Power tower molten salt

Hello,

A few questions on the power tower;

1. What exactly is the heliostat field multiple?
2.According to SAM help, the fossil dispatch mode/setting of fossil fill fraction should be in the power cycle page but can't seem to find any such option
3.Is the receiver set to external by default,looks like there aren't input parameters for cavity type
4.Is there any reference or indicative value of fossil back up cost ($/kWe) assuming you're using natural gas?
5.For the tower fixed cost,any indication on how this would vary with height?

NB:I'm using 2017 SAM.

Regards,
Mwende.

Dear Mwende,

1. The solar multiple (under "Heliostat Field" on the System Design page) determines the receiver's nominal thermal power. It is the ratio of the receiver thermal power to the cycle thermal power. For a system with no storage, the solar multiple should be close to or equal to one. The heliostat field multiple input is not used by the molten salt power tower model, so you can ignore it. We will remove it in the next update to SAM 2017.1.17.

2. Can you tell me specifically where in Help you saw mention of the fossil dispatch mode? The molten salt power tower model does not include an option for fossil backup. The fossil backup system costs are included on the System Costs page because the System Costs input page is designed to work with both the molten salt power tower model and the direct steam power tower model. The latter includes options for modeling fossil backup.

3. It is not possible to model a power tower system with a cavity receiver in SAM 2017.1.17. Please see this post for more details: sam.nrel.gov/node/70062

4. In general, you can find information about costs on the System Costs page , but the documentation there of power tower costs does not include fossil backup costs.

5. Again, for information about system costs and SAM, please see the documents listed on the System Costs page .

Best regards,
Paul.

Hello Paul,

Thanks for your response.

In regard to the fossil dispatch mode for MS power tower, under Help, if you open CSP then power tower molten salt,on the power cycle page there's a section on 'Fossil dispatch mode'. Perhaps this part should be excluded since it doesn't apply like you said, to avoid confusion.

www.nrel.gov/analysis/sam/help/html-php/index.html?power_tower_molten_salt.htm

Regards,
Mwende.

Dear Mwende,

That version of the Help system is for a 2012 version of SAM. The Help system in current version of SAM explains that fossil backup, along with the supercritical carbon dioxide power cycle and thermocline storage were removed from the power tower model after SAM 2015.6.30 because of the new dispatch and optimization models that do not support those features.

You can find the current version of Help in the SAM software, or you can download a (very large) PDF version from the Download page:

sam.nrel.gov/download

Best regards,
Paul.

Thanks for the clarification.

Regards,
Mwende.