GreenTower
1. Why must the chimney be so high?
2. Will the high chimney collapse under its own weight and pose a high risk?
3. Can the large chimney be blown over by heavy storms?
4. Can the high chimney be replaced by a shaft in a mountain?
5. Is the high chimney above the turbine really necessary?
6. Is it true that a chimney fell down?
7. Does this high chimney pose a threat during a catastrophe?
8. Has this Updraft Tower (Solar Chimney) / GreenTower ever been tested?
9. Is the leap from a small pilot to a 200/400MW plant not too risky?
10. Why is agriculture in the GreenTower more profitable than in standard greenhouses?
11. Are there additional advantages of humus?
12. Does vegetation in the greenhouse reduce power production?
13. Will the huge greenhouse not become too hot for plants?
14. Where does the water for the greenhouse come from?
15. Doesn't the huge collector waste too much land?
16. Does the enormous glass collector require cleaning?
17. Will hail not damage the glass of the huge collector?
18. Is the big greenhouse/collector a threat to or a blessing for the environment?
19. How can the GreenTower produce power during night hours? Can it produce peak power?
20. Isn't energy storage too expensive?
21. Doesn't power production decrease too much in winter?
22. Will the huge structure's cost of building and dismantling not be prohibitive?
23. Will a GreenTower without greenhouse be feasible?
24. Does the recently quoted cost of 8€cent/kilowatthour for Prof. Schlaich’s Updraft Tower (Solar Chimney) contradict the GreenTower price of 1,5€c/kWh?
25. Isn't the power delivery of 120MW in a recent paper by Prof. Kröger contradicting the values here presented?
26. Are there cheaper power technologies than the GreenTower?
27. Hasn't the GreenTower the lowest efficiency?
28. Can efficiency of the GreenTower be raised?
29. Is the technology protected by patents?
30. Can the GreenTower produce power with an overcast sky?
31. Where are GreenTowers / Updraft Towers (Solar Chimneys) coming up at present?
32. Can the GreenTower become a trigger for non-polluting transport technologies?
33. Isn't the chimney mainly driven by a Venturi effect at the flue top?
34. Can the solid chimney be replaced by a light weight structure to be held up by balloons?
35. Will the strong winds in the greenhouse affect the plants negatively?
36. Can the plants stand the high temperatures of a hot summer day + additional heating?
37. Will the shadow from the nets reduce plant production in the greenhouse?
38. Will the daily 22 hour airtight separation of corresponding greenhouse compartments for re-condensation of water during night hours cause CO2 deficiencies?
39. Will the puddles of re-condensed water on the floor cause root diseases?
40. Will certain (pseudomonas) bacteria in the soil, which are normally removed by frost, not cause serious root diseases?
41. How do you remove seeds from preceding crops from the greenhouse soil?
42. Will the big greenhouse's soil-based agriculture not sustain all sorts of plagues?
43. Will the intensive GT agriculture not exhaust the soil very fast?
44. Will the high greenhouse production not starve through nitrogen deficiency?
45. Is this humus agriculture not very expensive and thus financially risky?
46. What is the difference between CO2 sequestration and avoidance (Kyoto Protocol)?
47. Who will finance these new power stations?
48. Will the international finance crisis influence the GreenTower project adversely?
49. Is the German Federal Ministry of the Environment (BMU) biased against the GreenTower?
Also see Risk Assessment [5.] for questions and answers.
Q.1. Why must the chimney be so high?
ANSWER: The driving force in the GreenTower is the weight difference between the hot light air inside the chimney flue and the corresponding heavy cold outside air. Only a 60 km tall chimney would utilise this buoyancy in full. A 1,5 km flue only uses 15%, whilst in this domain sucking power is ± proportional to height. By reducing the height to 1,0 km or 500 m the sucking power is reduced to 2/3 or 1/3 respectively. Due to the lower updraft the air stays longer in the collector and gets hotter thus raising the collector glass temperature, which radiates in the infrared optical window of ± 10μ with an intensity of the fourth power of the absolute glass temperature. These combined huge collector and chimney losses reduce power output to 57% or 7% with a 1,0 km or 500 m flue and 7 km-collector diameter. A smaller flue does thus not make sense.
Q.2. Will the high chimney collapse under its own weight and pose a high risk?
ANSWER: No: A C85 (85MPa minimum strength used here) upright concrete pipe of constant wall thickness will collapse under its own weight only at 3 100 m. However, no engineer would design a flue with constant wall thickness but increase it downwards to limit pressure forces. Hence any engineer can by over-designing build such a chimney to be safe but at astronomic cost.
The art is to design such a wide-footed (± 200 m average diameter) cooling-tower-like flue thin-walled at affordable cost without compromising on safety. As groundbreaking research on structural risks and failure mechanisms of cooling towers was done in Germany, the risk of failure is now extremely small, if the safety rules and the relevant high construction standards are applied. Hence these German experts of the Bureau Krätzig in Bochum and Wuppertal University with the world’s highest safety record were taken on board so that this will be one of the safest structures ever built.
