Abstract. Depends on amount of water per person, Slovenia is among the richest countries in Europe with almost four times the European average. The production of energy from water to wire is basically possible on the whole country area. This work deals with the area near to Ledava river, where the water accumulation system was built around 1970. From economical point of view, the aforementioned system is not really exploited. There are different possibilities, how to exploit the whole system, as with fishing industry, soaking industry or with convertion of hydro energy into electrical energy as part of renewable production units. The last mentioned is the part of presented research work in proposed paper

G Štumberger

K Deželak

L Somi

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International Conference on Renewable Energies and Power Quality (ICREPQ’15) 
La Coruña (Spain), 25th to 27th March, 2015 
exÇxãtuÄx XÇxÜzç tÇw cÉãxÜ dâtÄ|àç ]ÉâÜÇtÄ (RE&PQJ) 
 ISSN 2172-038 X, No.13, April 2015 
 
 
 
 
Accumulation small hydro power plant on lake - Slovenian case 
 
L. Somi1, K. Deželak1, G. Štumberger1 
 
1 Power Laboratory Department 
University of Maribor 
Faculty of Electrical Engineering and Computer Science, Smetanova 17, 2000 Maribor, Slovenia 
Phone: +38622207180, Fax: +38622207272, e-mail: loris.somi@student.um.si, klemen.dezelak@um.si, 
gorazd.stumberger@um.si 
 
 
 
 
Abstract. Depends on amount of water per person, Slovenia 
is among the richest countries in Europe with almost four times 
the European average. The production of energy from water to 
wire is basically possible on the whole country area. This work 
deals with the area near to Ledava river, where the water 
accumulation system was built around 1970. From economical 
point of view, the aforementioned system is not really exploited. 
There are different possibilities, how to exploit the whole system, 
as with fishing industry, soaking industry or with convertion of 
hydro energy into electrical energy as part of renewable 
production units. The last mentioned is the part of presented 
research work in proposed paper. 
 
Key words 
 
Electrical system, accumulation small hydro power plant, 
lake, investment calculation. 
 
1. Introduction 
 
In paper the total analysis of present system for water 
accumulation is shown, where the solution for optimal 
exploitation of water energy by small hydro power plant is 
given. In that sense the whole aspects of an important and 
well preserved ecological zones, with a great diversity of 
animal and plant species are considered, firstly. Secondly 
the dimensions of accumulation systems and data about 
available and installed flow should be defined. 
Additionally some essential components of small hydro 
power plants, as penstock, power house and tailrace are 
dealt, as well. Penstock, that conveys water under pressure, 
can be made of steel, iron, plastics, concrete or wood. 
Power house contains most of the mechanical and 
electrical equipment and it is made of conventional 
building materials, whilst the tailrace carries the water 
from the turbine exit back to the river [1], [2]. Generally, 
such a system requires substantial initial capital 
investments and relatively low operating costs. Both of the 
aforementioned costs were evaluated inside the entireness 
economical analysis. 
 
 
 
2.  Installation of object into the 
environment 
 
In case of some object installation into the environment 
an important attention should be given into areas where 
strict nature protection is presented. Those nature 
protection areas are: 
a) landscape park (named "Goričko"), 
b) NATURA 2000 (SPA and pSCI areas), (Fig. 1), 
c) ecologically important areas (Fig. 2) and 
d) area with strong natural value (Fig. 3). 
 
 
Fig. 1: Slovenia - NATURA 2000 areas. 
 
The effect of the small hydro power plants on the 
environment is related to their development and varies 
according to the location and configuration of the project 
itself, since planning to construct a small hydro power 
plant at a less suitable location can trigger major effects 
on the environment. In case of constructing a small run-
of-river hydro power plant next to an already existing 
dam, in general, the effects on the environment are 
minimal. They are similar to those connected with 
enhancing the existing capacities. 
https://doi.org/10.24084/repqj13.431 634 RE&PQJ, Vol.1, No.13, April 2015
 
 
Fig. 2: Slovenia - ecologically important areas [3]. 
 
