Estimate shading losses on your solar array. Input shading percentages by month or time of day, and see annual energy yield impact. Free solar shading analysis tool for designers.
Shading is the single greatest source of underperformance in rooftop solar systems — and it is also the most frequently underestimated. A shadow covering just one panel in a string-inverter system can reduce the entire string's output, meaning a small tree branch could cost you thousands of kilowatt-hours per year. But the relationship between shade and production loss is non-linear, complex, and highly dependent on the type of inverter technology used.
This solar shading analysis tool lets you quantify that impact with precision. Enter your system size, peak sun hours, and shading percentages for each month of the year. The tool calculates your shaded annual production versus unshaded potential, the total annual shading loss in kWh and as a percentage, and the estimated dollar value of that lost production. It also recommends whether a string inverter, power optimizer, or microinverter is most appropriate given your shading scenario.
Use this tool in the design phase to decide whether to reposition panels, remove obstructions, or upgrade inverter technology before installation — before shading silently erodes your system's ROI year after year.
Enter a separate shading percentage for each month to capture how shadow length and sun angle change throughout the year — critical for trees, chimneys, and neighboring structures.
Calculates production loss for string inverters, power optimizers (SolarEdge), and microinverters (Enphase) under the same shading scenario — showing exactly how much more energy MLPEs recover.
Translates annual kWh production loss into a dollar figure using your electricity rate, making the financial case for shading mitigation strategies concrete and compelling.
Use before committing to a panel layout to identify months with significant shading, evaluate whether repositioning panels to a less-shaded roof section is worth the reduced area, and determine whether the inverter technology specified in your quote is appropriate for your shading conditions.
If a system is producing less than its estimated annual production, use this tool to determine how much of the gap can be explained by shading that was not modeled at design time. Compare the shading loss kWh against the actual production shortfall to isolate shading as the cause versus other issues like soiling, degradation, or inverter faults.
When a customer pushes back on the cost premium for power optimizers or microinverters, use this tool to show the annual kWh and dollar gain from upgrading, then calculate how many years the MLPE premium pays for itself in recovered production. This turns a cost objection into an ROI conversation.
Enter System Size & Peak Sun Hours
Input your solar system size in kW DC and your location's average peak sun hours (PSH). If you don't know your PSH, use our Sun Angle Calculator or reference NREL's PVWatts database. Average US PSH ranges from 3.5 (Pacific Northwest) to 6.5 (Arizona/Nevada).
Enter Monthly Shading Factors
For each month, enter the estimated shading factor as a percentage of the array that is obstructed during peak production hours. If you have access to a shade analysis tool (Solmetric SunEye, Polestar, or Aurora's shade tool), use those measured values. If estimating, consider that winter shadows are longest and summer shadows are shortest for fixed-tilt arrays.
Select Inverter Type
Choose your inverter technology: String Inverter (worst shading response), String Inverter + Power Optimizers (SolarEdge-style MLPE), or Microinverters (Enphase-style, best shading response). Each technology applies a different shade impact multiplier, reflecting how MLPEs recover energy that string topologies lose to the "Christmas light effect."
Enter Your Electricity Rate
Input your blended electricity rate in $/kWh from your utility bill. This is used to translate annual kWh production loss into a dollar figure, making the financial case for shading mitigation or panel repositioning immediately tangible.
Review Outputs & Recommendation
Review shaded vs. unshaded annual production, total annual shading loss in kWh and %, estimated revenue loss in dollars, and the tool's inverter technology recommendation. If annual shading loss exceeds 5–8%, the tool will recommend upgrading to optimizers or microinverters and calculate the production gain from doing so.
Output 1
Unshaded Annual Production (kWh)
The theoretical maximum annual production of your system if zero shading existed — calculated from system size × peak sun hours × 365 × system efficiency (default 80%). This is your production ceiling and the baseline against which shading losses are measured.
Output 2
Shaded Annual Production (kWh)
Estimated actual production after applying your monthly shading factors and the inverter-technology shade impact multiplier. For string inverters, shading losses are amplified. For microinverters, losses track more closely to the actual percentage of irradiance obstructed, resulting in significantly higher output under the same shading conditions.