Q.3. Can the large chimney be blown over by heavy storms?
ANSWER: This allegation has been made several times but is totally unfounded. The basic design wind speed at 10m height from the ground is 161km/h and in gusts 216km/h and 213/245 km/h respectively at a height of 450m, which values are taken from international standard tables. For most of Southern Africa, Arabia, India, Australia etc. such a GreenTower is significantly over-designed especially with its high safety factor. In hurricane areas construction will be adapted to higher wind loads. The wide-footed chimney is much less affected than high-rise television or office towers.
Incidentally, the real risk does not lie in steady high wind speeds but in periodic gusts coinciding with the flue’s resonance frequencies, the most common reason of failures. The foremost experts on this, Profs. Niemann and Höffer with the world’s leading wind tunnel research facility, were also taken on board and have already established that atmospheric gust strength decreases with rising flue height and vanishes at 1 500 m. The close co-operation between the Bureaus Krätzig and Niemann will address all possible risks and minimise them to practically zero.
Q.4. Can the high chimney be replaced by a shaft in a mountain?
ANSWER: No, since the excavation costs are prohibitive due to blasting etc. At €100 per m³ the cost would amount to €3b for the vertical shaft alone. Where is a plane with a slope of not more than 2° for the collector to be found directly alongside a vertical 1’500m steep rock? Uneven distribution of the collector with respect to the "chimney" will cause high flow resistance.
Q.5. Is the high chimney above the turbine really necessary?
ANSWER: This often asked question is caused by the misconception that the cold air of the atmosphere is pushing the light air inside the chimney upwards. Indeed, the higher average random speed of the hot air's molecules inside the chimney accelerates it towards the top so that a sucking action will keep the pressure inside collector and chimney below atmospheric pressure, with pressures being equal at the chimney top. Hence by cutting the chimney just above the turbine one would remove the sucking force and the updraft.
To operate the machine without chimney one needs to put up internal pressure and to convert the collector into a high-pressure vessel with fans at the periphery to press cold air in against the internal pressure for continuous operation. Obviously this structure would be more expensive by orders of magnitude than the, compared to its size, extremely cheap collector.
Q.6. Is it true that a chimney fell down?
ANSWER: The non-permanent chimney of the pilot plant in Spain with a design life-span of three years, the first lease period, was blown over in a heavy storm after nine years of service due to rusted guys, where the state funds for their replacement arrived just too late due to cumbersome bureaucracy. This misleading argument is often used by competitors.
Q.7. Does this high chimney pose a threat during a catastrophe?
ANSWER: No. Like any structure it can be destroyed by sabotage but loss of life will be less than with any other power technology. Even if the 1 500m flue tumbles side-wards, it can only hit the inner dry part of the GreenTower (radius = 2km), where normally only three persons are present. Greenhouse workers are automatically protected by shadow nets against broken glass.
Since GreenTowers are designed to withstand all natural disasters like storms, earthquakes etc. at the specific site, failure due to natural disasters is completely unlikely.
Nuclear power stations pose a threat to the entire region, hydro power stations a threat to the whole downstream valley. Coal-fired power stations pose a threat to the people working inside the power block (40 per shift) and nearby villages if the fuel stockpile of coal dust is blown up, which has one third of the blasting power of dynamite. Also oil- and gas-fired power stations pose serious threats to the neighbourhood. Oil spillage causes serious threats of fire and environmental pollution during storage and transport.
Q.8. Has this Solar Chimney (Updraft Tower) /GreenTower ever been tested?
ANSWER: A pilot plant in Manzanares with a chimney height of 200m, a collector diameter of 248m (without greenhouse) and a power generation of 50kW has been tested in Spain from 1982 to 1989. Predicted and measured values of power production for one year coincided within half a percent. After the falling down of the chimney in 1989 the German Department of Science and Technology financed a study Transferability of Results from the Manzanares Solar Chimney Plant to Larger Scale-Plants. This study has been reviewed and advanced much further by Prof.Kröger of ITM, Stellenbosch University and will eventually result in an insurable expert opinion. See also Question 9.
The pilot plant in Manzanares hit a world record in reliability by running seven years without a single second downtime on faults, operating for 32 months in fully automatic mode. The GreenTower represents thus the most reliable technology.
Q.9. Is the leap from a small pilot to a 200/400MW plant not too risky?
ANSWER: No, since the chimney structure will be completely insured against design and building failures. Construction will be double-checked. Power production is also completely insured, based on the guaranteed expert opinion of Prof. Kröger, University Stellenbosch.
To that end the collector area increase required to compensate the shortfall in power production will be insured. This will at the same time increase the greenhouse area by 150% of the collector area added. Hence the insurers carry no risk, since the additional greenhouse income will quickly pay for the additional collector area. This will lead to nearly negligible insurance rates.
