ABSTRACT Geothermal water in Bulgaria has only direct applications. Major types of direct utilization include balneology, space heating and air-conditioning, geothermal heat pumps, direct thermal water supply, greenhouses, and bottling of potable water and soft drinks. Electricity generation from geothermal water is not currently available in the country

Aleksey Benderev

Klara Bojadgieva

Vladimir Hristov

CiteSeerX

Proceedings World Geothermal Congress 2010 
Bali, Indonesia, 25-29 April 2010 
1 
Aspects of Regional Geothermal Water Use in Bulgaria 
Klara Bojadgieva1, Vladimir Hristov1 and Aleksey Benderev1  
1Geological Institute, Bulgarian Academy of Sciences, Acad.G.Bonchev str. Bl.24, 1113 Sofia, Bulgaria 
klaratb@geology.bas.bg; vhh@geology.bas.bg; aleksey@geology.bas.bg 
 
Keywords: hydrothermal basins, direct thermal water use, 
types of application 
ABSTRACT  
Geothermal water in Bulgaria has only direct applications. 
Major types of direct utilization include balneology, space 
heating and air-conditioning, geothermal heat pumps, direct 
thermal water supply, greenhouses, and bottling of potable 
water and soft drinks. Electricity generation from 
geothermal water is not currently available in the country. 
About 72% of the total discovered flow rate of the state-
owned reservoirs has a temperature up to 50oC. Flow rate 
varies within 1-20 l/s for about 75% of these reservoirs. 
The most prospective regions for geothermal application 
are located in the eastern part of Moesian plate (North 
Bulgaria, stratified horizons) and in Rila-Rhodopes massif 
(South Bulgaria, fractured intrusive and metamorphic 
rocks). The highest temperature (98oC) is measured in 
Sapareva banja (South Bulgaria). Thermal water use is 
dependent predominantly on water chemical content. TDS 
varies between 0.1 and 1.0 g/l in most of the reservoirs  in 
South Bulgaria, while in North Bulgaria it is much higher: 
from 0.1 g/l up to 150 g/l. For this reason, thermal water 
application is more diverse and mainly concentrated in the 
territory of South Bulgaria.  
Most of the hydrothermal sites are developed as 
mountainous and sea resorts, and currently, leading 
applications are for balneology, direct thermal water supply 
for domestic needs, and space heating. Geothermal heat 
pumps also mark significant progress but no official 
summary for their use is available at present.  
The focus of this analysis is on the quantity and type of 
thermal water use in the hydrothermal regions in Bulgaria 
in terms of temperature, flow rate, and application. A 
comparison between the quantity and type of water use in 
North and South Bulgaria is also made. Five leading 
regions are considered in more detail with respect to 
application. The major barriers for geothermal development 
are briefly presented. 
 
1. INTRODUCTION 
Bulgaria is situated on the southern part of Balkan 
Peninsula. Solid fuels (coal and wood) and hydro energy 
have dominant contributions among primary energy sources 
to the energy balances of the Balkan countries, as shown in 
Figure 1. Biomass is estimated to have the highest potential 
among the renewable energy sources (RES). The main 
domestic energy sources in Bulgaria are solid fuels , hydro 
energy, and nuclear energy.  
According to the evaluated accessible technical potential of 
RES in Bulgaria, biomass and hydro energy have a 
dominant role, while the geothermal potential is comparable 
to that of solar energy. (See Figure 2.) The existing installed 
capacities for electricity generation operating with RES are 
small hydro power plants (up to 10 MWt) and wind 
turbines. The photovoltaic share is very small.   
Electricity generation from renewables have marked 
progress during the last 10-15 years. Produced electricity in 
2008 (excl. PSHPP) amounts to 2891.9 GWh and covers 
6.5 % of the gross electricity generation in the country. 
Thermal waters have an ancient tradition in the country, but 
only for direct applications, which include balneology 
(therapeutic bathing), space heating and air-conditioning, 
greenhouses, geothermal ground source heat pumps, direct 
thermal water supply, and the bottling of potable water and 
soft drinks. 
Only nine state-owned reservoirs have temperatures higher 
than 76oC. (See Figure 3), and the total flow rate in each of 
them varies between 13 and 23 l/s (Bojadgieva et al.,2007). 
Thermal waters are found on all territories of the country 
and only six of 28 districts have no utilization.  Intensive 
construction in mountain, sea and rural regions has been 
taking place during the last 20 years, which has stimulated 
the realization of more effective and complete thermal 
water applications.   
The recent analysis of state-owned thermal water 
applications in Bulgaria is based on the officially published 
data by the Ministry on Environment and Water and 
Council of Ministers – Economic and Social Policy 
Directorate (Investment and Concession Department). The 
information on issued permits and concessions is being 
currently updated, presenting data on committed water 
quantities, types of applications for each particular site, 
terms of exploitation, etc. About twelve are the laws, 
referring to thermal water prospecting, exploration and 
utilization and major among them are Law on Water, Law 
on Energy, Law on Concessions and  newly adopted one in 
2008 - Law on Renewable and Alternative Energy 
Resources and Biofuels.  
The whole legislation has been changed in the last 20 years 
during the transition period from planned to market 
economy in the country.  The new laws have been amended 
and supplemented many times, which resulted in a delay of 
geothermal development. These obstacles decreasing with 
time and investor’s interest in this activity is expected to 
increase in the near future.  
 
