Physical model - Minimum required startup temp.

Dear Paul

In the Power Cycle of the physical model there is a parameter called Minimun required startup temp. The help of SAM defines this parameter as “The temperature at which heat transfer fluid circulation through the power cycle heat exchangers begins, typically near the power block design heat transfer fluid outlet temperature…..”, and in fact the default value when you create a new model is 300 °C.

Nevertheless, I have had access to real data of solar plants and the value of the minimum required temperature of HTF to heat the Steam Generator System is 250 °C approximately, in order to avoid a strong thermal shock in elements of the power cycle.

So, I have the two following questions:

1. I have a model with a Minimum required startup temp. of 250 °C. When I change this value to 300 °C, the electric power output increases 3 % - 4 %. How is it possible that I generate more energy with a Minimum required startup temp. of 300 °C? With this temperature, I should generate less energy than with a Minimum required startup temp. of 250 °C, because the power cycle should start up later.
2. I do not know how SAM works with this parameter, so it is possible that due to SAM analysis methodology it is better to set a figure close to 300 °C than to 250 °C. What do you suggest to define this parameter, knowing that I want to simulate a model of a plant where the power cycle starts up whit a temperature of 250 °C?

Best regards

Igor

Dear Igor,

When you changed the startup temperature from 300°C to 250°C, did you also adjust the power block startup time accordingly? Both are inputs on the Power Cycle page.

Best regards,
Paul.

Dear Paul,

I have only modified the Minimum required startup temp.

As I mentioned, I have real data of solar plants, so I have made a model with a Minimum required startup time of 250 °C (real data of my plants) and real data of Power block startup time.

Nevertheless, before reading the definition of the Minimum required startup temp. some doubts have arisen in me about what value should I establish, the real value of 250 °C or the suggested value of 300 °C. My doubts also increased when I saw that the model generated more energy with a higher Minimum required startup temp.

So, can you explain me how SAM uses this parameter in the simulation and what is the value you suggest me for it?

Best regards
Igor

Dear Igor,

The energy required for startup is affected by three input variables on the Power Cycle page: Power Block Startup Time, Fraction of Thermal Power Needed for Startup, and Minimum Required Startup Temp.

The startup energy calculation is described in Section 3.4.2 of the physical trough reference manual .

Best regards,
Paul.