Aeroplane manufacturers normally use a linear scale of 1 : 10 for wind channel models, the Solar Chimney uses the linear flow dynamic scale of 1 : 7,5 (200m : 1500m chimney height). Prof. Kröger's calculations, supported by large collector model testing, will easily meet the accuracy required by the insurance company.
Q.10. Why is agriculture in the GreenTower more profitable than in standard greenhouses?
ANSWER: One reason is that in desert areas standard hothouses use huge amounts of costly sprayed water to keep plants cool. The GreenTower's hothouse is air cooled at no cost.
Drip irrigation with collapsible, removable piping allows the use of machines contrary to other hothouses and ensures the lowest possible production cost as also the most efficient use of vegetation-evaporated water, which is re-condensed during night and early morning hours.
Humus in the greenhouse soil (volume content between 12% and 25%) ensures a root growth of up to 1m in three days, exceptionally high yields and a low cost organic agriculture with 30% higher prices through automatic nitrogen generation by microbial assimilation in humus soil at no cost. Due to antibiotic bacteria in humus no pesticides etc. are required.
Q.11. Are there additional advantages of humus?
ANSWER: Yes. Due to its extremely high internal surface (up to 1km²/g!) humus retains water like a sponge. It will not evaporate water to the air but only release it together with stored plant nutrients to the roots. These qualities supply an additional huge thermal store in the soil of the greenhouse and allow easy soil entry of re-condensed water under the shadow nets.
Humus generation and insertion into the soil will trap huge amounts of CO2 and improve soil structure decisively. GreenTower humus is a saleable commodity of high value and will automatically feed adjacent irrigation projects, since humus does not develop naturally in arid areas and will be manufactured in the GreenTower in large quantities. Therefore every GreenTower in a desert will automatically become the centre of a constantly growing oasis. Large-scale use of GreenTowers can reverse the effect of global warming.
Q.12. Does vegetation in the greenhouse reduce power production?
ANSWER: At first glance the evaporation of water due to vegetation in the greenhouse seems to reduce heat generation through latent heat losses. However, since the heat transfer from plants to air is about five times greater than from a plain surface to air, the plant cover stays correspondingly cooler and loses much less infrared radiation to the glass and to the sky (loss proportional to T^4, T in Kelvin). This over-compensates the latent heat losses so that vegetation improves heat generation and power production. This has been proved, also experimentally, by the Institute of Thermodynamics and Mechanics (ITM) at Stellenbosch University. With the newly developed infrared reflection layers at the bottom side of the collector glass IR losses and the above compensation will be much smaller. Therefore re-condensation is applied, saving all evaporation energy.
Q.13. Will the huge greenhouse not become too hot for plants?
ANSWER: No, since the greenhouse only comprises the outer 2/3 area of the collector with a radius of 58% of the inner "dry and hot part". Continuously adaptable and controllable shadow nets above the plants shield them against too much sun and too hot incoming air, effectively separating the cool lower plant space from the hot top wind space at hot midday temperatures. The black shadow nets absorb a great deal of the visible light and transfer as much heat to the bypassing air as a closed plant cover.
The greatly diffuse visible radiation below the nets reaches a bigger plant surface and enhances, compared to full sun, assimilation, plant growth and evaporation, which cools the plants down.
Q.14. Where does the water for the greenhouse come from?
ANSWER: There is often underground water available in desert areas. This water, however, always requires pumping and often desalination, i.e. cheap emission-free power. In the case of Namibia and the UAE sea water will be desalinated. Hence the GreenTower in conjunction with humus production is the natural nucleus for oasis formation and (re-) cultivation of desert areas.
Q.15. Doesn't the huge collector waste too much land?
ANSWER: Due to the low energy density of solar radiation all solar technologies have the problem of large-scale land use to collect a meaningful amount of energy. Contrary to other solar technologies the GreenTower uses 2/3 of the land not only for collecting solar energy but also for high-intensity agriculture. Due to four yields in the greenhouse against one yield in high-intensity open air agriculture the GreenTower will, in fact, increase production to 270% and add a virtual 170% to the existing highly productive land. In deserts the effect will be even stronger.
Q.16. Does the enormous glass collector require cleaning?
ANSWER: No. The self-cleaning effect of the glass is sufficient to remove dust by rain or by wind. No cleaning was necessary at the pilot plant in Spain during nine years of service. The secret is that even muddy clay will brake up on the hot glass surface into very fine dust which is carried away by the slightest breeze.
Earlier on an automatic sand removing device was contemplated by Prof. Schlaich for heavy sand storm areas but not pursued, since such areas can in general be avoided. This might change with GreenTowers in the Sahara.
Q.17. Will hail not damage the glass of the huge collector?
ANSWER: With site selection areas of too heavy hail are avoided. Note that the glass panels are elastically supported and that the chance of breakage is lower with larger panels due to a wider distribution of impact energy. Heavy rain runs off through 2 mm gaps between the panels. During nine years of service not a single glass panel in the pilot plant in Spain broke due to natural causes even with more than pigeon egg size hail. All high solar radiation sites investigated in different countries have a lower hail risk. Hence the risk of glass breakage is negligible. Tempering the glass at modest cost can make it completely hail-resistant.
