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Introduction

Why domotize the electric car?

Because in this way you can monitor the electric car parameters for a unique panel where you have all controls of your Smart Home.

Because you can easily monitor the state of charge of the car battery.

Because you can avoid charging when total imported power from the grid is very high, preventing electricity meter disconnections.

But the most important thing, you can also charge the electric vehicle using the most energy from renewable, for example if you have a solar photovoltaic system.

This article explain two different cheap and smart solutions to charge a battery electric vehicle (electric car, scooter, ...).

Below you will set two different battery level thresholds, in the domotic panel:

  1. a min battery level below which the car is charged using any kind of electricity source
  2. a max battery level above which the car stop charging: also, when state of charge is between min and max levels, the car will be charged only when the photovoltaic system produces enough to avoid imporing energy from the grid

Travelling with zero emissions and using only energy from the sun is really awesome!

Solution 1: using standard EVSE cable

In this case the electric vehicle is connected through the charging cable provided with the vehicle: no need for a wallbox or supplementary EVSE cables.

PROS:

  • very cheap solution: don't need for expensive wallbox or EVSE systems. Just use the standard cable provided with the vehicle, and few low-cost devices to enable/disable charge and, possibly, to monitor the energy used to charge the vehicle to make some statistics on energy consumption, EV battery charging efficiency, ...

CONS:

  • charging current/power can be manually selected on the EVSE cable, but not automatically, with the result that it's not possible to maximize the own consumption,  charging at higher or lower currents depending by the available power from photovoltaic.

Domoticz panel with electric vehicle controls

Prerequisites

  • electric vehicle with cloud connection, to know the battery state of charge
  • standard EVSE cable provided with the car / vehicle
  • electricity meter, to compute the current power and consumed energy (optional)
  • circuit breaker with differential protection (recommended)
  • 2P contactor (or relay) to enable/disable charging
  • Creasol DomBus23, to interface electricity meter and contactor to the domotic controller (Home Assistant, Domoticz), or Creasol DomBusTH + DomRelay2 to get 3 LEDs already available to show electric car charging power and total import/export power on the electricity grid.

Creasol DomBusTH is a domotic module that can be used with Domoticz and Home Assistant that implements all features needed by this project:

  • has 2 open-drain outputs (1 is needed) to enable an external relay (DomRelay2 module) to control the 25A/40A 2P contactor;
  • has 4 configurable inputs, 1 of which is configured as IN_COUNTER and connected to the electricity meter to measure the charging power and energy, and 1 input is connected to a dual button to set the charging level easily;
  • has 3 LEDs that are used to display the charging status (white led) and current import/export power (red and green leds);
  • has temperature and relative humidity sensors that are not important for this application, but can be used to monitor the room temperature.

Also, it has 1 or more analog inputs, buzzer output that are beyond the scope of this project. It's a small electronic board that can be fixed with 2 hot-glue points on a blank cover or modular cover.

Creasol DomBusTH - Domoticz I/O and sensors, RS485

It can be connected to the domotic controller (Raspberry, Nuc, PC, ...) by a common alarm cable (within 4 wires, 2 wires for power supply and 2 for data) using a cheap USB to RS485 adapter. Obviously, dozens of DomBus modules can be connected using the same bus/cable, forming a reliable domotic network optimized for low power consumption that does not use batteries and do not produce RF pollution.

Electric diagram

Electric car charging system

 

Electric car charging connections

Electric diagram of car charging solution using Domoticz + DomBus modules

Domoticz LUA script

In github repository it's possible to find script_device_power.lua, that should be placed in domoticz/scripts/lua directory, that manages EV charging, checks for power imported from the grid disabled or reducing loads when imported power is near the maximum permitted,  enable some loads (electric heaters, dehumidifiers, ...) in case of extra production from photovoltaic, shows current power usage/export on red/green LEDs, activate white leds in case of blackout, ...

The building power management can be easily configured through a separate text config file, config_power.lua , so there is no need to put your hands in LUA coding!

Solution 2: using a EVSE that permits to automatic control the charging current

This is an advanced solution, that needs to use an EVSE system that can be controlled by Home Assistant, Domoticz, ...

PROS:

  • charging current can be set by the domotic controller, so it's possible to reduce power consumption from the grid and increase the own consumption from the solar photovoltaic

CONS:

  • more sofisticated solution, and more expensive

Prerequisites

  1. electric vehicle with cloud connection, to know the battery state of charge
  2. EVSE board (TODO) with cable
  3. electricity meter, to compute the current power and consumed energy (optional)
  4. circuit breaker with differential protection (recommended)
  5. 2P contactor (or relay) to enable/disable charging
  6. Creasol DomBus23, to interface electricity meter and contactor to the domotic controller (Home Assistant, Domoticz)
  7. a pushbutton to force charging, if needed, and 1 LED to show charging status (recommended)

Electric diagram

TODO

Domoticz LUA script

In github repository it's possible to find script_device_power.lua, that should be placed in domoticz/scripts/lua directory, that manages EV charging, checks for power imported from the grid disabled or reducing loads when imported power is near the maximum permitted,  enable some loads (electric heaters, dehumidifiers, ...) in case of extra production from photovoltaic, shows current power usage/export on red/green LEDs, activate white leds in case of blackout, ...

The building power management can be configured through the config file config_power.lua

 

Efficiency charging a Renault Zoe R110 using single-phase and three-phase

Getting high efficiency conversion from AC to DC with single-phase mains supply is very difficult, due to the high ripple on AC/DC conversion: when rectified voltage decreases, the efficiency of the DC/DC boost converter decreases.
For this reason it's important to use 3-phase mains supply to get the higher efficiency while charing the car battery.

The following graphs represents the charging efficiency measured for a Zoe R110 using both single-phase and 3-phase, with different charging power: more info at https://www.azoenzo.com/tempi-di-ricarica-ed-efficienza/

EVcharging efficiency

Something about solar photovoltaic systems

 To charge the eVehicle, and most important to supply the heat pump in the winter, you should have solar photovoltaic system, but where? On the roof or on the garden? What inclination and orientation for the panels?

In the summer there are no problem at all... the day is long and we always have an over-production. But in the autumn and winter?

The following tables and graphs show a simulation of a 2.7kWp photovoltaic system in 5 configurations and 2 dates (Autumn and Winter), for the Northern Italy, using data from the very useful European website https://ec.europa.eu/jrc/en/pvgis

Simulation using data from 20 September 2016

The following table shows the simulation for the begin of Autumn:
The first column shows the time of the day (GMT+1, not DayLight Saving time!), then second column a simulation for the panels on the roof, oriented to EAST with inclination of only 15 degrees from the horizontal line.

The third column shows the simulation for panels oriented to south direction, 15 degrees inclination.
The forth column shows the simulation for panels in vertical, south direction.
The fifth column shows the simulation of panels in south direction and 70 degrees inclination.

Finally, the sixth column show the performance of a simple solar tracker with vertical axis that can rotate from east toward south and  west, with panel inclination 70 degrees.

Solar Photovoltaic simulation for the autumn

 

 Graph of simulation for 5 different configuration of solar photovoltaic system

It's possible to see that best performances can be achived using a solar tracker... since from Sunrise, the tracking system lead to a very high power that permits to start heat pump without using power from the grid.

 

Simulation using data from 1 January 2016

 Simulation using data from 1 January 2016

Simulation using data from 1 January 2016

 In this case, the solar tracking system does not help to improve the power, because the Sun in the Winter rise from south-east and fall to south-west.

 

 

 

 

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