Shade has three shapes, and only one of them is the obvious one
Most people picture shade as a dip in the middle of the day. That is the least common version. On real roofs, shade usually lives at the edges of the day — the sun is low, so anything to the east or west casts a long shadow across the array.
- Starts late. The panel produces nothing for the first hours of daylight, then comes up and joins its neighbours for the rest of the day. Something to the east: a tree, a neighbour's roofline, a hill.
- Stops early. The panel tracks its neighbours all day, then drops to nothing well before sunset and stays there. Something to the west.
- A bite out of the middle. Less common, and usually something small and close — a chimney, a vent pipe, a mast — crossing the panel as the sun passes it.
In all three the output goes to the floor, not to a gentle sag. A shaded microinverter stops; it does not idle. That sharpness is what makes shade recognisable once you have seen it once.
How to tell shade from a panel that is failing
This is the question worth answering, because the two cost you the same power and have completely different fixes. From a monthly or weekly total they are indistinguishable — both just read "low". From the shape of a single clear day they are obvious.
- Shade has edges. Output falls off a cliff and comes back up one. A fault has no edges — the curve keeps its normal shape at a lower height.
- Shade has a clock. It happens at the same time tomorrow, and the time drifts slowly through the year as the sun's path changes. A fault is there all day, every day, and does not move with the seasons.
- Shade lets go. Before and after the shadow, the panel matches its neighbours exactly. A failing panel never matches them.
One more discriminator, if you have per-panel data: compare the panel with the others on the same roof face, not with the array average. A north-facing panel is meant to produce less than a south-facing one — that is geometry, not a fault, and comparing across faces manufactures problems that are not there.
A caution worth stating plainly: production data can tell you that something is blocking the light. It cannot tell you what. A branch, a vent, bird mess, and a dirty patch all look identical from the electricity. Only a look at the roof settles that.
What shade actually costs
Across the roofs we currently monitor, a single residential panel is expected to produce roughly 600 to 700 kWh a year — measured from each roof's own orientation, tilt, and panel rating rather than a rule of thumb.
So a panel losing half its output to shade loses about 320 kWh a year. What that is worth to you depends on one thing: whether you would have used that power or exported it.
- One panel at 50% shade: about $95 a year if it offsets power you would have bought at roughly $0.30 a kWh, or about $16 a year if all of it would have been exported at a NEM 3.0 credit nearer $0.05.
- Ten panels at 50% shade: about 3,200 kWh a year — roughly $950 at the retail end, or about $160 at the export end.
- Over ten years, those ten panels are somewhere between about $1,600 and $9,600, before any rate rises.
Two honest notes on that range. First, shade concentrates in the early morning and late afternoon, which in many households is exactly when someone is home and the power is being used rather than exported — so the retail end is often the closer one. Second, we have deliberately not given you a single confident figure, because your rate plan and your usage pattern decide it, and a vendor quoting one number for every home is guessing at yours.
The reason any of this is worth knowing is that none of it shows up on your bill. A quarter of your array quietly producing less is invisible against seasonal swings, weather, and a rate change. It does not fail, it does not alarm, and it does not appear at the meter. It just never arrives.
How common is it, really
We can only tell you what we measure. Across 138 panels on five homes as of August 2026, 40 panels lost more than a tenth of their expected output to shade, 16 lost more than a quarter, and 5 lost more than half.
Five homes is a hint, not a national statistic, and you should treat it as one. What it does suggest is that shaded panels are not exotic — most arrays have a few, and almost nobody knows which.
What you can actually do about it
In rough order of how much it costs you to act:
- Find out which panels, and when. This is free and it changes everything else. "The array is a bit down" is not actionable; "these three panels lose most of their morning, and it starts around the same time each day" tells you where to stand and what time to look.
- Go and look at the roof at that time of day. The single highest-value step, and the one people skip. Shade at 8am is invisible at noon. If the data says mornings, go out in the morning.
- Wash the panel. Cheap, and worth ruling out first — soiling and shade both cut output, and a shadow tends to keep a patch damp and dirty. If a wash changes nothing, you have learned something.
- Trim it only if it is actually yours to trim. Sometimes a branch is a one-afternoon job. Often it is a neighbour's tree, a protected one, or a roofline — and then trimming is not on the table at all. Get the timing from the data first, so you find out which case you are in before you start ringing arborists.
