Geology: Geology and geological structures (such as faults) are not accounted for in the ranking system, which may impact on drilling costs and complexity, and the wider hydrogeology of the region;
Galwadau Gwresogi ac Oeri: nid yw’r radd yn ystyried ardaloedd presennol neu arfaethedig y llwythi gwresogi ac oeri, a fyddai’n pennu’r galw ac yn dynodi gwerth cyfle i adfer gwres dŵr mwyngloddiau.