Our house had a new addition to its electrical supply this week an Energy and Micro Generator (EMMA). This is part of the Thames Valley Vision project which sets out to understand energy consumption and to provide data to help to decide how to upgrade (and renew) the distribution networks in the region.
The EMMA unit measures how much more energy our solar panels are generating than we are using and switches on our electric immersion heater to heat our hot water. The EMMA adjusts the amount of power to be supplied to the immersion heater based on the amount of excess electricity available. Any remaining excess is sent back into the National Grid as before.
After a short survey a few weeks earlier, two engineers arrived to fit the ‘unit’.
Our electric immersion heater had never been used especially as it would draw 2 Kw and our gas boiler had always supplied us with enough hot water. To use gas efficeiently, advice of the gas engineer who had fitted our boiler we had it set to warm the water during the day only and to only use the immersion heater in an emergency.
Here is the unit in the airing cupboard:
The version of our Nest thermostat does not control the hot water but only the central heating. These are the two boxes to the side and below the original boiler controls. Up on the wall above is the on/off switch for the immersion heater.
This unit has a constant eerie green glow coming from the unit as well as three condition diodes (power, wireless and fault). The temperature of the hot water was adjusted for both the gas and for the immersion heater to be the same. This was slightly less than the temperature set for the gas.
Here is the control unit next to the distribution panel over my desk:
The second unit, the EMMA Control Hub sits next to the electrical distribution board. It is connected wirelessly to the second unit upstairs in the airing cupboard.
The control unit displays four numbers:
Output which is the current output of the solar system, Demand which is the current demand within the house and HW which is the amount of energy supplied to the immersion heater today.
The fourth display is the number of minutes that the immersion heater will work at full power after the boost button has been pressed. This enables the emergency use of the immersion heater should the gas heating not be available.
The control unit has a connection so that its log can be downloaded. Access to this information is part of the free trial of the EMMA that we have agreed to.