Does Solar Produce Less Near the Coast in Los Angeles? Measured Output by Area: Coast, Basin and Valleys
Not over a whole year, in our data. From 2023 to 2025, 18 systems on the Westside, in the beach cities and in the South Bay made a median 1,428 kWh per kW a year, about the same as 112 systems in the San Fernando Valley (1,397). The marine layer is real but brief: coastal roofs made 19.9% of their year in May and June against 21.0% in the Valley, roughly 1% of the year. The lowest area was the inland LA basin, at 1,289, and the highest the Santa Clarita Valley, at 1,514. Within any one area, roofs differed by as much as the areas did.
People near the beach often hear that May Gray and June Gloom make solar a poor bet there. Two measures answer two different questions: kWh per kW a year says how much a kilowatt of panels made; the share of the year made in each month says when, and it does not depend on which way a roof faces.
Output by area
Median of each system’s complete years, 2023–2025, both platforms.
| Area | Systems | kWh per kW a year | Middle half | Middle 80% | Share made in May–June | Share made in Dec–Feb | Against the Valley |
|---|---|---|---|---|---|---|---|
| Westside, beach cities & South Bay | 18 | 1,428 | 1,354–1,487 | 1,284–1,569 | 19.9% | 16.8% | +31 (within chance) |
| LA basin inland | 41 | 1,289 | 1,167–1,373 | 1,092–1,422 | 20.7% | 16.7% | −108 (clear) |
| Glendale, Pasadena & San Gabriel Valley | 32 | 1,356 | 1,241–1,430 | 1,184–1,498 | 20.4% | 18.0% | −41 (within chance) |
| San Fernando Valley | 112 | 1,397 | 1,288–1,506 | 1,220–1,588 | 21.0% | 17.1% | — |
| Santa Clarita Valley | 11 | 1,514 | 1,435–1,567 | 1,397–1,617 | 21.4% | 17.5% | +118 (within chance) |
| Conejo & Simi | 14 | 1,410 | 1,316–1,476 | 1,276–1,552 | 20.6% | 17.5% | +13 (within chance) |
| “Against the Valley”: difference of medians, kWh per kW, with a permutation test (clear = p below 0.05). Ventura’s coastal plain has only 4 systems (1,363 kWh per kW) and is left out of the table. Systems are ours, not a random sample of each area. | |||||||
https://cali-energy.com/research/solar-production-by-area-los-angeles. Aggregated data are free to use under CC BY 4.0 with a link to this page.May Gray and June Gloom, measured
Share of the year made in each month: coast minus San Fernando Valley, percentage points.
| Month | Coast | Inland basin | San Fernando Valley | Santa Clarita Valley |
|---|---|---|---|---|
| January | 5.8% | 5.7% | 5.8% | 6.3% |
| February | 6.5% | 6.4% | 6.4% | 6.3% |
| March | 9.1% | 8.9% | 8.5% | 8.1% |
| April | 10.4% | 10.4% | 10.1% | 9.9% |
| May | 9.7% | 10.1% | 10.2% | 10.3% |
| June | 10.2% | 10.7% | 10.8% | 11.0% |
| July | 11.5% | 11.7% | 11.3% | 11.1% |
| August | 10.8% | 10.8% | 10.3% | 10.0% |
| September | 8.5% | 8.2% | 8.2% | 8.3% |
| October | 8.1% | 7.5% | 8.1% | 8.1% |
| November | 5.7% | 5.4% | 5.5% | 5.9% |
| December | 4.9% | 4.7% | 5.0% | 5.4% |
The marine layer shows up exactly where expected. In May and June coastal systems made 19.9% of their year against 21.0% in the Valley, a difference of 1.1 points that is unlikely to be chance (p = 0.02). For the same annual total, that is about 5% less output in those two months. By July the gap is gone, and the rest of the year the coast makes a slightly larger share. Over a whole year, that costs the coast roughly 1% of its output, far less than is often assumed. The inland basin, farther from the water, shows no May–June dip of its own (20.7%).
