In short
- Start from the usable energy of the stack, not the nominal figure, and remove the reserve you keep.
- Divide by your average night load, then look at the peaks that empty it faster.
- A few real nights of data give a far better answer than any calculator.
Check the datasheet of your exact model for the nominal and usable energy, and the depth of discharge your inverter allows. Then the sum is simple.
Usable energy first
Multiply the usable energy of one module by the number of modules in the stack. Remove the reserve your inverter keeps at the bottom, often 10 to 20 percent. Two V5 modules with a 20 percent reserve leave a little over 8 kWh for the night.
Your night load
Many homes draw 200 to 500 W through the night once cooking is done: fridge, router, standby, a few lights. At 400 W, 8 kWh lasts about 20 hours. At 1 kW, with a heat pump or an oven in the evening, it lasts eight.
Peaks matter
The average hides the oven, the kettle and the washing machine. A busy evening can take a third of the battery in two hours, then the quiet night runs on what is left. Look at when the battery empties, not only how much.
Winter changes everything
Short days mean the stack may start the evening half full. A battery that lasts all night in June can run out at midnight in December. Plan on the season that matters most to you.
Measure your own nights
Pytes Monitor reads the stack on the console port of the master module and records charge, current and energy through the night. After a week you know at what time the battery reaches its reserve and how full it started. Try the runtime calculator, then check it in the free Cloud.
Common questions
How many hours does one Pytes module last?
It depends on your load. At 400 W through the night, one module with a usual reserve lasts around ten hours.
Should I add a module?
If the battery reaches its reserve before sunrise most nights, an extra module helps. If it stays half full, it will not.
Can Pytes Monitor read a whole stack?
Yes. One box per stack reads the master module and the modules behind it.
