Smart Solar Plus: surplus solar power becomes hot water

Updated 12 October 2026SmartKnob

Anyone with solar panels knows this: at midday the battery is full, the solar charge controller throttles back, and the best power of the day sits unused on the roof. Smart Solar Plus spots exactly this moment and sends the surplus where it is useful to you: as heat into the boiler, as cold into the cool box or as charge into your batteries. Fully automatic, without you having to stand next to it at midday.

Smart Solar Plus controls everything connected to Switchy or Ampy, from the charger to the boiler.

Smart Solar Plus widget with solar power, battery level and target

How the SmartKnob recognises a real surplus

It does not just look at a single value, but at four things at the same time:

  • how full the battery is,
  • how much power is coming from the solar panels,
  • whether the solar charge controller is already throttling back because the battery cannot take any more. Then there is a proven surplus.
  • and, if a battery monitor is installed, whether power is currently flowing into or out of the battery. This way your devices only run as long as the battery does not get emptier.

Once Smart Solar Plus is running, a cloud will not throw it off. The battery bridges short shadows, that is what it is there for. It only stops when the battery drops below your stop limit or really discharges over several minutes.

The tile always tells you what is going on, for example "Waiting · battery below 95%", "Waiting · not enough sun", "Checking stability · about 4 minutes" or "Active · using surplus".

What you do with the surplus

  • Charge batteries when the sun pays: e-bike, power station, tool, camera or laptop batteries charge exactly when the sun delivers more than your leisure battery needs. Whatever can wait, waits for the sun instead of nibbling away at your reserve.
  • Store heat: with the surplus, the boiler heats beyond its normal temperature and stores the energy as hot water. A warm shower in the evening with the sun from midday. The weekly hygiene programme and the hot water timer also prefer to use the surplus. Everything about the boiler is in Smart boiler control: the boiler widget.
  • Store cold: a cool box, freezer box or second fridge on Switchy or Ampy cools down properly at midday with the surplus and lives off it in the evening. The compressor stays quiet at night.
  • Run what can wait: dehumidifiers, roof fans or a fan that cools down the interior run along as long as there is a surplus, and then switch off again. Anything you switched on yourself stays on, of course.

Boost temperature for the boiler and devices that run along with the surplus

You decide, the SmartKnob does the work

You can set what matters: at which battery level it starts (default 95%), at which it stops (default 90%), how much solar power must at least be available and, for the boiler, up to which temperature it may heat. The SmartKnob takes care of the rest. If you have several solar charge controllers, it adds up their power, and a controller without sun does not slow down the automation.

Solar surplus settings with start and stop battery level

Safety stays in place: for the boiler, all protection functions apply, such as dry-run, overtemperature and fresh water protection. And you always have the last word. If you switch something yourself during surplus operation, your decision applies immediately, and the automation holds back until the surplus has ended once. Every start and every end is recorded in the log.

12V, 24V or 230V

Devices connected directly to the leisure battery at 12V or 24V run with the surplus straight away. This is the most efficient, because nothing needs to be converted. Devices with 230V, for example many e-bike chargers or power stations, need a running inverter.

  • Inverter automation: the SmartKnob switches your inverter on by itself as soon as there is a surplus for a 230V device, and off again afterwards. Supported are, for example, the Victron MultiPlus, inverters from Victron or Votronic or a relay on Volty.
  • Pre-cool the fridge: with the fridge widget, the surplus specifically lowers the target temperature of your fridge. The sun pays for the cold during the day, and in the evening the compressor stays quiet. This needs a RuuviTag in the fridge.

Licence and requirements

  • Smart Solar Plus is an add-on feature with a licence. You unlock it with a licence key in the settings, and it is active immediately, without a restart.
  • The SmartKnob and Volty with a solar charge controller. A battery monitor, for example a SmartShunt, is recommended for the exact battery level and for protection against discharging.
  • Switchy or Ampy for the devices that should use the surplus.
  • For heat storage, a set-up boiler widget with a temperature sensor.

Related questions

How do I connect a new module to the SmartKnob?

Pairing practically takes care of itself. You start it on the SmartKnob or in the dashboard and then power up the module. An LED and a sound on the SmartKnob confirm that the connection is up. That is all there is to it: no cable to the SmartKnob, no configuration, no searching for networks. The only thing that matters is that your SmartKnob is already running, because the modules always connect to it. With Lighty: right after pairing, its wall push buttons stop responding. Create a light widget for each light in the dashboard and switch on "Push button" in it, then they switch again.

Can I use several modules at the same time?

Yes, up to 20 modules at the same time, in any combination. That is enough for almost any camper conversion, from a compact panel van to a fully equipped motorhome. If you want to add several modules one after the other, the SmartKnob stays ready to receive for a short while after each successful pairing. You simply power up the next module.

What is the difference between AP and STA mode?

The two modes only decide which Wi-Fi network you use to open your dashboard on your phone or tablet. They have no effect on your modules. • AP mode: the SmartKnob opens its own Wi-Fi network and you connect your phone or tablet directly to it. You need no router and no internet, ideal when you are parked off-grid. • STA mode: the SmartKnob joins your existing Wi-Fi network, for example your camper router or your phone's hotspot. That is handy if you want internet access at the same time, for instance for online updates. You can switch between the two at any time.

What happens if my Wi-Fi drops out?

You are still never locked out. If the SmartKnob loses the connection to your Wi-Fi network, because the router is off, you have moved to another pitch or you are simply out of range, it automatically opens its own Wi-Fi network again. You can then reach the dashboard directly through it straight away. As soon as your usual network is back, it reconnects to it by itself. You do not have to do a thing.

What happens if the SmartKnob fails?

Ampy and Lighty keep their settings and carry on working. You simply keep switching and dimming lights and appliances at the wall switch, fuses and voltage protection stay active, and the outputs stay as they are. The display, dashboard, scenes, automations, the double tap for all lights and the wireless push buttons pause. This is a fallback, not a permanent state: without the SmartKnob you cannot change settings such as fuse values, and dimming only works with push buttons, not with switches. The one exception: an Ampy output set up as a heating element switches itself off after 10 minutes for safety, so that no boiler keeps heating unattended. We are also working on a backup function where a module takes over the dashboard, so that the whole system can still be operated from your phone and tablet.

What do I need to watch out for when mounting the SmartKnob?

The wall surface under the mounting plate must be flat: no more than 0.5mm of unevenness across the whole area of the mounting plate. If the wall is bent, curved or warped, the SmartKnob will not click in cleanly. Check the surface with a straight edge before screwing the plate on. Double-sided tape on the back of the mounting plate gives extra hold.

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