 
 
Fig. 3: Slovenia - area with strong natural value [4]. 
 
3. Classification of hydro power plants in 
Slovenia 
 
In Slovenia the hydro power plants are classified in to four 
different groups (Tab. I), depends on the rated power of 
individual object.  
 
Table I. - Classification of the hydro power plants in Slovenia 
 
 Rated power 
Micro <= 50 kW 
Small 50 kW <= 1 MW 
Middle 1 MW <= 10 MW 
Big > 10 MW 
 
4. Determination of design flow 
 
The power and produced energy of the hydro power plant 
are mainly dependent on the available flow [5] - [7]. In our 
case the average values of available flow for each month 
of year Q are shown in Fig. 4. To calculate the delivered 
energy, instead of curve in Fig. 4, the curve shown in Fig. 
5 should be considered in to the calculations. There, the 
values of monthly flows duration are defined. Apart from 
flow duration curve, the values of gross head, type of used 
turbine, design flow and generator efficiency are very 
important. The design flow is equal to 25 % of flow value, 
so 0.85 m3/s. 
 
2 4 6 8 10 12
0
0.2
0.4
0.6
0.8
1
 [JAN÷DEC]
F
lo
w
 [m
3 /
s]
 
 
 
Fig. 4: Average values of available flow. 
 
0 20 40 60 80 100
0
0.2
0.4
0.6
0.8
1
1.2
Time in one year [%]
F
lo
w
 [m
3 /
s]
 
 
 
Fig. 5: Monthly flows duration curve. 
 
5. Intake of water 
 
As presented in Fig. 6, the small hydro power plant 
include some essential components as penstock, power 
house and tailrace. Penstock, that conveys water under 
pressure, can be made of steel, iron, plastics, concrete or 
wood. Power house contains most of the mechanical and 
electrical equipment and it is made of conventional 
building materials, whilst the tailrace carries the water 
from the turbine exit back to the river. In our case the 
water intake is performed by steel penstock with length 
and diameter LC = 75 m and DC = 0,8 m. 
 
 
Fig. 6: Small hydro power plant system. 
 
 
 
 
 
 
 
 
 
https://doi.org/10.24084/repqj13.431 635 RE&PQJ, Vol.1, No.13, April 2015
6. Determination of the net head 
 
The net head Hn (1) could be determined from gross head 
and hydraulic losses by two methods: 
 
a) With the roughness factor kh (2), that could be 
found in Tab. II. 
 
2 1C
n b i b 2C
L v
H H H H
D g
λ= − = − ⋅ ⋅ ⋅  (1) 
0,3333
h0, 0055 0,15
1000C
k
D
λ = + ⋅
⋅
 
  
 
 (2) 
 
Table II. - Values of the roughness factor 
 
Steel 0,15 – 0,50 
Iron 0,25 – 1,00 
Concrete 1,00 – 3,00 
Copper 0,0015 
PVC 0,05 
 
In (1) the velocity of water is marked by v (3). 
inst inst
2
C
2
Q Q
v
S D
π
= =
⋅
 
 
   (3) 
 
Calculation of the net head by proposed method is 
shown below. 
 
0,85 minst 1,691 2 2 s0,80C
22
Q
v
D
ππ
= = =
⋅⋅
   
     
 
 
0,3333
h0, 0055 0,15
1000C
0,3333
0,325
0, 0055 0,15 0, 01661
0,80 1000
k
D
λ = + ⋅ =
⋅
+ ⋅ =
⋅
 
  
 
 
 
 
 
 
2 1C
n b 2C
275 1,691 1
7,30 0,01661 7, 0731 m
0,80 2 9,81
L v
H H
D g
λ= − ⋅ ⋅ ⋅ =
− ⋅ ⋅ ⋅ =
 
 
 
b) With the loss coefficient ki (4), that could be 
found in Tab. III. 
 
2
C
n b i b 1,33
2 C
i 4
v L
H H H H
D
k
⋅
= − = −
⋅
 
 
 
 (4) 
 
Table III. - Values of the loss coefficient 
 
Concrete 71 
Steel 83 
Wood 83 
PVC 120 
 
 
Calculation of the net head by proposed method 
is shown below. 
 
