Optimum Design for Solar Power Stations with Floating Solar Chimneys by salazarcannon


									Optimum Design for Solar Power Stations with Floating Solar Chimneys
Prof. Christos D. Papageorgiou School of Electrical & Computer Engineering N.T.U.A. Electrical Machines Laboratory Nymfon 1b Kifissia 14563 Athens Greece chrpapa@central.ntua.gr The floating solar chimney (FSC) invented by the author. The FSC can float in the air as a lighter than air balloon construction. Hence it can be designed with height up to 5 Km and appropriate internal diameter, in order its respective STPS to have a considerable efficiency combined with a low construction cost. In the proposed paper the various construction shapes for the FSC are presented. The material calculations and optimum choice for the internal diameter of a FSC with a given height and power output are presented also. It is shown that that for places with annual irradiation solar energy, on a horizontal surface, between 1600 to 2300 Kwh/sqm, the indicative cost for large STPSs (with rated output powers between 100 to 500 MW) is lower than 1000 USD per rated KW.

1. Operation Principles
The basic idea and principles of operation of a solar air turbine power station (STPS) have been introduced by prof. Schlaich see ref. [1]. A typical STPS diagram is shown in fig. (1) The STPS can be considered a set of three basic items - A cyclical solar collector made by a glass roof. - A tall chimney in the center of solar collector made by reinforced concrete. - A set of air turbines complied with appropriate electric generators near the bottom of the chimney.







Figure 1 The solar irradiation energy warms the air in the solar collector. The warm air tends to leave through the tall chimney. This produces a stream of hot air moving towards the center of the solar

collector. The air turbines transform part of this thermodynamic power, of the hot stream of air, into mechanical rotational power. This power, through a set of complied electric generators, is transformed to electric power. A STPS with rated power of 200 MW with a solar chimney made by reinforced concrete with a height of 1000 m is constructed already in Australia (see www.enviromission.au) The thermodynamic study of this power stations was introduced in a set of papers by Von Banckstrom and Cannon [2],[3],[4]. Following their method in ref. [5] the author introduced a fourth order polynomial equation that gives a fairly good approximate solution for the operation of STPS. In patent of ref. [6] the author introduced a novel idea for constructing very tall solar chimneys that are necessary for an efficient production of electric power, by STPSs. (see www.floatingsolarchimney.gr). These solar chimneys are named floating solar chimneys (FSCs) because of their property to float in the air as lighter than air constructions. In paper [7] the author proved that the FSCs can encounter effectively the external winds. As was shown the specially designed base of the FSC, permits to the FSC to decline under external winds. This decline, using wind statistics can be proved that decreases a few percent the average operational height of the FSC without any other major consequences. By the way of construction of the main part of the FSC the alteration of winds with altitude can be also encountered effectively. In the present paper the method and basic calculations for the construction of main body of the FSC are presented.

2. The basic shapes of the main body of the FSC
An FSC is composed by three parts as proposed in patent of ref. [6]. - The main body of the FSC, that is lighter than air construction, balloon type. The main body lifts up by its net lift force arising mainly by the lift gas that fills its walls made by light enduring fabric. - The heavy base, that keeps the main body attached to the top of the seat of the FSC. This seat is in the center of the solar collector of the STPS. Two heavy rings, united with a very strong fabric, make the heavy base. This construction gives to the main body the property to decline while it remains on the top of the seat, when external winds appeared (see fig.2). - A final accordion type part attached to the lower part of the heavy base that is unfolding only when the FSC declines and ensures the continuity of the FSC in its bottom (see fig.2).

D irection of

M ain Chim ney

H eavy M obile B ase
C him ney s ’ Seat

H olding Lower P art

Figure 2

The main body of the FSC is made by a set of successive balloon type rings made by balloon fabric with appropriate dimensions (fig.3). These rings are supported by a set of intermediate supporting rings (fig.4) made by strong material (aluminum, glass or composite material). These rings help the FSC to encounter the operational sub pressure acting on the wall of the FSC. Their internal lift gas pressurizes the balloon rings. They are attached appropriately on the supporting rings and form with them a strong hollow cylinder, the main body of a FSC.

