Are solar powered rooflights any good?

The panel is not there to power your house. It is a low-output cell, usually built into the top of the frame or the flashing, and its only job is to keep a small rechargeable battery topped up. That battery runs a quiet chain or spindle motor that pushes the sash open and pulls it shut. Most units come with a rain sensor as standard, so the roof closes itself the moment it starts to spit, and a handheld or wall remote for everyday use.

Because there is no mains feed, the whole thing is sealed. Nothing has to be run through the roof structure, no cable enters the weatherline, and there is no transformer sitting in the loft. The battery is the part that wears, not the motor, and on a good unit it is a replaceable module rather than a throwaway. A single charge holds enough to run the opening cycle many times over, and the panel tops it back up over the following days.

Worth being clear on one point: a solar powered rooflight and a solar-control rooflight are two different things. The first is about how the window opens. The second is about the glass and how much of the sun’s heat it lets through. You can, and on a south-facing roof usually should, have both.

The case for solar is strongest wherever getting a cable to the opening is awkward. On an existing roof, a mains opening rooflight means chasing a wire from a fused spur, up through the ceiling void and along the rafters to the frame, then making good the plaster afterwards. On a solar unit that work disappears. It is the obvious pick for a finished loft conversion, a plastered kitchen extension that is already decorated, or any roof where you would rather not open up a ceiling to feed one window.

It also suits a roof that is a long way from the consumer unit, a listed interior where hidden cable runs are difficult, or a room where you simply want one opening rooflight without the cost of first-fix electrics. Retrofit is where it earns its keep.

Mains still has its place. If you are running several opening units off one wall switch, or tying the roof into a smart-home system or a mechanical ventilation setup, a wired supply is tidier and never needs a battery thought about. On a new-build or a full renovation where the ceilings are open and the electrician is on site anyway, the cable is cheap to run while everything is exposed. And if a rooflight sits in permanent shade, behind a taller building or under heavy tree cover, the panel will struggle to keep the battery charged and mains removes that worry entirely. For most single retrofit openings, though, solar is the sensible default.

Here is the part most brochures skip. An opening rooflight and hot glass solve two different problems, and on a south-facing roof you need to think about both or you will be disappointed with an expensive window.

Opening the roof is your ventilation. Warm air rises, and a rooflight opened at the highest point of the room lets it escape, which is genuinely useful on a summer evening. What opening does not do is stop the sun heating the room in the first place. That is the glass. Southend faces south across the Thames Estuary, so a great many rear extensions and loft rooms here take direct sun from mid-morning until it swings west, with reflected light off the water adding to it. A clear double-glazed unit sitting around a G-value of 0.6 will pour heat into that room whether the sash is open or shut.

So on a south-facing or a flat roof, specify the solar-control glass first and treat the opening as a bonus on top. Ask for glazing with a G-value nearer 0.3, which blocks roughly half the solar heat of a clear pane while still letting plenty of daylight through. A solar powered unit with the right glass is a strong combination: the coating keeps the heat down through the afternoon, and the motor vents the room without you climbing a pole. Get the glass wrong and no amount of opening will rescue it. This is the heart of our energy-efficient skylight installation work, and it is why we ask which way a roof faces before we talk about which unit goes in it.

A few things separate a solar unit you will still be happy with in ten years from one that annoys you by year three.

• Battery replaceability. Ask whether the battery is a serviceable module you can swap, or sealed into the sash. A replaceable battery means the window keeps working long after the first cell has aged. This is the single most useful question to ask.
• Panel position and shading. Check where the cell sits and whether anything, a chimney, a parapet, a dormer cheek, will shade it for large parts of the day. A panel in permanent shade cannot do its job.
• Rain sensor and manual override. Confirm the rain sensor is included and that there is a way to close the unit by hand or on a backup if the battery ever runs flat.
• The glass specification. Get the G-value, the light transmittance and the U-value on a sheet, not a description. “Solar control” is a phrase; the number is what counts. Our guide to a good G-value sets out the figures to aim for by orientation.
• Fit with Building Regulations. A new or enlarged rooflight is notifiable, with Part L covering thermal performance and Part K covering safety glazing. That applies to a solar unit exactly as it does to a fixed one.

Work out the orientation of your roof first. If it faces north or is well shaded, a solar opening rooflight with standard glass will keep you comfortable and is an easy retrofit. If it faces south, east, west or is flat, put a low G-value on your list before anything else and treat the solar motor as the convenience it is. Either way, a solar unit spares you the cable run and the mess of chasing a wire through a finished ceiling.

If you would like us to specify one properly, tell us which way the roof faces and the rough opening size and we will come back with a glass specification and a price. We fit solar and wired opening units as part of our electric skylight installation service, and you can see typical figures on our skylight installation costs page. Ring 01702 898232 or request a quote, and we will look at the whole roof rather than just the hole in it.