A skylight cleaning robot covers 200 to 350 m2 per hour on flat glass and 120 to 220 m2 per hour on sloped glass. Battery runtime of 4 to 6 hours and a 15 to 20 litre tank usually cap a single continuous run well before the machine is worn out.
Vendors love the top number. Nobody cleans at the top number all day. Ramp turns, slope changes, mullion crossings and refills all eat into it, and the honest planning figure is closer to 60 to 70 percent of the peak rate.
What sets real output per hour?
| Surface | Peak m2/h | Planning m2/h |
|---|---|---|
| Flat glazing | 300 – 350 | 200 – 250 |
| Low slope (0-15 deg) | 220 – 300 | 150 – 210 |
| Steep slope (15-30 deg) | 150 – 220 | 120 – 170 |
| Cluttered geometry, mullions | 100 – 180 | 80 – 130 |
Geometry beats slope. A flat roof full of roof vents, skylight hatches and shading fins will run slower than a clean 20-degree slope, because the robot spends more time repositioning than cleaning.
How far does one battery charge actually go?
A 4 to 6 hour runtime sounds generous until you convert it. At a planning rate of 200 m2/h, that is 800 to 1,200 m2 on one charge, minus any downtime. Cold weather cuts runtime: below 5 degrees Celsius, expect 15 to 25 percent less, which on a winter job can mean a second charge or a tethered unit.
Here is where a tether wins. A corded or tether-powered machine like a tracked flat-roof unit runs all day without a recharge, at the cost of dragging a line. Battery units trade the line for a runtime ceiling. Pick based on roof size, not preference.
Is the tank or the battery the limiting factor?
Usually the tank. A 20 litre tank at 0.05 to 0.08 litres per square metre covers 250 to 400 m2. That is less than a full battery charge on flat glazing, so on big roofs you refill before you recharge. Plan refill points where a tap and a safe walkway meet, and you lose 10 to 15 minutes per refill instead of half an hour.
- Dry or minimum-water mode: no refill limit, slightly hazier finish.
- Wet mode, 20 L tank: refill every 250 – 400 m2.
- Two tanks or a refill cart on the roof: keeps the robot moving.
How do you plan a day of work?
Start with the total glass area, divide by the planning rate, then add refills and setup. A 1,500 m2 flat glass roof at 220 m2/h is about 7 hours of cleaning, plus 30 minutes setup and two refills, so one long day for one operator. Put that same roof at 25 degrees slope and the same job stretches to a day and a half. Quote the sloped roof at the higher rate and you will miss the schedule.
Who should care most about output numbers: teams paid by area, and anyone promising a client a one-day turnaround. Get the planning figure right and the promise holds. Use the peak figure and you will be back on site for free.
What wastes the most time on a real job?
Setup and repositioning, not cleaning. Getting the machine to the roof, fixing the tether, filling the tank and running the first self-check can take 30 to 45 minutes before a single square metre is cleaned. Then every slope change or obstacle costs another reposition. On a roof with twelve small skylights scattered across a plant area, the machine may spend more time moving than cleaning.
Cut that waste with staging. Group skylights that share a walkway into one run, leave the tank and water point at the midpoint, and keep the recharge point close to the hardest zone. A site that stages well gets 20 to 30 percent more area per shift than one that carries everything from a single corner.
How do weather and season reshape output?
Output is not constant through the year. In summer heat, cleaning early keeps water from flashing dry and leaving spots, and it keeps the operator out of peak sun. In winter, battery runtime drops and water can freeze in the tank and lines, so plan shorter sessions and drain the system after use. Shoulder seasons, spring and autumn, are the most productive because glass temperature is moderate and daylight is long enough.
Rain is the wildcard. A wet roof after rain is the most dangerous surface for any suction robot, and the day after rain the glass is often at its dirtiest. Build a flexible schedule that can shift a clean by a day or two rather than forcing it into the wrong weather window.
How do you compare machines on a level footing?
| Metric | What to ask for | Red flag |
|---|---|---|
| Output | Planning m2/h on 20 deg glass | Only a peak figure |
| Runtime | Hours at 5 deg Celsius | Only a warm-weather number |
| Tank | Litres and m2 per fill | Litres only, no area |
| Refill time | Minutes with a safe water point | Not mentioned |
Ask every supplier for the same four rows and the comparison becomes honest. A machine that wins on peak output but loses on cold-weather runtime will disappoint on a winter contract, and you will only know if you asked the right question before buying.
Key Takeaways
- Peak output is 200 – 350 m2/h flat, 120 – 220 m2/h sloped.
- Plan on 60 – 70 percent of peak to account for geometry and turns.
- Cold weather cuts battery runtime by 15 – 25 percent.
- Tank capacity, not battery, limits most wet jobs; refill every 250 – 400 m2.
- Quote from the planning rate, never the peak rate.
Want an output estimate for your glass area and slope? Send the numbers through the contact page, or read the cost and payback guide next.