- The performance of a PV power plant is often denominated by a metric called the capacity utilisation factor. It is the ratio of the actual output from a solar plant over the year to the maximum possible output from it for a year under ideal conditions. Capacity utilisation factor is usually expressed in percentage.
- Most research suggests that the plant load factor and the capacity utilisation factor basically represent the same parameter. The term capacity utilisation factor has replaced plant load factor in many a cases
- Capacity Utilisation Factor (CUF) =Energy measured (kWh) / (365*24*installed capacity of the plant)
- Calculation of CUF (Example):
Rated capacity: 2.1 MW or 2100 kW
Assumed annual generated energy: 48, 00, 000 kWh
Actual number of WTG operating days: 330 days
Actual number of operating hours: 330 × 24 = 7920 hours
Substitute the values in the above formula
CUF (%) = [48,00,000 / (2.1 X 1000 X 7920)] X 100 = 28.86%
- Studies from Ministry of Non renewable energy (MNRE) India reports that, the average capacity utilisation factor of solar PV plants in India is in the range of 15-19%.
Benefits of CUF method of performance evaluation
- The simplicity of evaluation and direct correlation of CUF with revenue makes it more favourable option for the investors
- The CUF measure does not take into the account the details of the particular location – for instance, the irradiation for the location.
- It doesn’t also consider degradation of the panels and grid availability
- CUF does not truly represent the potential of the solar-PV technology itself because it does not factor in the following:
- Solar PV systems do not work at night because there is no sunshine
- Solar irradiation changes during the seasons
- Plant output depends on temperature of the location too
- Considering the above, CUF technically doesn’t paint a highly accurate picture of the plant’s performance and it cannot be used as a measure of control especially for intermittent sources of energy like solar/wind
How relevant is CUF to solar farms?
- The C.U.F. is a measure of ‘how well a plant is utilized’. This is especially important because a PV plant is an asset with a limited life based on an intermittent energy source, and the investor would like to extract as much value from the plant as possible.
- Solar farms require a huge investment and computing the CUF for a solar farm, which has a direct correlation with the revenue that can be generated by the solar farm, is a favourable option for the investors.
In many cases, the C.U.F. is a metric generally used to evaluate the performance in terms of generation when comparing plants with various sources of energy (coal, nuclear, solar/wind etc.). If we take a look at the C.U.F. we see that the formula evaluates the energy generated from the solar plant against 100% of the existence of the plant i.e. 8,760 hours in a year in this case (including night times when it is impossible to generate any energy). In that sense, the CUF is unfair because it ignores radiation specific to locations and it ignores night times when the plant really cannot do anything. To overcome this, a more relevant measure called the Performance Ratio (P.R.) is a very useful tool to compare PV plants across the world as it directly reflects on the quality of construction and maintenance.