions. It reaches 50 MW power output by providing four times more power output with a 3935-m diameter collector. Koonsrisuk et al. [7] analyzed the Manzanares prototype with the detailed mathematical and CFD models. They compared the effect of the change in the chimney height ratio to the square of the collector radius on the system with two different models. The CFD model shows that the Manzanares prototype’s power output is 67–80 kW. They claimed that if the prototype H/R 2 ratio was 0.013 and the collector radius was 197.28 m at a fixed chimney height, the H/R 2 ratio would be 0.005 and the power output would be about 165 kW for both models. Similarly, they emphasized that the system’s mass flow rate will increase by 30%, from 765 kg/s in the reference state to 996 kg/s. Li et al. [79] analyzed the Manzanares prototype’s performance when powered by a turbine, using a theoretical model they developed. They stated that while giving 53.5 kW power output at a 122-m collector radius in the reference conditions at 1000 W/m 2 radiation, if the collector radius is set to 244 m, the power output will increase by 120.5% to approximately 118 kW. They claimed that increasing the collector radius above 500.5 m would not increase the system’s power output.

Status of the technology and its future market potential

Although the principle of an updraft solar tower has been known for long. in particular since it is based on a combination of the well-known chimney effect, wind energy and greenhouse effect. it has not been applied in practice on a large scale yet. In 1982, in Spain a prototype was built with financial support from the German Goverment (Haaf et al., 1983). It operated until 1989. It had a chimney of 195 metres tall and a collector area of 46 ha with a diameter of 224 metre. Its power production capacity was 50 kW at maximum.

Figure 3: Manzanares, Ciudad Real, experimental solar tower

In Ciudad Real, Spain, a new solar tower is planned with a chimney of 750 metres tall and a collector area of 350 ha (see Figure 2 above). It could produce 40 MW of electricity (Munoz-Lacuna, 2006).

In developing countries, the technology has been tested in Botswana in 2005 and there are plans to test it in Namibia. In Botswana, a small 22 metre tall chimney was built with a collector area of 160 m 2. The chimney was made of polyester material and the rool of the collector area of glass (Ketlogetswe, 2007). The ‘Greentower’ planned in Namibia (based on a proposal by the Namibian government in 2008) is expected to have a capacity of 400 MW electricity output, produced by a 1.5 km tall tower (280 m diameter) with a collector area of 37 km 2. This area will function as a greenhouse for growing crops (Cloete, 2008).

How the technology could contribute to socio-economic development and environmental protection

When applied on a large scale the technology could provide a considerable electricity output to the grid and thereby contribute to energy security of supply.

In case of small scale application in an off-grid system it could produce electricity for remote communities in, for instance, developing countries. This would especially be beneficial in case there are areas of low-value, degraded land available nearby the community. In such a case, the benefits from the technology can be reaped while the technology’s disadvantage of requiring a large collector area would not need to be felt as a problem. On the contrary, an important benefit from the collector area could be that it works as a greenhouse (largely supported by condensation underneath the collector roof at night) so that cash crops can be grown.

Climate

The contribution to greenhouse gas emission reduction from solar towers would lie in the possibility that it could replace fossil fuel based electricity production capacity. However, in term of the entire life cycle of the technology, including production of concrete and collector area roof material, the greenhouse gas balance is unclear.

For calculation of GHG emission reduction of a solar tower project, it is recommended to apply the Approved Consolidated Methodology ACM0002, which has been developed for renewable energy projects under the Clean Development Mechanism of the UNFCCC Kyoto Protocol (CDM). This methodology helps to determine a baseline for GHG emissions in the absence of the project (i.e. business-as-usual circumstances), how emission reductions below this baseline can be calculated, and how these reductions can be monitored. General information about how to apply CDM methodologies for GHG accounting can be found at: [[2]]

According to the modalities for greenhouse gas emission reduction calculations of the Clean Development Mechanism (CDM), the emissions caused by the construction of materials is not taken into consideration; only the effects from operating the plant are considered.

Financial requirements and costs

The investment costs of a solar updraft tower are relatively high. In particular the building of a tower and constructing a durable roof for the collector area are expensive. In combination with the relatively low energy conversion efficiency, investments costs have been estimated at USD 5 per watt of electricity production capacity (Schlaich et al., 2005). Levelised energy costs could be reduced with larger collectors and higher towers as this would create a stronger draft through the chimney. According to Climatelab.org, the cost of electricity produced by a 200 MW system could be 3 times lower than those of 5 MW system. Consequently, an economically more viable solar tower system would require a larger upfront investment.

However, for a clear cost figure further experience will be needed. According to Schlaich et al. (2005), producing electricity in a 200 MW solar tower would cost 7 eurocents per kWh and 21 eurocents per kWh for a 5 MW plant. On the other hand, operating costs are relatively low.