I believe it was some time in 2016 when the UK set out plans install smart energy meters in all UK homes.

At first glance it seemed like a good idea. It would remove the need to report meter readings manually each month and allow home owners to see (in realtime) their energy consumption. Hopefully that would lead them to adjust their usage, saving both energy and money.

Prototype circuitry for Watz energy monitor

It raised two concerns for me. The first is that the data would not be available locally. The meters report energy use to the supplier and there is no requirement for them to provide an API or access to the data they are collecting. Being able to see energy use over time would be a great way to spot trends and decide if we would be better suited to a different energy tariff.

My second concern was privacy. You can tell a great deal about a home and the people who live there from their energy use. You can determine what time they wake up, what time they make dinner, see if anyone is home and how efficient their fridge is. I would rather be in control of where that data goes.

By 2018 it was clear that we wouldn't be getting a smart meter any time soon and so I set about creating my own that would require zero modifications of our meter.

My solution is called Watz.

Watz is a WiFi smart meter built around a Particle Photon. It mounts to the LED on your electricity meter and measures the number of pulses in a given time period (sometimes referred to as a pulse counter). This is used to generate almost real time power information.

Screenshot of graphs showing energy use in Emoncms

The data is periodically pushed to the Particle cloud and can be subscribed to via server-sent events. To make the data a little more accessible I used Node-RED to subscribe to the events and push the data to the open source Emoncms. Emoncms is a platform designed to track energy consumption.

Energy meter in cupboard with wires and blue tack

Our meter sat outside by our front door so I ended up using a fairly large battery and a small solar panel to keep the device topped up with power. This meant I had to reduce the frequency of data being pushed to ten minutes as firing up the Wifi connection proved rather expensive in terms of power.

The firmware, component list, circuit diagram and code can be found on my GitHub account if you would like to build your own.

View the project on GitHub