The system is designed to maximise onsite usage of solar electricity, which is key for making the best savings in a post-FiT world. Powerwall soaks up energy for later use, and any excess is diverted to the immersion heater by the eddi or to charging the electric vehicles by the zappi.
Mr L opted for Octopus Energy’s Agile Octopus tariff, where the price of electricity varies half-hourly based on wholesale rates. The components in the system work together to shift any grid power usage outside of the peak hours.
The zappi chargers and eddi are controlled by eSense inputs via an adaptation of the Open Energy Monitor demand shaper module. This schedules them to operate from the grid only during the cheapest upcoming energy slots.
We connected these units grid side of Powerwall 2, so that the battery has priority to excess power from the solar panels. It also means Tesla’s algorithms are only influenced by the house loads (not the EVs) and Powerwall is not accidentally drained by the EVs, leaving power available for the home during peak slots.
As Mr L puts it, ‘We are saving a fortune. We also qualified for the £500 home charge scheme grant, reducing the cost of each of the zappi units installed by Spirit.’
For the zappi chargepoints, Mr L had a custom stand built to shelter them, lit for nighttime use. ‘The EV charging stand was designed to shield the zappi chargers from the weather so they’re not always dripping wet when you want to use them,’ he said. ‘It was also designed to shade the zappi chargers as many users had reported that the units slow down the charge rate to your EV when they get too hot in the sun!’