Use case
Solar surplus for the water heater: hot water from your own system
Every kilowatt-hour works at home first.
The scenario where your own surplus does the most work for you: it heats the water instead of disappearing to the grid for a minimum price.
In short
Solar surplus is energy that has already been produced and cannot be pushed back into the panels. With nothing managing it, it leaks to the grid for a minimum price, and in the evening you buy the same energy back at full tariff. HoumeOS routes it by priority: first to the battery, then to the water heater, and only then to export — so your own energy heats the water, not bought electricity.
Where the surplus goes today if nothing manages it
In an unmanaged system every surplus passes through the meter and out to the grid. Export is paid minimally, and in the evening the same energy is bought back at full price. The water heater is the largest flexible load in the house — and it is the first thing that can absorb the surplus instead of the grid.
The priority: battery, then boiler, then export
The battery has first claim on the surplus, but only up to its reserve — charged to the top, it stops looking for energy. Then the word passes to the boiler: heating toward a working threshold while there is solar fuel left. Whatever remains goes to the grid. The order is fixed in the server rules and holds even when no screen is on.
- The battery is protected: below the set minimum the boiler does not load
- The boiler gets the surplus once the battery is fully charged
- Export is the last stop of the flow, not the first
How the system decides when to switch the boiler on
The rule is purely local: production above consumption, battery charge above the reserve, boiler below the target temperature — close the contactor. The links are set with thresholds and hysteresis so nothing cycles by the minute. Everything runs on the server in the LAN, with a log of when and why it switched.
What works today — and what is still to come, honestly
The flow logic, the thresholds, the tariff in money and the screens work today — in the finished interface and in the simulation with real numbers. The driver that reads the production of your actual inverter over Modbus or TCP is the next step, and we do not present it as ready. The status of every transport is listed model by model in the table on the Integrations page.
The real scenario of one site
A house with 5 kW of PV, a 10 kWh battery and a 2 kW boiler: before noon the surplus charges the battery; in the afternoon, when it sits at eighty percent and the sun still gives, the boiler takes the rest and lifts the water toward sixty degrees. In the evening you heat with what the roof produced during the day — and you see it in the costs by tariff.
What works today and what is coming
We do not present upcoming work as available. This list matches the roadmap.
Works today
- The priority flow battery → boiler → export with thresholds and hysteresis
- The Energy screen: production, consumption, battery and grid as one flow
- Costs under a day and night tariff with a bill forecast
- Rules and journal run on the local server, without a cloud
Coming soon
- The driver that reads the real inverter (Modbus TCP) and switches the boiler contactor
- The first real site with self-consumption measured in kilowatt-hours
Later
- Built-in profiles for heat pumps and underfloor heating as a second flexible load
- A production forecast from weather data with automatic thresholds based on it
Frequently asked questions
How does solar surplus heat the water heater?
When production exceeds consumption, the system checks the battery charge: below the reserve, the surplus goes to it; fully charged, the word passes to the boiler — the contactor closes until the temperature reaches the target and the sun still gives. In the evening you heat water with your own energy instead of buying power at full tariff. The rule lives on the local server and works without internet too.
Do I need a battery to use the surplus?
No. Without a battery the priority is even simpler: all of the surplus goes to the boiler, and the remainder to the grid. The battery merely has first claim when it exists. The thresholds are configured for both variants, and the exact split is decided during a site survey.
Will the boiler drain my battery?
No, because the reserve is protected by a rule: below the set minimum charge the boiler gets no right to load, even while the roof produces. The system watches both devices together and decides by priority, not blindly. It is written in the journal too — you can always see which rule switched what and why.
How much do you really save by heating water with solar?
It depends on the roof, the boiler and your habits, so we do not promise numbers. The platform measures them: how many kilowatt-hours went into hot water and how that shows in the day and night tariff costs, with a bill forecast. During a site survey we estimate with your real consumptions.
Does it work with my existing boiler?
For most devices, managing the supply through a contactor and measuring the inverter production is enough. The exact inverter model decides when: the status per transport is in the table on the Integrations page, and for your installation we confirm it on a site survey.
We show the system on a live screen
The demo starts from your question: which devices, which protocols, which scenarios.