The shading problem. How one tree can kill 30 percent of your solar output.

Solar panels are surprisingly bad at handling partial shading. A single overhanging tree branch shadowing one or two panels in a 20-panel string-inverter system can reduce the entire system's output by 25-35%, not by the proportional area shaded. The reason is electrical: panels in a string are wired in series, and the weakest panel sets the output for the whole string.

This shading penalty surprises many solar owners. The system underperforms the installer's projection, and the cause is not the equipment but the design choice between string inverters and micro-inverters.

This post explains the shading problem, the two technical solutions, and the decision rules for each.

How string inverters work

In a string-inverter installation:

• Panels are wired in series into one or two "strings"
• Each string connects to a single central inverter
• The inverter converts DC to AC for grid feed-in

The string's voltage and current are determined by the lowest-performing panel in the string. If one panel is partially shaded and producing 30% of its rated power, the whole string is dragged down to roughly 30% output during the shading period.

The maths is brutal. A 6.6 kW system with 20 panels in two strings of 10. If one panel in one string is 50% shaded for 3 hours per day, the affected string drops to 50% during shading. The whole system loses approximately 18% of its annual output.

If the shading affects multiple panels across both strings, the loss escalates to 25-40%.

How micro-inverters work

In a micro-inverter installation:

• Each panel has its own small inverter mounted on the back of the panel
• Each panel operates independently
• Shading on one panel does not affect any other panel

A 6.6 kW system with 20 panels and 20 micro-inverters. If one panel is 50% shaded for 3 hours per day, that panel produces 50% less during shading. The other 19 panels are unaffected. The whole-system annual loss is approximately 1%.

The shading resilience is the primary technical advantage of micro-inverters.

Cost difference

Micro-inverters cost more than string inverters:

• 6.6 kW string-inverter system: $5,800-7,500 installed
• 6.6 kW micro-inverter system: $7,500-10,000 installed
• Premium for micro-inverter: $1,500-2,500

The premium reflects the higher hardware cost (20 small inverters vs 1 large one) and the additional installation labour.

DC optimisers: the middle option

A third architecture exists. DC optimisers (commonly Tigo or SolarEdge) are small devices mounted on each panel that decouple the panel from the rest of the string. The panel still feeds into a central string inverter, but the optimiser ensures the shaded panel's underperformance does not drag down the rest.

Cost: $400-1,200 above a standard string inverter system. Less expensive than full micro-inverters but provides most of the shading resilience.

The decision: when to pay the premium

The choice between string inverters, DC optimisers, and micro-inverters comes down to expected shading and aesthetic constraints.

Choose string inverters when

• Your roof faces are clear of shade from any direction
• No mature trees within 10m of the panel array
• No buildings, structures, or hills that cast shadows on the array during operating hours
• Cost minimisation is a priority

This is the right choice for most new suburban builds with cleared lots.

Choose DC optimisers when

• Some shading is expected (e.g. occasional tree shadows, a chimney, a satellite dish)
• The shading is on a small portion of the array
• You want better shading tolerance without paying full micro-inverter premium
• Your installer has experience with the chosen optimiser brand

Choose micro-inverters when

• Substantial shading from mature trees, neighbouring buildings, or terrain features
• The roof has multiple faces (e.g. east + west + north) that you want to use
• The roof has unusual configurations that produce shading
• Per-panel monitoring (which micro-inverters enable) is valued for fault detection

How to assess shading before install

Three approaches:

Approach 1: visual inspection at multiple times of day

Stand on the roof or look at it from across the street at:

• 9am (morning sun from the east)
• 12pm (sun at peak northern position)
• 3pm (afternoon sun from the west)

Note any shadows from trees, buildings, chimneys, or rooflines that fall on the proposed panel area at any of these times.

Approach 2: shading analysis software

Most professional solar installers use software (e.g. PVSyst, Helioscope) that models shading using the lot's terrain, the proposed panel position, and the sun path through the year.

A good installer will run this analysis as part of the quote process and tell you the expected annual yield with and without shading impact.

Approach 3: Google Solar API

The Google Solar API includes shading analysis for almost every Australian residential roof. The API returns the annual irradiance for each roof segment accounting for shading from neighbouring trees, buildings, and terrain.

SafeBuy's Solar & Energy tab surfaces this analysis directly.

What about deciduous trees?

Deciduous trees create a particular shading puzzle: they shade in summer but not in winter. The annual yield impact is moderated because winter (when leaves are off) is the lower-yield season anyway.

The implication: an installation shaded by a single deciduous tree may still perform reasonably well, particularly if the shading is morning or late afternoon. Detailed analysis matters.

The future-shading problem

Trees grow. A panel array that is unshaded today may be shaded in 5-10 years as nearby trees mature.

For long-term solar planning, consider:

• The neighbour's growing trees that may eventually shade your roof
• Your own garden trees and whether they will affect future solar
• Council planting on the verge that may affect roof access to sun

Some Australian councils have "solar access" provisions that prevent neighbours from planting trees that would unreasonably shade your existing solar. Most do not.

Shading is the single most important factor differentiating solar yield projections from actual performance. The decision between string and micro-inverter architecture happens at install time and is expensive to retrofit. Knowing your shading situation before the installer's quote saves you either money (no need for micro-inverters) or disappointment (string inverter where micro was needed).