∆ d d

h ∆


Figure 3

Figure 4

The cylinder is divided in parts that are separated between each other by an isolation balloon ring. The isolation balloon rings are open to the environmental air giving to the whole FSC the necessary flexibility to encounter the differential wind effects with altitude. For example a FSC of 3500 m height can be divided in 70 parts, each one having a height of 50 m including the isolation balloon. Each part is under the influence of the overall net lift force that is the sum of the net lift force of its balloons and the lift force arising by the friction forces of the warm air passing through it, during the operation of the STPS. Each part is attached separately by a number of appropriate ropes on the top of the heavy base that declines with the FSC (fig.2).

3. Other shapes of the main part of the FSC
The analysis of ref. [5] can be used to calculate the operational characteristics of the STPS and the operational sub pressure acting on the FSC. In fig.5 a typical set of operational curves relating the output electrical power and the mass flow through the FSC is presented with variable solar irradiance G.
d=70 m,H=3500 m,Dc=1770 m,k=1.67,a=1.1058

FSC d=70 m,H=3500 m, STPS 100 MW,

G=1000 W /sqm

G=800 W/sqm
maximum sub pressure in Pa

Power output in MW



G=600 W /sqm



G=400 W /sqm


G=200 W /sqm






8 6 mass flow in Kg/sec


12 x 10




2000 1500 altitude z in m




Figure 5

Figure 6

& The mass flow m is regulated in order the STPS to operate in the point of maximum power output. & It can be proved that m is almost independent of irradiance G. The sub pressure at the base of the FSC is proportional to the maximum power output. For a reasonable choice of the air speed inside the FSC between 10-15 m/sec, that is the operation point for the maximum power output of the STPS, it can be proved that the sub pressure on the FSC increases with its height. Making appropriate calculations using the equations of ref. [5] the maximum sub pressure for the maximum power output has been estimated and approximately is between 3400 Pa to 5800 Pa for heights of FSC between 3000 m and 5000 m. The operational sub pressure is decreasing with altitude and becomes overpressure near the top of the FSC. In fig. 6 the sub pressure as a function of altitude, for an STPS of 100 MW with a FSC 3500 m, is shown. The cut of the supporting rings and consequently their weight is proportional to the maximum sub pressure. The volume of the lifting balloon rings is also proportional to the weigh of the supporting rings. It can be proved that for tall FSCs the necessary balloon rings must have several meters local diameter. It is also known that, for a given operational sub pressure acting on the balloon rings, the tear force of their fabric is equal to the product of this sub pressure to the local radius of the curvature. For tall FSCs this tear force can become greater than the usual balloon fabric tear strength. Hence using the basic shape for the main FSC it will demand either special fabric or special way of constructing the balloon rings. To avoid this problem another way of construction of the main body of the FSC was proposed by Papageorgiou in patent see ref. [8]. With this proposal the wall of the main FSC and the lifting balloons are separated. In fig.7 are shown the basic shape A and the two alternative constructions (shape B and C) as proposed in patent of ref. [8].
Basic shape A

Shape B

Shape C

Figure 7 In the first alternative (shape B) the local radius of curvature of the wall balloons, that they accept the operational sub pressure, is limited, in order to minimize the tear force on them, bellow the safety limit of their fabric. The outer lift balloons accept only their internal pressure that is independent of the operational sub pressure and thus their diameter can be as big as it is necessary, in order their lifting force to raise the main body of the FSC. The wall balloons are used for thermal insulation.

In the next alternative (shape C) the wall of the FSC is proposed to be by a single layer of fabric. The small local wall curvature can be achieved keeping the supporting rings in constant distances by special fabric or plastic rods. The fabric length between two successive supporting rings is larger than the distance between the rings giving an appropriately small local curvature to the fabric in order to control the tearing forces on the fabric. As in the previous shape there exist outer lift balloons that they supply the main part of the FSC with the necessary lift force in order to float in the air. The successive external lifting balloons must be in contact in order to give to the main body the necessary thermal insulation. Both FSCs with the alternative shapes B or C, are divided in several parts of the same height, as was suggested for the FSC with the basic shape A. Each part it is independently attached to the heavy base with several aramid ropes, with appropriate breaking strength.

