Home energy monitors are quietly becoming one of the best first IoT projects, and Raspberry Pi just showed the idea scales to a whole office. At its Cambridge headquarters, the company clamped current sensors on every breaker, fed the readings into Home Assistant running on a Raspberry Pi 4 and Pi 5, and now sees where each kWh goes. The write-up is summarized on Hackster.
The build itself
Emporia clamp-on current sensors read each circuit, and Home Assistant logs and classifies the load. That gave the team a baseline power figure to attack, with 85.5 kW of rooftop solar already installed and a 219 kW solar carport planned. The bigger swap was the building controller: a 17-year-old proprietary Trend 963 system was replaced with an open source BACnet setup, Contemporary Controls’ BASview and BASpi, running on Raspberry Pi hardware. Reported cost was about 7,800 pounds against roughly 150,000 for a like-for-like replacement.
Technical takeaway
The pattern is simple: measure first, control second. Current transformer (CT) clamps give you per-circuit watts, a Pi aggregates them, and only then do you add rules such as CO2-based ventilation or weather compensation. Home Assistant’s built-in energy dashboard (see the docs) handles the first half without custom code. The gotcha is sensor placement: a CT clamp must wrap only the live wire, never live and neutral together, or the reading cancels to zero.
What to try next
Scale it down for a classroom or dorm: one ESP32 with an SCT-013 30 A clamp on GPIO34 (ADC1, so it works alongside WiFi), a burden resistor of 33 ohms, and an MQTT topic that Home Assistant subscribes to. Log a week of readings from a single appliance, then compare standby draw against active draw. ESP32 boards and Raspberry Pi kits are in stock at circuit.rocks, so the whole rig is a one-evening build.
Frequently Asked Questions
How did Raspberry Pi monitor energy use across its building?
It used Raspberry Pi 4 and 5 boards running Home Assistant, with Emporia clamp-on current sensors on every breaker and main supply, giving per-circuit power data.
Can I build a small version at home?
Yes. An ESP32 with an SCT-013 current clamp and a burden resistor can publish readings over MQTT to Home Assistant for a few hundred pesos in parts.
What will I learn if I build this?
You learn how current transformers work, reading analog values on an ESP32 ADC, publishing over MQTT, and turning raw watts into dashboards, all useful for ECE thesis projects.
