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GEOTHERMAL ENERGY IN FINLAND
Ilmo T. Kukkonen
Geological Survey of Finland, Address: P.O. Box 96, FIN-02151 Espoo, Finland
e-mail ilmo.kukkonen@gsf.fi
Key words
: Finland, geothermal energy, heat pump.
ABSTRACT
The use of geothermal energy in Finland is restricted to the
utilization of ground heat with heat pumps. This is due to the
geological conditions as Finland is a part of the Fennoscandian
(or Baltic) Shield. The bedrock is Precambrian covered with a
thin (<5 m) cover of Quaternary sediments. Topography is
subdued and does not easily produce advective re-distribution
of geothermal heat by groundwater circulation systems. Due to
crystalline character of the bedrock, rock porosity and its water
content are low. This practically excludes geothermal systems
utilizing hot wet rock.
The lithosphere is very thick in Finland (150-200 km), and
heat flow is mostly below continental average (< 65 mW m
-2
).
Measured heat flow density values in the uppermost 1 km of
bedrock range from very low (<15 mW m
-2
) values to 69 mW
m
-2
, whereas an average value of 46 sites (53 boreholes) is 37
mW m
-2
. Geothermal gradient is typically 8-15 K km
-1
, and
the annual average ground temperature at the surface ranges
from about +5ºC in the southern part to about +2ºC in the
northern parts of the country. Temperatures at 500 m below
surface are usually between 8 and 14ºC. At 1000 m the
temperature ranges from 14 to 22ºC. Values either extrapolated
from geotherms or calculated with thermal models suggest that
temperatures exceeding 40ºC should be encountered at 1-1.5
km depth. However, in order to reach 100ºC, depths from 6 to
8 km are required. These numbers suggest that Finland is not a
good candidate for either wet or dry hot rock systems, although
some formations with either anomalously high heat production
rate or thermal blanketing effects due to low thermal
conductivity should be investigated in more detail.
Nevertheless, promising applications can be found for
small-scale use of ground-stored heat in all parts of the
country.
About 10,000 heat pumps have been installed in boreholes,
lakes or Quaternary deposits since the early 1980's. About 70
% of them are horizontal ground coupled systems, 20 % are
using lake water and 10 % are vertical ground coupled
systems. Typical vertical installations are in small family
houses using a shallow 100-200 m deep borehole. The order of
magnitude of energy extraction from such holes is 50 W/m
3
.
The use of ground-heat with heat pumps is currently increasing
in Finland.
1. INTRODUCTION
Finland is situated between latitudes 60 and 70 N and has a
climate with average annual air temperatures varying from 5ºC
in the southern part to –2ºC in the northern part of Finland.
Because of the climatic conditions, space heating is usually
needed from September to May. The current population of the
country is about 5 million people.
The total annual consumption of energy in Finland in 1998
was 1.29 million TJ, which is divided according to various
energy sources as follows: oil 28.0 %, coal 11.0%, natural gas
10.7 %, nuclear power 17.7%, hydropower 4.1 %, peat 6.2 %,
wood and black liquors 19.2 %, imported electricity 2.6 % and
other sources of energy 0.7 %. About half of the energy (49 %)
is consumed by the industry, 22 % is used in space heating, 18
% in traffic and 11 % in households, agriculture, etc. (Energy
Review, 1999).
Geothermal energy is not used in Finland for electricity
production and there are no direct applications of geothermal
energy either. This situation is due to the Precambrian geology
with thick crust and lithosphere resulting in low geothermal
gradient values. However, there are about 10000 heat pumps
utilizing the ground-stored heat either in bedrock, Quaternary
sediments or water-sources (lakes). Heat pumps seem to
provide a feasible alternative for space heating in small family
houses or country farms. In the official energy statistics
(Statistics Finland, 1998) the consumption of ground heat is
combined with other ‘ambient sources’ of space heating
energy. This number accounts for a total of 1240 TJ in 1997
and it is about 1.2 % of the total energy consumed in space
heating in Finland. The value has more than doubled since
1995 (510 TJ).
This paper reviews the present status and potential of
geothermal energy in Finland, presents basic geothermal data
with temperature and heat flow maps, and reports the history
and development of heat pump applications in Finland.
2. GEOLOGICAL AND GEOTHERMAL CONDITIONS
Finland is a part of the Fennoscandian (also known as the
Baltic) Shield. The bedrock is Archaean (3100 - 2500 Ma) and
Proterozoic (2500 - 1300 Ma) in age, and it is covered by a
thin, usually less than 5 m thick layer of Quaternary sediments.
