This is the code for (hopefully) simulating a P1 smart meter.

CRC16.h

#ifndef CRC16_H
#define CRC16_H

// https://github.com/jantenhove/P1-Meter-ESP8266

#if defined(ARDUINO) && ARDUINO >= 100
  #include "Arduino.h"
#else
  #include "WProgram.h"
#endif

unsigned int CRC16(unsigned int crc, unsigned char *buf, int len)
{
  for (int pos = 0; pos < len; pos++)
  {
    crc ^= (unsigned int)buf[pos];    // XOR byte into least sig. byte of crc

    for (int i = 8; i != 0; i--) {    // Loop over each bit
      if ((crc & 0x0001) != 0) {      // If the LSB is set
        crc >>= 1;                    // Shift right and XOR 0xA001
        crc ^= 0xA001;
      }
      else                            // Else LSB is not set
        crc >>= 1;                    // Just shift right
    }
  }

  return crc;
}
#endif

Virtual-P1.ino

// Tim Koers - 2018


#include <WiFi.h>
#include <ESPmDNS.h>
#include <WiFiClientSecure.h>
#include <PubSubClient.h>
#include <SPIFFS.h>
#include <ArduinoOTA.h>
#include "CRC16.h"

/**
  "/ISk5\2MT174-001\r\n"\
  "1-3:0.2.8(50)\r\n"\ // DSMR version
  "0-0:1.0.0(%2d%2d%2d%2d%2d%2dW)\r\n"\ // Date-time timestamp of the P1 message (101209113020W) (2010, december 9th, 11h30m20s) -> (yymmhhmmss)
  "0-0:96.1.1(4B384547303034303436333935353037)\r\n"\ // Equipment identifier
  "1-0:1.8.1(%f*kWh)\r\n"\ // Active Energy Import (+A) Low tarrif
  "1-0:1.8.2(%f*kWh)\r\n"\ // Active Energy Import (+A) Low normal/high
  "1-0:2.8.1(%f*kWh)\r\n"\ // Active Energy Export (-A) Low tarrif
  "1-0:2.8.2(%f*kWh)\r\n"\ // Active Energy Export (-A) Normal/High tarrif
  "0-0:96.14.0(%4d)\r\n"\ // Tarrif indicator
  "1-0:1.7.0(%f*kW)\r\n"\ // Actual electricity power delivered (+P)
  "1-0:2.7.0(%f*kW)\r\n"\ // Actual electricity power received (-P)
  "0-0:96.7.21(00000)\r\n"\ // Number of power failures in any phase
  "0-0:96.7.9(00000)\r\n"\ // Number of long power failures in any phase
  "1-0:99.97.0(0)(0-0:96.7.19)\r\n"\ // Power failure event log
  "1-0:32.32.0(00000)\r\n"\ // Number of voltage sags in L1
  "1-0:52.32.0(00000)\r\n"\ // Number of voltage sags in L2
  "1-0:72.32.0(00000)\r\n"\ // Number of voltage sags in L3
  "1-0:32.36.0(00000)\r\n"\ // Number of voltage swells in L1
  "1-0:52.36.0(00000)\r\n"\ // Number of voltage swells in L2
  "1-0:72.36.0(00000)\r\n"\ // Number of voltage swells in L3
  "0-0:96.13.0(0)\r\n"\ // Other devices on M-Bus
  "1-0:32.7.0(%f*V)\r\n"\ // Instantaneous voltage L1
  "1-0:52.7.0(%f*V)\r\n"\ // Instantaneous voltage L2
  "1-0:72.7.0(%f*V)\r\n"\ // Instantaneous voltage L3
  "1-0:31.7.0(%d*A)\r\n"\ // Instantaneous current L1
  "1-0:51.7.0(%d*A)\r\n"\ // Instantaneous current L2
  "1-0:71.7.0(%d*A)\r\n"\ // Instantaneous current L3
  "1-0:21.7.0(%f*kW)\r\n"\ // Instantaneous active power L1 (+P)
  "1-0:41.7.0(%f*kW)\r\n"\ // Instantaneous active power L2 (+P)
  "1-0:61.7.0(%f*kW)\r\n"\ // Instantaneous active power L3 (+P)
  "1-0:22.7.0(%f*kW))\r\n"\ // Instantaneous active power L1 (-P)
  "1-0:42.7.0(%f*kW))\r\n"\ // Instantaneous active power L2 (-P)
  "1-0:62.7.0(%f*kW))\r\n"\  // Instantaneous active power L3 (-P)
  "!EF2F\r\n"
*/
#define SENDING_INTERVAL 1000
#define ENDING_LINE "!%4x\r\n"

