What is Solar Installation Score?
A solar installation benchmark evaluates your system against expected performance including energy generation, self-consumption ratio, cost per watt, and payback timeline.
The Formula
Performance Ratio = Actual Output ÷ Expected Output (PVWatts) × 100
Worked Example
An 8kW system in Charlotte, NC expected to generate 11,200 kWh/year (PVWatts estimate). Actual: 10,500 kWh. Self-consumption: 50%.
- Performance ratio: 10,500 ÷ 11,200 = 94%
- Self-consumption vs 55% target: 50/55 = 91%
- Annual saving: 10,500 × $0.12 × 0.50 self + 10,500 × $0.12 × 0.50 net metering = $1,260
- Net cost $14,000 (after 30% ITC) ÷ $1,260 = 11.1 year payback
📌 The system performs at 94% efficiency with an 11.1-year payback, within normal range for a $0.12/kWh rate. Self-consumption improvement or a higher-rate utility would shorten payback.
Why This Matters
Return on investment
Every 5% improvement in self-consumption ratio saves $100-200 annually by avoiding grid electricity purchases at full retail rate rather than receiving net metering credits.
System health
Performance dropping below 80% of PVWatts expected output indicates panel degradation, new shading, soiling, or inverter/optimizer problems. Most manufacturers warrant 85% output at year 25.
Battery decision
Low self-consumption ratios suggest a battery would capture excess generation for evening use, especially in states moving away from full retail net metering like California (NEM 3.0).
Common Mistakes
❌ Comparing across different climates
An 8kW system in Phoenix generates 14,000+ kWh/year while the same system in Seattle generates 9,000 kWh. Always benchmark against NREL PVWatts for your specific zip code, not national averages.
❌ Ignoring seasonal variation
US solar generates 60-70% of annual output between April-September. Winter performance is naturally much lower, especially in northern states. Net metering credits banked in summer offset winter shortfalls.
❌ Using gross generation only
Self-consumption ratio matters more than total generation. 10,000 kWh at 60% self-use beats 13,000 kWh at 30% because self-consumed kWh avoid the full retail rate while exported kWh may earn less.
Industry Benchmarks
| Category | Good | Average | Poor |
|---|---|---|---|
| Performance Ratio | 90%+ | 80-90% | Below 75% |
| Self-Consumption | 55%+ | 35-55% | Below 25% |
| Payback Period (post-ITC) | Under 7 years | 7-10 years | Above 12 years |
Source: NREL PVWatts, EnergySage & SEIA 2026
Benchmark data sourced from NREL PVWatts, EnergySage & SEIA 2026.