Monthly Archives: November 2018

Battery Storage Configuration for the Smart Tariff

Today I’ve been thinking about configuring the Powevault storage system around my smart electricity tariff in which costs can vary every half hour.

My battery has an ability to be configured around a tariff called TIDE. I don’t have TIDE, but the ability to configure around TIDE can be reused for my tariff. The unit can be configured using a table or the clock as illustrated. There are several sections:

  1. Force charge – the battery storage charges at its maximum power (only 800 Watts) for 3.5 hours while electricity is cheapest.
  2. Charge only – a period while electricity is not quite so cheap when the battery will charge proportionally to any solar surplus, but will not discharge.  It wouldn’t make sense to start discharging the battery when electricity is only marginally more expensive than when the battery was charged.  This also prevents the battery discharging into my electric car if the car charges for a longer period than the battery.
  3. Normal – storage system will either charge proportionally to solar surplus, or discharge to minimise input.
  4. Force charge – as previously charges at maximum power in this case to ensure that some power is stored prior to the most expensive period.
  5. Normal – as previously but intended to cover the peak rate 4:00 to 7:00 PM period and beyond if there’s still stored energy.

Now that this pattern has been created, it can be adjusted by dragging the tabs around clock to adjust for when the cheapest power is at a different time day-to-day.

In the longer term I hope to automate such adjustment, although my priority is getting the car charger to automatically operate when power is cheapest.

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 below).  

My understanding therefore is that the Eve 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 some 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 sIts 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.