You might think about running your kiln at night when the fridge is less likely to turn on. Depending on the temp there you might even be able to unplug the fridge overnight when the door wouldn't be constantly be opened up. To figure out how much power the kiln draws, divide the voltage (120/240) into the wattage. Eg.. 1500w/120v=12.5amps 1500w/240v=6.25amps. Batteries in parallel or series would require an inverter and a calculation for the system size. Batteries are rated in Amp hours. Let me know if you decide to go the electrical route and I could figure out the load for ya