Auxiliary Heating

Sorry but I am confused with some of the nomenclatures so I am sharing my doubts: On Thermal Storage Page,
Firstly,
Cold Tank Heater Set Points/Hot Tank Heater Set Points/Tank Heater Capacity/Tank Heater Efficiency
these 4 factors refer to the auxiiary heaters placed in the hot and cold tanks. These heaters are electric. Are they the same as Immersion heaters used for Molten Salt tanks in Solar Towers.?
For Oil Troughs, some plants only operate with Heat Tracing circuit and no additional heaters inside the tank (immersion). So does these heaters represent heat tracing enery as well or are they just immersion heaters.?

Secondly, Aux Heater Outlet Set Temp, which heaters does these represent because if it is for the tanks again, then its value will be different for both the tanks as the tanks are at different temperatures so which value can be put in there.?

Thirdly, in some plants (PT), they use Auxiliary HTF heaters for freeze protection but they are located somewhere along the field and are normally fossil fired, so where does SAM accumulate these heaters for heating HTF in the field at cold nights.? What I thought of fossil firing was in these heaters as I am simulating a system without the auxilary Boiler.

Lastly, it would be wise to enclose a flow diagram feature (and also based on a selection of components for Hybrid/TES/Solar Only) in order to get a visualisation of what SAM components actually indicate.

In SAM, we use the therm "auxiliary heater" to refer to the fossil backup system, which uses a gas boiler to provide heat to the HTF at the power block to supplement solar energy. The timing and quantity of fossil backup energy depends on the parameters you specify under Thermal Storage Dispatch Control on the Thermal Storage page. For the physical trough model, the "Aux heater outlet set temp" on the Thermal Storage page is for the fossil backup system, not the storage freeze protection system as suggested in Help. (I have corrected that mistake for the Fall 2012 version due for release in a few weeks.)

The hot/cold heater set point, tank heater capacity and efficiency are for the storage freeze protection system, which SAM assumes uses electricity to heat the fluid.

In SAM, freeze protection is provided by electricity. The auxiliary boiler is part of the fossil backup system and does not provide freeze protection.

Please see the diagram on p 80 of the physical trough reference manual. You can download the manual from the Performance Models page on the SAM website. I will put a copy of the diagram in the Help system.

Best regards,
Paul.






Ok perfectly understood the nomenclatures.
So I take that for Molten Salt and Oil storage tanks the freeze protection arrangements remain the same. No special arrangements for redundancy are provided for Molten Salt owing to its high melting point as compared to salt.
Also the heaters in storage tank account for freeze protection energy. There are no heat tracing arrangements around the tank.

Could you describe how these heaters are placed, are they around the tanks or within the tanks because I fail to visualise there location. Thanks for the diagram but I could not still visualise the location of heaters for the tank.

SAM uses a simple model to calculate the storage system freeze protection energy. This makes it possible to use SAM to represent a range of different physical arrangements. The specific placement of heaters and type of heating equipment in the system is beyond the technical scope of SAM.

SAM treats each storage tank as a fluid at a uniform temperature, and assumes that the tank heater converts electricity to heat with the electrical capacity and conversion efficiency that you specify (tank heater capacity, and tank heater efficiency). The heater delivers freeze protection energy to prevent the fluid from falling below the tank set point temperature. The cold and hot tanks each have a separate set point that you specify (cold tank heater set point and hot tank heater set point).

To model a system with redundant equipment (I assume you mean to improve reliability), you could account for the additional cost on the system costs page.

Best regards,
Paul.

Ok Thanks, now it is perfectly clear.
How can I estimate the Tank heater capacity.? Default value is 30MWt, any ideas on how can I change it with chaging salts and their freeze protection temperature.?
(There is one example in Help on how to get exact DNI for site from the DNI cosine values from the result, I just want to ask is there any way I can know the exact size of heaters to be designed)

Thanks.

You could try different values of the tank heater capacity to see how it impacts your metrics of interest. If your analysis includes a financial component, you would probably want assign different cost to different capacities.

We do not have suggested guidelines like the ones you describe for the reference DNI.

Best regards,
Paul.