Bojadgieva et al. 
 2 
0
20
40
60
80
100
Al
ba
nia
Bo
sn
ia 
an
d H
er
ze
go
vin
a
Bu
lga
ria
Cr
oa
tia
M
ac
ed
on
ia
Ro
m
an
ia
Se
rb
ia
pr
im
ar
y 
en
er
gy
 s
ou
rc
es
 (
in
 %
)
crude oil
solid fuels
gas
hydro and
nuclear
biomass
 
Figure 1:  Major primary energy sources in the Balkan Peninsula (Data source: www.eva.ac.at) 
 
0
500
1000
1500
2000
2500
3000
ktoe
hydro biomass solar wind geothermal
energy source
Figure 2: Accessible RES technical potential for different energy sources in Bulgaria (source: EEA) 
 
0
10
20
30
40
50
60
<25 25-50 51-75 76-100
temperature (deg C)
n
u
m
b
er
 o
f 
re
se
rv
o
ir
s
 
Figure3:  State-owned reservoir distribution by water 
temperature 
 
2. GEOLOGY AND HYDROGEOLOGY 
BACKGROUND 
Bulgarian territory falls within the region of the Alpine-
Himalayas orogen and this is the prerequisite for the 
relatively complex tectonic conditions. The country is 
divided in two parts (northern and southern) by the Balkan 
Mountains stretching from east to west across the whole 
territory. The northern part is built up mainly by sediments 
and includes two tectonic units: the Moesian plate and the 
Fore Balkan zone. The southern part consists of three major 
folded tectonic units: the Balkan zone, the Sredna Gora 
zone, and the Rila-Rhodope massif. The metamorphic and 
magmatic complexes are spread mainly in the southern part. 
Hydrothermal zones are closely linked to the main 
geological structures and are present in four tectonic units: 
the Moesian plate (North Bulgaria), the Sredna Gora zone, 
the Balkan zone, and the Rila-Rhodopes massif (South 
Bulgaria). The Moesian plate has a Caledonian-Hercynian 
basement and a cover of Upper Paleozoic and Mesozoic 
Bojadgieva et al. 
 3 
sediments. Their thickness decreases from about 6-7 km in 
the west down to several hundred meters in the east. The 
main geothermal reservoirs in the platform area were 
developed in the carboniferous strata of Malm-Valanginian, 
Middle Triassic and Upper Devonian age. 
The Sredna Gora zone is heterogeneous hydrothermal region 
where unstratifed (fault-fractured), stratified and mixed 
hydrothermal systems are present. 
The western Rila-Rhodopes massif is mainly composed of 
Precambrian metamorphic and granite rocks, fractured by a 
dense system of seismically active faults. The eastern part of 
the massif is not rich in thermal waters. 
The different geological conditions in the northern and 
southern part of the country define the variety of thermal 
water origin, chemical content and temperature.  
3. THERMAL WATERS CHARACTERISTICS 
Information on state-owned thermal water characteristics for 
the regions of north and south Bulgaria are summarized in 
Table 1. Data are taken from Petrov et al., (1998), from the 
web sites of the Ministry of Environment and Water 
(www.moew.government.bg) and from the National 
Concessions Register (www.ncr.government.bg/app). 
Higher temperatures are measured in South Bulgaria 
compared to the northern part. The discovered and utilized 
flow rates are also higher in the southern part, as shown in 
Figure 4.  Further, about 20.5% of the discovered flow rate 
in North Bulgaria have been utilized, compared to 14.5% in 
South Bulgaria.  
About 72% of the total discovered flow rate in state-owned 
reservoirs has a comparatively low temperature - up to 50oC. 
Flow rate varies within 1 - 20 l/s in 75% of the reservoirs 
(Bojadgieva et al., 2005). The highest temperature (98oC) is 
measured in Sapareva banja (South Bulgaria), while the 
highest flow rates are concentrated in the north-eastern part 
of Bulgaria. 
 
