Calculating overall plant efficiency

Hi Paul,

Is it reasonable to calculate the overall plant efficiency of a power tower as follows?

Total plant eficiency = (Net electric power output (MWh), Hourly)/(Total incident thermal energy (MWh), Hourly)

I'm wondering because if there's fossil fuel backup then this isn't really the efficiency of the plant on its own.

Thanks,
Jonathan

Hi Jonathan,

Your equation is reasonable as a measure of the amount of electricity delivered to the grid as a fraction of the solar energy incident on the field.

Your observation about fossil backup is correct. If you model a system with fossil backup, then some of the electrical energy represented by Net Electric Power Output was converted from natural gas. The Thermal Energy Delivered by Aux Backup variable quantifies that energy.

Also, be aware that the Net Annual Energy value that SAM reports in the Metrics table and for year 1 in the project cash flow includes the availability factor from the Annual Performance page. Its value is the sum of the hourly Net Electric Power Output values multiplied by the availability factor.

Best regards,
Paul.