Geothermal's environmental profile

The Government of Fiji is placing a high priority on minimising greenhouse gas emissions at a time when South Pacific nations are concerned about global warming.

Geothermal power plants are very environmentally “friendly”. As such they can add to Fiji’s considerable achievements in maximizing the use of renewable energy with minimal environmental impact.

The main environmental advantages of geothermal are as follows.

Clean air: Geothermal power plants meet the world’s most stringent standards for clean air.


Geothermal power plants emit only a tiny fraction (1/6000) of “greenhouse gases” compared with conventional power plants.

This plant in New Zealand is a similar size to the first plant to be installed by Geothermal Electric Limited once suitable flows of hot water at Savu Savu have been reached.

Greenhouse gases: They emit very small amounts of “greenhouse gases”: about 0.14 kg of carbon per megawatt hour while diesel plants emit about 6000 times more -- about 880 kg. This huge difference is highly significant: power plants in the United States of America, for example, release more than 40% of that country’s total emissions of carbon dioxide, the main global warming pollutant. [Source of data: U.S. Environmental Protection Agency, Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2005, April 2007. Based on calculation of CO2 emissions from tables 3-1 and 3-3.]

Other emissions are very low, or zero: Geothermal plants typically emit only about 0.20 kg of sulphur per megawatt hour while diesel plants emit about 100 times more -- about 23 kg (but see note below). Nitrogen, which is a significant pollutant emitted by diesel plants, is virtually nil from geothermal plants. [Source of data: South Pacific Applied Geoscience Commission Miscellaneous Report MR463, June 2002.] These emissions are particularly significant because sulphur dioxide and nitrogen oxides form “acid rain”.

[Note: Geothermal power plants in Fiji are expected to emit much less sulphur than the 0.20 kg quoted above, because on present indications it appears likely that sulphur dioxide gas will be zero, or close to it.]

Industrial development will produce very low emissions: Fiji’s present continuous generating capacity is similar to that of a 112 MWe geothermal power plant in the United States of America owned by Ormat. A conventional power station of that capacity produces -- each year -- 630,000 tonnes of greenhouse gases and toxic emissions [Source of data: http://www.ormat.com/fileserver/php?file=4&cmd=download]. Taking into account that about half of Fiji’s power production is from emission-free hydro, if geothermal replaced the present diesel power generation about 300,000 tonnes of greenhouse gases and toxic emissions less would be produced than is produced today.

More significantly, if geothermal powers new mines, metal refining plants and other industries for Fiji, the greatly increased electricity production will be achieved with only one six-thousandth (1/6000) of the increase in emissions that would occur with a conventional power station.

No transport-related hazards or emissions: Environmental hazards of accidental fuel oil spills and the environmental side-effects of oil transportation (200,000 tonnes per year in the above example) are eliminated.


Pumping geothermal water back into the ground from the power plant ensures that the same amount of hot water as before remains available for traditional community uses, such as cooking.

Only heat is removed, not water: When geothermal water is pumped back into the earth, as shown in the diagram, the result is that the underground geothermal reservoir retains the same amount of water. Therefore, the power station never runs out of water and any other places that use hot water (such as hot springs resorts and cooking places) continue to receive exactly the same quantity as they always have. Returning the water underground instead of draining it at the surface also ensures that animals and plants in nearby creeks are not affected by the temperature of the water or any minerals contained in it.

Low visual profile: A geothermal power plant blends easily into its surroundings.


In the binary power generation systems to be installed by Geothermal Electric Limited, all water is returned underground. The only component removed is heat.
 

Strictly speaking, is geothermal “renewable” energy?

“There is some ambiguity on the issue of geothermal energy being a ‘renewable’ resource. Some geothermal sites may be developed in such a manner that the heat withdrawn equals the heat being replaced naturally, thus making the energy source renewable for a long period of time.* At other sites, the resource lifetime may be limited to some decades. In any case, even if it is not technically a renewable resource, potential global geothermal resources represent such a huge amount of energy that, practically speaking, the issue is not the finite size of the resource but availability of technologies that can tap the resource in an economically acceptable manner.”

— ‘Geothermal Power Stations’, Lucien Y. Bronicki. Encyclopedia of Physical Science and Technology, 3rd edn, vol. 6, p. 710. See http://www.ormat.com/FileServer/89c903295b4b827872403195a8aeda04.pdf

* It is not yet known whether this will apply to Geothermal Electric Limited’s sites in Fiji.

 

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