Raspberry Pi blog

I don’t usually write a blog post about a blog post! However this particular blog post does merit a mention.

The lovely folks at the Raspberry Pi foundation have published a blog post about OpenEnergyMonitor:

Raspberry Pi Blog: Open-source Energy Monitoring Using Raspberry Pi

The Raspberry Pi as been an integral part of the development of the OpenEnergyMonitor system. We make extensive use of the Raspberry Pi in our emonPi and emonBase units. The Raspberry Pi Foundation has always been a big insperation to use, therefore we are honoured to get a little mention on their blog.


emonPi as a Home Automation Hub

I believe automation can play an useful role in helping to reduce energy consumption. For example being able to control my home central heating system remotely enables me to only turn on the heating when it’s required and not have it running on a set schedule when the house is empty.

As previously mentioned in a blog post, the emonPi (running emonSD pre-built SD card) can function as a powerful home automation hub. Utilising the emonPi as a home automation hub is a good fit for a number of reasons:

  • It’s already running 24/7 for energy monitoring
  • It’s optimised for robust long term operation: the root Raspberry Pi file-system is read-only to increase SD card lifespan
  • It’s already connected to your local network
  • It’s running Debian Raspbian Jessie therefore installing extra packages is easy and lots of support is available
  • Raspberry Pi 3 has plenty of space capacity
  • Extra radios / accessories can be connected via USB
  • It’s already running an MQTT server
  • emonSD pre-built SD card comes pre loaded with the following integrations nodeRED, OpenHAB and LightWaveRF

In this post I want to share with you how I use the emonPi in my own home.

Here is a video demo using Google Home to control my central heating and devices via MQTT:

Read on to learn how this is achieved using an emonPi and open-source software…

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MyHomeEnergyPlanner - open source home energy assessment

I would like to highlight a piece of work by Carlos Alonso Gabizón which I think is an important piece of the home energy monitoring and assessment toolkit and a really useful tool, which we would be keen to see more people use.

Carlos has been working for CarbonCoop over the last year and a half on MyHomeEnergyPlanner – an open source household energy assessment tool based on SAP 2012 – a monthly domestic energy model.


MyHomeEnergyPlanner started as a collaboration between OpenEnergyMonitor and CarbonCoop but this latest version and active work on it over the last year and a half is all down to Carlos and CarbonCoop.

MyHomeEnergyPlanner can be used to calculate the space and water heating requirements for a home from a detailed breakdown of the building fabric: floor, walls, roof, windows etc. It uses U-values and areas to calculate building fabric heat loss rates, combined with calculated heat loss from infiltration and ventilation and heat gains from solar radiation, lighting, household appliances, cooking and occupants.

It can be used to model a building in its current form and then create scenarios to explore the effect of undertaking measures such as adding insulation, improving air-tightness and changing heating systems.

MyHomeEnergyPlanner is free to use and open source and is now installed on (Login with your account)

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Launching Learn: Sustainable Energy

Over the years we have done a fair bit of work that explores sustainable energy documented to a varying degree on the site. The Sustainable Energy section of Learn brings all of this together in one place that’s easier to find and navigate as well as extending it with further improvements to the energy modelling tools, discussion and analysis.

New Front Page

It starts with a brief introduction and energy 101, which outlines the energy consumption of the average UK household and a quick run through the main demand and supply side solutions used by the ZeroCarbonBritain scenario:

There is then a brief write up of an energy study into 17 households in Snowdonia, North Wales that Glyn and I helped run in 2010 that illustrates how different energy consumption can be across a number of household. It uses the energy stack graphics style used by the sadly late David MacKay FRS who wrote Sustainable energy without the hot air, to visualise the different uses of energy from traditional electricity demand to heating and transport:

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New home page and Learn website!

As you may well have noticed we have recently launched a new front page for OpenEnergyMonitor and a common navigation bar theme across all our sites. We have also launched a new website called Learn to replace the Building Blocks section of the old site. All URL’s directed to building blocks should re-direct automatically to the relevant Learn page.


A key aim behind the redesign was to bring our interest and driving motivation of working towards sustainable energy and zero carbon more to the fore of the project. Energy Monitoring is a tool to help us understand our use of energy, and our motivation for starting the project was to understand our use of energy at home in relation to the wider context of what needs to be done if we are to get off fossil fuels and build a zero carbon energy system - We hope this update better reflects this interest.

This website redesign completes the shift away from using Drupal 6 cms that was started with the User Guide website launched April 2016 and a new Community Form using Discource launched May 2016. The old forums are still accessible as a read-only archive.

Alongside the new front page we have also launched a new website called Learn which includes what used to be called Building Blocks, resources for learning about AC Power Theory, CT Sensors, Measurement circuit design through to Timeseries data storage design.

Learn also includes a large updated section on Sustainable Energy which brings together and expands on our work on understanding the wider context, including a web-based 10 year hourly 100% renewable energy model based on ZeroCarbonBritain and resources on building energy modelling.