Output 3
Annual Shading Loss (kWh & %)
The difference between unshaded and shaded annual production, expressed both as an absolute kWh figure and as a percentage of unshaded potential. A loss below 3% is generally acceptable for any inverter type. 3–10% warrants consideration of MLPEs. Above 10% indicates severe shading that may require panel repositioning or obstruction removal.
Output 4
Estimated Annual Revenue Loss ($)
Annual kWh shading loss multiplied by your electricity rate. This converts an abstract energy number into a concrete dollar impact you can compare against the cost of mitigation. For example, $300/year in lost revenue from a tree has a compelling mitigation ROI versus a $150 tree trimming service.
Output 5
Inverter Recommendation
Based on your annual shading loss percentage and shading pattern, the tool recommends the most appropriate inverter technology. Mild shading: string inverter acceptable. Moderate shading: power optimizers recommended. Severe or complex shading: microinverters recommended. The potential production gain from upgrading is shown in kWh and dollars per year.
This tool uses a simplified monthly energy model based on NREL PVWatts methodology, modified by inverter-type shade impact multipliers derived from industry testing data (Enphase, SolarEdge, and independent academic studies on partial shading).
Example: 8 kW × 4.5 PSH × 365 × 0.80 = 10,512 kWh/year unshaded
The string multiplier represents the "Christmas light effect" — when one cell in a series string is shaded, the current of the entire string drops to that of the shaded cell. Bypass diodes partially mitigate this, but production losses remain disproportionate to the irradiance blocked.
References: NREL PVWatts System Loss model; Enphase IQ8 Field Performance Study (2023); SolarEdge partial shading whitepaper; IEEE P2800 inverter standards for shading response characterization.
Calculations sourced from SurgePV’s Shading Analysis Tool — surgepv.com/tools/shading-analysis-tool/
Annual production loss estimates for a 8 kW system (4.5 PSH, $0.16/kWh) under varying shading conditions. String inverter losses reflect the "Christmas light effect" on multi-panel strings. MLPE values reflect module-level maximum power point tracking.
| Annual Shading Factor | Unshaded Production | String Inverter Loss | Power Optimizer Loss | Microinverter Loss | MLPE Annual Gain | Recommendation |
|---|---|---|---|---|---|---|
| 2% shading | 10,512 kWh | 420 kWh / $67 | 210 kWh / $34 | 200 kWh / $32 | 220 kWh / $35 | String inverter acceptable |
| 5% shading | 10,512 kWh | 1,260 kWh / $202 | 525 kWh / $84 | 504 kWh / $81 | 756 kWh / $121 | Optimizers recommended |
| 8% shading | 10,512 kWh | 2,312 kWh / $370 | 840 kWh / $134 | 800 kWh / $128 | 1,512 kWh / $242 | Optimizers or microinverters |
| 12% shading | 10,512 kWh | 3,784 kWh / $605 | 1,261 kWh / $202 | 1,200 kWh / $192 | 2,523 kWh / $404 | Microinverters strongly recommended |
| 18% shading | 10,512 kWh | 6,307 kWh / $1,009 | 1,892 kWh / $303 | 1,800 kWh / $288 | 4,415 kWh / $706 | Microinverters required; reconsider layout |
| 25% shading | 10,512 kWh | 9,461 kWh / $1,514 | 2,628 kWh / $420 | 2,502 kWh / $400 | 6,833 kWh / $1,094 | Reassess panel placement first |
The sun's altitude angle is at its lowest during December and January, causing shadows to extend 3–5 times farther than in summer. A chimney that causes no shading in June may shade half the array in December. Always model your worst winter shading case — even if winter production is lower overall, severe winter shading can still cause significant annual losses in northern latitudes.
Not all shading is created equal. Hard shading (solid objects like chimneys, HVAC units, dormer walls) is far more damaging to string inverter systems than soft shading (diffuse shade from haze, clouds, or distant trees). Hard shading on even one cell of a panel forces all bypass diodes in that panel's string to activate, disproportionately cutting output.
Power optimizers and microinverters dramatically reduce shading losses, but they do not eliminate them. Even with module-level electronics, a shaded panel still produces less irradiance. MLPEs prevent the string "Christmas light effect" but cannot manufacture energy that the sun's photons never delivered. Typical MLPE shading recovery is 50–80% of what a string inverter loses.