Q.18. Is the big greenhouse/collector a threat to or a blessing for the environment?
ANSWER: In 2000 a big South African utility assessed that the GreenTower's large greenhouse/collector would pose a serious threat to the environment and would require an exceptionally intensive impact study. This statement is invalid, because then all intensively used agricultural areas would require such environmental impact assessments. Due to the high humus content in the GreenTower's soil and its very high adsorption of plant nutrients these cannot leach into the ground-water. No emissions to the atmosphere occur.
Since all unsold plant matter in the GreenTower is converted into humus and is ploughed into the soil, this desert soil becomes extremely fertile and water retaining, also for related irrigation projects. Hence the GreenTower's "environmental impact" is extremely advantageous. In fact, GreenTowers will become nuclei of ever increasing oases in desert areas.
Enormous amounts of CO2 per GreenTower including related irrigation projects are trapped/sequestrated in the soil, i.e. up to the equivalent of 2 000 MW of coal-fired power station emissions. Hence the GreenTower presents at present the quickest way to compensate for CO2 emissions and to reverse the CO2 threat to the atmosphere, for which it is, so to speak, the best vacuum cleaner.
Q.19. How can the GreenTower produce power during night hours? Can it produce peak power?
ANSWER: Due to its high heat capacity water, covered by plastic sheeting, will absorb much heat during the day in these thermal energy stores and release it to incoming cold air during the night. A 20 cm water layer will equalize power production over a 24 hour period. 1,2 m deep controllable water ponds store and release heat for 6 days.
A very effective means has been developed to stop or magnify heat transfer from these quick-response thermal energy stores so that power generation can be increased from 10% to 100% within four minutes. Hence high-priced peak power can be delivered at any time. Additional seasonal storage can be supplied at very modest cost.
By increasing the collector size to 37,5 km² (diameter = 6,9km) full power production throughout the 24 hour cycle is achieved. By switching off related irrigation schemes (pumping, desalination) during high demand periods their power can be fed into the grid as peak power. The more water is desalinated the more high-priced peak power can be sold.
Q.20. Isn't energy storage too expensive?
ANSWER: In the 1997 pre-feasibility study for the Sishen project in South Africa the tenders showed that a thermal energy store for the inner dry section added only 5,7% to the (dry) investment cost. The present re-designed 6-day quick-response store will even be cheaper. Re-condensation in the 2/3 greenhouse section will additionally act as an (medium-response) 24h thermal energy store at no extra cost due to controllable heat release through the shadow nets. The cheap quick-response energy store is one of the great advantages of the GreenTower.
Without energy store the power station would only utilize one third of the possible power production and lose 2/3 of power revenues. Moreover, most of the power produced would be useless, since at the times of high demand, in the morning and after sunset, little or no power would be available. Against this background the additional 5,7% investment for the energy store is financially very rewarding, increasing the power revenues from 30% to 100% and the plant load factor from 30% to 89%.
Q.21. Doesn't power production decrease too much in winter?
ANSWER: In a recently published paper Prof. Kröger showed for the Sishen site that power production in July would only reach 50% of the January production. The intrinsic reason is that for this horizontal collector power generation is very roughly proportional to the third power of the cosine of the midday solar altitude off the vertical (not too far from the equator).This contra-productive high seasonal power variation will completely be flattened out through:
* a new seasonal rock store;
* an IR-reflecting layer (10μ, reduced IR radiation loss during clear winter nights);
* pump storage from the irrigation dams of the greenhouse and related schemes;
* no power consumption by related irrigation schemes during the frost period in winter;
Q.22. Will the huge structure's cost of building and dismantling not be prohibitive?
ANSWER: The present estimate of €460m for a "dry" 400MW GreenTower (without greenhouse), which compares well with €500 for a 400MW coal-fired power station including gas and particulate cleaning, is based on tender prices in 1997 and 2002 and continuous upgrading. Since 1997 glass prices dropped by 60% (GreenTower's own solar glass factory + cast instead of float glass) and interest rates by 50%, staying low due to the “US Feds” aggressive low interest policy. Improved flue design also saves about 40%. Hence building and finance cost considerably decreased. Note that running cost of a GreenTower is less than 0,2% of investment compared to 2% + for fossil fuel of other technologies so that cost of power is nearly equal to cost of finance.
The greenhouse equipment like adjustable shadow nets, water piping, initial humus content etc. amounts to €90m with an overall price of €550m which, however, has to be seen against a threefold increase of revenues.
With a design life-span of 160 years the GreenTower has a minimum life-span of 80 years and will outlast 2 nuclear reactors (40 years), 2,7 coal-fired power stations (30 years) and 4 gas-fired combined cycles (20 years). The respective 80 year life cycle costs are according to the pre-feasibility study of 1997 for a Solar Chimney (without greenhouse) in the Northern Cape Province (page 204), South Africa: GT = R5 312m; Nuclear = R23’543m; Coal-fired = R17 430m; gas-fired CC = R29 919m. Hence the extremely long life-span of the GreenTower is also extremely cost saving. The cost of power (including finance) amounted to 4,26Rc per kWh against 7,00Rc for half depreciated coal-fired power stations without gas cleaning (Eskom).
