What Shade Really Costs a Garden Solar Array

The kinked hosepipe

Panels wired in series — a string, the standard arrangement on a single inverter — share one current. Shade a single panel and it cannot pass as much current as its sunlit neighbours, so it throttles the entire string, the way one kink stops a whole hosepipe. Bypass diodes inside each panel soften this by letting current skip shaded cell groups, but they sacrifice that panel's contribution and only work in coarse thirds. The result: shadow covering a tenth of your array's area can remove a quarter to a half of its instantaneous output, depending on geometry. Shade is not proportional. That is the single most important sentence in garden solar.

What an hour of hedge shadow costs over a year

Take the standard garden case: a 1.8kWp PD-sized array, well-oriented, yielding a potential 1,700kWh a year, with a two-metre hedge to the south-west that throws shadow across the lower panel row from about 2pm in winter and 4pm in summer. Model it honestly and the loss lands between 18% and 28% of annual yield — call it 350–450kWh, or roughly £90–£120 a year at 2026 import prices. Compounded over a 25-year panel life, that polite-looking hedge costs more than the entire installation's inverter budget. The same shadow falling at 8am instead would cost half as much: midday hours carry several times the energy of morning and evening hours, so when the shade falls matters as much as whether.

The one-Saturday shade-watch

Pick a clear day within a month or two of an equinox if you can (March, April, September, October give the fairest annual average). Put a broom handle, cane, or chair where the array's centre would be. Photograph it from the same spot every hour from 9am to 5pm. By evening you have the only shading survey that matters for your garden — better than any generic calculator because it captures your hedge, your neighbour's trampoline net, and the washing line nobody mentioned. Two refinements: winter sun runs about 15 degrees lower than your equinox photos, so anything that grazes the site in October blankets it in December; and deciduous trees that look innocent in March cast their real shadows in August, so a second look in high summer is worth the phone storage.

Designing around shade you cannot remove

First preference: move the array. Three metres of repositioning routinely outperforms hundreds of pounds of electronics, and the ground mount guide covers siting flexibility — it is the format's whole advantage. Second: if partial shade is unavoidable, break the string's tyranny with micro-inverters or DC optimisers, which let every panel produce independently; expect to pay £80–£150 per panel extra and recover most of the shade loss that bypass diodes were donating. Third: orient the array so the unavoidable shadow arrives at the cheapest hour — an array shifted to face south-east trades a little afternoon yield for clean morning production ahead of a western shade source. And fourth, the gardener's option: the hedge is sometimes simply negotiable. A metre off its height costs nothing and pays in kilowatt-hours every year.

What does not work: trusting a satellite-view solar calculator that has never met your fence line, or assuming a "small" tree will stay small. Shade is the one input where ground truth beats every model — and you own the ground. Once your shade-watch photos exist, the costs page turns the surviving sunlight into a budget, or send the photos through the contact form and we will read them for you.