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Cali Energy research · Daily index

Was It the Weather or My System? A Daily Solar Index for Los Angeles Since 2022

Every day since January 2022, a median of 162 rooftop systems in our Los Angeles monitoring fleet reported their output. This index shows how much they made as a share of each roof’s own typical clear day: near 100 when the sky is clear, far lower in a storm. On the darkest day of the record, December 24, 2025, it fell to 5.5. If your system was low on a day the index was low too, it was the weather. If it stayed well below the fleet for three days or more while the index was normal, look at the system.

Updated October 15, 2026 · Data through October 9, 2026 · Cali Energy research team · CSLB #1032379 · verify license

1,698
Days in the index, 2022–2026
162
Systems reporting on a typical day
5.5
Lowest day: December 24, 2025, % of a typical clear day
0.7
Times a year a working system runs 3 days in a row 20+ points below the fleet

Check a day

Choose a date. Optionally enter your production that day and on a recent clear day, from your monitoring app.

Was it the weather?

The fleet index is the median of rooftop systems across the Los Angeles area, as a share of each roof’s typical clear day.

Daily fleet index since 2022 (CSV)
How to cite: Cali Energy, “A Daily Solar Index for Los Angeles,” updated October 15, 2026, https://cali-energy.com/research/la-solar-daily-index-weather-or-system. Aggregated data are free to use under CC BY 4.0 with a link to this page.

The darkest days since 2022

Fleet output as % of a typical clear day, with rainfall in the San Fernando Valley that day.

Darkest days in the index
DateFleet indexSystems reportingRain, mm (ERA5)Event
December 24, 2025619577Storm
February 5, 2024615859February 2024 atmospheric river, day 2
January 14, 202378039Storm
February 13, 2025817156Storm
November 15, 2025918440Storm
January 9, 2023107972Storm
February 24, 2023118582Storm
August 20, 20231113759Tropical Storm Hilary
February 16, 20261319744Storm
December 31, 20251419510Rain and cloud
November 14, 20251418436Storm
December 23, 2025141952Rain and cloud
March 14, 2023169243Storm
February 20, 20241615618Rain and cloud
March 10, 2023169114Rain and cloud

Almost every dark day was a storm day: 11 of the 15 darkest brought 20 mm of rain or more, and all 15 left the fleet at under a fifth of a clear day. Tropical Storm Hilary on August 20, 2023 brought the index down to 11, against 102 in the days around it, and the second day of the February 2024 atmospheric river to 6. Panels keep producing in the rain, just very little; how much on each kind of day is measured in solar on cloudy and rainy days.

October 2024: low output that the weather data miss

Mid-October 2024: the fleet against the sky
DateFleet indexSatellite sunshine, % of clear sky (NASA)
October 14, 20246695%
October 15, 20245791%
October 16, 20241672%
October 17, 20243374%
October 18, 202482100%

Mid-October 2024 shows why a fleet index is worth having. Satellite data saw a clear to partly cloudy sky over Los Angeles and almost no rain, yet the fleet made as little as 16% of a clear day; a partly cloudy day normally gives about 70%. It was not one platform’s glitch: our SolarEdge systems, reported separately, made 21% less in October 2024 than in October 2023. Low cloud that a 25–100 km weather grid smooths over is one possible reason. For a homeowner the lesson is simple: when every system around you was low, yours being low was not a fault.

Month by month

Average of the daily index in each month. Darker = less sun reached the panels.

Monthly average of the daily fleet index, % of a typical clear day
YearJanFebMarAprMayJunJulAugSepOctNovDec
2022—10098979810210310195949779
20237585779578781019884989384
2024897287868190979384768082
2025858580838292959386958085
202687869289879393—————
Months with at least 20 days in the index. 100 = a typical clear day for each roof over 2021–2026.
The index year by year
YearDaysMedian dayDays at 90 or moreDays below 50Days below 25
2022350104281184
2023365100231469
202436691200338
2025365952343413
202625297181102
2022 starts on January 16, 2022; 2026 runs to October 9, 2026.

Winter storms and the late-spring marine layer (“May Gray” and “June Gloom”) show up as the darker cells; July and August are the steadiest months. 2023 had the most dark days of the record. The index runs lower in 2024 and 2025 than in 2022 for two reasons: more cloud in some months, and output on clear days that stayed below its 2022–2023 level — a shortfall described in real-world solar production in Los Angeles.

