Are solar powered rooflights any good?

What is actually inside one

A small photovoltaic panel sits in the top of the outer frame, above the glass, angled with the roof. It charges a rechargeable battery concealed in the frame head. That battery drives the chain mechanism, the rain sensor and the radio receiver that listens for the remote or keypad. Nothing connects to the house at any point.

The panel is not sized to run the window continuously. It is sized to trickle charge a battery that only ever has to deliver short bursts of work, a handful of times a day. That is why a component people expect to be marginal in an English winter is usually not.

The case they win outright

A finished, plastered, decorated room with a rooflight in it, and no cable anywhere near. Running a mains supply there means lifting floorboards in the room above, chasing plaster, or dropping trunking down a wall in full view. Then making good, then redecorating.

The solar unit removes all of it. There is no fixed wiring, so no electrician, no certificate and no disturbance beyond the rooflight opening itself. In an older Oxford property the argument goes further still, because a lath and plaster ceiling is original fabric and every hole in it is a small permanent loss. Where you would have to damage something historic to run a cable, solar is not a compromise at all.

Where they are the weaker choice

Three situations, and we will name them rather than let you find out.

• Deep shade. A slope overhung by a mature tree, or overshadowed by a taller building next door, gives the panel very little to work with. Charging slows, and in midwinter a heavily used unit can end up waiting.
• A large, heavy sash. The bigger the window, the more work each cycle demands. Mains mechanisms can be sized for the sash; a solar mechanism is sized for the energy available.
• Constrained appearance. The panel is a visible band across the top of the outer frame. On a roof seen from the street, in a conservation area, or where a planning condition speaks to the appearance of the slope, that visibility is a real consideration.

North-facing is worth a sentence of its own. A north slope still receives diffuse daylight and solar units do work there, but the margin is thinner and we would want to look at what else is shading it before recommending one.

How the movement feels compared with mains

Slower, and slightly less determined. A mains unit runs on continuous power and can afford a faster, stronger cycle. A solar unit takes its time, which most people stop noticing within a fortnight, and which is arguably better suited to a bedroom anyway.

The rain sensor behaves identically on both. So does the remote. What differs is that a solar unit will limit itself if the battery is low, deferring a cycle rather than draining itself flat. That is sensible engineering and it is also the moment people ring up thinking something has broken.

Battery life, and what happens at the end of it

The rechargeable cell inside is a consumable, like any battery. Expect many years of service before capacity falls far enough to notice, and expect eventual replacement rather than permanent failure. Manufacturers supply the cell as a spare part and it is changed at the frame head, from inside, without touching the roof.

That is a considerably better position than it sounds. The alternative on a mains unit is not a battery change; it is a cable that was buried in a wall fifteen years ago, and whatever the electrician finds when they trace it.

Solar against mains, honestly compared

The outage point people underrate

A solar rooflight does not know your street has lost power. It keeps its rain sensor live, keeps its receiver listening and keeps its mechanism able to close. A mains unit in the same street stops dead, and if it was open, it stays open until the supply returns.

For a vent over a stairwell or in a room nobody is in during the day, that is not a small difference. It is the strongest technical argument for solar and it rarely appears in a sales conversation.

How we decide which one to put on your roof

Four questions at survey, in this order. Is the ceiling open or finished, and if finished, what is it made of. How far, and through what, would a cable have to travel to reach a sensible control unit position. What falls across that part of the roof between mid-morning and mid-afternoon. And how big is the sash.

Open ceiling, easy route, large unit: mains, with the electrician on first fix. Finished ceiling, awkward route, decent daylight: solar, and the disruption you avoid is worth more than the difference in the box price. Finished ceiling and deep shade is the only genuinely difficult combination, and there the honest answer is sometimes a manual unit with a pole, which we would rather tell you than sell around.

The technical detail of installing without a mains run sits on solar powered rooflights without a mains run, and the cost comparison on how much an electric rooflight costs.

We install new rooflights and full replacements across Oxford and up to twenty five miles by road, with fifteen years in the trade and a ten-year workmanship guarantee, fitting VELUX, Fakro, Keylite and Roto units. Call 01865 704245 or email info@heritageskylightsoxford.co.uk.