ROI from solar tower and Value adding design thoughts

http://www.solar-tower.org.uk/la-paz-solar-tower-project.php

Looking through this article the other day I was curious to know how and when the solar tower would be paid off, based on the numbers provided.

They stipulate $6.6mil per year for 30 years - so thats 198Mil excluding growth (if any). I doubt the 6.6 mil will be for all the output. I think previously the SCCPA was only for 106 of the 200MW.

The Cost of the tower is approx 750mil.

If you had tourism dollars (say 100,000 vistors per year at $20 per head - so thats 60Mil in 30yrs.

So the return on investment has to occur over a significantly longer term than 30 years. if 106/200 is 6.6 mill then total income is 12.5mil so $750/ 12.5 = 60 years to break even this seems ridiculous or 55 i you have 60mil in tourism.

How else would it generate income? tax rebates, carbon offset?  

The articles shows some more detail about technical info - I wonder how close this article is to the design?

I have often wondered if EVM could increase the output by adding turbines in series (outer ring and inner ring etc) and what impact would that have (obviously less turbulence is better).  Could you have more output by putting in another row of turbines or having them in the chimney section. Ie have a series of VAWT (turbulent flow is okay) on trusses in the chimney. Once you have generated the airflow you surely can use more of it than just one row of 32 turbines. Could they get a 500MW station?

Would there be any benefit in having a direction vent structure on the top of the chimney so a 35mph wind doesn't cause a weird vertical airflow that cause enviro problems.

Being fanciful - Could they use an Insulated (air filled) fabric and GPS lock balloons to make the chimney taller than a concrete one to increase temp differential and thus increase airflow.