Renewable and sustainable energy to provide dispatchable, stable power with realistic cascading energy applications
Energy 101: Geothermal Energy
This sub 4 minute video courtesy of the U.S. Department of Energy outlines the basic principles of Geothermal energy production.
What is Geothermal Energy?
Mary H. Dickson and Mario Fanelli
Istituto di Geoscienze e Georisorse, CNR , Pisa, Italy
Prepared in February 2004
Please click here to read the article published on the International Geothermal Association website.
GEOTHERMAL IN AFRICA
Kenya – An African Reality
- Producing 240MW at Olkario (Hell’s Gate National Park) – expansion to 330MW underway
- Development of 400MW field at Menengai commenced (120 wells)
- Target to produce 50% of Kenyan electricity requirement by 2018
- Operated by Geothermal Development Company – a Kenyan para-statal
Zambia – Recognised Potential
- Sedimentary Basins which occur in regions of active extensional tectonics provide a geologic setting conducive to geothermal systems. The Karoo era basins within Zambia which have regionally massive strike/slip faults are being found to contain geothermal systems that justify exploration
- Geological Survey of Zambia reconnaissance of Hot & Mineralised Springs in 1974
- Zambian-Italian joint Geothermal Project mid 1980’s
- Hydrochemistry, geophysics and shallow drilling (<200m)
- 220KW geothermal pilot plant installed near Lake Tanganyika
- Original program curtailed due to lack of geo technical data and funding for further exploration
Conceptual Model (USGS)
In the context of Southern Africa, the
conceptual model is of meteoric fluids
circulating in deep-seated faults being
heated by the regional geothermal gradient
and rising, to be held beneath low porosity
rocks (the Cap Rock) within the sedimentary
basin, so forming a geothermal reservoir.
Thermal springs are an indicator of, but
are not themselves an integral part of a
GEOTHERMAL ENERGY - Conceptual Model & Power Production
There are two distinct methods of using geothermal Energy to produce power; both are indirect applications, converting heat to mechanical energy which turns a turbine. Geothermal power is constant (base-load), has high operability, is sustainable due to re-injection of cool fluids and is environmentally sound.
- Steam from high enthalpy geothermal reservoirs (often associated with volcanism, such at Olkaria, Kenya) is used to drive a turbine, typically of 25+MWe capacity requiring a number of interconnected wells
- In lower enthalpy systems (such within the USA Basin and Range) a binary plant is used, in which the geothermal fluids heat a working fluid (either diluted ammonia or iso-butane) with a much lower flash boiling point than water – see schematic below
While less efficient that direct steam driven turbines, binary units are modular and suited to well-head generation that can be increased as a field is developed. Binary plants are closed circuit and emission free.
THE VALUE OF GEOTHERMAL ENERGY
Direct applications of geothermal energy could play an important role in rural energy & rural industrialisation policies, leading to Food and rural skills based Job Security. Also localised reduction in de-forestation. Bweengwa River 90,000 cattle in Target area.
Direct Applications of Relevance to Zambia and Sub-Saharan Africa: