"good" and "bad" energy consumption
After a few weeks of thinking on the concept I came to the conclusion that there is "bad" energy consumption and "good" energy consumption. With more and more households getting their own solar power system they have plenty of energy left over during summer and day time. So as much energy consumption as possible should be shifted to these times and this is "good" energy consumption. This energy is cheaper than average or in the best case doesn't cost you anything and it releases the power grid so that power supply gets cheaper and more reliable.
Typical "good" times are when:
- solar power is available (daytime, summer)
- wind power is available (stormy times)
- local battery storage is full (shortly after sunset on a sunny day)
- low demand in the power grid (usually late in the night)
shift-able energy consumption
Unfortunately not every energy consumption can be shifted to the "good" times. For example power for lighting is needed when it is dark outside and this is a "bad" time.
In a typical household this energy consumption can be shifted:
- charging of electric car (10 to 100 kWh per charging)
- charging of electric bicycle, scooter and power tools (0.5 to 1 kWh per charging)
- laundry dryer (2 kWh per cycle)
- dish washer (1 kWh per cycle)
- washing machine (0.5 kWh per cycle)
- electrical heating
Dish washer, washing machine and laundry dryer are difficult to control because you have to interact with the internal electronics to remote control and start these devices. Electric cars are usually charged with charging stations or wall-boxes. These devices usually have an interface to get information on energy flow and to control the charging. The interfaces and protocols are more complex so this topic is moved to a later time.
At the moment I will concentrate on the chargers connected to a regular power outlet. This means charging of electric bicycles, scooters and power tools. Their chargers start charging as soon as they are connected to a power outlet and stop charging when power is removed.
I will keep them connected to the power outlet and switch the power with a relay. Additionally I will add a power meter to measure the power consumption of the chargers.
power controller
As already mentioned in the introduction I will use a Raspberry Pi and MQTT to control power consumption. To keep installation and configuration simple I will create the topic "power_priority". The Raspberry Pi will determine how much power is available and publish to power_priority. It will set power_priority to a high level when only little energy is available and set power_priority to a low level when much energy is available.
The Arduino will subscribe to the topic power_priority. The Arduino will have its own local power priority and compare it to the global power_priority. If the global power_priority is lower than the local the Arduino will enable its output and thus enable charging.
Power and data sources
Unfortunately I don't have my own solar power system so I can't use its energy.
But there exist the power supplier aWATTar (https://www.awattar.de/) which offers a tariff based on the hourly whole sale energy tariffs and this should reflect grid usage. And the best thing is they offer an API to get this prices: https://www.awattar.at/services/api/
I will use this information to control my consumption.