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We serve MA, NH, CT, RI, ME, VT, NJ, PA, and TX
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NuWatt designs, installs, and manages solar, battery, heat pump, and EV charger systems across 9 states. One company, one warranty, one point of contact.
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NuWatt’s solar production estimates are within 3% of actual output across 2,500+ installations in 9 states. We use NREL PVWatts irradiance data combined with site-specific shading analysis and conservative panel derating. Most systems fall within +/- 5% of their estimate in any given year, with weather being the primary variable.
How close are our solar production estimates to what systems actually produce? Here is the data, methodology, and transparency you deserve.
Overall Accuracy
97%
Estimated vs. actual kWh
Systems Analyzed
2,500+
Across 9 states
Typical Variance
±3%
First-year production
Every NuWatt proposal includes a production estimate built from these inputs. Each factor is measured, not guessed, and the combined model is validated against years of real production data.
| Factor | Data Source | Weight | Accuracy |
|---|---|---|---|
Solar Irradiance (GHI) | NREL NSRDB / PVWatts | Primary | 98% |
Roof Orientation & Tilt | Site survey + LiDAR | High | 99% |
Shading Analysis | Aurora Solar / Suneye | High | 95% |
Panel Efficiency | Manufacturer datasheet | Medium | 99% |
Temperature Coefficient | Panel specs + local climate | Medium | 97% |
Inverter Efficiency | CEC-weighted efficiency | Low | 99% |
Soiling & Snow | Regional defaults + tilt | Low | 94% |
System Losses (Wiring, Clipping) | Engineering model | Low | 98% |
Conservative by Design
NuWatt intentionally uses conservative assumptions. We apply a 2% general derate on top of component-level losses. This means most systems slightly outperform their estimate. We would rather you be pleasantly surprised than disappointed.
Five representative systems from different states showing estimated vs. actual first-year production. Positive variance means the system produced more than estimated.
| System | Location | Size | Estimated | Actual | Variance | |
|---|---|---|---|---|---|---|
| MA-001 | Chelmsford(MA) | 8.8 kW | 10,450 kWh | 10,280 kWh | -1.6% | |
| NH-014 | Nashua(NH) | 7.0 kW | 8,200 kWh | 8,380 kWh | +2.2% | |
| CT-008 | Glastonbury(CT) | 10.1 kW | 12,100 kWh | 11,850 kWh | -2.1% | |
| TX-022 | Austin(TX) | 11.0 kW | 15,800 kWh | 16,150 kWh | +2.2% | |
| NJ-009 | Princeton(NJ) | 9.2 kW | 11,000 kWh | 10,870 kWh | -1.2% | |
| Average Across Sample | 11,510 kWh | 11,506 kWh | -0.1% | |||
System IDs are anonymized. All data from calendar year 2025 (full 12-month production). Actual production sourced from Enphase Enlighten monitoring platform.
Production accuracy varies by state primarily due to weather variability and solar resource consistency. States with higher irradiance (like Texas) tend to have more predictable output.
| State | Accuracy | Avg Variance | Sample Size | Solar Resource |
|---|---|---|---|---|
| Massachusetts(MA) | 97.2% | -1.1% | 680 | 4.2 kWh/m²/day |
| Connecticut(CT) | 97.5% | -0.8% | 310 | 4.3 kWh/m²/day |
| Rhode Island(RI) | 96.8% | -1.5% | 185 | 4.2 kWh/m²/day |
| New Hampshire(NH) | 96.9% | +0.4% | 290 | 4.1 kWh/m²/day |
| Maine(ME) | 96.5% | -1.8% | 245 | 4 kWh/m²/day |
| Vermont(VT) | 96.3% | -2.0% | 95 | 3.9 kWh/m²/day |
| New Jersey(NJ) | 97.8% | -0.5% | 340 | 4.4 kWh/m²/day |
| Pennsylvania(PA) | 97.1% | -1.0% | 155 | 4.2 kWh/m²/day |
| Texas(TX) | 97.9% | +1.2% | 200 | 5.4 kWh/m²/day |
Highest Accuracy: Texas (97.9%)
Higher and more consistent solar irradiance (5.4 kWh/m2/day) makes production more predictable. Less snow and fewer overcast days reduce weather-related variance.
