Clean Earth Energy Limited, of Bess Park Road, Trenant Industrial Estate, Wadebridge, Cornwall, pleaded guilty to breaching Regulation 4(1) of the Work at height Regulations 2005.
It was fined £20,000 with £1,704 in costs.
Bodmin Magistrates' Court heard how a senior roofer working for the company was installing solar panels at Homeleigh Garden Centre in Launceston on 15 August 2015.
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However, while walking across the roof , the cement fibre sheeting he was walking on gave way.
The worker fell around 15ft and suffered multiple injuries including several fractured vertebrae.
A Health and Safety Executive (HSE) investigation into the incident found the work was not properly planned or appropriately supervised.
HSE inspector Nicole Buchanan said after the hearing: "Working on fragile surfaces is a particularly high risk activity in which many serious accidents occur. Duty holders should do everything possible to protect their workers from the risk of a fall."
(LM)
