How does smart solar water heater control save energy?

It avoids unnecessary use of the electric resistance when solar gain already exists or is predicted soon, activating the water heater only when it is really needed.

What should the electrician pay attention to in smart boiler control?

It must check load current, contactors, protections, manual override and overall circuit safety, especially when dealing with large thermal loads.

Solar Water Heater Control (Smart Boiler): How to automatically turn on the water heater only when there is no sun, pulling data from the weather forecast

We have reached the end of Category C and, of course, we could not close the sub-pillar of comfort and savings without touching the absolute "holy cow" of the Greek residence: the Solar Water Heater (Boiler).

The solar water heater is an amazing passive technology. The problem, however, arises in the winter with the changes in weather. How many times have you woken up in December to cold water, turned on the electric heater to take a shower, and two hours later a bright sun has come out? In other words, you burned 4000W of electricity to heat a water that nature would have heated for free a little later.

As engineers, we see the electrical resistance of the water heater as the ultimate scope for "Smart" algorithms. Let's see how to connect the panel relay to the internet so that the house can make decisions based on... Meteorology.

1. The Basic Infrastructure (The Hardware)

As we detailed in Category B, the first step is to check the circuit.

In the electrical panel, the electrician installs a Smart Rail Relay (eg Shelly Pro 1) which commands a powerful 25A or 40A Power Relay (Contactor).
This ensures our safety (no melting wires) and the basic Auto-Off function (whenever it turns on, it will strictly turn off after 30 or 40 minutes so as not to forget).

Now, the water heater is on our Wi-Fi. It's time to give it a "brain".

Illustration for 1. The Basic Infrastructure (The Hardware)

2. The Forecast Algorithm (Weather API)

A simple timer (that turns on the water heater every day at 06:30 in the morning) is "dumb" and wasteful. Our goal is for the system to control the weather before it consumes power.

Inside the Central Hub of the Smart Home (eg Home Assistant, SmartThings, Hubitat), we install a weather data plugin (such as OpenWeatherMap or AccuWeather), which reads the coordinates of our home.

The Scenario (Morning Shower): We set up a routine that runs automatically every day:

What we achieve: If the forecast shows sunshine at 09:00, the automation will not turn on the water heater. He knows the sun will take the job for free. If the day is "off" and rainy, it will turn it on so you don't have to take a cold shower before leaving for work.

Trigger (Time)

The time went to 06:15 am.

Condition 1 (Weather)

Check the Cloud Coverage forecast for the next 4 hours. If cloud cover is > 70% OR if rain is forecast.

Action

Instruct Shelly to turn on the water heater for 30 minutes.

3. The Ultimate Solution: The Temperature Sensor (Dallas Probe)

The above algorithm is excellent, but it has a blind spot: The weather forecast is not always 100% accurate, and the system does not know if the water inside the boiler is already warm from the previous day.

The solution for professional installers is to place a physical Temperature Sensor (such as the waterproof DS18B20 "Dallas" type sensor) directly on the Solar Boiler on the roof or roof.

The sensor goes into the special slot (cab) that all modern boilers have.
It is wired to the smart relay (either via a special "Add-on" if the relay is nearby, or via a wireless Zigbee temperature sensor).

The "Bulletproof" Scenario (The Ultimate Smart Boiler): Now, the system also has "eyes" in the water. The algorithm is refined:

In this way, you guarantee that you will always have hot water when you need it (afternoon or morning), consuming exactly the minimum required electricity, without overheating the water to 70°C unnecessarily.

Illustration for 3. The Ultimate Solution: The Temperature Sensor (Dallas Probe)

Trigger (Return Time)

The time is 17:00 (the sun has gone down, the day's solar gains are over).

Condition (Absolute Necessity)

If the actual water temperature in the boiler is below 38°C (not enough for a bath).

Action (Smart Heating)

Turn on the electric resistance UNTIL the water reaches 45°C and then turn it off.

Summarizing

The connection of the solar water heater with the weather and temperature is the "Masterclass" of the Smart Home. It combines hardware (Relay Panel), software (Weather Algorithms) and physical measurements (Sensors). The savings on winter bills are so drastic (once you cut out the waste completely), that this particular installation often pays for itself in less than one winter season.

Smart Bathroom Ventilation: Automatic start of ceiling fans based on integrated humidity sensors (Humidity Sensors) Smart Thermostats (Nest, Tado, Netatmo, etc.): Are they worth their money to save in Greece and how are they connected to the boiler? DIN Rail Equipment (e.g. Shelly Pro): Professional smart installations directly inside the central electrical panel Local Control vs. Cloud: Why your "smart" home should continue to work flawlessly even when the Internet goes down

Smart Home, Building Automation (BMS) & Security

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