Sunshine and hot weather are among the suspects after four lorries were badly damaged by fire at Gulval this morning.
Firefighters were called to near Ridgevale Close, Gulval, at 5:19am this morning after a number of 999 calls about smoke and lots of banging noises coming from the compound of a business at the site.
Now it has come to light that the fire could have been caused by the hot weather.
Following an investigation Cornwall Fire and Rescue Service say that sunshine hitting the engine could have caused an electrical fault, after CCTV footage showed that the lorry's lights switched on, with no-one in the cab, before the engine caught fire.
Two appliances with nine crews from Penzance were mobilised and had to use crash rescue equipment to make their way into the premise through large gates.
A fire and rescue service spokesman said that once inside the crews confirmed that there were four lorries involved in the fire.
"The Lorries were well alight and crews used four breathing apparatus with one hose reel and one jet supplied by a hydrant to extinguish the fire. At 5.59am crews confirmed that the fires had been extinguished," said the spokesman.
Fire investigator Mark Salter told the BBC: "There was no other ignition source. There has been a short circuit, we think as a result of sunlight which might have broken down a component."
He added that this was first time in almost four years as an investigator that he had come across "this possible cause".