Wybot S2 Solar not charging in the sun: a solar panel reality check

What Wybot publishes about power on this machine

The device specification table in Wybot's official S2 Solar user manual lists a battery voltage of 25.9 V, a battery capacity of 5,200 mAh, a charging time of 3 hours labelled DC charging, a runtime of 2.5 hours, a power figure of 90 W, a charger input of 100 to 240 V at 47 to 63 Hz, and a charger output of 29.4 V at 2.2 A. The US product page for the same machine states a DC output of 29.4 V at 3 A alongside the same 90 W figure, so the two published sources disagree on the charger current. Notice which way the 90 W label points: 29.4 V at 3 A is 88.2 W, while 29.4 V at 2.2 A is 64.7 W, so the 90 W figure is coherent with the product page's current and not with the manual's own. We record both rather than pick one, and the battery arithmetic below is computed without either.

The Wybot S2 Solar record on this site carries the rest of the published sheet: an ideal pool size of up to 3,229 sq ft on an in-ground basis, a working cycle of up to 150 minutes, a 3,962 GPH figure that Wybot's own table labels average suction rate, a 180 micron filter basket with a 40 ppi sponge, and self-parking with an auto return to the solar dock when the battery drops below 20 percent. What appears nowhere across the product page spec table or the user manual is a wattage, current, or area rating for the solar panel itself.

• Battery: 25.9 V, 5,200 mAh (user manual specification table).
• Charging time: 3 hours, stated as DC charging. Runtime: 2.5 hours.
• Charger output: 29.4 V at 2.2 A in the manual, 29.4 V at 3 A on the US product page. Conflicting.
• Solar panel output rating: not published in the spec table, the product page, or the user manual.
• Solar yield: no rating published; a Wybot FAQ card gives one best-case outcome, up to 50 percent of the battery over a full clear day.

The arithmetic the published numbers do support

Two published figures multiply into something useful. A 25.9 V pack at 5,200 mAh is about 135 watt-hours of nameplate battery energy. That is the energy a full charge represents, before any conversion or charging losses, and it is computed only from Wybot's own spec table.

It is worth sanity-checking that against the DC charge path. The manual's charger output of 29.4 V at 2.2 A is about 65 W of nameplate delivery, and 135 watt-hours at 65 W is about 2.1 hours of ideal charging against a published DC charging time of 3 hours. The gap between those two numbers is what taper and conversion losses look like in practice, and the published charge time sitting above the ideal figure rather than below it is the right way round for those two rows to sit together. That coherence is local: as noted above, the manual's own 90 W row does not reconcile with its 2.2 A charger output.

Now the solar side, with our assumptions stated rather than borrowed from Wybot. To replace one full charge, a dock has to deliver at least those 135 watt-hours into the battery, and more than that at the panel once conversion losses are counted. If a dock delivered a steady output of X watts, the hours needed would be 135 divided by X. Assume a usable-sun window of 5 hours and the average delivered power required is about 27 W. Assume 8 hours and it is about 17 W. Those windows are our assumption, not Wybot's, and they are deliberately generous: real panel output is not steady across a day, and neither of those figures accounts for charging losses. The point of running the numbers is not the result but the shape. The answer is entirely determined by the panel's delivered wattage, and that is the one input Wybot does not publish. What Wybot publishes instead is an outcome, on a short FAQ card rather than in the spec table or the manual: that on clear, sunny days with unobstructed sunlight the solar kit can recharge up to 50 percent of the robot's battery over the course of a full day. Read that as the maker's own best-case ceiling, stated as an up-to figure under ideal conditions. Against the 135 watt-hour nameplate above it works out to roughly 67 watt-hours on a perfect day, which is half a charge rather than a charge, and it still does not let anyone compute what an ordinary day of real weather returns.

Wybot's own documented limits on the solar dock

Wybot does put its expectations in writing, and they are more conservative than the marketing. The FAQ block on its US S2 Solar product page states that for heavily soiled pools, such as the first cleaning in spring, relying on the solar-powered dock to charge the robot may not provide enough energy for frequent cleaning, and directs owners to the AC adapter for those cases. For routine maintenance it says to adjust scheduled cleaning intervals based on the sunlight available at the dock location, with less sunlight meaning cleaning every two days or less often.

The user manual says the same thing in its own words. Among the notes on charging with the solar panel it states that if the weather is not favourable, or the robot is at low battery, the recommendation is to put the robot onto the docking station directly. Elsewhere it instructs owners to keep the docking station always powered on for a favourable working status. Read together, Wybot's published position is that the solar dock is a top-up path sized to a maintenance schedule, with the AC adapter as the documented fallback whenever demand or weather exceeds it.