Dismantling of the GreenTower will not be necessary within the foreseeable future, since even without turbine the greenhouse can still be used. After 160 years it would surely pay to fit a new turbine of higher efficiency, since the structure has a much longer life expectation due to heavy steel galvanizing, pozzolanic concrete (Roman buildings still stand today) and glass lasting hundreds of years (European cathedrals).
Once it is paid off the GreenTower, even without greenhouse, will not become obsolete with the arrival of new technologies, since they will not easily match its very low cost of power.
Q.23. Will a GreenTower without greenhouse be feasible?
ANSWER: Yes, it will, as can be seen from the figures in the preceding answer.
Q.24. Does the quoted cost of 8,0€cent/kilowatthour for Prof. Schlaich’s Updraft Tower in 2008 contradict the GreenTower price of 1,5€c/kWh?
ANSWER: By no means, since the Updaft Tower’s efficiency is much smaller due to a smaller flue height of 750 m to 1 000 m (see Q.1), only half of the present GreenTower efficiency, the lack of greenhouse revenues (more than double of power revenues) and the lack of CO2 certificate revenues, the latter presently fetching €540 million or 98% return on capital at €30/ton CO2. These high revenues ensure the shortest pay back period and lowest finance cost. Hence 80% of the GT’s 1,5€c/kWh can be seen as pure profit.
Q.25. Isn't the power delivery of 120MW in a paper by Prof. Kröger contradicting the values here presented?
ANSWER: No, since the very low maximum power output of 115MW in the paper Performance Evaluation of a Solar Chimney Power Plant at the 2001 ISES congress in Australia represents the worst case according to the understanding with our company (compare Q.9), whilst the best case is beyond the envisaged 400MW power delivery mark. This surprisingly great difference is caused by the small weight difference (buoyancy) between the much heavier inside and outside air column. Small errors in the latter will multiply with the calculation of the difference and inflate the error in buoyancy. The minimization of this difference in power generation to less than10% for insurance purposes is one of the main tasks of the feasibility study.
In addition none of today's design improvements were included like the use of solar glass, anti-reflection layers at top and bottom of the glass, IR reflection layer at the glass bottom in the whole collector improving power output over the whole collector area, streamlined support profiles, boundary layer fences, optimization of the collector parameters etc. With these improvements even this first worst case result will not be far below the envisaged 400MW. The refined calculations will surely meet this power output.
Q.26. Are there cheaper power technologies than the GreenTower?
ANSWER: No, since due to the high greenhouse revenues power can be given away for free. But even the GreenTower without greenhouse has at present no competition after it has been paid off (see Question 22). Even written off hydro power stations have considerably higher running costs.
Sometimes people are confused by very low power prices from (East Block or French) written off nuclear power stations, the capital layout of which has been carried by the state for strategic reasons. These prices might become even lower, if these power stations try to catch business to improve their plant load factor. These prices are, however, below cost and not sustainable, since new nuclear power stations are extremely expensive, also with respect to future storage of nuclear waste (5,5 to 6,0€c/kWh).
Whilst hitherto photovoltaic cells represented the most expensive power technology, Boeing's Spectrolab Inc. claims that their new cells challenge the presently cheapest power technologies: The cells consist of flat concentrators (400 suns) and small triple junction high performance cells with an efficiency of 34%. Mass produced future cells would only cost 0,5 US$/W. However, these cost estimates are misleading, since the price of present day cells doubles in practical use through the necessary energy storage, controls etc. Therefore the price reduction for the full sets is less than 50%. Hence Spectrolab's surely remarkable cells will not challenge the GreenTower's low cost of power within the foreseeable future, also since they lost the advantage of using diffuse radiation.
Q.27. Hasn't the GreenTower the lowest efficiency?
ANSWER: Generally speaking, this is true at present, although apples are often compared with pears. Large concentrating technologies do for efficiency purposes not refer to the total surface required for their devices, large arrangements of parabolic or trough mirrors, but only to the aperture of these devices, although the land in between cannot be used for anything else. They also do not refer to their high production losses with an overcast sky.
After all, the decisive parameter is not efficiency but the cost of the solar field (including plant load factor) for a given power output, since sunshine is free. Incidentally even with the present low efficiency of 2% to 4% the Updraft Tower without greenhouse has the lowest solar field costs of all solar technologies, whereby the GreenTower will cut them by a further 67%. Only Updraft Tower/GreenTower solar field costs are lower than the fuel costs of conventional power stations.
Q.28. Can the efficiency of the GreenTower be raised?