The crystalline bedrock is characterized by granitoids, gneisses
and other metasedimentary or metavolcanic lithologies.
Heat flow and subsurface temperature data in Finland have
been presented by Puranen et al. (1968), Järvimäki and
Puranen (1979), Kukkonen and Järvimäki (1992) and
Kukkonen (1988, 1989, 1993, 1999). The current geothermal
data is based on the temperature logs on 46 sites and 53
boreholes shallower than 1100 m, as well as laboratory
measurements of thermal conductivity of corresponding drill
core samples. The measurements and the databases are from
the Geological Survey of Finland.
Measured heat flow density (Fig. 1) correlates with the tectonic
age, heat production and lithology of the sites (Kukkonen,
1989, 1993). The lowest values are encountered in the
Archaean and Early Proterozoic areas in eastern and northern
277
Proceedings World Geothermal Congress 2000
Kyushu - Tohoku, Japan, May 28 - June 10, 2000
Kukkonen
Finland (13-30 mW m
-2
), whereas the higher values are
related to Early Proterozoic late-kinematic and anorogenic
(rapakivi) granitoids in southern Finland (40-70 mW m
-2
).
Arithmetic mean of heat flow data is 37±11 mW m
-2
(one
standard deviation).
The climatically controlled average annual ground surface
temperature varies from +6ºC in southern to +2ºC in the
northernmost Finland. The ground temperature can also be
estimated directly from meteorological annual air temperature
in ºC averages as
T (ground) = 0.7, T (air) + 2.93
(Kukkonen,
1987).
Temperature maps are presented for 500 and 1000 m depths
below surface (Fig. 2 and 3). The variation of temperatures
reflects both climatic conditions as well as the crustal
geothermal conditions. Temperature at 500 m is highest in
southern Finland (12-14ºC) and lowest in northern Finland (6-
9ºC). The values at 1000 m are 20-22ºC in the south, and 12-
4ºC in the north, respectively. Extrapolation and calculation of
temperatures at greater depths indicate that the 40ºC isotherm
would be reached at 2-3 km, and the 100ºC isotherm at depths
of 6-8 km (Kukkonen, 1999).
Topography in Finland is subdued and does not easily produce
advective re-distribution of geothermal heat by the
groundwater circulation systems. Due to low hydraulic
permeability and low porosity of crystalline rocks the water
content of bedrock is low (< 1 %), and thus the water content
of the bedrock is low as well. These data indicate that the
prospects for utilizing geothermal energy either in wet or dry
rock systems are not very promising (Kukkonen, 1999).
However, earlier interest in geothermal energy in Finland in
1970-80's was much concentrated in discussing the potential
for such applications (e.g. Kivekäs, 1978, 1979, 1981; Risku-
Norja, 1987, Risku-Norja et al., 1987).
Temperatures in the soil at 1 m depth vary annually between
+2 to +12ºC in southern Finland, and -2 - +12 C in northern
Finland. Temperature in the uppermost (< 200 m) bedrock
below the penetration depth of annual variations is +2 to +8ºC.
Such temperatures are favorable for heat pump systems in the
scale of small family houses, country farms or sometimes in
district heating systems of small communities.
3. USE OF GEOTHERMAL ENERGY: HEAT PUMPS
Due to the cool thermal regime of bedrock, the only type of
geothermal energy used in Finland is ground heat with the aid
of heat pumps installed either vertically in boreholes, or
horizontally in Quaternary sediments as well as lakes and
rivers. The ground heat is considered here as geothermal
energy, although it is a combination of deep geothermal energy
and solar energy stored in the near-surface layers of the earth.
Interest towards such energy sources grew rapidly in the late
1970's after the increase of oil price. Several thousands of heat
pumps were installed in soil, typically in farms in eastern
Finland during 1980's. During the 1980's and 1990's the
relatively low prices of oil and electricity reduced
competitively the heat pump applications, and their popularity
decreased. From 1985 to mid-1990 there were sold only about
100-200 heat pumps annually. However, there is currently an
increasing interest in heat pumps. In 1998 about 800 heat
pumps were sold.
Technological research on the heat pump systems has also
been carried out during the years. Pilot test plant projects and
other studies were carried out in 1970-1980 by the Technical
Research Center of Finland (e.g. Aittomäki and Wikstén,
1978), universities (e.g. Aittomäki, 1983) and by the
governmentally owned electricity producer, Imatran Voima
Company (e.g. Kankkunen, 1985; Tinell et al., 1986).
