Why Did My Solar Production Drop This Year? Year-to-Year Results From LA Systems
On the same Los Angeles-area systems, a year’s solar production usually lands within a few percent of the year before: half of all 288 year-over-year changes fell between -6.3% and +2.0%. Large drops come when the whole fleet moves together. In 2023 the median system produced 10.7% less than in 2022 and 92% of systems fell, while NASA satellite data show about 7.3% less sunlight over the San Fernando Valley. A drop much larger than the fleet’s in the same year is the signal worth checking.
How much annual solar output changes from one year to the next
288 year-over-year changes on 83 systems, each compared with itself.
| Year | Systems | Median change | Middle half | Typical range (p10–p90) | Up / down | NASA sunlight change |
|---|---|---|---|---|---|---|
| 2021 vs 2020 | 34 | +2.3% | +0.1% to +5.6% | -4.9% to +9.3% | 76% / 24% | +1.4% |
| 2022 vs 2021 | 47 | +1.1% | -1.3% to +3.4% | -5.6% to +5.7% | 57% / 43% | +0.5% |
| 2023 vs 2022 | 63 | -10.7% | -12.1% to -7.9% | -14.9% to -2.1% | 8% / 92% | -7.3% |
| 2024 vs 2023 | 70 | -1.8% | -5.3% to +0.9% | -10.1% to +4.1% | 31% / 69% | +3.6% |
| 2025 vs 2024 | 64 | +0.6% | -1.1% to +2.8% | -3.5% to +4.3% | 64% / 36% | -0.3% |
| Sunlight: NASA POWER all-sky surface irradiance, annual mean, 34.24°N 118.50°W. 2020 vs 2019 omitted (10 systems). | ||||||
https://cali-energy.com/research/solar-production-year-to-year. Aggregated data are free to use under CC BY 4.0 with a link to this page.When the whole fleet moves: sunlight versus production
Median change on the same systems, with independent satellite sunlight data.
| Month | Production change, median | NASA sunlight change |
|---|---|---|
| January | -15.6% | -15.9% |
| February | -17.3% | -17.2% |
| March | -21.4% | -19.5% |
| April | -2.0% | -2.5% |
| May | -24.1% | -16.1% |
| June | -23.1% | -14.8% |
| July | -1.9% | +1.0% |
| August | -0.9% | -1.5% |
| September | -10.1% | -4.2% |
| October | +5.1% | +4.6% |
| November | -7.2% | +0.0% |
| December | +4.6% | +5.5% |
| 63 systems with complete 2022 and 2023. | ||
2023 is the clearest case. Production fell in January, February, March, May and June — the same months in which satellite data show 15–20% less sunlight than a year earlier. In July, August, October and December, sunlight and production were both close to 2022. When nearly every system falls in the same months that the sun does, the cause is the year, not the equipment. May and June fell further on rooftops than in the satellite record, which is consistent with low coastal clouds that the coarse satellite grid only partly captures.
Other years are quieter. Production changes of +1.1% (2022), -1.8% (2024) and +0.6% (2025) sit within a few points of the sunlight record. In 2024 the two moved in different directions, mostly because of October and November; monthly totals cannot tell a short monitoring gap from local haze, so we do not attribute it.
Is your drop unusual? Compare your system with the fleet
Subtract the fleet’s change in the same year from your own. What is left is your system’s own change.
| Your change vs the fleet | Where it sits among measured results | Suggested next step |
|---|---|---|
| -2.3 to +2.4 points | Middle half: in line with the fleet | None from this signal alone |
| -5.3 to -2.3 points | Below the middle half, within the usual spread | Compare month by month with last year |
| -7.9 to -5.3 points | Lowest tenth | Find the months where output was lost; check alerts and shade |
| Below -7.9 points | Lowest 5% | Look for flat or zero days, offline panels or inverter faults; consider a check |
| Based on 288 year-over-year comparisons. A screening signal, not a diagnosis of the equipment. | ||
Example: a system that made 9,000 kWh in 2022 and 7,900 in 2023 fell 12.2%. The fleet fell 10.7% that year, so the system was only 1.5 points below the fleet — an ordinary result in a poor solar year. The same 12% drop in a year when the fleet was flat would put the system in the lowest tenth.
