The man, who was 23 at the time, fell from the roof of the house on Sherfield English Road while working for EE Renewables Limited on 16 December 2022.
He had been adjusting a solar panel when he slid and fell four metres onto the ground below, sustaining a broken femur as a result.
An HSE investigation found EE Renewables Limited had not properly planned the work at height and failed to take suitable steps to prevent a fall. The company had been hired by the homeowner to move nine solar panels higher up on the roof.
EE Renewables Limited, of Fareham, Hampshire, pleaded guilty to safety breaches and was fined £120,000 and ordered to pay £4,716 in costs at Swindon Magistrates’ Court.
HSE inspector Sam Applebee said: “EE Renewables Limited did not properly plan this work so it could be carried out in a safe manner. There were inadequate means of protecting the workers from falling off the roof, with the company failing to provide edge protection.
“Working at height remains one of the biggest causes of injuries and fatalities in Britain, so it is important that companies ensure they implement the correct control measures and safe working practices.”