Power Your Heater with Solar Surplus and Save on Your Electricity Bill

PV Hot Water (Boiler) Control System

The PV Hot Water Control System helps you reduce electricity bills by ensuring that your electric water boiler (hot water system) is primarily powered by solar energy. This increases the self-consumption rate of your PV system and minimizes your grid electricity usage.

This system is commonly implemented using the WEM3050T Wi-Fi energy meter and the WPC3700 Wi-Fi power controller from IAMMETER.

🎬 Video Demo: WPC3700 Working with WEM3050T

Who Can Benefit from This System

This solution is ideal for homeowners whose systems meet the following conditions:

• Your home includes a solar PV system
• The feed-in tariff is much lower than the grid electricity price
• You have resistive loads, such as electric water boilers or hot water tanks
• Your system has a low self-consumption rate

Overview of the PV Hot Water Control System

The system is built with the Energy Cost Reduction Kit, which includes:

• One WEM3050T three-phase Wi-Fi energy meter — suitable for both single-phase and three-phase solar PV systems.
• One WPC3700 Wi-Fi power controller used to dynamically control your hot water boiler according to solar surplus power.

How it works:

• The WEM3050T monitors grid power (and optionally inverter output) in real time.
• The WPC3700 automatically adjusts the output of your electric water boiler (hot water system) based on the available surplus solar energy.

Operating Principle

1. The WEM3050T energy meter continuously measures grid power.
2. The WPC3700 Wi-Fi power controller adjusts the boiler’s output according to real-time solar surplus data.

• When excess PV power is being exported to the grid, the controller increases the boiler’s heating power.
• When grid import occurs, it reduces or pauses heating to prevent drawing power from the grid.

This ensures your hot water system uses solar energy first, maximizing your PV investment and reducing electricity bills.

Integration with Home Assistant or Node-RED (Open-source Automation)

Both the WEM3050T energy meter and WPC3700 power controller support open communication protocols such as MQTT and Modbus/TCP, making them ideal for integration into open-source home automation platforms like Home Assistant (HA) and Node-RED.

With this setup, you can easily create an automation rule that dynamically adjusts the power output of your hot water boiler based on real-time solar surplus data:

• WEM3050T measures grid power and publishes real-time data (via MQTT or Modbus/TCP).
• WPC3700 subscribes to these values and automatically increases or decreases the boiler’s power level.
• Home Assistant or Node-RED can visualize this data and implement additional logic (for example, heating only during daylight hours or when PV export exceeds a threshold).

This open integration makes the PV Boiler Control System highly flexible — it can work standalone, or be fully automated and customized through your preferred smart home platform.

Learn more: Enable MQTT Discovery in Home Assistant (Firmware i.76.058.8)

Electricity Savings Example

Before vs. After deploying the PV boiler control system:

Before

After

Electricity cost mainly depends on:

1. Boiler energy consumption
2. The proportion of energy supplied by solar power
3. The price difference between grid electricity and feed-in tariff

Example:

Suppose you have a single-phase electric boiler or hot water tank (maximum power < 3.7 kW) with a solar PV system.

• Daily energy consumption: 10 kWh
• Solar contribution before installation: 50%
• Solar contribution after installation: 100% (fully solar-powered)
• Feed-in tariff: 0.05 AUD/kWh
• Grid electricity price: 0.25 AUD/kWh

💡 Daily savings = (0.25 – 0.05) × (10 × 0.5) = 1 AUD/day

You can estimate potential savings based on your own solar generation and boiler usage.

How to Use the WPC3700 in Different Modes

Depending on your setup, the WPC3700 solar boiler controller can operate in several modes:

1. Auto Mode (with WEM3050T) Use WPC3700 together with the WEM3050T energy meter to automatically control the hot water system based on surplus solar power — this is the standard IAMMETER PV Boiler Control System.
2. MQTT / Home Assistant / Node-RED Mode If you don’t have an IAMMETER meter but use Home Assistant or Node-RED, you can integrate the WPC3700 through MQTT. → Enable MQTT Discovery in Home Assistant (Firmware i.76.058.8)
3. API Integration Mode Integrate the WPC3700 directly into your own platform via the WPC3700 API.

Select the operating mode that best fits your system requirements.

This document was last updated on October 15, 2025.