4. The materials
The main materials for the construction of the main body of the FSC are the following • Fabric for wall and lifting balloons. • Aluminum or reinforced glass or composite material for the supporting rings. • Strong plastic for the connecting rods. • Special ropes for the attachment of the parts of the main body of the FSC to its heavy base. • NH3 or He as lift gas. The main properties of these materials as exist in the market are given bellow: • Wall fabric could be ordinary balloon fabric that according to Cubicek company (see. www.cubicekballoons.cz) has the following characteristics: o Tear strength not less than 11000N/m. o Weight not more than 60 gr/m2. • Balloon fabric should be impermeable to He or NH3, not very strong because the lifting balloons do not accept strong pressures, and as light as possible. I estimate that its weight could be not more than 200 gr/m2. • For the shape A where, wall and lifting fabric is the same, the fabric must combine strength and impermeability hence could be of special construction and unknown properties. • The most common materials for supporting rings could be either Al, alloy 6082-T6 or reinforced glass. The properties of these materials are : o Aluminum: G = 70 GPa, strength limit fo=260 Nt/mm2 and density ρ=2,7 gr/cm3 o Glass (reinforced):G = 74 GPa, strength limit fo=1000 Nt/mm2 and density ρ=2,5 gr/cm3 • The attaching ropes could be special ropes with breaking strength 50 KN and weight 60 gr/m. • The material for connectors or connecting rods could be an appropriate plastic material with estimated density ρ=1,2 gr/cm3. • The lifting gas could be NH3 or He. For To=303oK and Po= 101000 Pa their lifting ability is 0,48 Kg/m3 and 1 Kg/m3 respectively. The cheaper price of NH3 indicates that the use of NH3 as lifting gas is economically the best choice. However because NH3 is slightly toxic the alternative of using He could be chosen.

5. Typical calculation procedure for the main FSC.
In this paragraph we will give the necessary steps for the calculation of the dimensions and material quantities for an FSC, made as one of the previous shapes, with a chosen set of material, as an example. The same procedure can be followed for any shape made by any material choice. Let us consider the FSC of a STPS with a rated power of 100 MW occupied with turbo generators of maximum power of 125 MW, achieved with the maximum solar irradiance G=1000 W/m2. Let us consider that this FSC has a height H of 3500 m and that its wall and lifting balloons are made by

appropriate balloon fabrics and its supporting rings by reinforced glass. Let us assume that the supporting rings, of the FSC, are connected with vertical plastic rods. Let us assume the following values for the FSC coefficients and its environment, kinetic correction coefficient α=1.1058, friction loss coefficient k=1.667, To=303.2oC, Po=101000Pa. The overall efficiency of the STPS is in the order of 5%. This will give an approximate solar collector surface Ac area of 125 MW Αc = = 2,5 ⋅ 10 6 m 2 0,05 ⋅ 1000 W / m 2 For Pmax=125 MW choosing d=70m and H=3500 m a final calculation gives the accurate value of Ac=2.46x106 m2 and a solar collector diameter Dc=1770 m. Using the equations of appendix I for a given Ac, k, H, G, α, Po, To we can produce the fig.8 where Pmax is function of d for G=800 W/m2,.
H= 3500 m ,Dc = 1770 m ,G= 800,k= 1.667,a= 1.1058



Maximum Power output in Mw







90 55


65 70 75 FS C internal diam eter d in m



Figure 8 The main body of the FSC is divided in 70 parts independently attached to the upper part of the heavy base with several ropes. Each part has a height of 50 m. It is estimated that the overall net force will not exceed the breaking strength of the ropes. Let us calculate the dimensions of the lifting balloons and supporting rings of the first part near the bottom of the FSC. This part accepts the maximum sub pressure that can be calculated using the equations of ref.[5] and is approximately 3700 Pa. We are choosing to use fifty supporting rings equally distanced using appropriate connecting plastic rods, to connect them vertically. The successive parts are separated between each other using strong fabric of appropriate length in order to have the necessary flexibility between them. This helps to encounter the differential forces between them, arising by wind velocity alterations with altitude see paper of ref. [7]. The supporting rings and their connecting rods form a strong cylindrical wall that must withstand the maximum operational sub pressure of the FSC (3700 Pa). The fabric of the wall must also withstand this sub pressure. In order to achieve that the fabric between two successive supporting rings, that are in 1 m distance, has a height of 1,05 m. Hence, under the external sub pressure, the wall fabric will form locally a radius of local curvature approximately 1 m. This will give tear force on it 3700 Pa x 1 m = 3700 Nt/m that is below the tear strength of the wall fabric. Because of this phenomenon if the internal diameter of the FSC is 70 m the diameter of the supporting rings is slightly larger say approximately 71 m. The wall fabric for the first part can be estimated as the product of (π x 71 x 50) x 1.05 =11670 m2 that leads to a wall fabric weight of WF,W=700 Kg for a fabric weight of 60 gr/m2. The force acting on each supporting ring is approximately equal to the product of the sub pressure (3700 Pa) to the radius of the ring (71/2 m) and the distance between two successive rings (1 m), hence is equal to F=131350 Nt.

