Use Solar Surplus to Heat Water and Save Electricity | IAMMETER

Use Solar Surplus to Heat Water and Save Electricity

The IAMMETER PV Heater Control System helps solar users use more surplus solar energy inside the home instead of exporting it to the grid at a low feed-in tariff.

With an IAMMETER energy meter and the WPC3700 Wi-Fi Power Controller, the system can dynamically adjust the power of an electric boiler or water heater according to real-time solar surplus.

The goal is simple:

• Reduce grid import
• Reduce low-value solar export
• Increase solar self-consumption
• Lower electricity bills
• Improve the return on a home solar PV system

This application is a natural next step after setting up a home solar PV monitoring system. Monitoring tells you when surplus solar exists. PV heater control helps you use that surplus energy.

Video Demo: WPC3700 Working with WEM3050T

1. Why Solar Surplus Control Matters

Many solar PV systems export unused solar energy to the grid during the day. In many markets, the feed-in tariff is much lower than the price of electricity purchased from the grid.

For example:

• Grid electricity price: 0.25 AUD/kWh
• Feed-in tariff: 0.05 AUD/kWh

In this case, using 1 kWh of surplus solar energy inside the home may be worth much more than exporting it.

That is why increasing self-consumption is often one of the most practical ways to reduce electricity bills after installing solar.

Typical high-value controllable loads include:

• Electric water boilers
• Hot water tanks
• Immersion heaters
• Other resistive heating loads within the WPC3700 power range

2. How the PV Heater Control System Works

The standard IAMMETER setup uses:

• WEM3050T Wi-Fi Energy Meter to measure grid power in real time
• WPC3700 Wi-Fi Power Controller to adjust the boiler or heater power
• IAMMETER-Cloud or local integration logic to monitor and optimize energy use

The control logic is based on grid power:

1. The IAMMETER meter measures whether the home is importing electricity from the grid or exporting surplus solar energy.
2. When surplus solar power is available, the WPC3700 increases the boiler/heater power.
3. When the home starts importing from the grid, the WPC3700 reduces or pauses the boiler/heater power.
4. The system keeps the boiler using as much surplus solar energy as possible while avoiding unnecessary grid import.

3. Required Devices

The system can also work with other IAMMETER meters if they provide the required real-time grid power data. WEM3050T is commonly used because it is cost-effective and flexible for home solar monitoring.

Before using this application, make sure your solar monitoring system can correctly identify grid import and grid export. For setup details, see:

• How to Monitor Your Home Solar PV System
• Home Solar Wiring Diagram

4. Important Load Compatibility

WPC3700 is designed to control resistive loads by adjusting output power.

Suitable loads include:

• Electric water boilers
• Immersion heaters
• Resistive hot water tanks
• Other resistive heating loads within the WPC3700 rated power range

Do not use WPC3700 to directly control:

• Heat pump compressors
• Motor loads
• Inverter-driven appliances
• Loads that require fixed voltage/frequency operation

For non-resistive loads, use a control method designed for that equipment type. If you are not sure whether your load is suitable, confirm with a qualified electrician or the equipment manufacturer before installation.

5. Control Example: Boiler Powered by Solar Surplus

Assume a home has a solar PV system and an electric boiler.

Without PV heater control:

• Some solar energy is exported to the grid during the day
• The boiler may still use grid electricity at other times
• The solar self-consumption rate remains low

With PV heater control:

• IAMMETER detects surplus solar energy
• WPC3700 increases boiler power when surplus exists
• WPC3700 reduces boiler power when grid import starts
• More solar energy is converted into hot water

This can shift boiler energy consumption from grid electricity to solar surplus.

Before

After

6. Savings Calculation

The savings depend mainly on:

• Boiler energy consumption
• How much boiler energy can be shifted to solar surplus
• Grid electricity price
• Feed-in tariff

A simple estimate is:

Daily saving = shifted energy x (grid electricity price - feed-in tariff)

Example:

• Daily boiler energy consumption: 10 kWh
• Solar contribution before control: 50%
• Solar contribution after control: 100%
• Shifted energy: 5 kWh/day
• Feed-in tariff: 0.05 AUD/kWh
• Grid electricity price: 0.25 AUD/kWh

Daily saving = 5 x (0.25 - 0.05) = 1 AUD/day

The actual result depends on your solar generation profile, hot water usage, feed-in tariff, grid electricity price, and local wiring conditions.

7. Operating Modes

WPC3700 can be used in several ways depending on your system.

Auto Mode with IAMMETER Meter

This is the standard IAMMETER PV heater control setup.

The IAMMETER meter measures grid power, and WPC3700 adjusts the boiler/heater power according to the available solar surplus.

MQTT / Home Assistant / Node-RED Mode

Both IAMMETER meters and WPC3700 support open integration. Advanced users can build custom control logic in Home Assistant or Node-RED.

Examples:

• Heat water only during daylight hours
• Start control only when PV export exceeds a threshold
• Add temperature or schedule conditions
• Visualize solar surplus and boiler power in a smart home dashboard

Learn more:

• Enable MQTT Discovery in Home Assistant
• Home Assistant Energy Meter Integration

API Integration Mode

Developers and system integrators can control WPC3700 directly through its API.

• WPC3700 API

8. How This Fits into the IAMMETER Solar Workflow

PV heater control is not a replacement for solar monitoring. It builds on top of accurate monitoring.

Recommended workflow:

1. Monitor solar production, home consumption, grid import, and grid export.
2. Identify when surplus solar energy is available.
3. Use WPC3700 to shift suitable resistive loads to surplus solar.
4. Track self-consumption and electricity savings over time.

Related pages:

• Home Solar PV Monitoring System
• How to Monitor Your Home Solar PV System
• Home Solar Wiring Diagram
• WEM3050T Wi-Fi Energy Meter
• WPC3700 Wi-Fi Power Controller

9. Summary

The IAMMETER PV Heater Control System helps solar users move from passive monitoring to active energy optimization.

By combining real-time grid power monitoring with WPC3700 power control, users can heat water with surplus solar energy, increase self-consumption, and reduce grid electricity costs.

For homes with a solar PV system, a suitable electric boiler, and a low feed-in tariff, this can be one of the most direct ways to turn solar monitoring data into real savings.