In the 2008 edition of Geothermal Today, the DoE's EERE estimated that conventional geothermal electricity costs, before any reductions related to resource credits, between $0.63/kWh and $0.102/kWh to produce. Using crude (WTI), natural gas and retail electricity data from the EIA, I created the graph below to put this into perspective. The graph's geothermal cost band is static and does not reflect actual cost evolution overtime - if it did it would probably be sloping downward with perhaps a lump in 2007/2008 when the prices of construction commodities peaked.
As mentioned by Tom in his original article, risks in the geothermal industry are heavily concentrated in the resource assessment and exploration phases, although the largest component of total development cost is facility construction. According to the investment bankers who underwrote a large chunk of the financing for the North American geothermal pure-plays, each hole drilled while looking for geothermal resources costs around $5 million, which is a fair chunk of change for companies with market caps of under $100 million.
EERE breaks down development costs for a "typical geothermal power plant" - which account for the bulk of geothermal power's levelized cost
Although geothermal's high capacity factors and inherent predictability give it a clear edge over wind and solar PV, economical geothermal development is currently constrained to a handful of areas with the right geological conditions. This led Tom to call conventional geothermal "boutique" clean power, meaning it can never account for an appreciable proportion of total power production (although in certain regions it can definitely be scaled up substantially.)
Needless to say, the current financing environment is not favorable to either the mining exploration business model or the project development by inexperienced teams business model. This has resulted in more expensive capital for geothermal firms - Nevada Geothermal got a loan last September with an interest rate of 14% plus other fees, a punishing cost for any company.
Read more about ARRA Money For Geothermal from altenergystocks