spatial assessment of nsge potential of cerkno …...the greta project is co-financed by the...

The GRETA project is co-financed by the European Regional Development Fund through the Interreg Alpine Space programme.

Simona Pestotnik, Geological survey of Slovenia

Spatial assessment of

NSGE potential of

Cerkno Municipality in

Slovenia

GRETA MIDTERM CONFERENCE, “NEAR-SURFACE GEOTHERMAL ENERGY (NSGE) USE IN THE ALPINE SPACE”Tuesday 7th November 2017, Hotel NH Salzburg City, Franz-Josef-Strasse 26, A-5020 Salzburg - Austria

07/11/20172

See more at www.alpine-space.eu/projects/greta

1. Cerkno municipality

2. Energy needs for heating in Cerkno

3. Geological data

4. Measurements of thermal conductivity of rocks

5. Ranking of rocks for evaluation of typical geothermal properties

6. Characteristic soil temperatures

7. Closed-loop geothermal potential in Cerkno

8. Next steps…

Spatial assessment of NSGE potential of CerknoMunicipality in Slovenia

http://www.alpine-space.eu/projects/greta

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CerknoMunicipality

Town Cerkno, photo Kalanj, https://ssl.panoramio.com/photo/20335520

+ Located in the western part of Slovenia. + Area of 132 km2, 29 settlements, 5000

inhabitants. + Climate is heating dominated, number of

Heating Degree Days range from 2311 to 4136.

+ There are rare territories in our country with such of complex geology such as municipality Cerkno: on the detail map we can list 28 different geological units on the surface of 2 x 3 km2.

+ As a result, we have a variety of options for using geothermal energy.


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Energy needs for heating in Cerkno

Overall calculated energy needs:

+ Public buildings: 1,200 MWh/year

+ Commercial buildings: 8,200 MWh/year

+ Residential buildings: 29,900 MWh/year

+ Data on characteristics of buildings: year of construction, roof, facade, window renovation, actual use of the building, useable area [Real estate registry (GURS, 2016)].

+ Data about specific energy needs for heating (q, kWh/m

2) from Project TABULA (ZRMK,

2014), Long-term national building renovation strategy – DSEPS (MzI, 2015), Local energy concept Cerkno (GOLEA, 2011)].

+ Calculation of energy needs for each part of the building (kWh/y).

+ Used grid cell dimension 25 x 25 m to display energy needs (MWh/y/cell).


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+ Review of existing archive data and maps from which the data were collected, reclassified, aggregated, and harmonized.

+ Additional field validations were performed.

+ Most of the Cerkno covered by clastic rocks, the rest mostly composed of carbonate rocks, dominantly dolomites.

+ Alluvial sediments as gravel, sand and silt are of very limited extent, along main rivers, with a few meters of depth. Soils and unconsolidated sediments are generally a thin cover, less than 1m thick.

+ Clastic and carbonate rocks are mostly of fissured porosity, mainly aquitards. Dolomites and limestones can be considered as aquifers with a lower permeability.

Geological data


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Measurements of thermal conductivity of rocks

+ Rock samples were collected from all more representative geological units on the ground.

+ Samples were appropriately prepared for laboratory measurements using the Thermal Conductivity Scanning (TCS) method.

+ Total of 32 samples (51 single rock pieces) from the Cerkno was analysed.

+ Dolomites, quartz sandstones and conglomerates, dolomitized limestones and certain tuffs proved to be most conductive lithologies, and therefore have the best potential for dimensioning NSGE.

+ The observed thermal conductivity closely matches well with the values in SIA, VDI standards, other literature values.


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+ Geological units at the municipal level were converted into 9 lithological categories (on the basis of the lithological characteristics of geological units and internationally established standards of geothermal properties of rocks - VDI, 2010; Eugster et al., 2010; ASHRAE; UNI 11466):

1-Limestone, 2-Limestone in changing with clastic rocks, 3-Dolomite, 4-Dolomite in changing with clastic rocks, 5-Alternation of clastic rocks of different granularity and carbonate rocks, 6-Extrusive (magmatic rocks) and their tuffs, 7-Predominantly thick grained volcanoclastic rocks, 8-Gravel and pebbles - saturated with water (alluvial), 9-Gravel and pebbles - dry (sloping sediments)

+ The lithology was interpreted down to a depth of 100 m.

+ Values of thermal conductivity and capacity were therefore estimated as the depth-weighted average values for each rock type, according to a simplified lithological distribution.

Ranking of rocks for evaluation of typical geothermal properties


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+ For the ground-surface temperature map, temperatures profiles from 458 boreholes in Slovenia were processed and 157 synthetic points based on purely conductive regime were added.

+ Linear correlations with the altitude were found, with the ground temperature about 1°C higher than the annual mean air temperature, and a high resolution GIS layer (25 x 25 m) was derived based on a DTM.

+ Cerkno: Typical mean annual soil temperatures are between 5.6 °C at an altitude of about 1250 m (Črni Vrh) to 10 °C at altitude of 263 m at Želin.

Characteristic soil temperatures


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+ G.POT method was applied, taking into account site-specific ground thermal parameters and usage profiles depending on climate conditions (Casasso &Sethi, 2016).

+ The shallow geothermal potential is here defined as the quantity of heat which can be efficiently exchanged by a BHE with a 100 m length.

+ The resulting map highlights that the closed-loop geothermal potential is quite high for a mountain area, since it ranges between 8 and 10 MWh/year with even higher values, up to 15 MWh/year, observed in the western part of the municipality which is covered by a highly conductive dolomite.

Closed-loop geothermal potential in Cerkno


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Next steps…

Known energy needs for heating

Known natural potential for NSGE

Map of technical potential for NSGE

• What proportion of energy needs can be covert by NSGE in terms of natural potential, economics, market.


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Thank you for your attention!

Different rock samples from Cerkno. Photo: Tomaž Prestor


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spatial assessment of nsge potential of cerkno …...the greta project is co-financed by the...

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