Minimal work was done until 1883, when a thermal plant was built to process the extracted sulfur.

So will solar thermal plants secure the planet's future?

Other expenses relate to the cost of bringing old thermal plants out of retirement to meet the demand for power.

The plant load factor of thermal plants has gone up from the low sixties in 1991 to 72.7 per cent in 2003-4.

Large hydropower and thermal plants dominate the current expansion plans.