How the system works, in plain terms
Written for the person who will live with the system, and for the electrician who has to wire it.
Why LFP and not NMC
Both are lithium-ion. The difference that matters at home is not energy density, it is what happens when something goes wrong.
Thermal stability
LFP has a higher thermal runaway onset temperature and does not release oxygen when it degrades, which is why it does not sustain the same fire behaviour as NMC. In a cabinet inside a house, that is the deciding property.
Cycle life
LFP is rated for more cycles at the same depth of discharge. A house cycling daily cares about cycles, not about kilograms per kWh.
The cost of the trade
LFP is heavier and slightly larger for the same energy. In a wall cabinet that costs space, not capability, and it is the trade we take.
What "10 kWh" does not tell you
| Term | What it means | Why buyers get caught |
|---|---|---|
| Nameplate energy | Total capacity printed on the pack | It is not what you can use |
| Usable energy | Nameplate minus the depth of discharge the BMS allows | A 10 kWh pack at 90% DoD gives 9 kWh, and 80% gives 8 |
| Round-trip efficiency | Energy out divided by energy in, including the inverter | Every kWh stored and returned loses 5–12%, and the inverter is part of that |
| Continuous vs peak power | What it supplies all day vs for a few seconds | A pump starting is a surge, and the inverter rating decides whether it starts |
How a backup circuit is designed
Split the board
Essential loads move to a backup sub-board: lights, fridge, internet, pumps, a few sockets. The air conditioner, oven and water heater usually stay on the grid side.
Measure the essentials
Their combined running load, and their pattern over 24 hours. This sets kWh needed for the outage window you care about.
Check the surge
The largest motor on the backup side, with its starting method. This sets the inverter rating, and it is why two houses with the same kWh need different inverters.
Set the reserve
How much capacity stays reserved for outages rather than sold to the grid or used for arbitrage. A setting, not a hardware choice.