Inverter power, battery capacity and panel capacity are three different things

Almost every difficult conversation about a solar quotation comes back to the same confusion. Someone has been told they need a 10 kW system, and nobody has said which of the three numbers that refers to.

They describe genuinely different things, they are priced separately and a system can be generous in one and badly short in another.

This is how much can run at the same moment. It is a rate, not a quantity. A 5 kVA inverter can carry roughly 5 kW of simultaneous load, and if you ask for more than that it will either limit or trip.

This is the number that decides whether the system feels adequate day to day. If the kettle, the microwave and the pool pump together exceed it, you will find out immediately.

This is how much energy is stored. It decides duration rather than rate. A 10 kWh usable battery carrying a 1 kW load runs for roughly ten hours. Carrying a 4 kW load it runs for two and a half.

Watch for the difference between nominal and usable capacity. They are not the same figure, and quotations do not always make clear which one is being offered.

This is the peak output of the array under standard test conditions. It is a laboratory figure, and a real roof will not match it. Orientation, pitch, temperature, soiling and the time of year all reduce it.

Panel capacity determines how much you generate over a day, which is what reduces your bill. It has no effect on how much can run at once, and it does not by itself help you through an outage at night.

A useful way to picture it: inverter power is the width of the pipe, battery capacity is the size of the tank and panel capacity is the rate the tank refills during daylight.

Undersize the pipe and things trip. Undersize the tank and you run out in the evening. Undersize the refill and the tank never recovers. A good design balances all three against how the property actually behaves.

Ask for all three figures, ask whether the battery capacity quoted is usable or nominal and ask what load the runtime estimate assumes. A runtime figure with no stated load underneath it does not mean anything.