Unfortunately, there are no detailed statistics available on the
existing heat pump installations, and this branch of business is
divided into a number of small engineering and drilling
companies that makes it difficult to compile such data.
Therefore, the exact statistics of the numbers and properties of
heat pump applications are not easy to obtain, and the present
data are based on the estimates by the specialists working in
the heat pump business. Further, the Finnish Heat Pump
Association (Suomen Lämpöpumppuyhdistys) was established
only in 1999 for promoting the use of heat pumps and
distributing information on such energy systems.
It is estimated that at the end of 1999 there were a total of
about 10,000 heat pumps in Finland, which were utilizing
ground-stored heat in bedrock, soil, lakes or rivers (J.
Hirvonen, The Heat Pump Association of Finland, pers.
comm., 1999). Most of the early installations in 1980's were
made in soil or lakes. About 70% of the heat pumps are
horizontal soil installations, 20% in lakes and 10% in vertical
boreholes (Table 1). Presently there seems to be a trend of
shifting to the vertical ground coupled installations in
boreholes.
A typical small-scale user of a heat pump is a family house
(130-150 m
2
) with an annual demand of heating energy of
about 13,000 kWh/a (including the domestic hot water). This
demand can be satisfied with either a vertical ground coupled
(borehole) installation or horizontal (soil or lake water
coupled) installation, depending on the type and size of
property at use. It is common that the heat pumps work at
about 60 % power of the required maximum heating power
(about 8-9 kW). This is due to the fact that the duration of
extremely cold periods, when the maximum heating power is
required, is only few weeks annually. Thus, the heat pump
satisfies about 90 % of the annual demand of heating energy,
and the remaining heating energy is usually supplied by
electricity.
The vertical ground coupled heat pumps are typically installed
in boreholes 80-130 m deep. Deeper holes (150-200 m) were
preferred in the 1980's. The coefficient of performance (COP),
defined as the ratio of the energy produced to the energy used
by the heat pump, has increased from the values of the early
installations (COP = 2.5) to about 3.3 in the modern
applications. Energy is extracted about 40-60 W/m of
borehole. An ethanol-water solution is used as the heat
exchange fluid and it is circulated in a U-shaped plastic
installed in the borehole.
The horizontal ground coupled systems use pipes that are
buried about 1.0-1.5 m below surface and separated
horizontally by about 1.5 m. In the typical installation for a
130-150 m
2
family house the total length of the pipes is about
150 - 300 m. Horizontal coupled systems in lakes or rivers are
usually dimensioned with slightly shorter pipes than those in
sediments, but no detailed data on the properties of the existing
278
Kukkonen
horizontal installations can be given. Therefore, the data given
in Table 1 are estimates and provide the orders of magnitude
only.
Heat pump technology is utilized in a 0.5 MW district heating
plant in Forssa, southern Finland (Tinell et al., 1986). The
plant provides district heating for a small area with a few
hundred family houses. The heat pump is extracting heat stored
in a shallow (<50 m below surface) aquifer (7ºC) in a
Quaternary esker formation. The water is returned to the
aquifer at a temperature of 2–4ºC. The heat pump is connected
to series with a boiler using heavy fuel oil. Contribution of the
ground heat to the total energy production of the plant amounts
to about 50 %, and the heat pump is operated with a COP value
of 2.1.
Abandoned underground mines provide sometimes an easy
access to utilizable heat sources. Hiiri (1985) investigated the
possibility to use the closed Outokumpu mine in eastern
Finland as a heat source for the district heating plant of the
Outokumpu town. The calculations were based on a heat pump
system with 7 MW heating power. In principle, Hiiri (1985)
found the project technically and economically feasible, but
the sensitivity involving economic and technical parameters
was regarded as considerable. The application was not built,
but the Outokumpu case indicated that the heat pump
applications are worth investigating when a mine is closed.
4. DISCUSSION AND CONCLUSIONS
Geologically Finland represents an environment where the
classical forms of utilizing geothermal energy (hot and dry
rock or steam) are not economically feasible. The remaining
alternative is ground-stored heat extracted with heat pumps
from boreholes, surface sediments as well as lakes and rivers.
At the moment there are about 10,000 vertical or horizontal
ground or lake coupled heat pumps in Finland used for space
heating mainly in family houses and some small district
heating systems in small communities. The majority of the
heat pumps were installed in the 1980's as horizontal ground
coupled systems. The numbers of delivered ground-heat
systems decreased dramatically after 1985 and heat pumps
almost vanished from the heating business. Currently about
800 heat pumps are sold annually, and there has been a slowly
increasing volume of heat pumps sold since 1995. It is
estimated that the total energy produced by heat pumps from
ground heat sources is of the order of 500 TJ/a (Table 1). This
is still less than 1 % of the total consumption of energy in
space heating in Finland.
