Solar charging and battery

MIYO sensors and valves are solar-powered: an integrated solar panel charges the built-in battery. No battery replacements are needed – provided the devices receive sufficient brightness outdoors. The Cube itself runs on mains power and has no battery.

This page summarizes how charging and the battery work, what you see in the app, and what matters for placement, the start of the season and winter.

Basic principle

The solar panel converts light into electrical energy and recharges the battery.
The battery powers wireless communication, measurements and, on the valve, opening and closing – including at night and in cloudy weather.
Indoor use of the sensors and valves is not intended: behind window glass, the panel practically does not charge.

The panel is efficient and also works with diffuse light. Direct sunlight is helpful but not essential. Devices facing north can also charge well as long as it is bright. Installations in greenhouses work with some systems – whether the solar yield is sufficient must be checked on site; there is no general guarantee.

Solar charging guidelines (reference values)

Topic	Orientation
Light requirements	Continuous full sunlight is not necessary – brightness is sufficient
Maintaining the charge	Usually, approx. 1 hour of strong light per day is sufficient (for the double valve, often only approx. 15 minutes per day)
Fully charge	approx. 40 hours of sunlight until the battery is fully charged
Start of season	Ideally pre-charge the devices in the sun for approx. 5 days
Capacity	approx. 800 mAh – roughly up to 60 days of runtime without recharging (depending on use and temperature)

To maintain the charge during operation, a small amount of daily light is often sufficient; a fully discharged battery needs considerably more time in the sun.

Commissioning and empty battery

Before first use: place the devices in the sun for at least approx. 2 hours.
Battery empty: charge for a day instead; after heavy discharge in the evening, do not expect a long irrigation cycle immediately.
No LED during pairing: the battery is often empty → place the device in the sun for at least approx. 4 hours (not behind glass).
Charging behind a windowpane does not work reliably.

After the first successful installation, automatic irrigation is often locked for safety reasons until the valve's battery has been sufficiently recharged (in practice, this includes a charging period of around 60 minutes). Manual operation (Water now) is often still possible during this time.

What the app displays—and what it does not

There is no classic battery percentage display like on a smartphone. The bars next to the Sensor and Valve in the app generally show wireless signal strength, not the charge level.
In the device details and statistics, you can see, among other things, brightness (lux)—which is closely related to the expected solar yield—as well as messages/alarms for problems.
The Cube calculates charging hours only after the device is connected to the Cube. If the devices were previously left in the sun while unconnected, the counter still starts at 0. Therefore, the app may report “not charged enough yet” even though the device has already been outside for some time.

Solar voltage: The voltage measured at the panel plays a role in the device data and system context (including as an indicator of whether charging can currently be carried out effectively). For firmware updates of the Sensor and Valve, for example, the update is installed wirelessly as soon as the device's solar voltage is above approximately 3.9 V—that is, when sufficient light reaches the panel.

Impact on irrigation

If the circuit setting take battery charge into account (or take battery charging into account) is active:

If the charge is too low or insufficiently replenished, the automation may be unable to open the Valves or may lock the circuit.
Start button greyed out or irrigation does not start: this may be due to an ongoing update or the minimum charging time not yet having elapsed (e.g. approximately 2 charging hours since connection to the Cube). Check the status in the detail view of the Sensor and Valve.

If you are sure that the Valve is sufficiently charged, you can temporarily deactivate the take battery charging into account option for the irrigation area—then the charging logic will no longer block irrigation (devices may still be offline or actually empty). For details on the automation, see Automatic irrigation.

Location: Keep the solar panel clear

Do not cover the solar surface with leaves, soil, or covers.
Choose a bright location if possible; avoid permanently dark niches.
Do not “hide” the Sensor in a depression where little light reaches it.
The antenna is located behind the solar panel, so positioning affects both charging and wireless communication (see Wireless communication).

In very shady locations, devices may use longer communication intervals to save energy (visible in the app). The minimum interval can be adjusted if the location receives little sunlight. Our energy management, enabled by default, automatically adjusts the communication intervals.

Winter and spring

Frost can damage plastic and batteries. At the latest when temperatures fall below approx. 4°C:

Charge the devices well (in plenty of sunlight), then activate winter mode in the app and bring the devices indoors (store them in a dry place).
In winter mode, devices transmit less frequently (e.g., every 4 hours), and the battery often lasts several months at full charge without recharging.
Charging in winter mode is possible and advisable as long as it is above approx. 4°C and bright – charging works regardless of the operating mode.

In spring: reconnect the Cube, place the devices in the sun, end winter mode, and mount them. Before starting the season, follow the solar charging rules again (e.g., charge them for several days in advance).

Typical problems

Symptom	Common cause	What to do
Device unreachable, battery alerts	Battery empty	At least approx. 4 hours of sun (not behind glass)
Automatic mode off / does not start	Insufficient charge, charging counter at 0, update	Check the status in the app and the location; charge if necessary
“Start watering” is grayed out	Update or minimum charging hours missing	Check the detailed view; the counter only starts after connecting to the Cube
Poor charging despite “sun in the garden”	Panel in the shade, leaves, glass, overly dark niche	Clear the panel, choose a brighter location
Firmware update is stuck	Too little light / solar voltage	Wait in sunlight / bright light (solar voltage above approx. 3.9 V)

Quick overview

Sensors and valves: solar panel + battery, no battery replacement
Outdoor brightness is often sufficient; no reliable charging behind glass / indoors
Maintaining the charge with little daylight; fully charging and starting the season require more time in the sun
App: no battery percentage display; charging hours shown only after connecting to the Cube; solar voltage is relevant for updates, among other things
Automatic mode may lock when the charge is low – enable Take battery charge into account and pay attention to alerts
Winter mode in frost, store fully charged, recharge in spring

If problems persist: support@miyo.garden or the FAQ.