The only place in your sketch that seems to send data to the lcd is the setup function. When that is called, you have not calculated any figures yet.
lcd.print(watt_buf[x]);What is the value of x when this line is executed ?
Why is x declared as a char ?
What is in the watt_buff array and how does it get there ?
Is the ‘-’ character on the second line of the LCD significant ? Where could it have come from I wonder ?
Why is there nothing in the loop() function ?
Why use do while(1) in setup() instead of the loop() function ?