Spain: Renewable energy advisory firm Renovetec has conducted research into fires at a number of concentrating solar power (CSP) plants in Spain. According to the company, mineral wool used to line the piping containing the heat transfer fluid (HTF) in these plants' solar fields is to blame.
"On occasions the causes of the fires have been unclear," explains Santiago García Garrido, Technical Director of Renovetec. "The HTF has behaved differently to the specifications on its safety sheet".
Renovetec has published an article on its work which examines the relationship between the thermal insulation used to line heat transfer piping and the fires, after the company managed to reproduce the conditions leading to certain fires under laboratory conditions. The tests performed by Renovetec show that the thermal insulation can ignite at below 200°C, whereby there is a risk of spontaneous combustion even if there is no ignition spark or other ignition source.
"This explains some of the incidents at a number of CSP plants," says the company especially given that the ignition point of the HTF generally used in CSP plants (biphenyl and diphenyl oxide) is 615°C – a temperature which is highly unlikely to be reached anywhere on site.
Witnesses of some of the fires recall that the incidents arose when some of the HTF escaped from the piping installed in the solar field soaking the thermal insulation (which is normally mineral wool) covered by an aluminium jacket. On removing the aluminium jacket, the mineral wool occasionally ignited spontaneously. These fires started despite the technical specifications of the HTF manufactured by Dow Chemical and Solutia indicating that the fluid would not ignite.
The outcome of Renovetec's experiment to reproduce the conditions leading to the fires is conclusive: on certain occasions the point of spontaneous combustion is not as reflected in the safety sheets of these HTF, with the liquid igniting at temperatures below 203°C.
