Monthly Archives: November 2018

Going through the (Eve) Motions

The other day I was involved in a discussion about how Eve Motions work. Some participants were concerned that Eve Motions always show motion for just the configured ‘on’ time and then go off until retriggered. The effect of this would be that if, for example, you were controlling a light, that light would always go off briefly before being triggered again which would be annoying and inconvenient.

However, this log (above) from my own lounge Motion, that is used to curtail the heating when the room is unused, shows ‘on’ events often being much longer that the 30 minutes that I have set (see right).  My understanding therefore is that the Motions trigger on first movement and continue to report ‘Motion’ until the delay time after motion ends.  I can’t otherwise explain Motion evens that last for variable lengths and, in s9me cases, multiple hours.

Home Energy Management System (HEMS) hardware

My current energy management arrangements are designed to maximise use of the output of my solar panels for lowest energy cost by diverting any excess to PowerVault storage system, car charger or immersion heater.  I can also manually configure the PowerVault and ImmerSUN to minimise costs of bought energy from the grid (I get 7 hours of cheaper night time electricity) by setting time periods for charging.

However as I move to a smart meter and smart tariff then I’m looking to start automating the selection of when to draw power from the grid based on costs that change half-hour-to-half-hour and day-to-day.  The hardware to achieve this is illustrated here.  To the right is a Raspberry Pi – a small computer with a wide range of connectivity – and to the left is a module that sets on top and has four relays able to switch mains loads, although at the moment I only anticipate needing 2 of them.

One of the relays will switch the boost input to the ImmerSUN to enable water heating, potentially when electricity is cheaper than gas, and a second relay will operate the transmitter that turns the car charger on alongside the ImmerSUN’s relay output during the cheapest available energy times.

The image to the right shows the timers that can be used to enable the ImmerSUN outputs to draw power from the grid.  I never use this for water heating as currently gas is always cheaper than bought electricity, but do use it to more or less effect seasonally to charge the car from cheap night rate power when there isn’t enough daytime solar.  For the new HEMS I plan a table of 7 days specifying the number of hours required for each output and let the HEMS find the cheapest half hours to deliver the total hours required and enable the charger or water heating as required.