Six systems, year by year
Each system against its own typical year (= 100), next to the fleet.
| System | 2019 | 2020 | 2021 | 2022 | 2023 | 2024 | 2025 |
|---|---|---|---|---|---|---|---|
| System A | — | 107 | 104 | 85 | 97 | 102 | 98 |
| System B | — | 107 | 102 | 105 | 98 | 97 | 90 |
| System C | — | 108 | 109 | 108 | 92 | 92 | 92 |
| System D | — | 103 | 105 | 106 | 97 | 95 | 95 |
| System E | 102 | 99 | 102 | 101 | — | 81 | 92 |
| System F | — | 101 | 103 | 102 | 95 | 96 | 99 |
| Fleet median | 100 | 101 | 105 | 108 | 100 | 97 | 98 |
Most of these system-years (64%) sit within 5 points of the fleet line: in a good year everyone is up, in a poor one everyone is down. The exceptions are the useful part. System A fell to 85 in 2022 while the fleet stood at 108, then returned to its usual level in 2023. System E dropped to 81 in 2024 against the fleet’s 97 and moved back toward the fleet in 2025. System B ended 2025 at 90, 9 points below the fleet. One system moving apart while the others hold steady is exactly what a year-to-year check is designed to catch.
The fleet line itself is lower in 2024–2025 than in 2021–2022. Satellite sunlight in 2024–2025 was still about 4% below those years, and three more years of normal aging (typical home systems lose 0.5–1.3% a year; see degradation data) explain part of the rest; dust between rains and the difference between a regional satellite grid and individual rooftops are other possible contributors.
Methodology
- Data source
- Monthly AC energy recorded by SolarEdge inverters in Cali Energy’s monitoring fleet. These are readings from the monitoring system, not from utility revenue meters.
- Systems
- 96 monitored systems; 4 excluded (1 customer system we service but did not install, 1 expanded mid-period, 2 whose output does not match the capacity recorded in the monitoring account). 89 systems have at least one complete system-year.
- Complete system-year
- One system over one calendar year, 2019–2025, with production recorded in all 12 months. Years below 75% of the same system’s own median were treated as downtime and kept out of the benchmark (3 of 388). Result: 385 complete system-years. 2026 is incomplete and not used.
- Unit
- kWh per kW: yearly or monthly energy divided by the system’s DC nameplate rating (kW) as recorded in the monitoring account. It removes system size, so a 4 kW and a 12 kW system can be compared.
- Statistics
- Medians and percentiles (p10, p25, p75, p90), not averages, so a few unusual systems do not move the result. “Middle half” means p25–p75.
- Geography
- Assigned by ZIP code: 49 systems in the San Fernando Valley and Burbank, 21 elsewhere in Los Angeles County, 4 in the Santa Clarita Valley, 4 in Ventura County and 11 elsewhere in Southern California.
- Limits
- Not a random sample of Los Angeles roofs: these are systems we monitor, weighted toward the San Fernando Valley. Roof direction, tilt and shade vary from system to system and are not adjusted for. Customer names and addresses are never published; only aggregates are.
- Year-over-year change
- The same system’s annual production compared with its previous complete year. Years treated as downtime are left out on both sides.
- Your change vs the fleet
- A system’s change minus the fleet’s median change in the same year. It removes the change every system shared.
- Sunlight
- NASA POWER satellite-derived all-sky surface shortwave irradiance (ALLSKY_SFC_SW_DWN) at 34.24°N, 118.50°W. The source grid is about one degree wide, so it describes the region, not a single rooftop.
- Trajectories
- Six systems with at least six complete years, picked at even steps from lowest to highest output. Shown without size, location or install date.
Frequently asked questions
Why did my solar production drop this year?
Most often because the year had less sun. Half of all year-over-year changes on our measured systems fell between -6.3% and +2.0%. Compare your change with the fleet’s change in the same year; a gap of more than about 5 points is the signal worth checking.
Is a 10% drop in solar production normal?
It can be. In 2023 the median system fell 10.7% and 63% of systems fell more than 10%. In a year when the fleet was flat, a 10% drop would put a system in the lowest tenth.
How much does solar output vary from year to year in Los Angeles?
On the same systems, 58% of year-over-year changes were within ±5% and 78% within ±10%.
Why was 2023 a bad year for solar in LA?
Less sunlight. NASA satellite data show 7.3% less sunlight over the San Fernando Valley than in 2022, concentrated in January–March and May–June — the same months in which production on our systems fell.
How do I tell a real problem from a bad solar year?
Subtract the fleet’s change for the same year from your own. If what remains is several points below zero, look month by month for where output was lost, then check alerts, shade and the daily graph for flat or zero days.
More research
Next steps
Your system fell more than the fleet?
Prepared by Cali Energy, October 7, 2026. Figures describe systems in our monitoring fleet and are not a guarantee of what any specific roof will produce; orientation, tilt, shade, equipment and weather change results. Not engineering, financial or utility advice. See our Content Disclaimer.