Solar Shading by Time-of-Day Calculator

Enter obstruction height, distance, and direction — get a 6am–6pm shading table, shade-free window, and annual energy loss estimate.

Location & obstruction details

City / location?

Obstruction height?

Obstruction distance?

Obstruction direction (S)?

Panel tilt angle?

Panel azimuth (facing direction)?

Month to analyze?

Shading analysis — December

9 shaded hrs, 0 shade-free hrs of 9 daylight hrs

Hour	Sun Altitude	Sun Azimuth	Status
6:00	-12.7°	110°	Below horizon
7:00	-1.3°	118°	Below horizon
8:00	9.3°	126°	SHADED
9:00	18.6°	137°	SHADED
10:00	26.1°	149°	SHADED
11:00	31.1°	164°	SHADED
12:00	32.9°	180°	SHADED
13:00	31.1°	196°	SHADED
14:00	26.1°	211°	SHADED
15:00	18.6°	223°	SHADED
16:00	9.3°	234°	SHADED
17:00	-1.3°	242°	Below horizon
18:00	-12.7°	250°	Below horizon

This month shade loss100% of daylight hours shaded

Annual energy loss estimate~42% annual production loss

Best month (least shade)March (0% shaded)

Worst month (most shade)January (100% shaded)

Recommendation: Severe shading. Relocating panels is strongly recommended. This obstruction will reduce production by more than 30% — the financial case for solar at this location is compromised.

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How to Use This Calculator

Enter your location and obstruction details

Select your city from the dropdown — this sets the latitude for accurate sun position math. Then measure your obstruction: height above the panel level in feet, horizontal distance from your panels to the base of the obstruction in feet, and compass direction from your panels to the obstruction (180° = directly south). If you don't have a compass, stand at your panels and face the obstruction — a compass app on your phone gives the bearing.

Enter panel orientation

Panel tilt is the angle from horizontal (flat = 0°; steep pitched roof = 35-40°). Panel azimuth is the direction your panels face: 180° is true south (optimal for northern hemisphere), 90° is east, 270° is west. These inputs refine when during the day your panels are most productive and how obstruction angle interacts with panel geometry.

Read the hour-by-hour shade table

The table shows sun altitude (degrees above horizon), sun azimuth (compass bearing of the sun), and whether your panels are shaded for each hour from 6am to 6pm in the selected month. Red "SHADED" means the obstruction's shadow angle exceeds the sun's altitude in that direction. Green "Sun" means full sun. The annual energy loss estimate averages all 12 months.

The Formula

Hour Angle (deg) = (Solar Hour - 12) x 15 Sin(Altitude) = Sin(Lat) x Sin(Decl) + Cos(Lat) x Cos(Decl) x Cos(Hour Angle) Cos(Azimuth) = (Sin(Decl) - Sin(Lat) x Sin(Alt)) / (Cos(Lat) x Cos(Alt)) Obstruction Angle = arctan(Height / Distance) Effective Obstruction = Obstruction Angle x Cos(Sun Azimuth - Obstruction Direction) Shaded = Sun Altitude < Effective Obstruction Angle Annual Loss = Average(Monthly Shaded Hours / Monthly Daylight Hours) x 100%

The sun position model uses hour angle (15° per hour from solar noon) and monthly solar declination — the sun's angle above/below the celestial equator, which drives seasonal variation. The effective obstruction angle decreases with angular separation between the sun's azimuth and the obstruction's direction — a tree due south only shades you when the sun is near south; a tree due east only matters in the morning. This geometric model produces accurate results to within 1-2 degrees.

Example

David — 40-foot tree directly south of panels in Atlanta, GA — December

David installed 12 solar panels on his south-facing roof. A 40-foot oak tree is 30 feet due south of the panels. He wants to know if trimming it is worth the cost.

LocationAtlanta, GA (33.75°N)

Obstruction40 ft tall, 30 ft south (180°)

Obstruction anglearctan(40/30) = 53°

Month analyzedDecember (sun declination: -23.4°)

Result

Solar noon altitude (Dec)32.9° (Atlanta 33.75° - 23.4° decl)

Shaded hours (Dec)7 of 9 daylight hours (77% shaded)

Best monthJune (sun rises high enough to clear the tree)

Annual energy loss~38% annual production loss

The tree's shadow angle (53°) exceeds the December solar noon altitude of 33°, meaning it shades the panels almost all day in winter. David's annual loss is 38% — tree trimming to 20 feet would drop the shadow angle to 34°, saving most of that winter production. The trimming cost ($500-1,500) pays back in 1-2 years of recovered solar production.

FAQ

How much does shading reduce solar panel output? ▼

In traditional string inverter systems, even partial shading of one panel can reduce output of the entire string by 30-80%. With microinverters or DC power optimizers (SolarEdge, Enphase), each panel operates independently, so one shaded panel only loses its own production. The energy loss calculation in this calculator represents direct irradiance loss — add 5-10% for string inverter losses if you don't have microinverters.

What direction is worst for shading obstructions? ▼

In the northern hemisphere, obstructions to the south (150°–210°) cause the most damage because the sun is always in the southern half of the sky. An obstruction directly south blocks the sun at peak altitude — when it produces the most power. Obstructions to the north have almost no effect (the sun is never in the north). East obstructions reduce morning production; west obstructions reduce afternoon production — both are less impactful than south obstructions because those hours generate less power per hour than midday.

At what distance does a tree stop shading my panels? ▼

The shadow angle formula is: arctan(tree height / distance). A 30-foot tree at 30 feet away creates a 45° shadow angle. The same tree at 60 feet away creates a 26° shadow angle. In Atlanta with a December solar noon altitude of 33°, the tree stops causing noon shading when the shadow angle drops below 33°, requiring it to be at least 44 feet away. Use this calculator to test distances — enter the same height with increasing distances until shaded hours drop to zero.

Should I get microinverters or power optimizers if I have shading? ▼

Yes — if you have unavoidable shading and can't relocate your panels, microinverters (Enphase) or power optimizers (SolarEdge) are highly recommended. They prevent the "Christmas lights effect" where one shaded panel drags down the whole string. The premium over string inverters is $500–1,500 and pays back in 2-4 years in recovered production from partially shaded installations. This is standard advice for any installation with more than 5% shading.

Why does a south-facing tree cause more shading in winter than summer? ▼

In winter, the sun stays low in the sky all day (low solar declination of -23.4° in December). In Atlanta, the sun only reaches 33° above the horizon at noon in December, versus 79° at noon in June. A 40-foot tree at 30 feet has a shadow angle of 53° — it blocks the sun all winter but not the high summer sun. This is why shading analysis must cover the entire year — a tree that causes no summer shading can devastate winter production when solar irradiance is already lower.

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