0,85 minst 1,691 2 2 s0,80C
22
Q
v
D
ππ
= = =
⋅⋅
   
     
 
 
2
C
n b 1,33
2 C
i 4
21, 691 75
7,30 7, 0353 m1,33
0,80283
4
v L
H H
D
k
⋅
= − =
⋅
⋅
− =
⋅
 
 
 
 
 
 
 
 
7. Selection of proper turbine 
 
Turbines are devices that convert the energy from falling 
water into rotating shaft power. Turbines used in 
examples of small or medium high heads (Fig. 7), are 
reactionary type. That type of turbine includes Francis 
and Kaplan turbines. In case of high heads (Fig. 7), the 
action turbines are used. The Pelton turbines, the Turgo 
turbines and the cross flow turbines are all examples of 
the action turbines. The proper turbine could be defined 
by values of design flow and head as is shown in Fig. 7. 
 
https://doi.org/10.24084/repqj13.431 636 RE&PQJ, Vol.1, No.13, April 2015
 
Fig. 7: The turbine selection. 
 
8. The power and efficiency of turbine 
 
Figs. 8 and 9 shows the available power and efficiency 
curves of chosen turbine. The rated power is equal to 51,3 
kW. 
 
 
Fig. 8: The curve of turbine efficiency. 
 
 
Fig. 9: The curve of available power. 
 
9. Initial costs 
 
Investment to the project depends on: 
• penstock costs, 
• turbine and generator costs, 
• energy equipment installation costs, 
• connection to the electrical grid costs, 
• construction work costs, 
• design documents costs, etc. 
 
The value of total investment is approximately equal to 
365.000,00 €. 
 
10. Financial analysis 
 
Finally the cost of produced energy, credit ratio, credit 
interest rate, credit term, inflation and discount rate were 
considered, leading to result of cumulative cash flow 
presented in Fig. 10. 
 
 
 
Fig. 10: Cumulative cash flow of the project. 
 
11. Conclusion 
 
This paper deals with an accumulation small hydro power 
plant on Ledavsko lake located in Slovenia. The possible 
project is built on an already existing environment or 
infrastructure, consisting of an embankment, a tower and 
a lake outflow. The choice of technical equipment, 
location and the planned operation regime, as well as the 
construction and investment cost of the small hydro 
power plant project are presented in the paper. 
 
References 
 
[1]  C. Dragu, T. Sels, R. Belmans, "Small hydropower - state 
of the art and applications", Int. Conf. on Power Generation and 
Sustainable Development, AIM, 2001, Liege, Belgium 
[2]  P. R. Gingold, "The optimum size of small run-of-river 
plants", Water Power Dam Construct,  1983, pp. 35 - 39 
[3]__http://geopedia.si/?params=L11410_T105_vL_b4_x48347
9_y102619_s9#T105_L11410_x466839_y109019_s9_b4. 
[4]__http://www.arso.gov.si/narava/naravne%20vrednote/karta/
karta_naravne_vrednote.jpg, [11. 07. 2014]. 
[5]  B. Munson, D. Young, T. Okiishi, W. Huebsch, 
Fundamentals of fluid mechanics, 6th edition, 2010, Wiley 
[6]  C. Alonso-Tristán, D. González-Peña, M. Díez-Mediavilla, 
M. Rodríguez-Amigo, T. García-Calderón, “Small hydropower 
plants in Spain: A case study”, Renewable and Sustainable 
Energy Reviews, 2011, Vol. 15, pp. 2729-2735. 
[7]  S. Mishra, S.K. Singal, D.K. Khatod, “Optimal installation 
of small hydropower plant—A review”, Renewable and 
Sustainable Energy Reviews, 2011, Vol. 15, pp. 3862-3869. 
 
https://doi.org/10.24084/repqj13.431 637 RE&PQJ, Vol.1, No.13, April 2015


Accumulation small hydro power plant on lake -Slovenian case

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Accumulation small hydro power plant on lake -Slovenian case

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