Two eclipses, barely visible in the data

Partial solar eclipses in Los Angeles
DateFleet indexMedian of the 3 days before and after
October 14, 202398101
April 8, 202499104

Los Angeles saw both recent eclipses only as partial ones, for about two hours in the morning. The fleet index dipped to 98 and 99, a few points below the days around them — a smaller loss than an ordinary hazy day.

When low output is not the weather

How often a working system lands 20+ points below the fleet on the same day.

Runs of days at least 20 points below the fleet index
Days in a rowTimes a year, typical system
1 or more8.1
2 or more1.7
3 or more0.7
5 or more0.3
7 or more0.2
Counted over all systems and days in the index, including systems with real faults, so the true rate for a healthy system is lower still.

One low day against the fleet is common — about 8 times a year for a typical system: a shadow from a passing cloud, a short monitoring gap, a neighbor’s tree in the low winter sun. Three days in a row at 20+ points below the fleet happened less than once a year (0.7). That is a good trigger: check the app for offline panels or alerts, look at the roof for new shade, and if nothing explains it, ask for a check. Step by step: solar not producing; if the app itself has gone silent: solar app says offline.

Methodology

Systems
Enphase systems in our monitoring fleet with clean daily data (219 systems, 234,215 system-days in the index). A day enters the index when at least 30 systems report; the median day has 162.
Clear-day reference
For each system and date: NASA POWER clear-sky sunlight that day times the system’s 90th-percentile ratio of output to clear-sky sunlight within ±10 days of the year, over all its years. This puts each roof’s direction, tilt and shade into its own reference.
Index
Median across systems of output ÷ reference, rescaled so that the median clear day (ERA5 sky 90% or more) equals 100. Values above 100 happen on very clear, cool days.
Weather
Rain and sky from ERA5 (ECMWF / Copernicus, via Open-Meteo) at the San Fernando Valley point; NASA POWER satellite sunshine as a check.
Excluded
March 8, 2026, a daylight-saving recording fault in Enphase data. Days with fewer than 30 systems.
Limits
One index for the whole Los Angeles area: local fog, a neighborhood storm cell or a power outage on your street can differ from it.

Sources: Cali Energy monitoring fleet (Enphase); NASA POWER daily solar data (power.larc.nasa.gov); ERA5 reanalysis, ECMWF / Copernicus, via Open-Meteo (open-meteo.com).

Frequently asked questions

How do I know if low solar production was the weather?

Look up the same date in the index above. If the fleet was low that day too, the weather explains it. If your system stayed 20 points or more below the fleet for three days in a row, look at the system.

What was the worst day for solar in Los Angeles recently?

In our index, December 24, 2025: rooftop systems made 6% of a typical clear day, in a storm that ERA5 puts at about 77 mm of rain in the San Fernando Valley.

How much did Tropical Storm Hilary cut solar output in LA?

On August 20, 2023 the fleet made 11% of a typical clear day, against about 102% in the days around it.

Did the 2024 eclipse affect solar panels in Los Angeles?

Only a little. On April 8, 2024 the fleet index was 99, a few points below the days around it; in Los Angeles the eclipse was partial and brief.

Why was solar output so low in mid-October 2024?

Our fleet made as little as 16% of a clear day while satellites saw a mostly sunny sky. Both Enphase and SolarEdge systems showed it; the cause has not been established.

More research

ResearchHow Much Do Solar Panels Produce on Cloudy and Rainy Days?Partly cloudy about 70%, mostly cloudy about 44% of a clear day, measured day by day.ResearchHow Much Did LA Heat Waves Cut Rooftop Solar Output?215 roofs, every heat wave since 2022: 2.6% less per unit of sunlight on 95 °F days, about 0.2% of a year.ResearchSolar App Says Offline or Shows an Alert?What an offline app means for production: how long gaps in monitoring data last, and what SolarEdge alerts turned out to be.ResearchDid Wildfire Smoke Cut Rooftop Solar Output in LA?January 8, 2025: basin systems at 64% of their pre-fire output for the sunlight; every hazy day since 2022 costs about 2% per 0.1 of aerosol.

Next steps

Low output that the weather does not explain?

ServiceOutput looks low? Ask us to check itSend a year of production and your system size. We compare it with this data and look for shade, offline panels or an inverter fault.Case studyThe inverter said nothing was wrong. The output disagreed.A Tarzana system underproducing with no error code, traced and fixed on site.Case studyThe portal said no production. The system was running fine.Eight days of zeros in a monitoring app — and why that is not always lost production.InstallationSolar sized for your roof and usageWe size from 12 months of kWh and your roof’s direction, tilt and shade, not a city average. Terms in writing.

Prepared by Cali Energy, October 15, 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.

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