ANSWER: Very much so. With today´s new design collector efficiency will most probably exceed 90% and the temperature at the turbine will reach 76°C above ambient. With a resulting Carnot efficiency of 26% the practical limit of real efficiency will be 14%, related to 1 400MW for a GreenTower with the specifications of GT Short Executive Summary. The development potential is thus very high. Since the loss areas are well defined and will be attended to in the feasibility study, considerably more than 400MW will be produced in the future GreenTowers. With 14% efficiency it will compare well with present day mono-crystal photovoltaic cells.
Q.29. Is the technology protected by patents?
ANSWER: With the present stage of development about 34 patents have already been applied for or are in preparation.
Q.30. Can the GreenTower produce power with an overcast sky?
ANSWER: Yes, contrary to all concentrating solar technologies, since the GreenTower also utilizes diffuse radiation. The effect is enhanced through a sharp increase of collector efficiency due to a sharp increase in infrared radiation from clouds. Overall annual production has been found to be equal for sites in Ghana and Kenya, although solar radiation in the latter is significantly higher.
The GreenTower is thus very well suited for the tropical belt. It will in general generate the cheapest power in the belt between 30° north and 30° south. This belt can be increased to 55° south and 55° north through 1,6 megavolt DC power lines for quantities ≥ 20 000 MWel due to then low transmission cost and losses (0,25€c/kWh for 3 300 km, power loss = 10%). Including its environmental advantages the GreenTower has the potential to supply 70% of the world’s future power.
Q.31. Where are GreenTowers/ Updraft Towers coming up at present?
ANSWER: GreenTowers are to be built in Namibia. The Updraft Tower in Mildura in Victoria, Australia seems to have lost its base of finance. Presently Prof. Schlaich is pursuing a 750 m Updraft Tower in Spain. Interest for GreenTowers has also been shown from many other countries, which can unfortunately not be disclosed at present due to the confidential nature of the negotiations.
The first place where an Updraft Tower was to be built (1996) was the Radjastan Province of India. The imminent danger of a war between India and Pakistan made Radjastan the likely battle field. Hence investor's interest vanished for the time being.
Q.32. Can the GreenTower become a trigger for non-polluting transport technologies?
ANSWER: Very much so, since emission-free power transport technologies like battery cars and vehicles running on compressed air or hydrogen require an emission-free, cheap primary power source not to become an environmental and economic nuisance: Drawing power from an oil-fired power station results in an overall efficiency of 16% at the car’s gearbox due to the many steps of energy conversion, whilst modern diesel-engines exhibit an average 33% efficiency: Using polluting primary energy for non-polluting transport often results in doubling (CO2) emissions.
The GreenTower generates not only emission-free power but also at the lowest possible price, so that hydrogen fuel, generated by electrolysers at the fuel-station, would today be cheaper than untaxed diesel-fuel at present crude oil prices.
Q.33. Isn't the chimney mainly driven by a Venturi effect at the flue top?
ANSWER: No. For the small pilot plant in Manzanares the venturi effect contributed less than 1% to power generation. For the 1 500m chimney the contribution is obviously much smaller.
Q.34. Can the solid chimney be replaced by a light weight structure to be held up by balloons?
ANSWER: Only if there is no wind from the side and the flue could stand 0,15 bar pressure difference! The envisaged light weight structure would not be stiff enough to stand the wind load, would fold and stop the updraft. Stiffening rings with guys to the ground would increase the downwards force and require enormous balloons, which in turn would increase the wind load requiring stronger guys with higher downwards forces etc.
Q.35. Will the strong winds in the greenhouse affect the plants negatively?
ANSWER: No, since the horizontal shadow nets will effectively separate the air space above and below. Strong winds will only occur above the nets.
Q.36. Can the plants stand the high temperatures of a hot summer day + additional heating?
ANSWER: The continuously adaptable shadow nets will limit the visible radiation below in a controlled manner during the day, so that incoming radiation, causing heat, will be restricted. Water evaporation associated with CO2 assimilation during the day causes strong cooling, so that these combined effects keep the plants always below the stress temperature.
Q.37. Will the shadow from the nets reduce plant production in the greenhouse?
ANSWER: On the contrary: With a 50% translucency of the shadow nets the visible radiation is nearly 100% diffuse, reaching all parts of the plants and not only the top leaves. Assimilation and plant growth is thus much higher as also cooling by evaporation.
Q.38. Will the daily 22 hour airtight separation of corresponding greenhouse compartments for re-condensation of water during night hours cause CO2 deficiencies?
ANSWER: No, since additional CO2 will be supplied from other GT sources at no cost.
Q.39. Will the puddles of re-condensed water on the floor cause root diseases?
ANSWER: No, since the soil will absorb the condensed water like a sponge due to its high humus content and distribute it evenly in the soil through the fine humus capillaries.
Q.40. Will certain (pseudomonas) bacteria in the soil, which are normally removed by frost, not cause serious root diseases?
ANSWER: In the GT greenhouse frost does not occur, but the killing of these germs can also be done by heat. With open shadow nets at mid-day 90°C at the soil surface will kill them.
Q.41. How do you remove seeds from preceding crops from the greenhouse soil?