0 500 1000 1500 2000
North
Bulgaria
South
Bulgaria 
flow rate (l/s)
utilized flow
rate
discovered
flow rate
 
Figure 4:  Discovered and utilized thermal water flow 
rate in Bulgaria 
4. THERMAL WATER USE IN BULGARIA  
The analysis of thermal water application in the country is 
based mainly on the information for state-owned reservoirs 
taken from the issued permits and concession. Some data 
from the concessions issued for the municipality–owned 
reservoirs are also available.  
Geothermal water in Bulgaria has only direct application, 
which includes balneology (prevention, treatment and 
rehabilitation, bathing and swimming pools), space heating 
and air-conditioning, greenhouses, geothermal ground 
source heat pumps, direct thermal water supply, bottling of 
potable water and soft drinks, and for some other uses. Most 
of the hydrothermal sites are developed as mountainous or 
sea resorts. Currently leading applications in terms of water 
quantity are in balneology, direct thermal water supply and 
space heating (incl. greenhouses). Geothermal heat pumps 
also mark significant progress but no officially summarized 
information is still available.  
The hydrothermal regions (defined by Petrov et al.,1998) 
with direct application are presented on Figure 5.  The used 
flowrate is higher than 500,000 m3/year (about 16 l/s) in 
only five regions: the Razlog, South Sredna Gora, 
Sandanski, Chepino, and NE Bulgaria basins. North 
Bulgaria combines several basins on the northern territory of 
the country.  
The types of application for the state-owned thermal waters 
are presented in Figure 6. The highest water quantity (56%) 
is used for balneology (relaxation and sanitary needs, 
prevention, treatment and rehabilitation, drinking out of taps 
and swimming pools), followed by direct thermal water 
supply for domestic needs (19%) and heating of buildings 
and greenhouses (17 %).  
The applications of thermal water use in North and South 
Bulgaria are shown in Figure 7.  Balneology is the biggest 
application in both parts of the country with higher share in 
South Bulgaria.  Other applications such as bottling, space 
heating and greenhouses have a larger share in the southern 
part than in the northern one, where bottling and 
greenhouses are poorly developed. The dominant application 
in North Bulgaria is the direct thermal water supply for 
domestic use in the sea resorts located on the northern Black 
sea coast: Golden Sands, Albena, Balchik and Kavarna. This 
is a solution for those regions where no alternative water 
sources are available. Another advantage for developing this 
application is the low water salinity (TDS), which makes it 
suitable for drinking and domestic use.  
The geographic locations of the five basins of highest water 
quantity use (Razlog, South Sredna Gora, Sandanski, 
Chepino and NE Bulgaria) are shown in Figure 8. The types 
of applications in each region are shown in detail in Figure 
9.  Mountainous spa resorts have been developed in Razlog, 
South Sredna Gora and Chepino basins, while NE Bulgaria 
is famous for sea resorts.  
 