char *DSMR_5_0_2_TELEGRAM[] = {"/ISk5\\2MT174-001\r\n",
                               "1-3:0.2.8(50)\r\n",
                               "0-0:1.0.0(%02d%02d%02d%02d%02d%02dW)\r\n",
                               "1-0:1.8.1(%07.3f*kWh)\r\n",
                               "1-0:1.8.2(%07.3f*kWh)\r\n",
                               "1-0:2.8.1(%07.3f*kWh)\r\n",
                               "1-0:2.8.2(%07.3f*kWh)\r\n",
                               "0-0:96.14.0(%04d)\r\n",
                               "1-0:1.7.0(%f*kW)\r\n",
                               "1-0:2.7.0(%f*kW)\r\n",
                               "0-0:96.7.21(00000)\r\n",
                               "0-0:96.7.9(00000)\r\n",
                               "1-0:99.97.0(0)(0-0:96.7.19)\r\n",
                               "1-0:32.32.0(00000)\r\n",
                               "1-0:52.32.0(00000)\r\n",
                               "1-0:72.32.0(00000)\r\n",
                               "1-0:32.36.0(00000)\r\n",
                               "1-0:52.36.0(00000)\r\n",
                               "1-0:72.36.0(00000)\r\n",
                               "0-0:96.13.0(0)\r\n",
                               "1-0:32.7.0(%03.1f*V)\r\n",
                               "1-0:52.7.0(%03.1f*V)\r\n",
                               "1-0:72.7.0(%03.1f*V)\r\n",
                               "1-0:31.7.0(%03.2f*A)\r\n",
                               "1-0:51.7.0(%03.2f*A)\r\n",
                               "1-0:71.7.0(%03.2f*A)\r\n",
                               "!\r\n"
                              };
//"1-0:21.7.0(%f*kW)\r\n"\
//"1-0:41.7.0(%f*kW)\r\n"\
//"1-0:61.7.0(%f*kW)\r\n"\
//"1-0:22.7.0(%f*kW))\r\n"\
//"1-0:42.7.0(%f*kW))\r\n"\
//"1-0:62.7.0(%f*kW))\r\n"\
//"0-1:24.1.0(003)\r\n"\ // Device type
//"0-1:96.1.0(0)\r\n"\ // Equipment identifier (Gas)
//"0-1:24.2.1(101209112500W)(12785.123*m3)\r\n"\ // Last 5-minute value gas delivered to client in m3 (time value)(gas delivered)

long previousMessage;

float previousActiveEnergyImport; // 1.8.0
float previousActiveEnergyExport; // 2.8.0

float activeEnergyImport; // 1.8.0
float activeEnergyImportLowTarrif; // 1.8.1
float activeEnergyImportNormalorHighTarrif; // 1.8.2

float activeEnergyExport; // 2.8.0
float previousActiveEnergyExportLowTarrif; // 2.8.1
float previousActiveEnergyExportNormalorHighTarrif; // 2.8.2

float activeEnergyExportLowTarrif; // 2.8.1
float activeEnergyExportNormalorHighTarrif; // 2.8.2

float voltagePhaseOne; // 32.7.0
float voltagePhaseTwo; // 52.7.0
float voltagePhaseThree; //72.7.0

float currentPhaseOne; // 31.7.0
float currentPhaseTwo; // 51.7.0
float currentPhaseThree; // 71.7.0

float activeImportPowerPhaseOne; // 21.7.0
float activeImportPowerPhaseTwo; // 41.7.0
float activeImportPowerPhaseThree; // 61.7.0

float activeExportPowerPhaseOne; // 22.7.0
float activeExportPowerPhaseTwo; // 42.7.0
float activeExportPowerPhaseThree; // 62.7.0

float actualPowerDeliveredToClient; // 1.7.0 (kW)
float actualPowerReceivedFromClient; // 2.7.0 (kW)

const int timeZone = 1;     // Central European Time
//const int timeZone = -5;  // Eastern Standard Time (USA)
//const int timeZone = -4;  // Eastern Daylight Time (USA)
//const int timeZone = -8;  // Pacific Standard Time (USA)
//const int timeZone = -7;  // Pacific Daylight Time (USA)

char* p1Buffer;

long sendingInterval;
long p1Length;