ANSWER: Even with meticulous working one cannot remove all seeds before planting a new crop. One thus prepares the soil well and let the seeds germinate. A temperature of 90°C (shadow nets open) and no water will kill the unwanted shoots. As the wanted crop is planted thereafter, the old seed cannot interfere anymore.
Q.42. Will the big greenhouse's soil-based agriculture not sustain all sorts of plagues?
ANSWER: This would be true with a standard soil but is not true with the GT's humus soil, containing high concentrations of natural antibiotics, which will check all plagues. The very fast root and plant growth in the GT often causes the plant to outgrow the plague/disease.
Q.43. Will the intensive GT agriculture not exhaust the soil very fast?
ANSWER: The assumption underlying this question is that all nutrients for a given crop have to be added to the soil before planting. In general, however, the nutrients are already in the soil. It needs the right microbes to break these mineralized nutrients down and to make them root accessible. As the GT's special humus will enhance soil life by the factor 1’000, all the necessary microbes will be present and will find the best possible environment to abundantly supply plant nutrients. The more humus is present in the soil and the better the quality, the more new high quality humus will be formed from old root material, as artificial resting periods for the soil can be managed in the GT greenhouses.
Q.44. Will the high greenhouse production not starve through nitrogen deficiency?
ANSWER: As nitrogen assimilating bacteria, free-living in the soil, can supply enough nitrogen to the plants, if the humus content in the soil exceeds 10%, 12% humus and the corresponding bacteria will be added to the soil (33cm deep) at the beginning. Thereafter no further nitrogen fertilization will be required.
Q.45. Is this humus agriculture not very expensive and thus financially risky?
ANSWER: At present eight million tons of "mature compost" have been offered to GreenTower Ltd free of charge and f.o.b. port North Sea. As the big SA ore freighters return home empty from the North Sea ports, the compost transport will only cost cheap back freight charges of around €6,00/ton. Adding another €6,00/ton for rail transport the cost for the first humus lot (600 000ton/GT) will be around €14m/GT on site Aransis (Namibia), i.e. negligible compared to its financial benefits. The composting units now under design will be very cheap in relation to turnover. Hence the GT humus agriculture is significantly more rewarding in financial terms than its current power production, which in turn is the most rewarding of all present power technologies.
Q.46 Is there a difference between CO2 sequestrating and avoiding (Kyoto)?
ANSWER: There is indeed an important difference. The aim of the Clean Development Mechanism of the Kyoto Protocol is to help developing countries avoid coal-fired CO2 emissions by building for instance a solar instead of a coal-fired power station, financed by a developed country, which then uses these CDM certificates to subtract the “avoided CO2” from its own emissions. This mechanism was later extended to individual CO2 emitters. Present EU legislation restricts these CDM certificates obtained in developing countries to 22% of total emissions of a certain EU emitter. A 400MWel GreenTower power station in Namibia with a plant load factor of 90% thus avoids/neutralizes for instance the CO2 emissions of a 400MWel coal-fired power station in Germany, if it were fully financed by this emitter.
To illustrate the difference of direct sequestration we look at a power plant of German utility RWE, where according to 2007 announcements CO2 will be separated from the flue gases before or after combustion. RWE intends to pipe this CO2 to former natural gas deposits and to bury it there, however, with a chance of less then 1% due to the inertness of CO2 and its very high diffusion. Instead of going into this low-chance exercise, they could pipe the CO2 to Namibia, where the GreenTower high-quality composting would transform it into high-quality, extremely stable humus with a carbon content of roughly 90%, which would stay in the soil for the next 10 000 years. But since it would not make a difference to the atmosphere, RWE could cut out the pipeline and release the CO2 in Germany, whilst the GreenTowers could sequestrate this amount in Namibia from the atmosphere. By releasing the CO2 in Germany the preceding CO2 separation would also be unnecessary and the gas could directly be released into the atmosphere and save RWE doubling the cost of power, as they themselves admit. Hence these GT CO2 sequestration certificates (± 15m ton CO2/y) per GT could be used by any emitter worldwide to reduce his CO2 emissions and liabilities, as long as it is certified by an accredited expert.
Q.47 Who will finance these new and “high-risk” power stations?
ANSWER: Since CO2 certificates in the EU are in deliberate short supply with steeply rising cost (presently €30/ton CO2), the only cost-neutral way for a emitter to reduce his liabilities is to invest in GT power stations, for instance in Namibia, and use his share of GT carbon certificates for CO2 compensation. These emitters in the EU mainly comprise coal-fired power stations, steel producers, cement producers, aluminium works, chemical industry, air companies, car producers, fleet owners etc. Though they might by lobbying buy some time in the near future, the lack of certificates would thus the more be felt in the mid-term. The present EU penalty for emitters not meeting their targets is €40/ton CO2 and will rise to €100/ton in 2013. Within short these emitters will queue up, since GT share participation is at present their only chance to stay in business without crippling CO2 costs.