Trees grow. Neighbors build additions. A 25-year solar investment deserves a 25-year shading analysis. If a nearby tree is currently 20 feet tall and grows 1 foot per year, it could cast a significant new shadow on your array by Year 10 at the latest. Model the future shading scenario, not just today's conditions — and discuss tree trimming rights with the property owner upfront.
Shading reduces the amount of sunlight reaching solar cells, directly cutting current output. In a string inverter system, all panels are connected in series — like Christmas lights — meaning the current in the entire string is limited by the output of the weakest (most shaded) panel. Even partial shading of one panel can reduce the entire string's output by 20–50%, far more than the actual percentage of irradiance blocked. Bypass diodes help but do not fully restore production. Module-level power electronics (microinverters or optimizers) allow each panel to operate at its own maximum power point, virtually eliminating the string effect.
A shading factor is the estimated percentage of an array's irradiance that is blocked by obstructions such as trees, chimneys, neighboring structures, or HVAC equipment during peak solar hours. A 10% monthly shading factor means 10% of the direct-beam irradiance that would otherwise hit the panels is obstructed. Shading factors vary dramatically by month due to changing solar altitude angles — the same chimney may cast a 0% shading factor in June and a 25% shading factor in December. Professional shade analysis tools (Solmetric SunEye, Aurora Solar) measure shading factors with sun-path overlays.
In a string inverter system, all panels in a string share the same DC bus voltage, so shading on one panel forces the inverter's MPPT to find a compromise operating point for all panels — dramatically reducing total output. Microinverters convert each panel's DC output to AC independently, meaning a shaded panel only affects itself. Power optimizers (SolarEdge) provide a middle ground: each panel gets its own DC-DC optimizer that allows individual MPPT, then feeds a central inverter. Both MLPEs reduce shading losses by 50–90% compared to a string inverter with no optimizers.
For string inverter systems, annual shading loss above 5% of total irradiance is generally considered significant and warrants adding power optimizers. Above 10% suggests microinverters are the better choice. For microinverter or optimizer systems, up to 15–20% annual shading is still typically acceptable for a financially viable installation, as MLPE technology recovers most of the lost production. Above 25% annual shading, regardless of inverter type, a serious redesign of panel placement or obstruction removal should be considered before installation proceeds.
The most effective solutions in order of priority: (1) Remove or trim the shading obstruction — tree trimming or removal, relocating HVAC units, or adjusting dormer elements. (2) Reposition panels to a less-shaded roof section, even if it means a slightly smaller system. (3) Upgrade to microinverters or power optimizers to minimize the electrical impact of unavoidable shading. (4) Adjust string configuration — split panels across multiple strings so shading on one string does not affect others. (5) Avoid putting panels in heavily shaded zones entirely.
The Solmetric SunEye is a handheld shade analysis device that uses a fisheye camera and sun path software to precisely measure the solar access percentage for each hour and month of the year at a specific roof location. It produces a detailed shading factor report used in Aurora Solar, PVWatts, and permit documents. SunEye measurements are the gold standard for shading analysis and are required by some utilities and AHJs for interconnection applications. Alternatives include the Polestar shade tool, SolarPathfinder, and software-based tools like Aurora Solar's Lidar-derived shade analysis.
Yes — in most cases. Trees that cause only morning or late afternoon shading (low-angle sun) have far less impact on production than trees shading the array during peak midday hours (10am–2pm). If tree shading is primarily in the morning and evening, annual production loss is often under 5–8%, which may still make solar viable. Dense, tall trees directly to the south (in the northern hemisphere) casting midday shade are the most problematic. Use this tool to quantify the actual annual impact, then decide whether tree trimming, panel repositioning, or microinverters make the project financially viable.
Solar Panel Layout Estimator
Plan how many panels fit on your roof and estimate array dimensions before shading analysis.
Solar Power Calculator
Calculate total system power output, annual production, and capacity factor for any array configuration.
Sun Angle Calculator
Find the solar altitude and azimuth angle for any location and time — critical for calculating shadow lengths.
System Size Calculator
Determine optimal solar system size based on energy usage, peak sun hours, and roof constraints.
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