General Questions About SAM's Stochastic Simulations

Dear Sirs,

Greetings.

I am working on an analysis using the CSP Power Tower Molten Salt with a single-owner financial model. If possible, can you please answer my questions below?

With regards to the new update of SAM, I have a problem with selecting the Specify IRR target on the Revenue page. There is a message that says: The Specify IRR target option is not available with the Use PPA Price option on Electricity Purchase Page. Either change the option on the Electricity Purchases page or use the Specify PPA Price option. Where can I find this page? 

For stochastic analysis, I set a uniform distribution for the number of heliostat facets so I got a range of decimal values. Does SAM take the integer values of this parameter to calculate the LCOE?

How can I get the overall optical efficiency for all the simulations as an output?

Can I use the parameter named Fraction of rated gross power consumed all times to reflect the variability in power grid demand? And is there any variable that can reflect the variability in demand within the day for multiple locations?


I look forward to hearing from you. Thank you.

King regards,
Nada

Hi Nada,

The Specify IRR Target option requires that you specify the purchase price of electricity for freeze protection and other night-time parasitic loads on the Electricity Purchases input page instead of using the PPA price for the purchase price. This is because for the Specify IRR Target option, SAM does not know the PPA price at the beginning of the simulation, so it cannot calculate the cost of electricity purchases unless you set the purchase price.

To set the electricity purchase price:

1. Go to the Electricity Purchases page.



2. Choose Use retail electricity rate(s).



3. Under Energy Charges, set the Buy rate to the electricity purchase price. You can set this price to a retail rate, or to an estimate of the PPA price. After running a simulation to calculate the PPA price based on the target IRR, you can change the buy rate to the calculated PPA price and run another simulation to generate the final cash flow.

Best regards,
Paul.

Hi Nada,

Regarding using stochastic simulations to calculate a range of number of heliostat facets: I would avoid this approach because of the non-decimal values that SAM calculates based on the distribution you provide. If you want to calculate the LCOE for a range of different heliostat facet values, you might consider using Parametric simulations where you can set the values explicitly to integer values.

SAM reports the optical efficiency for each time step of the simulation as Field optical efficiency. You would have to calculate the "overall efficiency" from this hourly or subhourly data.

SAM uses the Fraction of rated gross power consumed at all times input to calculate the electricity consumption of parasitic loads in the power plant. SAM assumes that the grid can absorb all of the power generated by the system. You can use the inputs on the Grid Limits page to limit the amount of power the system can deliver to the grid.

Best regards,
Paul.