Ann: Geothermal Potential of Millungera Basin Confirmed, page-17

ORC technology is just the power plant, and was the technology used by GDY for the Habanero 1 MWe demo plant which ran for 160 days in 2013 and then was dismantled.

Geothermal hot water/steam is the energy input to the ORC plant. It comes from wells in the ground. The geological problem is where does the water come from, at what depth and at what temperature and volume? There are three main sources: volcano-hosted, sediment-hosted and EGS. Volcano- and sediment sources exploit natural reservoirs of hot water - volcanic is best because the water/steam steam is usually shallow and high temperature.

EGS is where an artificial reservoir is created by opening cracks in a large volume of hot rocks - typically deeply buried granite. The GDY project was an EGS project with wells around 4 km deep. Deep wells in granite are very expensive, and the volume of hot water that can be pumped through the EQG reservoir is limited - therefore EGS projects are relatively expensive and I don't know of any which can survive without considerable taxpayer support.

This GRV release is also talking about an EGS project with drilling down to 5 km deep basement to get temperatures above 150 C. This is different compared to their earlier concept of middle to low temperature resources and relatively shallow drilling in sediments.

The key is "economic" drilling depths - "economic" is a complex function of fluid temperature and flow-rate, number of wells, plant capital and operating costs, and electricity sale prices. In my view, neither EGS or low-T concepts are likely to produce income scale that is acceptable to an ASX company. On the other hand GDY had volcanic-hosted in the Solomon Islands and Vanuatu that would make much more sense. They are hot, shallow and the lower power markets are dominated by high-cost diesel generators.