As well as making the castle suitable for writers to work in, the Trustees of the Hawthornden Foundation desired to make the Castle and the whole Estate Net Zero.  Achieving this was a complex task.  Key was to use the historic walled garden to generate sufficient power from a large photovoltaic array.  Fortunately the slope, too steep for effective cultivation, was ideal for PV panels and is well hidden from view.

The energy powers two industrial size air source heat pumps, also in the walled garden.  Power and 100m of buried insulated pipework heats new radiators in the castle, which is now comfortable for the writers even on the coldest days.

Surplus power is exported to the grid.