Direct and indirect measurement methods can be used to evaluate the performance of a power plant. The Heat Rate direct method is commonly used to measure efficiency in PPA. It includes measuring the actual output of the plant, such as the amount of electricity generated, while indirect methods involve assessing the efficiency of the plant and its components. This method is commonly used for monitoring purposes. Here are some pros and cons of each method:
Direct measurement:
Pros:
- Provides accurate and precise results, when properly and accurate devices are used in the field.
- Can be easily verified. However, assuring accurate measurement of weight and fuel quality is an arduous task.
- Provide a comprehensive analysis considering that few key parameters are measured for this method.
Cons:
- Does not necessarily provide information on the efficiency of the plant or its components. It offers limited information on overall performance.
- May not consider external factors that affect plant performance, such as fuel quality or weather conditions, heat transfer problems or de-rate of turbine performance.
Indirect measurement:
Pros:
- Can provide information on the efficiency of the plant and its components. It is very useful to identify each area of the plat directly related to the performance, from boiler and steam-cycle performance.
- Can use the current pressure, temperature and flows normally measured in a power station to control normal operation.
- Can consider external factors that affect plant performance
- Contrary to general opinion is more accurate and precise than the direct method when proper devices are located on the field.
- Can be cost-effective considering the use of the regular measurement equipment installed in a power station.
Cons:
- May rely on assumptions or models that can introduce errors. However, thermodynamic models properly implemented give a lot of valuable information for the process, regular operation, and efficiency of the power plant.
Lessons learned
I used to measure direct and indirect Heat Rates to establish and monitor power plant performance. Both methods are useful to identify improvements and issues in power plants.
Last developments in real-time monitoring software have enabled operators to quickly detect abnormalities, malfunctions, or deviations from expected performance by indirect method.
Recommendation
Overall, both direct and indirect measurement methods have their advantages and disadvantages. Depending on the specific goals and circumstances, a combination of both methods may provide the most comprehensive assessment of power plant performance.