TES capacity and fill fraction

Hi,
I have some question about molten salt power tower, in particular about thermal energy storage.
I saw that this version of SAM (2016.3.14) only allows grid-connected systems
and so is not not possibile to integrate a fossil fill fraction by the hours with not sufficient
radiation. It is right?
My questions are:
1-Are full load hours of TES the hours when the TES has to overcome the insufficient radiation?
2-After different attempts I noted that changing the full load hours of storage, the power cycle output hourly trend does not change, why?
3-What is solar field hours of storage, automatically calculated from SAM?
4-What is the purpose of tank heater?

Thanks.

Dear Elisa,

You are correct that SAM only models grid-connected systems. The power tower model only works with the PPA financial models, which assume that all of the power generated by the system is delivered to the grid. The power tower model in SAM 2016.3.14 has a new dispatch optimization model and does not support fossil backup. (You can use SAM 2015.6.30 to model a tower system with fossil backup.)

1. The "hours of storage at power cycle full load" is the storage system's capacity. For example, for a 100 MW system with 6 hours of TES capacity, the TES tanks would be large enough to supply sufficient heat to run the power cycle at 100 MW for 6 hours.

2. Beyond a certain capacity, the storage system will not affect the system's output. Even if the storage system is very large, the power cycle will not exceed its rated capacity.

3. The definition in SAM's help system for "solar field hours of storage" (on the System Design page) is: " The nominal thermal storage capacity expressed in hours of the solar field's design thermal power output. Solar Field Hours of Storage = Full Load Hours of Storage ÷ Solar Multiple"

4. The tank heater is an electric heater that maintains the storage tank temperatures above the minimum levels that you set.

Best regards,
Paul.