Tower cost calculation equation

Hello,

This question is about the calculation of tower system cost in the case of a molten salt tower plant.

The manual says that:

"
Total Tower Cost ($)

Total Tower Cost = Fixed Tower Costs x e ^ (Tower Height x Tower Cost Scaling Exponent)
"

I will refer to the above equation as the published equation in the following table where I compare the above equation to what SAM (version 2011.12.2) gives me for two cases. These two cases have the same values of tower height, scaling exponent as well as Fixed Tower Costs. While net annual energy output of these two cases are different, all the parameters that enter into the above published equation are the same for two cases, so tower cost should be the same, but SAM gives a close but different answer to the actual result of the equation.

CASE 1 | CASE 2
Tower Cost Scaling Exponent | 0.0113 | 0.0113
Tower Height (m) | 183.33 | 183.33
Fixed Tower Costs ($) | 1,927,000.00 | 1,927,000.00
Total Tower Cost (Published Equation) | 1.5296e+007 | 1.5296e+007
Total Tower Cost (SAM) | 1.4526e+007 | 1.3636e+007

Is it possible that SAM uses a more complicated equation but the help file is not updated?

Thanks,

Hello!

I encountered this issue as well. It has to do with the heliostat chord length. The tower height evaluated in the formula takes into account the length of the heliostat pylon height (sqrt(heliostat area)) and substracts it from the tower height to attain an optical tower height. I'm not sure if the receiver height is accounted for as well, but maybe you can figure it out yourself with this info.

Regards
Timo

The equations for total tower cost (on the System Costs page) in Help are incorrect. I will revise them. Here are the correct (hopefully) equations:

For molten salt receiver with rectangular heliostats:

cost.tower.fixed * exp[ tower.scaling_exp * ( twr.height - rec_height/2 + heliostat_height/2 )]

For molten salt receiver with round heliostats:

cost.tower.fixed * exp[ tower.scaling_exp * ( twr.height - cost.rec_height/2 + ( 3.1415926/4 * heliostat_width ) / 2 ) ]

For direct steam receiver with rectangular heliostats:

cost.tower.fixed * exp[ tower.scaling_exp * ( h_tower - h_boiler + h_sh + h_rh ) / 2 + hel_height/2 ) ]

For direct steam receiver with round heliostats:

cost.tower.fixed * exp[ tower.scaling_exp * ( h_tower - ( h_boiler + h_sh + h_rh ) / 2 + ( 3.1415926/4 * hel_width) / 2 ) ]

Best regards,
Paul.