- Decide, and stop paying attention. If it is a chimney, a dormer, or a neighbour's protected oak, the answer is that this panel produces less and always will. Knowing that is worth real money in attention you stop spending, and it stops you chasing a fault that was never there.
And one thing not to do: don't order a replacement microinverter because a panel reads low. On SunPower Type E / IQ7X systems, replacements must be voltage-matched — standard Enphase IQ7+ or IQ8+ units are destroyed by the high-voltage X-Series panels they would be fitted to. Diagnose freely; buy parts carefully.
How to see this on your own system
Your gateway already knows
If you have a SunPower or Enphase microinverter system, every panel already reports on itself. A PVS6 gateway holds per-panel output on its local interface, and free open-source projects read it directly if you are willing to run and maintain one.
SunStrong Premium
The official route for SunPower owners. Panel-level monitoring and history sit in the Premium tier at $9.99/mo or $99.99/yr. The free Basic tier does not include per-panel data, and without per-panel data none of this page is checkable on your own roof.
Plug a monitor into the gateway you already own
The WattHacker monitor reads the same local per-panel data, and per-panel output is free, forever — no subscription, no card on file. That is enough to do everything above yourself: pick a clear day, look at the panel's shape, compare it with its neighbours.
The shade measurement — each roof face sampled on its clearest days, month after month, each panel compared with its own neighbours, and the loss added up in kWh — is part of the premium plan, because it needs history a free account does not keep. Being straight about that: the free tier holds 7 days, and a cloudy week can hold no clear day at all. Where a year is not yet complete we say how many months were actually measured rather than filling in the gaps quietly.
And we say a panel looks like shade, never that we detected it. The shape test is sound; we have not measured how often it is wrong. So we tell you which part of the day it falls in, show you your own curve, and let you check it. That is the honest version of this feature, and it is the one we ship.
Where WattHacker fits
The WattHacker monitor is a small box that plugs into your existing SunPower PVS6 gateway on your own home network and reads it directly. It doesn't rely on SunPower's or SunStrong's servers, because for owners like you those are either gone or behind a paywall. No technician, no electrician, no rewiring — you plug it in yourself.
- The monitor is $99 once, with a 30-day money-back guarantee.
- Free to see your panel data, forever — every panel, live, no subscription, and no card on file.
- An optional premium plan at $6/mo (billed annually) adds the memory: full history kept for good, year-over-year comparison, and alerts told to you in dollars.
- Built by an electrification superfan who wants to help others use their solar smarter, lower their utility bills, and clean up the planet. Who's behind it.
Still have questions about your own system? I'll go through it with you — your panels, your bill, and what's worth doing about it.
Book an energy reviewReal panels, real production, no signup.
Common questions
How can I tell if a solar panel is shaded or broken?
By the shape of a single clear day. Shade takes a panel's output to near zero for part of the day and lets it go — the drop has edges, and it happens at the same time tomorrow, because it is the sun moving past a fixed object. A failing panel is down all day in proportion: the curve keeps its shape and loses height, with no edges and no recovery.
What does shade on one panel cost per year?
A residential panel on the systems we monitor is expected to produce roughly 600 to 700 kWh a year. A panel losing half its output to shade loses about 320 kWh a year. What that is worth depends on whether you would have used that power or exported it: at a retail rate near $0.30 a kWh it is about $95 a year, and at a NEM 3.0 export credit nearer $0.05 it is about $16.
What does shade on ten panels cost?
Ten panels each losing half is roughly 3,200 kWh a year — about $950 a year at a $0.30 retail rate, or about $160 if all of it would have been exported. Shade usually falls in the early morning and late afternoon, which for many households is when someone is home using power, so the retail end of that range is often the closer one.
Does shade on one panel drag down the whole string?
Not on a microinverter system, which is what SunPower and Enphase installations use. Each panel has its own inverter, so a shaded panel loses its own output and nothing else. Older string-inverter systems without optimisers are the ones where a single shaded panel can pull down its whole string.
Can shade be fixed?
Sometimes. A branch can be trimmed, a dish or an aerial can be moved, and soiling under a shadow can be washed. A chimney, a dormer, a roofline, or a neighbour's protected tree usually cannot — and knowing which one you have is worth more than guessing, because it tells you whether to spend money on it or stop thinking about it.
See your own panels, live.
See plans Try the demo Back to home