G.E.V.A.: Geothermal electricity venture analysis model

The Monte Carlo technique is a powerful method for quantifying the various risks in geothermal development. G.E.V.A. uses this method to allow users to realistically estimate the range of costs to be expected in geothermal electricity development. Such risk analysis offers a number of distinct advantages over the conventional single estimate approach:

• 1.(1) Risk is made explicit: the uncertainty perceived in the resource estimates are incorporated directly into the cost analysis. Knowledge of both the most likely outcome as well as the range of possibilities helps to create a more rational and informed decision-making process.
• 2.(2) Variability of outcome is measured: the dispersion in the possible outcome is estimated. Other things being equal, lower variability in the estimated cost of power is desirable.
• 3.(3) Promotes better decisions: the simulation approach requires more judgement in estimating the values for the uncertain elements in the investment. Recognizing what is known and not known with regard to the resource, leads to a more careful analysis. The analysis process is documented so that decision makers can build on past experiences.

The simulation program is easy to use and designed for widely available microcomputers. With site specific data on hand, plant costs can be estimated quickly. A comprehensive levelized cost model is used with the ability to distribute uncertain values with triangular probability distributions. The user need know nothing about the nature of the mathematics involved. The most likely value for each uncertain parameter along with the range of possible values are input. Results are given in terms of the levelized cost in mills/kWh for which the geothermal electricity can be produced. A mean value is computed along with range of possibilities and their relative chance. Solution for a two hundred sample run takes only about twenty minutes on an IBM personal computer. Use of a fast structured code, such as C-language, using the 8087 match co-processor could reduce the runtime by an order of magnitude.G.E.V.A. is a useful tool for geothermal assessment. It provides improved insight into the economics of high temperature geothermal resources for investment decisions. As with any such model, the greatest benefits will result when coupled with detailed geological information, skilled analysis and expert opinion.     

The thermochemical hydrogen program at N.C.L.I.

This short communication describes work now underway at the National Chemical Laboratory for Industry (N.C.L.I.) in Tokyo, Japan on the production of hydrogen from H₂S or H2O by thermochemical processes. Emphasis is placed on the chemistry of the processes and the use of catalysts in various reactions.