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This is an energy diverter that helps storing excess solar energy in a storage heater (“thermal battery”) or boiler. This helps to enhance PV self-consumption (the amount of PV energy that is used directly “on the spot”) and allows prosumers to avoid unnecessary energy transfer into the distribution network (which you have to pay for), or in the case of zero-export to increase your PV production.
As indicated by its name, the devices regulates the amount of energy diverted to the thermal storage. It does so by controlling a 'dimmer' or TRIAC circuit. What this allows to do is let only a part of the 230V sine wave – and thus only part of the power – through to the load (storage heater, etc.). The circuit implemented in the TA-Regulator features a zero-crossing detection to do this 'cutting' of the sine wave in the most clean way, to avoid generating noise and interference on the grid. You can see the result of this in the image taken from the oscilloscope.
Work on the prototype started in 2020, and during 2021 the regulator was intensively tested and optimised. It builds heavily on the Regulator project as developed by Juraj Andrássy: https://github.com/jandrassy/Regulator.
Check his version first – it provides many additional modules and functionalities that are not included in this version and is excellently set up.
Where the TA-Regulator featured in this repository differs mainly from the Regulator setup, is that it can work under strict zero-export (0%) conditions. For this to work, another mechanism to assess the excess energy had to be established than reading the PV export from a smart meter: a small reference PV Solar panel, mounted next to the main array. PV power can be reading the short-cut current (Isc over a low-value power resistor) from the reference panel with the help of a DAC (digital to analog converter). After calibrating the data, the potential output of the PV array can be established, while data from the PV inverter tells what is actually generated. The difference between the two tells what is potentially available, but not captured – this power can now be 'regulated' towards a thermal storage.
The load is matched to the max available PV solar: high self-consumption (yellow).
In addition, a weather forecasting algorithm has been included to make use of the possibility to supplement PV energy with low-tariff (night time) electricity in the winter. During winter time solar irradiance is rather low and there's chance of 'disruptions' like fog or snow, while the need for heating is high. With the weather prediction algorithm, the TA-Regulator looks at the forecasted weather and sets a night time pre-charge depending on the expected degree of sun. The algorithm is based on the Zambretti forecaster (1905), that in conjunction with a barometer can achieve over 90% accuracy for 12 hour forecasts. To read the barometric pressure, a temperature/pressure sensor (BME280) is used.
Since 2022 the TA-Regulator has been put in active use (during the heating season).
The TA-regulator uses off-the-shelve hardware components that are easy to find, while it is programmed in open-source Arduino code that runs on a MKR Zero board. The code is modular, making it possible to change or add specific functionality if you are at ease with the Arduino language.
Be warned: it is a rather complicated project, and works currently only with Fronius or SunSpec Modbus compatible inverters! If you are not a determined tech-enthusiast, you may be better served with a ready-to-go commercial solution.