For a safety factor 1.7, and reinforced glass material with fo=1000 Pa, the cut area (in mm2) of the supporting ring is equal to 1.7F/fo=224 mm2 and its weight per m will be equal to the product of the material volume multiplied by its density ρ=2.5 gr/cm3. This weigh is W=(1.7F/fo)ρ=560 gr/m. We can choose for example an orthogonal cut with external dimension 3.2 cm and internal 2.8 cm (with 2 mm thickness) that will have an approximate surface cut of 240 mm2. The supporting ring will be made by pieces united between them using appropriate connectors. Thus we can assume an average weight per m 0.65 Kg/m. Hence the weight of all the supporting rings will be equal to Wsup=50(0.65(π71))=7250 Kg. Assuming rods every 1.5 m we will have a total rod length equal to (π71/1.5)•50=7430 m. Assuming a weight of 120 gr per m, the rod weight will be equal to Wrod= 890 Kg. Let us assume that the lift balloon rings will have a local diameter equal to d1. The number of lift balloons will be equal to 50/d1. In order to estimate d1 we must use the following inequality: F > W F , L + W F ,W + Wsup + Wrod Where WF,L is the weight of the fabric of the lift balloons and F is the lift force. The lift balloon fabric has a weight of 200 gr/m2 thus 50 W F , L = 0.20 ⋅ π ⋅ d 1 ⋅ (π ⋅ (71 + 2 ⋅ d1 )) ⋅ = 10 ⋅ π 2 ⋅ (71 + 2 ⋅ d1 ) = 98.7 ⋅ (71 + 2 ⋅ d 1 ) d1 The lift force F will be calculated assuming NH3 as lifting gas hence 2 d 50 F = 0.48 ⋅ π ⋅ ⋅ 1 ⋅ (π ⋅ (71 + d1 )) ⋅ = 6 ⋅ π 2 ⋅ (71 + d 1 ) ⋅ d1 = 59,16 ⋅ (71 + d1 ) ⋅ d 1 4 d1 This inequality leads to the relation d 1 + 67.66 ⋅ d 1 − 145.3 > 0 hence d1>4.1676 m. We receive d1 approximately equal to 5 m hence for the first part there will be 10 lifting balloon rings. These balloon rings filled with NH3 will rise the first part supplying this part with the necessary net uplift force. However to total net uplift force will be the sum of this force plus the operational uplift force arising by the friction forces of the up drafting mass the of air on the internal wall of the chimney. The next parts of the FSC will accept lower sub pressure and will demand a lower number of the previously calculated supporting rings, or will demand lift balloon rings with smaller diameter. It is better to keep the same diameter for the balloon rings and to fill them partly by lifting gas in order to have the appropriate net lift force in every part. In case that we choose the option of smaller diameter the number of the balloon rings will increase hence it can be proved that we will have almost the same fabric surface but increased costs for fabricating more balloon rings. Hence to keep the diameter of the external lifting balloon rings constant is a reasonable choice. Thus the number of the lift balloon rings with diameter 5 m will be 70 x 10 =700. On the other hand, the total number of supporting rings is not 3500 for the whole FSC of 70 parts. Because of the decreased sub pressure with altitude, the upper parts will demand less supporting rings than the lower parts. Hence the total number of the supporting rings will be not more than the 60 % of 3500 as a rough estimation. This will give 2100 supporting rings for the whole FSC. In a similar way we can calculate the dimensions of lifting balloons when the supporting rings are made by Al or the lifting gas is He instead of NH3. As an approximate rule aluminum rings will have a minimum weight four times the minimum weigh of glass rings. Also using He instead of NH3 the local radius of lift balloons must divided by two.

