Cost/efficiency
Zaslavsky, et al., estimate that depending on the site and financing costs, costs would be in the range of 1-4 cents per kwh, well below alternative energy sources other than hydro. Pumping the water requires about 50% of the turbine's output. Zaslavsky claims that the Energy Tower would achieve up to 70-80% of the Carnot limit. If the conversion efficiency turns out to be much lower it is expected to have an adverse impact on projections made for Cost of Energy.
Projections made by Altmann and by Czisch about conversion efficiency and about Cost of Energy (cents/kWh) are based only on model calculations, no data on a working pilot plant have ever been collected.
Actual measurements on the 50 kW Manzanares pilot solar updraft tower found a conversion efficiency of 0.53%, although SBP believe that this could be increased to 1.3% in a large and improved 100MW unit. This amounts to about 10% of the theoretical limit for the Carnot cycle. It is not unreasonable to expect a similar low conversion efficiency for the Energy tower, in view of the fact that it is based on a similar principle as the solar updraft tower.
Read more about this topic: Energy Tower (downdraft)
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