// https://remotemonitoringsystems.ca/time-zone-abbreviations.php
const char* NTP_SERVER = "de.pool.ntp.org";
const char* TZ_INFO    = "CET-1CEST-2,M3.5.0/02:00:00,M10.5.0/03:00:00";

struct tm local;

void setup(){
  Serial.begin(115200);
  
  pinMode(LED_BUILTIN, OUTPUT);
  
  configTzTime(TZ_INFO, NTP_SERVER);
  getLocalTime(&local, 1000); // wait up to 10sec to sync

  while (local.tm_year == 1970) {
    getLocalTime(&local, 1000); // wait up to 10sec to sync
  }

  Serial.println(&local, "%B %d %Y %H:%M:%S (%A)");

}

void loop(){
  getLocalTime(&local);
  if ((millis() - sendingInterval) > SENDING_INTERVAL && p1Length > 0) {
    sendingInterval = millis();
    char outputBuffer[27][32];
    if (snprintf(outputBuffer[2], 27, DSMR_5_0_2_TELEGRAM[2], (local.tm_year - 100), local.tm_mon + 1, local.tm_mday, local.tm_hour, local.tm_min, local.tm_sec) <= 0) {
      client.publish(debug_topic, "Failed to set line 2");
    }
    if (snprintf(outputBuffer[3], 30, DSMR_5_0_2_TELEGRAM[3], activeEnergyImportLowTarrif) <= 0) {
      client.publish(debug_topic, "Failed to set line 3");
    }
    if (snprintf(outputBuffer[4], 26, DSMR_5_0_2_TELEGRAM[4], activeEnergyImportNormalorHighTarrif) <= 0) {
      client.publish(debug_topic, "Failed to set line 4");
    }
    if (snprintf(outputBuffer[5], 26, DSMR_5_0_2_TELEGRAM[5], activeEnergyExportLowTarrif) <= 0) {
      client.publish(debug_topic, "Failed to set line 5");
    }
    if (snprintf(outputBuffer[6], 26, DSMR_5_0_2_TELEGRAM[6], activeEnergyExportNormalorHighTarrif) <= 0) {
      client.publish(debug_topic, "Failed to set line 6");
    }
    if (snprintf(outputBuffer[7], 20, DSMR_5_0_2_TELEGRAM[7], (local.tm_hour > 23 && local.tm_hour < 7) ? 1 : 2) <= 0) {
      client.publish(debug_topic, "Failed to set line 7");
    }
    if (snprintf(outputBuffer[8], 25, DSMR_5_0_2_TELEGRAM[8], actualPowerDeliveredToClient) <= 0) {
      client.publish(debug_topic, "Failed to set line 6");
    }
    if (snprintf(outputBuffer[9], 25, DSMR_5_0_2_TELEGRAM[9], actualPowerReceivedFromClient) <= 0) {
      client.publish(debug_topic, "Failed to set line 9");
    }
    if (snprintf(outputBuffer[20], 23, DSMR_5_0_2_TELEGRAM[20], voltagePhaseOne) <= 0) {
      client.publish(debug_topic, "Failed to set line 20");
    }
    if (snprintf(outputBuffer[21], 23, DSMR_5_0_2_TELEGRAM[21], voltagePhaseTwo) <= 0) {
      client.publish(debug_topic, "Failed to set line 21");
    }
    if (snprintf(outputBuffer[22], 23, DSMR_5_0_2_TELEGRAM[22], voltagePhaseThree) <= 0) {
      client.publish(debug_topic, "Failed to set line 22");
    }
    if (snprintf(outputBuffer[23], 21, DSMR_5_0_2_TELEGRAM[23], currentPhaseOne) <= 0) {
      client.publish(debug_topic, "Failed to set line 23");
    }
    if (snprintf(outputBuffer[24], 21, DSMR_5_0_2_TELEGRAM[24], currentPhaseTwo) <= 0) {
      client.publish(debug_topic, "Failed to set line 24");
    }
    if (snprintf(outputBuffer[25], 21, DSMR_5_0_2_TELEGRAM[25], currentPhaseThree) <= 0) {
      client.publish(debug_topic, "Failed to set line 25");
    }

