Wednesday, June 9, 2010

Hot spot

Iceland is lucky in more respects than it is unlucky. For this we who live here are eternally grateful. One of the things that deserve a spot in the lucky column are our geothermal fields. I have previously mentioned that the mid-Atlantic ridge runs through the country making it geologically active which in layman‘s terms means volcanoes and geysers. The ridge can clearly be seen on the globe on the right, Iceland being located within the red circle. The country is young in a geological sense; the oldest bedrock above sea level is a mere 14 million years old. To give the reader something to compare to, the dinosaurs had begun to develop into the world’s dominant vertebrates about 230 million years ago, the oldest known dinosaur fossil dating back 235 million years (found in Brazil). Further to this, the oldest known bedrock (located in Canada) is believed to be 4.25 billion years old. Oddly enough I have a reason to spend so much space discussing the age of rocks and will get to it a bit further on.

Hot springs are found all over Iceland. There are about 250 low-temperature geothermal areas with a total of about 800 hot springs with an average temperature at the surface of 75°C (170°C). Geothermal energy stems from the heat contained within the earth, the core’s temperature being estimated at about 5000°C (8500°F). The surface temperature of the earth is a whole lot less than this (praise the lord) so a heat gradient from the core to the surface exists, i.e. the temperature will increase the deeper you go. In most places of the world this heat gradient is 25-30°C per km of depth (about 2.5°F per 100 ft of depth) but at plate boundaries the heat increases considerably.

In Iceland we classify our geothermal fields into two categories, low temperature and high temperature fields. The low temperature fields provide temperatures of under 150°C at a depth of 1 km about 5 times the temperature that could be expected in non active areas of the world. The geothermal fluid extracted from boreholes in these fields is utilized for space heating, greenhouses, swimming pools and snow melting. High temperature fields on the other hand are the areas where the temperature of the fluid at this same depth is about 200-350°C (400-650°F) and the geothermal fluid from these areas is used to produce electricity and for industry. Producing electricity from geothermal water requires steam and once condensed the still extremely hot water can be used for space heating.

Now back to the bedrock. Anywhere in the world one can bore a hole into the ground and reach high temperatures but that in itself is not enough to extract this heat (energy) and use it. You need a medium of transport and this medium is groundwater. However if the bedrock is very old then it is more compressed and settled than young bedrock which is typically cracked. These cracks provide access for groundwater flow so if you drill into it you will pass through multiple seepage paths, filling your borehole with hot water eager to come out and get to work. Like here, where the prerequisites for economical utilization come together: a high geothermal gradient, underground water inflow into the fields and cracked (porous) bedrock.

About 60% of the geothermal energy we extract from the earth is used for space heating, 20% to produce electricity and the rest to operate year round outdoor heated swimming pools, melt snow from streets, driveways and sidewalks, heat greenhouses, operate fish farms and for other small industry. About 90% of all Icelandic houses and homes are heated using geothermal water operated through district heating systems which provide hot water via underground pipelines into our radiators in addition to hot tap water. Once used for heating, the water (now at approximately at body temperature) exits the house system and is run through loops of plastic piping that lie underneath driveways, walk paths etc. and melt the snow. Cheap and efficient, not to mention environmentally friendly as can be seen by the comparison between Reykjavík of yesterday when coal was used for house heating and Reykjavik of today with geothermal district heating.

I will let photos of what has been done to improve life here in the arctic using this bountiful resource, these show: a beach where the sea is heated for swimming, swimming pools, snow melting and the blue lagoon spa.

Yrsa - Wednesday

1 comment:

  1. Yrsa

    This is so interesting and beautiful. I've seen a wonderful show on Discovery about your geysers. It is really something unique.

    Perhaps if we had this source for energy here in the states, we wouldn't be filling the Gulf of Mexico with oil right now.

    I love your posts, Yrsa.