# Power use from solar panels

When a domestic solar system is installed, the DNO supply and inverter supply are physically connected in the same terminal block, supplying the house load.

When the sun is shining and/or the batteries able, the power controller of the solar power system will ensure the load of the house is supplied (up to its limit)

If the solar system has the capacity to supply the house load, what prevents the DNO supply from supplying power to the house load as well (an thus the DNO charging), as the two supplies are connected?

Parents
• Ultimately it's just down to the small voltage differences in the interconnecting cables. Every conductor has some resistance, and a current flowing along it will result in a voltage difference between its ends. If the current flows in the opposite direction then the voltage is also reversed (in a.c. that typically means the current is then 180 degrees out of phase with the voltage but that's just the mathematical convention). For a PV system to output a certain power, it need to raise its output voltage until the required power flows. When the power it generates exactly equals that consumed on-site, then the voltage at the connection point due to the PV inverter will exactly match the grid voltage, so no current flows to or from the grid. When the PV inverter produces more power, the voltage will be slightly higher and currents flows back to the grid, lower power and the voltage will be reduced and some current from the grid will make up the deficit.

It's the same kind of thing as "how does a consumer unit know how to route the right amount of current to the individual circuits" - in short, it does nothing clever - it's just down to Ohm's law and things trying to find a natural steady state.

- Andy,