Research Projects and Publications



Feasibility study including preliminary design of a Micro-cycle binary power project with direct use applications for a single low temperature production well in Grafarbakki, Icelanf

  Author: Victoria Nyawira Nyaga                                                                                                                        Year: 2019                                                                                                                                            Supervisors: William S. Harvey, Juliet A. Newson

Abstract:

Low temperature geothermal systems are located outside the volcanic zone passing through Iceland with the largest of these located in southwest Iceland. Grafarbakki is a small hamlet in Flúðir, a small village in the Hrunamannahreppur municipality that overlies the greater Miðfell-Flúðir low temperature geothermal system. Low temperature geothermal utilization in Iceland and the production wells drilled in most of this field have historically focused on the supply of hot water for district heating. Hot water wells and springs have been providing district heating and hot pools for residents for several decades. This research focusses on harnessing one such free-flowing well GB-02 drilled in Grafarbakki with a production of 100 l/s of 105°-110°C water. The well is currently partially utilized for greenhouse heating and space heating for 2 households at approximately 5 l/s. In a bid to fully utilize the well, this thesis presents an analysis of the several selected scenarios for a project conceptual design and their profitability. The works are broken down into several sections. An introduction briefly describes the study area, scope and incentive for the project. A resource assessment section presents the resource structure, properties of the fluid and flow test results to establish the resource capacity and limits for the utilisation scenarios to be considered. A mass flow rate of 60 kg/s is selected and the lower temperature limit due to Silica scaling set to 45°C. An analysis of current direct use application and future applications proposed by the well owners as well as their market opportunities for the product have been presented to select the cascading option. A Power Plant Selection section gives an overview of available geothermal power plant technologies with special focus on low temperature technologies and market players. Three vendors were selected from this research to make a comparative technical and indicative cost study on the scale of production. The lowest costs are used for the economic analysis of the conceptual project. The Project conceptual design section models a base case scenario with a binary power plant and an aquaculture farm, then an aquaculture farm scenario, a power plant only scenario and a full well capacity production with a power plant and aquaculture farm. An overview of energy laws, electricity markets and policies is presented to shed light on the laws governing new electricity generators in Iceland, Feed in Tariffs (FITs) and Power Purchase Agreements (PPA) as a precursor to an economic analysis on the profitability of the scenarios presented. The base case scenario produces a net power output of 1257 kWe and 450 tonnes/ year of Arctic Char. The power plant model operated at a thermal efficiency of 10.38% and Specific Power Output of 20.94 kW/(kg/s) with a seasonal variation of 840 – 1640 kWe. The Aquaculture farm comprises of 100 ponds spanning over an area of 5000 m2 operating at 15.8°C and consuming 90 kg/s of fresh water. With the price of electricity at $40/ MWh, the power plant alone is only profitable at a 5% discounting rate with an NPV of $ 186,168. With the growing market in Arctic Char, low capital costs associated with a simple flow through system and at a price of $8/ kg, the base case scenario is profitable even at a 15% discounting rate yielding an NPV of $ 6,092,631. Due to the considerably low price of electricity, this case study shows that for a profitable power generation only option of utilisation, the power plant would have to produce a net power output 1800 kWe to yield a positive NPV at a 15% discount rate. Smaller levels of production will be unprofitable without a cascading utilisation like that addressed in this study.