Do solar-powered skylights work?

A solar-powered roof window carries three working parts. A photovoltaic panel, usually built into the outer frame or sat just above it, turns daylight into a small current. A rechargeable battery stores that current. A motor lifts the sash when the control says so. Remote handsets or wall plates send the commands wirelessly, which is why no switch cable is needed either.

The panel does not need bright sun. Daylight is enough to feed it slowly, and the battery smooths out the gaps. The motor draws power only while moving, so a unit that is opened a couple of times a day for ventilation uses very little. Where the sash must also close for rain, the rain sensor and the motor draw from the same stored charge.

None of this changes the glass. The roof window or rooflight has to meet the same Part L limit for its type as a mains version: 1.4 W/m²K (or Window Energy Rating band B) for a roof window, 2.2 W/m²K for a rooflight on a kerb.

A chalet bungalow bedroom with a freshly plastered and decorated ceiling is one fit, and a loft stair with the nearest socket two floors away is another. Chasing a cable through that is the bulk of the work on a mains retrofit. A solar unit goes into the roof and takes its power from above, so the interior stays untouched.

It also suits a roof window that replaces an old manual one. The opening is already there, the frame sizes follow the same codes, and the fitting day is largely a swap. In a code such as MK04, the letters give the width and the digits the height, and the replacement is matched to that.

An outbuilding or a garden room with no mains supply to its roof is another fit. So is a unit on a roof slope that faces the sun for much of the day.

Shade comes first. A north-facing slope behind a chimney stack gives the panel less to work with, and a battery that is not replenished eventually runs flat. In a Kent winter, short days and low cloud reduce charging for weeks, so a unit that you expect to open and close constantly may stall in January. The panel position is part of the survey: we look at the aspect and at what shades the slope across the day.

Battery life is the second limit. Rechargeable batteries age, and one inside the frame or an adjoining housing may need replacing during the unit's life. We specify a unit where that part can be reached, and the access is described on the quote.

Power for extras can also be restricted. A heavy sash on a large flat-roof lid needs a stronger motor than a small roof window, and a larger motor is a bigger draw. For a large lid, a mains supply is often the better route. Our guide to powering an electric rooflight compares the options in order, and the power cut answer explains what each drive does when the supply drops.

The survey starts with the slope. We note which way it faces, how much of the day it sits in shade from trees, neighbouring roofs or your own chimney, and whether a panel on the frame or beside it would see the sky. We then ask how the glass will be used: a bathroom vent opened once each morning draws far less from a battery than a kitchen rooflight that opens and closes with the weather.

We also look at the size and weight of the sash, since that sets the motor, and at who will operate it. A remote that lives by the bed suits some households, a wall plate by the door suits others. Where the answer comes out as mains, we explain the cable route; where it comes out as solar, the quote names the panel, the battery and the control. Free survey and fixed written quote come either way, with the Building Control notification handled where the work is notifiable, and you can start with the form.