The Gendex Limited employee, who does not wish to be named, stepped through a rooflight at the New Milton and District Community Centre last February.
He fell more than three metres before landing on a raised platform, which broke his fall, allowing him to walk away uninjured.
Southampton Magistrates’ Court heard that Gendex was installing 68 solar panels on the flat roof of the building over three days.
An HSE investigation found that a scissor lift had been provided for employees to access the roof, as were safety harnesses and training.
But the harnesses could only be used in the lift because there were no attachment points on the roof itself.
HSE also found that no protection had been provided for either the edge of the roof or the two rooflights that were present.
Magistrates were told the company had decided it was sufficient to merely warn employees about the potential fall risks rather than install any safety measures that may have damaged the roof fabric.
The court also heard that Gendex was served with a Prohibition Notice by HSE in March 2006 relating to unsafe ladder work.
Gendex Limited, of Court Road, Swanage, was fined a total of £13,000 and ordered to pay £2,477 in costs after pleading guilty to two separate safety breaches.
After the hearing, HSE inspector Adam Wycherley said: “Thankfully the worker avoided injury on this occasion, but he was extremely fortunate to do so.
“The fall was entirely preventable and Gendex Ltd has no excuse for failing to do more than they did to mitigate the risks he and others faced.
“Roof work must be properly planned and appropriate safety equipment provided.”