Utilization of low enthalpy geothermal energy in Bulgaria

Abstract

Bulgaria is relatively rich in geothermal water of temperature in the range of 25°C-100°C and the total flow-rate exceeds 3,000 L/s. Generally, there are more than 170 geothermal fields: 102 of them are state-owned and the rest of them – belong to some municipalities. Up to 72% of the total known flow-rate from the reservoirs has a comparatively low temperature - up to 50°C. Flow-rates for individual sources vary within 1-20 L/s for most of the reservoirs. The highest temperature (approximately 100°C) is measured at the surface in Sapareva Banya near Rila Mountain. TDS (total dissolved solids) vary between 0.1 g/L and 1.0 g/L for most of the reservoirs in Southern Bulgaria, while in Northern Bulgaria it is significantly higher – the maximum is up to 150 g/L. The installed capacity amounts to about 97.5 MWt (for 2017), excluding the low grade energy use by ground source heat pumps (GSHP). Geothermal energy has only direct utilization - in balneology, heating of buildings, air-conditioning, greenhouses, geothermal ground source heat pumps, direct thermal water supply for industrial processes. Geothermal water is also used for bottling of potable water and soft drinks. Most of the hydrothermal sites are developed as mountainous or sea resorts. Electricity generation from geothermal water is not currently available in the country.