Why the coast keeps up, and the inland basin does not
A daily-total dataset cannot prove causes, but the measured pieces point one way. Coastal air is cooler: on the hottest days we measured a loss of about 2% of output per 10 °F of daily high, and coastal summer afternoons often run 15–20 °F cooler than the Valley’s, so cooler panels can make up much of what the June overcast takes; see how much heat waves cut output.
The inland basin ran 108 kWh per kW below the Valley, a difference unlikely to be chance (p = 0.002), and it is not a May–June pattern. Two candidates fit. The basin’s air carries more haze, which we measured at about 2% of output per 0.1 of aerosol (smoke and haze, measured); and dense neighborhoods bring more shade from trees and nearby buildings, which daily totals cannot measure.
It is not the equipment: within the Valley, Enphase systems made a median 1,383 kWh per kW and SolarEdge systems 1,403. Weather models see little difference in sunlight between these areas either: ERA5 puts the year at 1,998–2,079 kWh per square meter across our four weather points, with a 25 km grid that smooths over the coastal marine layer.
What it means for your roof
Location within Los Angeles moves output by less than the roof does. The middle 80% of Valley systems spans 368 kWh per kW, and even the middle half spans 218; the gap between the highest and lowest area medians is 225. Orientation, tilt and shade decide more. For a planning number, use the LA-wide figure in real-world solar production in Los Angeles, adjusted for your roof, and check months against the monthly benchmark. If you are near the coast, expect a softer May and June, not a weaker year. Sun-hour figures by city are in Los Angeles sun hours; which utility serves your address is in LA-area electric utilities by city.
Methodology
- Systems
- 232 systems monitored by Cali Energy on Enphase and SolarEdge with at least one complete year in 2023–2025, under the rules of the platform comparison: 12 valid months, no downtime year, a plausible output per kW and a verified DC rating.
- Areas
- Assigned by ZIP code by hand: the coast is the Westside, the beach cities and the South Bay, roughly within six miles of the ocean; the inland basin is central, east and southeast Los Angeles, the Gateway cities and north Long Beach; Glendale, Pasadena and the San Gabriel Valley; the San Fernando Valley with Burbank; the Santa Clarita Valley; Agoura, Calabasas, Thousand Oaks and Simi Valley.
- Measures
- Each system’s median kWh per kW over its complete years, then the median across systems. Monthly shares are each system’s month as a share of its year, which removes the effect of orientation and size.
- Tests
- Permutation tests on the difference of medians against the San Fernando Valley, 10,000 shuffles.
- Limits
- These are systems we monitor, not a random sample; the coast has 18 systems and the Santa Clarita Valley 11, so treat those rows as a signal. Roof direction is not adjusted for in kWh per kW.
Frequently asked questions
Does solar produce less near the coast in Los Angeles?
Not over a year in our data: coastal systems made a median 1,428 kWh per kW a year in 2023–2025, the San Fernando Valley 1,397. The coast makes less in May and June, about 5% less in those months, roughly 1% of the year.
How much do May Gray and June Gloom reduce solar output?
Coastal roofs made 19.9% of their year in May and June against 21.0% in the San Fernando Valley, about 5% less output in those two months and roughly 1% of the year.
Which part of Los Angeles produces the most solar?
In our data, the Santa Clarita Valley, at a median 1,514 kWh per kW a year; then the coast (1,428); the Conejo and Simi area (1,410); the San Fernando Valley (1,397); Glendale, Pasadena and the San Gabriel Valley (1,356). The inland basin was lowest at 1,289.
How much does a solar system produce in the San Fernando Valley?
A median 1,397 kWh per kW a year in 2023–2025 across 112 systems; the middle half made 1,288–1,506. A 6 kW system at the median makes about 8,400 kWh a year.
Does my ZIP code decide how much my panels make?
Less than your roof does. Area medians span 225 kWh per kW; the middle 80% of roofs within the Valley alone spans 368.
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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.