The new sites are all designed to be responsive for viewing on mobile as well as desktop screen sizes:

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OpenEVSE EV Charge Controller

OpenEVSE (recently renamed to OpenEV) design and build fully open-source EVSE (Electric Vehicle Supply Equipment) charge controllers for electric vehicles.

An EVSE charging station, is a device an electric car (EV) is plugged into to charge. It communicates to the car to agree on a charging rate that is the fastest and safest rate both the car and the power supply can support.

Update March 17: OpenEnergyMonitor and proud to announce that we are now the UK / Europe reseller for OpenEVSE charging stations, see OpenEnergyMonitor Online Shop.

openevse leaf

openevse build9

Note: this review is my account of using the OpenEVSE in the UK (240V single-phase AC), see OpenEVSE website for official build guides


The features that make the OpenEVSE charge controller interesting to us are:

I recently swapped my ageing diesel car for an all-electric Nissan LEAF (it’s fantastic), so it felt like the perfect time to build and test an OpenEVSE charge controller unit!

Nissan LEAF charging from solar PV on a frosty morning:


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Introducing emonTH V2

The emonTH V2 is an open-source, wireless, battery-powered temperature and humidity monitoring node.

The emonTH V2 features a Silicon Labs Si7021 temperature and humidity sensor instead of the DHT22 sensor. The Si7021 is more accurate and significantly (2000 times!) lower power then the DHT22. This will result in an increase in the emonTH battery life; from 10 months to several years (at least two years). The Si7021 is also much smaller than the DHT22.

emonTH V2

The Si7021 sensor can be seen in the top right-hand corner of the PCB. The white film on top of the sensor is a dust film and should not be removed. The dust film is factory fitted and will protect the sensor from dust and air contaminants.

emonTH image

The emonTH V2 is now shipping via our online shop

As with all our hardware units the emonTH V2 is fully open-source and manufactured locally in North Wales, UK using non-conflict materials lead-free processes.

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Summer Placement

Hi! My name is Eben I’ve been working with OpenEnergyMonitor for the past 10 weeks as part of a summer placement organised by Arloesi Gwynedd Wledig; a local project aimed at highlighting the local tech sector employment opportunities on Parc Menai the business park where we are located in North Wales, and the difficulties that they face, as well as the great perks of living in such a beautiful area.


The scheme organised placements for four students in four seperate tech companies in Parc Menai. Here is a video with highlights the whole 10 week scheme:

Working in a small company in a rural area, that has such a large online community has really opened my eyes to the possibilities that the internet and the digital age can offer, in that people are no longer bound to cities. Increasing infrastructure development in terms of roads and internet speeds has increased this mobility further, and I look forward to the growth that this will no doubt provide in Gwynedd. OpenEnergyMonitor is for me the perfect example of a growing business that has been made possible by opensource development, global connections and communities, and new technology.

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EcoHome Lab: From Monitoring to Control

Last night I attended EcoHomeLab meetup in Manchester organised by the CarbonCoop.

EcoHomeLab monthly meetups at MadLab brings householders and green-technologists together to take control of home energy use and generation.

It was great fun to catch up with regular faces as well as meet many new interesting people.

I gave a short presentation overview of our efforts as OpenEnergyMonitor to make it as easy as possible for people to get started with energy monitoring and control (home automation) with a sustainability / energy saving focus.

I presented the recent work we have been doing to integrate platforms such as MQTT, Node-RED and openHAB ready-installed and pre-configured on the emonPi, our RaspberryPi based energy monitoring platform. These additional platforms run alongside Emoncms on the emonPi.

See the Integrations section of our user guide for more info

Here are copy of my slides from the event:

HTU21D / Si72021 Temperature and Humidity Sensor

I have been been evaluating the HTU21D temperature and humidity sensor made by Measurement Specialties as a possible DHT22 replacement for the emonTH. This is quite a new sensor, released in 2013. The Si72021 is also a posiblity with an identical pin-out and specs.


The metrics speak for themselves:

Metric HTU21D Si72021 DHT22 DHT22 vs HTU21D Difference
Cost in 1k off £1.42 (July16) £2.15 £4.57 (July16) 3.2 times cheaper (£3.15 less!)
Vcc 2.1v - 3.6V 1.9V - 3.6V 3.3-6V  
Humidity accuracy ±2% RH ±2% RH ±2%RH n/a
Humidity Range 0-100% RH 0-100% RH 0-100% RH n/a
Temperature accuracy ±0.3°C ±0.4°C ±0.5°C 40% more accurate
Temperature Range -40°C +125°C -40°C +125°C -40°C +80°C 56% more accurate
Sleep Current 0.02uA 0.06uA 15uA 750 times less power
Measurement Current 0.045mA 0.09 mA 0.5mA 11 times less power
Measurement time 0.01s - 0.0026s 0.01s - 0.0026s 2s 200 times faster
Energy consumed per sample 1.5uJ 2.97uJ 3300uJ 2000 times less power
Time sampling per day* 14.4s   2800s  
Time sleeping per day* 86386s   83600s  
Energy consumed per day* 2.36mW [1]   2836mW [2] 1201 times less energy per day!
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