parabolic trough empirical model

Hello,

A few questions on the parabolic trough empirical model;

1. I'm trying to check the effect of using different types of fuels i.e natural gas/biomass for the fossil back up by changing the boiler LHV efficiency value, but the output doesn't seem to be changing at all for a wide range of efficiency values-I've attached the SAM file here.

2.Is it possible to check the % of annual output production from fossil fuel back-up? or is there a way to select fossil fill fraction for various dispatch periods in order to reflect a certain cap on power production from the back up?

3. Are the solar field inlet & outlet temperatures a function of the HTF in use, rather do you need to change these values when switching between different HTFs say molten salt and Dowtherm Q?

Regards,
Mwende.

Dear Mwende,

1. You can see the thermal output of the fossil backup system by looking at the "Fossil thermal power produced (MWt)" hourly variable in the results. In your file, for an LHV efficiency value of 0.65, the total annual fossil energy value is 129,366 MWht/year compared to 93,431 MWht/year for a LHV value of 0.9.

2. You can see the total value of the hourly fossil MWt values on the Statistics tab of the Results page. I don't understand the second part of your question -- the empirical trough model does not report TOD period numbers in the results. I see that you are using the fossil fill fraction inputs on the Thermal Storage input page to control how much fossil backup is used at different times.

3. Yes, the HTF properties are one factor to consider in choosing the design inlet and outlet temperatures. You want to avoid exceeding the fluid's maximum and minimum operating temperatures, which are typically provided by the HTF manufacturer.

Best regards,
Paul.

Hello Paul,

Thanks for your response.

About the LHV efficiency value,would you happen to know why the lower value of 0.65 produces a higher thermal energy output than the higher efficiency value? I would expect it to be vice versa, not sure if this is due to some error in my model.

Regards,
Mwende.

Dear Mwende,

The "fossil thermal power produced" output variable of the empirical trough model represents the quantity of fossil fuel required to provide supplemental heat to the HTF. A fuel with a lower heating value requires a higher quantity to supply the same amount of heat as a fuel with a higher heating value. SAM uses this value to determine the cost of fuel, based on the fossil fuel cost you specify on the System Costs page.

You can explore this further on the Time Series tab on the Results page by comparing the following variables:

Fossil thermal power produced
Cycle thermal power input

Cycle electrical power output (gross)
Cycle electrical power output (gross, solar share)
Cycle electrical power output (gross, fossil share)

Field thermal power absorbed

For two cases that are identical except for the boiler LHV efficiency assumption, you should see that the fossil share of the gross cycle electrical power output does not change, but the fossil thermal power produced does.

Best regards,
Paul.