Storage Tank Volume

Hi Paul. 
What does the temperature difference in storage tank volume equation consist of? Why isn't it just (Tsf,out-Tsf,in)?
What is the physical meaning of T hx,hot and T hx,cold?

Best regards,
Bernardo.

Hi Bernardo,

Thx_hot and Thx_cold are the heat exchanger approach temperatures for the hot side and cold side, respectively, as defined on the Thermal Storage page. SAM assumes there is a heat exchanger between the solar field and TES when the solar field HTF is different from the TES storage medium. (See the diagram on the System Design page.)

Best regards,
Paul.

Hi Paul.
Why do we have to define Thx_hot and Thx_cold on the heat exchanger between solar field and TES and not on the heat exchanger between solar field and power cycle?
Is there any reason or it's just an assumption? 

Best regards,
Bernardo.

Hi Bernardo,

This is a simplifying assumption for the power cycle model as described in Section 3.1.2 of the Physical Trough reference manual. The model calculates the power cycle heat exchanger sizes as shown in Table 12.

Best regards,
Paul.

Hi Paul.
It doesn't mention that assumption there... 
Realistically we needed to define the heat exchanger approach temperatures too, but SAM assumes that the inlet HTF temperature and the outlet boiler temperature are the same, right?

Just another doubt. If we model an indirect storage system, after defining the heat exchanger approach temperatures, the storage will never provide the design temperature to the power cycle, right?

Best regards,
Bernardo.

Hi Bernardo,

Realistically we needed to define the heat exchanger approach temperatures too, but SAM assumes that the inlet HTF
temperature and the outlet boiler temperature are the same, right?
 
SAM uses normalized power cycle maps to represent off-design behavior. The maps are a function of HTF inlet temperature, HTF mass flow rate, and condenser pressure. So, it is correct that the heat exchanger approach temperatures are not explicitly modeled. Instead, the influence of any cycle-specific design change should be represented by a change in SAM’s design-point cycle efficiency. For example, if you want keep all default assumptions except assume smaller approach temperatures, then you should estimate how cycle efficiency would increase (and probably how cycle cost would increase to pay for the more effective heat exchanger).

Just another doubt. If we model an indirect storage system, after defining the heat exchanger approach temperatures, the storage will never provide the design temperature to the power cycle, right?
 
Correct. However, the solar field will send HTF at the design temperature directly to the power cycle when both are operating simultaneously.

Best regards,
Paul.