See Also
Four characteristic curves describe the efficiency and resulting costs associated with operating a particular generating unit. These four curves plot
- Fuel Cost
- Heat Rate
- Input-Output
- Incremental Cost
Simulator can display plots of all these curves. To display a particular plot for a generator, right-click on the generator in Run Mode to display its local menu, and then select the plot you wish to see. The plot will be presented in its own window. The windows for all plots exhibit identical characteristics. For example, the current operating point is identified by a red filled circle. Right clicking on an open area of the window displays the plot’s local menu which allows you to print the plot, save it to a file, or copy it to the clipboard for use in other programs. To adjust the length and number of intervals shown on an axis, right-click on the axis (not on the numbers) then specify the min and max display values and number of intervals. To close a plot window, simply click the X button in its top right corner.
The Run Mode generator local menu also provides access to a fifth type of plot curve - the "All Area Gen IC Curves" plot. This plot simply shows the incremental cost curves and present operating points of all generators in the same area as the generator on which you clicked.
Fuel Cost Curve
The fuel cost curve specifies the cost of fuel used per hour by the generating unit as a function of the unit’s MW output. This is a monotonically increasing convex function.
Heat-rate Curve
The heat rate curve plots the heat energy required per MWH of generated electrical output for the generator as a function of the generator’s MW output. Thus, the heat rate curve indicates the efficiency of the unit over its operating range. Generally, units are least efficient at the minimum and maximum portions of their MW output capability and most efficient somewhere in the middle of their operating range. The vertical axis is plotted in MBtu/MWH and the horizontal axis is plotted in MW. You may interpret the heat rate for a generator producing X MW as follows: the heat rate indicates the amount of heat input energy per MWH of generation required to produce X MW of power. The lower this number, the less input energy is required to produce each MWH of electricity.
Input-Output Curve
The input-output curve is derived simply from the heat-rate curve by multiplying it by the MW output of the unit. This yields a curve showing the amount of heat input energy required per hour as a function of the generator’s output.
Incremental Cost Curve
By multiplying the input-output curve by the cost of the fuel in $/MBTU, one obtains the cost curve for the unit in $/hr. By taking the derivative of the cost curve, one obtains the incremental cost curve, which indicates the marginal cost of the unit: the cost of producing one more MW of power at that unit.