How to get Accurate kWh reading from JSY-MK energy module

Other Hardware Sensors
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I recently revised my hot water control to use JSY-MK-354 energy module to measure the supply power for controlling when to turn the hot water on/off to use the excess solar power.

I also calculate the daily electicity cost based on the Import / Export kWh.
However I found that the JSY-MK-354 module was grossly in-accurate.
The report on testing is here

Fortunately there is a simple software fix. Just integate the instaneous power and accumulate the Import / Export kWh in your software.
A 2sec sampling rate proved to accurate to better than 1.5% when compared to the electricity supply company's meter.

The code is

void integrate(float Power_W) {
  static unsigned long lastTime_ms = 0;
  unsigned long currentTime_ms = millis();
  if (lastTime_ms > 0) { // Skip first reading
    unsigned long deltaTime_ms = currentTime_ms - lastTime_ms;  
    if (deltatTime_ms < 6000) { // not a too large gap between measurements
      float deltaTime_hrs = (float)deltaTime_ms / (3600.0 * 1000.0);     
      float power_kW = (float)Power_W / 1000.0; // power in kW     
      float energy_kWh = power_kW * deltaTime_hrs; // kWh for this time interval     
      // Update daily accumulators based on whether importing or exporting
      if (power_kW >= 0) { // Importing
        dailyImport_kWh += energy_kWh;
      } else { // Exporting (power_kW is negative)
        dailyExport_kWh -= energy_kWh; // Store as positive value
      }
    }
  }
  lastTime_ms = currentTime_ms;
}

This is a very basic integration, but the results show it is sufficient.

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