Lowest Accuracy: Vermont (96.3%)
Lower irradiance (3.9 kWh/m2/day), heavy snow coverage, and higher weather variability make Vermont the most challenging state for production forecasting. Still within 4% average variance.
Even with 97% overall accuracy, individual systems can vary from their estimate. Understanding why helps you know when to investigate and when variance is normal.
An unusually cloudy or sunny year can shift production by 3-8% from the TMY average. Our estimates use 30-year typical meteorological year (TMY) data, so single-year variance is expected.
Trees grow. A tree that was 20 feet tall at installation may shade panels 3-5 years later. Annual monitoring catches this early. Tree trimming is the most common corrective action.
Panels at low pitch (under 20 degrees) hold snow longer. New England systems lose 2-5% annually from snow. Steeper roofs (30+ degrees) shed snow within hours and lose under 1%.
A failed microinverter takes one panel offline (4-8% of a typical system). Enphase monitoring alerts NuWatt within 24 hours. Replacement is covered under the 25-year warranty.
Accumulated dirt reduces light reaching cells. Rain washes most soiling naturally. Heavy pollen seasons (spring in NE) or bird-heavy areas may benefit from annual cleaning ($150-250).
Without battery backup, grid outages shut down solar production (grid-tied requirement). In most areas this is under 0.5% annually. Texas ERCOT events may cause slightly higher curtailment.
Solar irradiance data from NREL's National Solar Radiation Database (NSRDB), the gold standard used by the entire solar industry. 30-year typical meteorological year (TMY) data smooths out year-to-year weather variation.
Every system gets a LiDAR-based shading analysis using Aurora Solar. Hour-by-hour shade simulation accounts for seasonal sun angles, nearby structures, and trees. No generic "15% shading loss" assumptions.
Our estimation model has been continuously refined against actual production data from every NuWatt installation since 2020. Each year of data makes the model more accurate.
We apply a 2% general derate on top of all component-level losses. Industry practice is 0-1%. This means our estimates lean toward under-promising rather than over-promising.
Every system includes Enphase monitoring so homeowners can verify production against estimates from day one. If a system underperforms, NuWatt is alerted automatically.
We don't just estimate Year 1. Production projections for years 1-25 use manufacturer-specific degradation rates (0.25-0.40%/yr) and account for inverter efficiency aging.
Across 2,500+ installations in 9 states, NuWatt's production estimates are within 3% of actual first-year output on average. This 97% accuracy rate uses PVWatts irradiance data, site-specific shading analysis, and manufacturer panel specifications. Individual system variance ranges from -5% to +5% depending on weather and site conditions.
NuWatt uses NREL's PVWatts calculator as the foundation, supplemented by Aurora Solar for detailed shading analysis using LiDAR data. We apply site-specific adjustments for roof pitch, azimuth, local weather patterns, soiling, and snow. The combined model has been validated against 5+ years of actual production data.
The most common reasons for variance are: (1) weather — an unusually sunny or cloudy year can shift production 3-8% from the 30-year average; (2) new shading from tree growth; (3) snow coverage at low roof pitches; (4) a failed microinverter (detected within 24 hours via monitoring). Most systems fall within +/- 5% of estimates.
Our estimates account for panel degradation using manufacturer-specified rates: 0.25%/yr for REC 460W, 0.30%/yr for Silfab 440W, and 0.40%/yr for Hyundai 440W. Year-1 estimates reflect full rated output. Year-10 estimates are derated accordingly. The degradation rates we use are conservative (worse than typical real-world performance).
Every NuWatt system includes Enphase monitoring that shows real-time and historical production. Compare your annual kWh to the estimate provided at installation. If production drops more than 5% below estimate (after accounting for weather), contact NuWatt for a complimentary system check. Common causes are tree growth, a failed microinverter, or dirty panels.
Industry-average production estimate accuracy is around 90-95%, with many installers over-estimating by 5-10% to make proposals look better. NuWatt's 97% accuracy reflects a deliberate choice to use conservative assumptions. We would rather under-promise and over-deliver than the reverse.
Get a personalized production estimate and price based on your roof, location, and energy usage. Our estimates are backed by the 97% accuracy rate documented above.
See What Solar Costs for Your HomeLast updated: 2026-03-27 · Source: NuWatt Energy / Enphase Enlighten monitoring data
Based on 2,500+ installations across MA, CT, RI, NH, ME, VT, NJ, PA, and TX. Updated quarterly with new production data.