Since China and India experience grave power shortages impeding economic growth, they quickly need to add new capacity, where the rich coal deposits of both countries would at first glance lead to new coal-fired power stations. But as both countries also experience great smog and pollution problems, the clean and significantly cheaper GreenTower power is the better option. Due to their high agricultural production GreenTowers could also be put in rice fields and would never compete with food production but rather enhance it. As both countries wish to raise exports to the EU they have to reduce their carbon emissions by GreenTower power stations. Whilst in China the state would finance them, India would probably supply state guarantees.
The new Australian government put itself in a corner by refusing new nuclear power plants and at the same time signing the Kyoto Protocol, thus being forced to strongly reduce CO2 emissions of its coal-fired power stations. Only the large GreenTower CO2 sequestration can presently supply the necessary carbon certificates, preferably in Australia itself. As the GreenTower is due to its 97% availability an excellent stand alone power plant and can well be used in the outback where most of the mining activities take place, the big mining houses could use this very cheap power for mineral beneficiation and add value to their precious minerals, the lack of which is a long-term concern of Australian economists. The government could facilitate and speed up this development by supplying state guarantees for the project financing of these GreenTower power stations. With GreenTowers taking over the Australian power market the price of power would constantly decrease.
Concerning the perceived "high risk" of the GT, see Questions 1, 2 and 3, or see Risk Assessment.
Q.48. Will the international finance crisis influence the GreenTower project adversely?
ANSWER: The advantage of the present financial crisis is the determination of the US Federal Reserve Bank to keep interest rates low, which forces other countries to do the same, facilitating the financing of GreenTower power stations. The stricter credit control will not impede GT project finance, as the power stations will be backed by state guarantees. The investors above will therefore not have to use their own capital so that to them the CO2 certificates will be cost-neutral. Another advantage is that the sliding US dollar forces China, Japan and the oil producing Arab countries to get rid of their huge dollar reserves and to invest it preferably in (their) infrastructure, where the GreenTower’s low cost of power, large-scale job creation, cheap water desalination, rewarding agricultural production and high CO2 sequestration are irresistible incentives.
Q.49. Why is the German Federal Ministry of the Environment (BMU) now opposed to the GreenTower, whilst the government formerly supported Prof. Schlaich’s Updraft Tower and financed a pilot plant in Spain?
ANSWER: Until 1994 the Section Renewable Energies (SRE, then Education & Research, now BMU) strongly supported the Updraft Tower (Solar Chimney), financed the pilot plant + further studies and committed itself to a further DM1million grant.
But since 1995 the new head, Dr. v. Stackelberg maintained, in violation of the earlier grants and commitments, that after financing the pilot plant (in 1989) the SRE saw, for the lack of economic viability, no reason to further support the Updraft Tower.
In 2002 the author (Wolf-Walter Stinnes) learned that all positive documents were removed from the corresponding BMU files. Though written proof of this was supplied to the BMWi (Economic Affairs) in 2002 and BMU in 2007, no action was taken
Dr. v. Stackelberg in 1995 also began, against all available evidence, spreading statements about production costs of more than DM1,00/kWh for the Updraft Tower and other solar-thermal technologies, denied their economic viability and in 1998 wrongly informed parliament that photovoltaics produced the cheapest solar power. Hence parliament decided on an exorbitant fee of DM0,99 (€0,51) for every PV-kilowatthour to be fed into the German grid, which would have, cost the German economy, according to the NWI (Essen), an unnecessary €31 billion, had this fee been discontinued by January 2008. As there is no chance to discontinue it now, the final damage to the German economy will be much bigger. Incidentally, Shell also started, in 1998, building the world’s biggest photovoltaic cell factory, the products of which had no market without this fee, but sold out in ± 2000 at a healthy profit. Pure coincidence appears quite improbable. Dr. v. Stackelberg was also actively engaged in spreading wrong information about the GT and has caused severe damage to the GT project.
When in 2007 a GreenTower expert team presented 18 fundamental GT improvements on the Solar Chimney (Updraft Tower) to the BMU, also asking for BMU participation in the GreenTower pre-feasibility study in Namibia, the BMU reply rejected this by invalid pretensions, neglecting all improvements mentioned above. It also omitted the offer for CO2 certificates, though desperately needed by German industry and (air) traffic. This strange reaction might be explained by a contribution of the environment economist, Prof. Richard Tol (Dublin-Hamburg-Amsterdam-Pittsburg) in the German newspaper Handelsblatt on 28.12.2007: “The climate policy of the Federal Government is directed by a belief in planned economy … Controls and prices are … not determined by the market. Many of today’s subsidies have the smell of nepotism”. As the BMU letter/website also contains basic errors regarding the physics of solar power generation, the BMU cannot be regarded competent or unbiased with regard to the GreenTower. This also holds for BMU-related other bodies.
The low GreenTower power price and other unique advantages provoke, seemingly, unfair competition.
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Environmental Impact and Human Health
The Greenhouse Short Executive Summary
Frequently Asked Quenstions Working Mechanism