 
  
Bojadgieva et al. 
4 
Table 1: Characteristics of state-owned geothermal water according to region 
Regions water 
temperature 
discovered flow 
rate 
used flow rate TDS 
(oC) (l/s) (l/s) (g/l)
North Bulgaria 20-70 1241,65 254,7 0,1 - (100-150)
South Bulgaria 20-98 1823,81 263,5 0,1 - (1-15)
 
0
2000000
4000000
6000000
8000000
 R
ho
do
pe
s a
nd
 M
alk
a A
rd
a b
as
ins
Ch
ep
ela
rsk
a b
as
in
Va
ch
a r
.
Pla
na
 an
d P
ern
ik 
ba
sin
So
fia
 ba
sin
Ra
zlo
g b
as
in
Dz
erm
an
 ba
sin
Kj
us
ten
dil
 ba
sin
Do
lna
 ba
nja
 ba
sin
So
uth
 Sr
ed
na
 G
or
a b
as
in
Sli
ve
n a
nd
 St
ral
dja
 ba
sin
Ka
za
nla
k b
as
in
Sa
nd
an
sk
i b
as
in
Bo
ur
ga
s b
as
in
Ka
rlo
vo
 ba
sin
Ch
ep
ino
 ba
sin
Br
ats
igo
vo
 ba
sin
NE
 B
ulg
ari
a b
as
in
No
rth
 B
ulg
ari
a
u
se
d
 fl
o
w
 r
at
e 
(m
3/
ye
ar
)
hyrothermal basins
Figure 5: Thermal water use by hydrothermal basin in Bulgaria (state-owned reservoirs) 
19%
5%
56%
3%6%
11%
balneology
others
greenhouses
space heating
bottling
water supply
2005 - 2010
 
  Figure 6:  Percentage of flow rate used by each type of application in Bulgaria (updated 2009) 
 
Bojadgieva et al. 
 5 
         
38%
1%
11% 2% 46%
2%
prevention,trea
tment, pools
and relaxation
 water supply
bottling
space heating
greenhouses
others
North Bulgaria
         
1%
8%
12%
9%
5%
65%
prevention,
treatment,pools
and relaxation
 water supply
bottling
space heating
greenhouses
others
South Bulgaria
 
Figure 7:   Percentage of flow rate used by each type of application in North and South Bulgaria 
 
Figure 8: Locations of the five leading hydrothermal basins in Bulgarian thermal water use 
 
Balneology has a leading role in all of them varying from 
42.9% in NE Bulgaria basin up to 90 % in the Sandanski 
basin. Several resorts in the four selected basins in South 
Bulgaria are considered in greater detail in Table 2.  
Remains of ancient Tracian and Roman mineral baths are 
found in all of them. Today, they are rapidly developing spa 
centers, but only Hissarya and Sandanski resorts have more 
effective thermal water use at 66% and 82% of the 
discovered resource, respectively. 
The widest varieties of applications exist in Sandanski and 
NE Bulgaria, although only three are dominant utilizations 
in the NE Bulgaria basin.  Space heating is available in two 
basins in South Bulgaria (Chepino and Sandanski,) and one 
in North Bulgaria (NE Bulgaria) accounting for 7-22% of 
use. Thermal water utilization for domestic needs has a large 
share (42.6 %) in NE Bulgaria and a smale share (4%) in  
the Razlog basin.  
DISCUSSION 
Only about 15-20 % of the discovered thermal waters are 
currently used in Bulgaria. On the other hand water 
temperatures are relatively low and about 72% of the total 
discovered flow rate of the state-owned reservoirs has a 
temperature up to 50oC. For these reasons, the future 
geothermal resource exploitation will preserve the present 
trend of application in the existing locations. 
Extremely good bio-climatic resources, combined with the 
existing ancient Mediterranean traditions in thermal water 
use, provide a base for a successful balneological activity in 
the country. Most of the resorts currently in use were 
developed in places of ancient centers. As early as Roman 
times, they were used on a large scale for floor heating in 
public baths (hypocausts). The factors mentioned above 
could explain the balneology’s dominant share of thermal 
water utilization. The intensive construction of hotels in 
mountain and sea resorts during the last 20 years also 
created favorable conditions for better resource 
development.  
Bojadgieva et al. 
6 
Table 2 
spa resort water 
temperature 
discovered 
flow rate  
used flow 
rate (%)
treatment
Sandanski 
(Sandanski basin)
42 - 81 19,6 82 upper respiratory tract and lung 
diseases,  inflammation of 
joints,etc.
Velingrad (Chepino 
basin)
27 - 88 115 42 respiratory, locomotory, 
neurological,cardiovasculars 
diseases, etc.
Dobrinishte (Razlog 
basin)
33 - 40 13,6 25 urologiucal, 
locomotory,gynecological, skin 
diseases, etc.
Hissarya (South 
Sredna Gora basin)
47 31,5 66 nephro-urological, gynecological, 
locomotory diseases,etc.  
 
