Overall they place the risk at just 0.1%, which is fine as long as you’re not part of the 0.1% of course.
Seems pretty high to me, 1 fire in 1000 installation-years; it implies a small development of 100 homes all with solar panels (similar to the development my daughter has just moved into) would experience a fire in the next 10 years.
If that resulted in a fatality in just 1 in 10 off these fires the risk would be classed as unacceptable by the HSE.
And then there's the insurance cost implication. Damage of £250k at a likelihood of 0.1% implies an annual expected loss of £250. That would be added to the insurance premium of everyone with a solar panel.