Excess Solar for Hot Water

Smart Controller for Hot Water

Overview of my journey to create an automated control system to use surplus electrical power for heating hot water. There are commercial products on the market but they cost over £500

The Basics

We have solar panels on our roof that provide electrical power (400V DC) to an inverter that outputs 240V AC that powers our house. We also have batteries with built-in 240V AC inverters that power the house when there is no sun. Excess power, when the generation exceeds the demands of the house and when the battery is charged powers the local grid and the National Grid (Grid Operators) and power companies (Generators) see this as a drop in demand.

These are the summary stats for 2020 Jan-April so plenty of Solar

The Plan

We have an immersion heater. It is operated with an on / off switch. The plan is to introduce an automated control system that will

Detect that the system will go into surplus
Turn on the immersion heater
While the battery has sufficient charge, power the immersion heater
When there is less solar, say in Winter use cheaper overnight energy from Wind farms in the North Sea for cheap power

Key Requirements

Safe Electrical Setup
Use reliable, low cost, components that meet or exceed electrical safety regulations
Simple Design
Waterproof enclosure - It's going to be near water
Wireless integration e.g. Wifi to the home network as there is no wired network in the boiler room
Visual monitoring of system via software
Optional email alerts / web page
Phone-based App to control
Local Physical switch must still operate e.g, to isolate the system for maintenance
Log data to allow AI to be trained
Allow overnight cheap power to be used when solar feeds are not large enough to power the house and the hot water heating