The major factor retarding the increase of using ground-heat
systems in Finland has been the price of heat pump systems. In
building a typical family house, the cost of installing a heat
pump using ground-heat is about twice the price of installing
systems based on oil or electricity, although the running costs
of ground-heat systems are much lower. It should also be noted
that the dispersed heat pump business may not be very good
against major oil and electricity selling companies in the
country. Additionally, we must also consider the lack of
knowledge on heat pumps among the general audience.
However, the present demand for environmentally better
acceptable and sustainable technologies is constantly
increasing the public interest in this field.
Acknowledgements
J. Hirvonen (the Finnish Heat Pump Association) is
acknowledged for discussions on heat pump business in
Finland.
5. REFERENCES
Aittomäki, A. 1983.
Soil, lake and river systems as sources of
energy.
Tampere University of Technology, Dept. of
Mechanical Engineering, Report 37, 116 p. (in Finnish with
English abstract).
Aittomäki, A. and Wikstén, R.,1978.
Kokemuksia
lämpöpumppulämmityksestä.
Valtion teknillinen
tutkimuskeskus, LVI-tekniikan laboratorio, tiedonanto 36, 40
p. (in Finnish).
Energy Review, No. 2/99. Ministry of Trade and Industry,
Helsinki, 1999.
Hiiri, P., 1985.
Louhostiloista saatavan maalämmön
hyväksikäyttö lämpöpumpun avulla Outokummun kaupungin
lämmöntuottovaihtoehtona.
Master’s thesis, Lappeenranta
University of Technology, Institute of Energy Technology, 68
p. (in Finnish).
Järvimäki, P. and Puranen, M., 1979. Heat flow measurements
in Finland. In:
Terrestrial Heat Flow in Europe
, V. ermák and
L. Rybach (editors). Springer, Berlin, pp. 172-178.
Kankkunen, A., 1985.
Boreholes as sources of heat.
Imatran
Voima Oy, Central Laboratory, Research Report, 24/85, 40 p.
(in Finnish with English abstract).
Kivekäs, L., 1978. Prospecting for geothermal energy in
Finland: Geothermal data. In:
Nordic Symposium on
Geothermal Energy, Göteborg, Sweden, May 29-31, 1978,
C.
Svensson and S. Å. Larson (editors), Chalmers University of
Technology and University of Göteborg, Dept. of Geology,
Gothenburg, Sweden, pp. 112-119.
Kivekäs, L., 1979. Geotermisen energian hyödyntäminen.
Kunnallistekniikka-Kommunalteknik,
No. 6, 10-12 (in Finnish).
Kivekäs, L., 1981. Lämpö kalliossa, kalliosta, kallioon.
Hakku,
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Kukkonen, I., 1987. Vertical variation of apparent and palaeo-
climatically corrected heat flow densities in the central Baltic
Shield.
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, 8, pp. 33-53.
Kukkonen, I., 1988. Terrestrial heat flow and groundwater
circulation in the bedrock in the central Baltic Shield.
Tectonophysics
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Kukkonen, I., 1989. Terrestrial heat flow and radiogenic heat
production in Finland, the central Baltic Shield.
Tectonophysics,
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Kukkonen, I.T., 1993. Heat flow map of northern and central
parts of the Fennoscandian Shield based on geochemical
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Tectonophysics,
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13.
Kukkonen, I.T., 1999. Geothermal resources in Finland. In:
Atlas of Geothermal Resources in Europe,
S. Hurter (ed.),
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and V. Zui (Editors), Hermann Haack, Gotha, p. 29.
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280
281
Kukkonen
.
Table 1. GEOTHERMAL (GROUND-SOURCE) HEAT PUMPS AS OF DECEMBER 1999.
Locality Ground or water
temp (°C)
Typical heat
pump capacity
(kW)
Number of
units
Type COP Equivalent Full
load Hr/year
Thermal energy
Used (TJ/year)
Not spec. +2 - +5 8 1000 V 2.5-3.3 4000 50
Not spec -2 - +14 8 7000 H 2.5-3.3 4000 330
Not spec. +1 - +5 8 2000 L 2.5-3.3 4000 95
Forssa S-
Finland
+7 500 1 G 2.1 4900 9
10000 484
Notes: V = Vertical ground coupled, H = Horizontal ground coupled, L = lake or river source, G = groundwater coupled district heating
plant.
282