Power Tower Annual Energy & System Output to Grid Differences

Dear Paul,

Hello again. Sorry for my long messages but i try to describe problems in detail so we can all benefit from it.

I have another problem regarding the annual energy & system output to grid reported in the metrics table and loss diagram correspondingly.

I have simulated a 50MW power tower with 50MW fossil fuel backup. My fossil fill fraction is set to 1.05 same as tub.out. fraction and max. turbine over design op. Storage dispatch is set to 0 for both w/o solar and w/solar.
The problem in results is that SAM reports the SYSTEM OUTPUT TO GRID 887,322 MWhe while in the metric table the ANNUAL ENERGY is 374,003,360 kWhe.

I have found a post in these forums that you have replied saying that the annual energy must be equal to the system output to grid and that's perfectly understandable. So i removed the fossil fill fraction from my simulation and both reported values were the same as expected. By the way at this point the reported annual energy was not the same (less) as the one with fossil fuel backup in my previous simualation so i presume that fossil fuel backup contribution is added in the annual energy for systems that utilise it.

Now why when i put the fossil fuel backup to 1.05 for all my periods (2 totally) i get much much higher energy output in the loss diagram? I took the time series hourly values for net electric output and compared them withthe values below:
Net electric power output (kWh), hourly is 389,586,850.15 kWhe
Thermal energy delivered by aux backup, hourly is 496,491,531.37 kWht. If i make a rough calculation of the thermal energy to electric conversion by using my rated cycle conversion efficiency (0.42) i get 208,526,443.18 kWe from the aux. backup and this is not even calculated with my 96% annual performance adjustment.
Thermal energy from thermal storage is 119,844,280.000 kWh(positive values calculated with 0.42 conversion efficiency).

Now if you add the numbers of Net electric + Electric from aux. backup 6 thermal energy from storage i will still be missing 169,364,426.67 kWhe.

Also in the time series i get 44,473.00 KWhe hourly net electric output approx. which is my target for guarantee provided energy. However according the loss diagram the electricity provided to the grid is much higher which results to 101,000 KWhe hourly. approx.(not reported in the time series).

I have attached a .PDF file with 2 photos of my loss diagram and metric table.
What am i missing here?
What is the annual energy value reporting exactly? Does it include the electricity generated by the power cycle from the provided thermal energy of fossil fuel?

I am using SAM 2013.1.15 (windows XP).

Thank you in advance.

Hello,

For the concentrating solar power (CSP) models with a fossil backup option, as you observed, SAM seems to be reporting a different value for "Annual Energy" in the Metrics table and for "System Output to Grid" in the loss diagram. I am working with the development team to see why that is and will follow up when I hear back from them.

Best regards
Paul.

Dear Paul,

Thank you for the fast response. I presume that the value of the Annual Energy Output in Metrics is the correct one since it is the same as the sum of the hourly values in the time series. Please be aware that all values in the loss diagram alter when simulating a fossil fuel backup system and they don't seem correct either i.e the thermal energy delivered by the receiver to the power block exceeds the design point of the power block and as i have understood this should never happen.

Your support is invaluable to the community, much appreciated.

Hello,

There is a problem with the energy loss diagram that causes it to display incorrect values under some conditions. We will fix this for the next update to SAM 2013.9.20, which we plan to release in the next few weeks.

Best regards,
Paul.