6. Quantities of material and construction cost
Estimated results of the previous paragraph it is that for the main body of the FSC of the STPS of 100 MW with internal diameter d=70 m and height H=3500 m the following material quantities are necessary: • Wall fabric 820.000 m2 with a weight of 79.000 Kg. • Lifting balloon fabric 2.830.000 m2 with a weight of 566.000 Kg.

Supporting rings by reinforced glass 286.000 Kg. Connecting rods by strong plastic 95.000 Kg. Ropes approximately 1.000.000 m with a weight of 60.000 Kg. 17 • NH3 ⋅ (1.200.000 Kg ), of which 70.000 Kg is the net uplift force =1.700.000 Kg. 12 Alternatively could be used He. In this case the He quantity should be 4 • He ⋅ (1.200.000 Kg ) ≈ 192.000 Kg that is about 1.194.000 m3. 25 The overall construction cost of the FSC can be calculated taking approximately the following prices including material, labor, transportation, e.t.c. • Fabric 3.5 USD/m2 • Reinforced glass 1.5 USD/Kg • Al alloy 6082-T6, 3.5 USD/Kg • Connecting rods 1 USD/Kg • Ropes 1 USD/m • NH3 1 USD/Kg • He 5 USD/m3 Thus the following items give the overall construction cost for the FSC. • Fabric 3.650.000 m2 x 3.5 USD/m2 = 12.775.000 USD • Reinforced glass 286.000 Kg x 1.5 USD/Kg = 430.000 USD • Connecting rods 95.000 Kg x 1 USD/Kg = 95.000 USD • NH3 1.700.000 Kg x 1 USD/Kg = 1.700.000 USD • Ropes 1.000.000 m x 1 USD/m = 1.000.000 USD • Heavy base including accordion end = 600.000 USD Total cost 15.600.000 USD If He has to be used instead of NH3 the cost will be increased by 4 m USD leading to a total approximate cost of 19.6 mUSD. If Al had to be used instead of reinforced glass the Al quantity should be 1.100.000 Kg. The lifting balloon diameter should be around 10 m hence the lifting balloon fabric will increase about 10 % i.e. about 300.000 m2 (or 75.000 Kg). Hence NH3 has to be increased by 1.250.000 Kg and in case of He its quantity must be increased by 140.000 Kg (or 800.000 m3). Hence taking into consideration the cost of Al, the cost of FSC with Al and NH3 will be equal to 21.1 mUSD. If He will be used this figure jumps to 29.4 mUSD. Hence the (shape C) FSC construction cost will be between 15.6 mUSD (glass, NH3) to 29.5 mUSD (Al, He). In a similar way the FSC with shape B, will have a construction cost that will be between 19 mUSD (glass, NH3) to 32.5 mUSD (Al, He). Shape A must be a rather more expensive construction taking into consideration that its fabric must be very strong and impermeable to NH3 or He. This means that for large STPSs the basic shape A is not preferable.

• • •

7. Cost estimation of an STPS of a given power output
The approximate construction cost of an STPS with rated power output of 100 MW can be estimated taking into consideration the following approximate data. Solar collector 17 USD/sqm x 2.46 x 106 sqm = 41.820.000 USD Air Turbines 50 USD/KW x 125 MW = 6.250.000 USD Gear Boxes 30 USD/KW x 125 MW = 3.750.000 USD Electric Generators with power electronics 100 USD/KW x 125 MW = 12.500.000 USD Electric Equipment 20 USD/KW x 125 MW = 2.500.000 USD FSC = 15.600.000 USD, Auxiliary works = 1.580.000 USD Total cost 84.000.000 USD

Hence the cost per KW is estimated to 840 USD For alternative materials or shape of construction for the FSC the following table 7.1 indicates approximately the cost of the STPS per rated KW. Cost of the STPS in USD / rated KW NH3, glass NH3, Al He, glass 840 895 880 874 930 915 He, Al 978 1010