10%
34%
32%
2%
22%
prevention
and
treatmment 
bottling
space
heating
greenhouse
s
others
Sandanski basin
28%
4%
68%
prevention
and pools
water supply
others
Razlog basin
8%
7% 1%
84%
prevention,
treatmment
and pools
bottling
space heating
others
Chepino basin
 
90%
10% prevention,
treatmment,
drinking and
pools
bottling
South Sredna 
Gora basin
42,6%
0,4%
11,0%
42,9%
1,9%
1,2%
prevention,
treatmment,
drinking and pools
water supply
bottling
space heating
greenhouses
others
NE Bulgaria
 
Figure 9: Percentage of thermal water flow rate used by each type of application for leading regions in Bulgaria (updated 
2009)  
 
The application of thermal water for space heating hasn’t 
marked a significant progress for several reasons. These 
barriers are related to the harmonization of new legislation 
governing this activity, the complicated and time consuming 
procedure for obtaining permits or concessions, and the lack 
of investment interest in constructing new heating systems. 
Most of the existing installations are old and not in good 
technical condition. 
The application of ground source heat pumps and air-to-
water pumps continue to grow particularly in private and 
business buildings. It is difficult to assess the share of their 
contribution, as only a few companies publish information 
on their systems.    
Great progress has been made in the policy related to 
promotion of renewable sources development in Bulgaria, 
but it is focused mainly on wind and solar energy.  
Bojadgieva et al. 
 7 
Specific policy support for producers of thermal energy is in 
place. It concerns replacement of conventional fuels for heat 
production with renewables, complex utilization of 
renewable energy sources, and issuing of certificates 
corroborative to the origin of the produced thermal energy. 
ACKNOWLEDGEMENTS 
The authors would like to express their thanks to V.Toshev 
and K.Barokov from the Ministry of Environment and Water 
for data discussion. 
REFERENCES 
Bojadgieva,K.,Hristov,V., and Benderev,A.: General 
overview of geothermal energy in Bulgaria. J.Acta 
Montanistica Slovaca, vol.12, 86-91, (2007). 
Bojadgieva,K., Hristov,H.,Hristov,V., Benderev,A. 
and.Toshev, V: Geothermal update for Bulgaria (2000-
2005). Proceedings, World Geothermal Congress’2005, 
Antalya, Turkey, 24-29 April2005, (2005). 
Petrov,P.(ed.) et al.: Reassessment of hydrogeothermal 
resources in Bulgaria, Report for the Ministry of 
Environment and Waters, National Geofund, Sofia, 
Bulgaria (1998). (in Bulgarian).  
Phare Project BG 9307-03-01-L001-Report Writing: 
Technical and Economic Assessment of Bulgarian 
Renewable Energy Resources. Ministry of Energy and 
Mineral Resources, Sofia, Bulgaria, (1997). 
Vladeva,L. and Kostadinov, D. - Bulgarian Potable Mineral 
Waters,I part, M-8-M, S.pp.175, (1996). (in Bulgarian) 
 
 


Aspects of Regional Geothermal Water Use in Bulgaria

http://citeseerx.ist.psu.edu/viewdoc/download;jsessionid=29D4559E781A631539FBD4C159187D87?doi=10.1.1.1075.3524&rep=rep1&type=pdf

Aspects of Regional Geothermal Water Use in Bulgaria

Abstract

Similar works

Full text

Available Versions

CiteSeerX