Blogs

Performance Ratio

The performance ratio is a measure of the quality of a PV plant that is independent of location and it therefore often described as a a quality factor. The performance ratio (PR) is stated as percent and describes the relationship between the actual and theoretical energy outputs of the PV plant.

“Performance Ratio (PR)” is defined as below:
Performance Ratio (PR) of a plant for a period of time ═ Energy generated (kWh /) / Irradiance (kWh/m2) x Active area of PV module (m2) x PV module efficiency

Alternatively, the following formula may be used for calculation of PR
PR ratio = ((Energy generated / (installed plant capacity in KW *solar insolation in KWH/m2/ day))

The Yearly Performance Evaluation Test shall be done in the last month of every year

DEFINITIONS

1.1   Ht – 1-minute integrated total irradiation (in kWh/m2) measured at the plane of modules by 1 no. Class-II integrating pyranometer installed
1.2   Jt – 1-minute average irradiation (in W/m2) measured at the plane of modules by 1 no. Class-II integrating pyranometer installed
1.3   EGEN,t – Net electric energy (DC) generated from solar system (in kWh) during each 1-minute interval measured at the Inverter/PCU input by integrated/separate multi-function energy meter installed
1.4   PN – Total installed PV capacity (Wp), where PN varies as below during the PGT/various Yearly Performance Evaluation Tests as per the deration value of the Solar PV Modules as specified in Clause 3.1 of Technical Specifications in Job Specifications chapter:

	Value of P_N
For PGT : P₀	Total installed capacity of Solar PV Modules (in W_p)
For Yearly Performance Evaluation Test during Free O&M as per Part-A of Clause 3.1 of SCC : P₁	97.5% of P₀
For Yearly Performance Evaluation Test during 1^st year of O&M as per Part-B of Clause 3.2 of SCC : P₂	96.8% of P₀

For Yearly Performance Evaluation Test during 2^ndyear of O&M as per Part-B of Clause 3.2 of SCC : P₃	96.1% of P₀
For Yearly Performance Evaluation Test during 3^rdyear of O&M as per Part-B of Clause 3.2 of SCC : P₄	95.4% of P₀
For Yearly Performance Evaluation Test during 4^th year of O&M as per Part-B of Clause 3.2 of SCC : P₅	94.7% of P₀

1.5 GSTC – Standard irradiance i.e. 1000W/m2
1.6 Rt –Percentage regulation value as recorded by controller of Solar Grid DG Management System every 1-minute

Where, subscript ‘t’ used above is the count of 1-minute interval for recording of average/net values of parameters defined above. There will be such 4320 nos. of 1-minute intervals (1440 intervals in a day x 3 days) during the Performance Test Period (PTP), i.e. t ranges from 1 to 4320.

2. CONDITIONS TO PROCEED WITH PGT
The PGT will be executed after fulfilment of following conditions:

1.1   Commissioning of the entire PV Plant shall be achieved.
1.2   The Monitoring System shall be completely installed and under operation with all the sensors calibrated.
1.3   The Contractor shall undertake to submit all the technical documentation requested by IOCL as mentioned in the sections of tender document.
1.4   Only qualified personnel from the Contractor or personnel from other companies appointed by the Contractor, with suitable skill in electrical equipment’s, measurement shall be allowed to perform the prescribed inspections.
1.5   Before inspection, the area subject to inspection has to be cleaned and any installation that could hinder any functional tests shall be removed.
1.6   The 1-minuteduration, t, as defined in Clause 1 should be same for 1.1, 1.2, 1.3 and 1.6 and the recorded parameters by different measuring instruments as described in the respective clauses shall be available through single data logger having time stamping facility.

3. PROCEDURE AND CALCULATION
The PGT/Yearly Performance Evaluation Test shall be carried out during a 3-day period (referred to as the Performance Test Period – PTP).
Total Reference Energy during PTP shall be calculated through the formula:

For calculation purposes, when Jt<100W/m2 or Rt<100%, Ht shall be taken as zero, i.e. such values of Ht shall be rejected (not considered in above summation).

Total Energy Generated from solar during PTP shall be calculated through the formula:

For calculation purposes, when J_t<100W/m² or R_t<100%, E_GEN,t shall be taken as zero, i.e. such values of E_GEN,_t shall be rejected (not considered in above summation).

There should be at least 1440 nos. of non-zero readings of E_Ref and E_GEN considering the above mentioned condition on availability of J_t& R_t. If the required numbers of readings are not available, then the duration of PGT shall be extended beyond 3-days to have at least 1440 nos. of non-zero readings of E_Ref and E_GEN.

The Performance Ratio during PTP shall be calculated through the formula:

In order to consider the Performance Guarantee Test positively passed, the following condition must be satisfied:

PR ≥ 75%

In order to consider the Yearly Performance Evaluation Test positively passed, the following condition must be satisfied:

PR ≥ 75% or PR last established during PGT/Yearly Performance Evaluation, whichever is low.

Energy losses attributable to following events shall not be considered for performance guarantee evaluation:

Shut-downs caused by factors not controlled by the Contractor or it’s subcontractors
Force Majeure
Vandalism or theft.
Modifications at the site or its surroundings due to factors out of control of the Contractor (i.e. shadowing due to new installations on the site or next to the site, etc).