Kevin Brookes, 35, from Tamworth, suffered fatal injuries in the incident at the Kineton Road Industrial Estate, Southam on 31 May 2012.

Principal contractor Alumet Renewable Technologies Ltd was jointly prosecuted with subcontractors Midlands Solar Solutions Ltd, who employed Brookes to install the panels, and Rugby Scaffolding Services Ltd, responsible for installing edge protection.

Coventry Crown Court heard that Brookes was attempting to retrieve a drill that had started to slide down towards the edge of the roof when he slipped and slid through the handrail, over the edge of the building, landing on his head.

Brookes, who was the sole carer for his elderly disabled father, fell into an immediate coma and died 19 days later in hospital.

The HSE investigation found that Alumet had failed to put an adequate health and safety plan in place.

The measures outlined in their plan were not sufficient to protect the workers, and those measures that were in place were not being followed by Alumet or the other two companies involved in the work.

The investigation identified that the edge protection did not meet nationally agreed standards.

It also revealed that employees of Rugby Scaffolding Services Ltd weren’t properly trained to install the protection and didn’t have appropriate supervision.

The investigation also revealed that there were unsuitable provisions in place to prevent people falling through the skylights.

Alumet Renewable Energy Technologies Ltd, of Bourne End, Southam, was fined £66,000 and ordered to pay £12,491 in costs after admitting a safety breach.

Rugby Scaffolding Services Limited, of Rugby, Warwickshire, admitted the same charge and was fined £60,000 and ordered to pay costs of £12,491.

Midlands Solar Solutions Ltd, of Sutton Coldfield also pleaded guilty and was fined £50,000 and ordered to pay £12,491 in costs.

After the hearing, HSE inspector Amy Kalay, said: “This fatal fall was entirely and easily preventable.  The health and safety plan and mechanisms put in place to carry out the work fell far below the required standards.

“All three companies had copious experience of working at height to install solar panels and as such should have been experts.

“Alumet Renewable Technologies Ltd knew that the work was a high-risk activity, and the company should have known what measures to put in place to keep workers safe and making sure these precautions were followed by everyone involved.”