First-run checks and what each light means

The manual's solar charging sequence starts with a check that answers most first-week complaints. Press the start button on the solar kit to turn on the solar panel and docking station, and, in the manual's own parenthetical, if no light is indicated, leave the solar kit and docking station under the sun for two hours. A dock that arrives flat cannot signal anything until it has taken on some charge itself.

The manual publishes a full LED table for both halves of the system. On the robot, solid blue is power on, flashing blue is under working, solid purple is connecting to the app and current cleaning mode, flashing yellow is low battery or self-parking in the pool, flashing green is charging in progress, solid green is fully charged, and red solid or flashing is a fault. On the solar kit, solid blue is power on, solid purple means it is able to control the robot, green solid or flashing is charging, and red solid or flashing is a fault. So the specific answer to whether the dock is charging the robot is a flashing green on the robot, and a green solar kit light means the kit itself is charging.

The manual's troubleshooting table separates the red states that owners most often conflate. Under a device that does not work, it attributes a solid red light to the impeller or filtration basket being stuck, with the published action being to open to clean, and a flashing red light to overheat protection, with the action being to relaunch the device after a while. A flashing yellow light in the same table is low battery, with charging as the action.

• No light on the solar kit at first use: the manual says leave the kit and dock in the sun for two hours.
• Robot flashing green: charging in progress. Robot solid green: fully charged.
• Robot flashing yellow: low battery or self-parking in the pool.
• Robot solid red: impeller or filtration basket stuck, open to clean. Robot flashing red: overheat protection, relaunch the device after a while.
• Solar kit green solid or flashing: charging. Solar kit red: fault.

Placement and maintenance causes Wybot documents

Wybot's Solar Kit Maintenance page is where the solar-specific causes live. It instructs owners to avoid installing the solar kit in shaded areas such as under trees or near buildings, gives an optimal angle of roughly 30 degrees toward the sun adjustable for conditions, and states that dust and dirt accumulating on the panel surface reduce its efficiency, with monthly cleaning using a soft cloth and no sharp tools, strong acids or alkaline solutions. It also notes that hot environments can reduce panel efficiency and that ventilation matters. Its list of things to investigate when charging efficiency drops is worth reading as a checklist: insufficient sunlight or cloudy weather, dirt or debris blocking the panel, scratches or cuts or other surface damage, panel misalignment relative to the sun, loose or damaged connectors, worn or damaged cables, and reduced active panel area after an impact.

The manual adds the physical installation constraints on both halves. The solar kit goes on a flat section of pool deck with no steps or ladders around it, levelled with the level screws and hooked tight against the wall with the angle adjustment screw. For the docking station it specifies that the water depth of the installation area shall reach 1.2 m at least, and that there should be no steps, sitting area or light under the docking station, on a flat spot that will not damage a PVC pool surface. It also states that the docking station should be kept beneath the water when charging starts and that the dock should not be used to charge devices on shore.

For DC charging the manual publishes its own conditions: keep the device at least 3 m (about 10 ft) from the edge of the pool while charging, keep the device and adaptor away from direct sunshine or water when charging, and treat 32 F to 95 F (0 C to 35 C) at 5 to 95 percent relative humidity as the best charging environment. A cold snap or a charger left in full sun both sit outside what Wybot recommends.

The cannot-charge table, and the gap it leaves

The manual's troubleshooting table publishes four rows that bear directly on charging. Under cannot charge, all LED indicators showing green is attributed to sealed parts or the charger being damaged, with contact for change as the action, and no LED indicators showing at all is attributed to the device not having good contact with the docking station, with the action being to adjust the position. Under charger light dies, plugging into a working power supply with no light showing is attributed to a damaged charger. Under cannot be turned on, no LED indicators is attributed to low battery, with charging as the action. And under cannot call the device back to the docking station, the two published causes are no power supply for the docking station, with connect to the power supply as the action, and a docking station that needs calibration, which routes to Wybot for calibration.

That last pair is the one to check before concluding the panel is at fault, because a robot that never reaches the dock produces exactly the same symptom as a dock that cannot charge it. The self-parking behaviour Wybot publishes, an automatic return to the solar dock when the battery drops below 20 percent, depends on the dock being powered and calibrated.

Where this leaves an owner is worth stating plainly. Wybot publishes the conditions that reduce solar output, the LED states, a fallback to the AC adapter, a scheduling instruction tied to available sunlight, and one best-case outcome figure, up to 50 percent of the battery over a full clear day. It does not publish the panel's power rating or any charge-rate curve, so beyond that single up-to ceiling nobody, including us, can compute from the datasheet what a given day of real weather pays for. If your pool needs cleaning on a schedule that the dock is not keeping up with, Wybot's own documented answer is to use the AC adapter and to lengthen the interval, not to expect a specific daily solar yield. Our guides to runtime and battery and cleaning modes cover how the S2 Solar's other published figures compare.