About the Metering Class Selector
Metering class selection determines the accuracy grade of energy meters and associated instrument transformers (CT, PT) for a solar plant — balancing the cost of higher accuracy equipment against the revenue impact of metering errors over the plant's 25-year life.
How to calculate it
- 1Revenue metering (billing by DISCOM): class 0.2 or 0.5 meter with class 0.2 CTs and PTs (per CEA Metering Regulations 2006 and state DISCOM specifications).
- 2Plant performance monitoring (owner's internal meter): class 1.0 acceptable; class 0.5 preferred for accurate PR calculation.
- 3Net metering (bidirectional meter): class 1.0 minimum per most state net-metering regulations; class 0.5 preferred.
- 4Combined meter class error at rated current: total system error ≤ CT error + PT error + meter error. For class 0.2 system: 0.2 + 0.2 + 0.2 = max 0.6% total error.
- 5Revenue impact: for a 1 MWp plant at 1,500 kWh/kWp/year generating ₹2 Cr/year, a 1% metering error = ₹2 L/year lost or over-billed.
Worked example
An 11 kV grid-connected 2 MWp solar plant: DISCOM billing meter — class 0.2S with class 0.2 CTs and 0.2 PT/CVT. Owner check meter — class 0.5. Both meters read simultaneously; discrepancy > 0.3% triggers recalibration. Annual generation: 3,000 MWh. Revenue ₹1.05 Cr/year. 0.5% metering uncertainty = ₹52,500/year — motivates the owner to use a check meter.
What you can calculate
- Class 0.2S
- CEA Regulations
- Annual error ₹
- IS 14697
Frequently asked questions
What does the 'S' suffix in meter class 0.2S mean?
Class 0.2S (IEC 62053-22) is a special subclass with tighter accuracy requirements at low load currents (down to 1% of rated current) — standard class 0.2 only guarantees accuracy from 5% of rated current. Class 0.2S is required for net metering applications where partial load accuracy matters (e.g., small solar export during low-generation periods). DISCOM specifications for smart meters under RDSS (Revamped Distribution Sector Scheme) typically require class 0.2S.
How often should solar plant energy meters be calibrated?
CEA Metering Regulations 2006 require DISCOM meters to be verified every 5 years and replaced if found in error. Best practice for owner-side check meters: calibration every 2 years. For class 0.2 meters, calibration by an NABL-accredited lab is recommended, as it provides traceability and is accepted in any revenue dispute. Meters that have been exposed to surges (lightning) or operating continuously near maximum rated current should be calibrated more frequently.
Ready to build your solar project?
Get free quotes from verified EPCs and installers across India.
You might also need
Step-Up Transformer Sizing
Calculate MVA rating, standard IS 2026 size, impedance and loss budget for solar grid step-up transformers
OpenTransformer Impedance & Losses
Calculate transformer impedance voltage, no-load/load losses and efficiency per IEC 60076
OpenPSS Busbar Sizing
Size substation busbars for continuous current, thermal limits and short-circuit withstand per IS 5082
OpenCT Sizing & Class Selection
Select current transformer ratio, accuracy class and knee-point voltage for protection and metering per IEC 61869
OpenPT / CVT Selection
Select voltage transformer or capacitor voltage transformer class, burden and accuracy for HV/EHV systems
OpenCircuit Breaker Rating
Rate circuit breakers for fault interrupting capacity, rated voltage and operating duty per IEC 62271
Open