Shape C Shape B

8. Optimizing dimensions for STPS.
Using the equations of appendix I it can be proved that the increase of the height of the FSC of the STPS increases its power output and its efficiency. As an example let us consider STPS of rated power of 100 MW with Dc=1770 m, d=70 m, and height H=3500 m. Varying its height from 2500 m to 5000 m its maximum power output (and its efficiency), is increased as shown in fig.9. Increasing the height H and keeping the solar collector diameter Dc constant, there is an increase only in FSC’s construction cost thus the STPS cost per rated power output decrease as shown in fig.10.
d=70 m,Dc=1770 m,G=800 W/sqm,k=1.667,a=1.1058,T0=303.2,p0=101000 Pa 150

d=70 m,Dc=1770 m,k=1.667,a=1.1058,Gav=800 W/sqm



Maximum Power output in MW


construction cost in USD per rated KW



FSC with Al and NH3








70 2500


3500 4000 Height of the FSC in m



750 2500


4000 3500 FSC Height in m



Figure 9

Figure 10

It can be proved using the equations in appendix I, that in order to double the power output of a STPS, keeping its FSC ’s height H constant we should multiply the collector diameter Dc and the chimney internal diameter d by 2 . Taking into consideration that the cost of the FSC is roughly proportional to d it is evident that making the STPS with bigger power output the cost per KW of rated power decreases. In fig.11 the construction cost in USD per rated KW is shown for STPSs with FSCs (Al, NH3) with increased dimensions d and Dc proportional to square root of rated power output. It is evident that the construction cost per rated KW is decreasing with the increase of power output. However making the internal diameter of the FSC larger or its height bigger depends on its material construction behavior under unpredictable external conditions, that their effect cannot be accurately considered due to their nature. I believe that the experience that could be accumulated, as similar constructions will be materialized, will give the opportunity to optimize the dimensions of the FSC and solar collector in order to minimize the construction cost per rated KW.

H = 3 5 0 0 , k = 1 . 6 6 7 , a = 1 . 1 0 5 8 , n T= 0 . 8 , G a v= 8 0 0 W / s q m


construction cost in USD per Rated KW F S C w it h A l a n d N H 3

d a n d D c p ro p o rt io n a l t o s q rt (P ra t e ), in it ia l va lu e s 7 0 m & 1 7 7 0 m





0.76 100



400 500 600 700 S TP S R a t e d P o w e r O u t p u t in M W




Figure 11 For the time being we have shown, that under reasonable assumptions, the cost of STPS with a FSC of 3500 m and rated power outputs of the order of 100 MW can be less than 1000 USD/KW, if is installed in appropriate sunny places, of average annual solar irradiance of 800 W/m2. If the height of its FSC or its power output is increased, the construction cost could be less than 700 USD per rated power output. These STPS will have efficiencies including night operation that will range between 4.5% to 7.8% for FSCs with heights 3000 m up to 5000 m and will produce 3 MWh per KW of rated power output, per year.

9. Conclusions
A novel idea of designing and constructing solar chimneys as lighter than air floating in the air constructions is presented in details. These solar chimneys are named floating solar chimneys (FSC). Solar power stations working with appropriate air turbines named solar turbine power stations (STPS) using FSCs could be low cost electric power production units, completely friendly to the environment. The basic materials for constructing FSCs are fabric similar to that used in balloon or airship applications, aluminum, or reinforced glass and aramid ropes. The basic materials for constructing the solar collector are glass and steel. The experience gained already by the wind turbines and the electric generators for them should be used in order to design the appropriate turbo generators for the STPS. I believe that STPSs have to play an important role in order to release the power production industry by harmful fuels and their negative results to the environment.

[1] Schlaigh J. 1995, “The Solar Chimney : Electricity from the sun” Axel Mengers Edition. [2] Gannon A. , Von Backstrom T 2000, “Solar Chimney Cycle Analysis with System loss and solar Collector Performance”, Journal of Solar Energy Engineering, August Vol 122/pp.133-137. [3] Von Backstrom T, Cannon A. 2000, “Compressible Flow Through Solar Power Plant Chimneys”. August vol 122/ pp.138-145. [4] Von Backstrom T. 2003,“Calculation of Pressure and density in Solar Power Plant Chimneys“, Journal of Solar Energy Engineering, February 2003, Vol125 pp.127-129 [5] Papageorgiou C. 2004 “Solar Turbine Power Stations with Floating Solar Chimneys”. Proceedings of Power and Energy Systems, EuroPES 2004. [6]Papageorgiou C. 2003, “Floating Solar Chimney” PCT/GR03/00037/27-03-2003 [7] Papageorgiou C. 2004, “External Wind Effects on Floating Solar Chimney”. Proceedings of Power and Energy Systems, EuroPES 2004. [8] Papageorgiou C. 2004 “Wall Construction for Floating Solar Chimneys” Patent G.R. 20040100092/16-03-2004

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