    memcpy(outputBuffer[0], DSMR_5_0_2_TELEGRAM[0], 19);
    memcpy(outputBuffer[1], DSMR_5_0_2_TELEGRAM[1], 17);
    memcpy(outputBuffer[10], DSMR_5_0_2_TELEGRAM[10], 22);
    memcpy(outputBuffer[11], DSMR_5_0_2_TELEGRAM[11], 21);
    memcpy(outputBuffer[12], DSMR_5_0_2_TELEGRAM[12], 31);
    memcpy(outputBuffer[13], DSMR_5_0_2_TELEGRAM[13], 22);
    memcpy(outputBuffer[14], DSMR_5_0_2_TELEGRAM[14], 22);
    memcpy(outputBuffer[15], DSMR_5_0_2_TELEGRAM[15], 22);
    memcpy(outputBuffer[16], DSMR_5_0_2_TELEGRAM[16], 22);
    memcpy(outputBuffer[17], DSMR_5_0_2_TELEGRAM[17], 22);
    memcpy(outputBuffer[18], DSMR_5_0_2_TELEGRAM[18], 22);
    memcpy(outputBuffer[19], DSMR_5_0_2_TELEGRAM[19], 18);

    // Calculate the CRC
    unsigned int currentCRC = 0;

    for (int i = 0; i < sizeof(outputBuffer); i++) {
      currentCRC = CRC16(currentCRC, (unsigned char*)outputBuffer[i], strlen((char*)outputBuffer[i]));
    }

    if (snprintf(outputBuffer[26], 9, ENDING_LINE, currentCRC) <= 0) {
      client.publish(debug_topic, "Failed to add CRC");
    }


    for (int i = 0; i < 27; i++) {
      Serial.write(outputBuffer[i]);
    }

    digitalWrite(LED_BUILTIN, !digitalRead(LED_BUILTIN));
  }
}

void fillInValues(){
 previousActiveEnergyImport = activeEnergyImport;
  previousActiveEnergyExport = activeEnergyExport;
  char* lines = strtok(p1Buffer, "\r\n");
  char* line = lines;
  bool reachedEnd = false;
  while (!reachedEnd) {
    if (sscanf(line, "1-0:1.8.0*255(%f*kWh)", &activeEnergyImport) > 0) {

    }

    if (sscanf(line, "1-0:1.8.1*255(%f*kWh)", &activeEnergyImportLowTarrif) > 0) {

    }

    if (sscanf(line, "1-0:1.8.2*255(%f*kWh)", &activeEnergyImportNormalorHighTarrif) > 0) {

    }

    if (sscanf(line, "1-0:2.8.0*255(%f*kWh)", &activeEnergyExport) > 0) {

    }

    if (sscanf(line, "1-0:2.8.1*255(%f*kWh)", &activeEnergyExportLowTarrif) > 0) {

    }

    if (sscanf(line, "1-0:2.8.2*255(%f*kWh)", &activeEnergyExportNormalorHighTarrif) > 0) {
      reachedEnd = true;
    }

    /*
      if (sscanf(line, "1-0:1.7.0*255(%f*kW)", &actualElectricityPowerDelivered) > 0) {
      client.publish(debug_topic, "Failed to find 1.7.0");
      }

      if (sscanf(line, "1-0:2.7.0*255(%f*kW)", &actualElectricityPowerReceived) > 0) {
      client.publish(debug_topic, "Failed to find 2.7.0");
      }*/

    if (sscanf(line, "1-0:32.7.0*255(%f*V)", &voltagePhaseOne) > 0) {

    }

    if (sscanf(line, "1-0:52.7.0*255(%f*V)", &voltagePhaseTwo) > 0) {

    }

    if (sscanf(line, "1-0:72.7.0*255(%f*V)", &voltagePhaseThree) > 0) {

    }

    if (sscanf(line, "1-0:31.7.0*255(%f*A)", &currentPhaseOne) > 0) {

    }

    if (sscanf(line, "1-0:51.7.0*255(%f*A)", &currentPhaseTwo) > 0) {

    }

    if (sscanf(line, "1-0:71.7.0*255(%f*A)", &currentPhaseThree) > 0) {

    }
    line++;
  }
  if (previousMessage != 0) {

    long timeDifference = ((millis() - previousMessage) / 1000);

    float importWattHour = ((activeEnergyImport - previousActiveEnergyImport) * 1000.0f);
    float exportWattHour = ((activeEnergyExport - previousActiveEnergyExport) * 1000.0f);

    actualPowerDeliveredToClient = (importWattHour / 1000.0f) / (timeDifference / 3600.0f); // Needs to be in kW
    actualPowerReceivedFromClient = (exportWattHour / 1000.0f) / (timeDifference / 3600.0f); // Needs to be in kW
  }
  previousMessage = millis(); 
}