Guides
What shade actually costs a solar array
Far more than its area suggests. Panels wired in a string behave somewhat like links in a chain, so one shaded panel drags the whole string below what the unshaded panels could produce. A boundary wall shading a corner for two afternoon hours can cost a disproportionate share of the day.
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Why the loss is not proportional
Current through a series string is limited by its weakest panel. Bypass diodes route around the worst of it and stop hot spots forming, but they cannot restore the lost current. So shading a tenth of the array does not cost a tenth of the output — depending on layout it can cost a great deal more, which is what surprises people reading their first generation log.
The shade nobody surveys for
Morning and late-afternoon shade from a neighbouring plot, a water tank, a stairwell housing, or a tree that will be taller in three years. None of these appear on a satellite image, and all of them are obvious standing on the roof at the right hour. A shading survey means visiting at more than one time of day, not glancing once at noon.
String layout as the free fix
Before spending on electronics, group panels into strings so that shaded ones share a string rather than being scattered across all of them. That contains the loss to one string instead of dragging the whole array. It costs nothing at design time and is awkward to change afterwards, which is why layout deserves attention at the quoting stage.
When to spend on optimisers
Where shade is unavoidable and falls on specific panels, an optimiser behind those panels lets them produce independently of the string. Fitting them only where needed captures most of the benefit for a fraction of converting the whole array. Full microinverters are for arrays where shade moves across many panels or roof faces point different ways.
How much does shade reduce solar output?
A tree shades my roof for an hour. Is it worth removing?
Work out when that hour falls. An hour of shade at 7am costs little because generation is low anyway; an hour at 1pm costs a great deal. Measure which panels it touches and at what time before deciding, because tree removal is permanent and occasionally the array can simply be shifted instead.
Do bypass diodes solve shading?
They limit the damage rather than solving it. A diode routes current around a shaded section so the rest of the panel keeps contributing and no hot spot forms, but the shaded section's output is still lost and the string still runs below its potential. They are a protection feature, not a shade-tolerance feature.
Will panels shade each other?
They will if rows are spaced too closely, and the problem appears in winter when the sun sits low and shadows run long. Proper row spacing is calculated for the worst case rather than for summer. Squeezing an extra row in by tightening spacing is a common way to lose more in December than the row adds in June.
Rather have it done?
When a solar system stops producing, the fault is usually the inverter, a string connector or a tripped protection device rather than the panels themselves. Diagnosis in Islamabad or Rawalpindi starts at PKR 5,000, taken off the bill if you go ahead with the repair.
Solar inverter and panel repair in Islamabad — prices and scope