digraph xfdepend
{
 size="8,6"; ratio=fill; node[fontsize=12];

 "Diesel Gen" -> "300W"; 
 "Batteries" -> "50W";
 "Solar/Wind" -> "150W";
 "Bottled CO2"; "Diesel CO2";

 subgraph "Power1" { label="P1"; "Diesel Gen";  }
 subgraph "Power2" { label="P2"; "Batteries"; "Solar/Wind"; }
}