This study evaluates the performance of a flat-plate solar collector thermal system located in Bucharest, Romania, by combining experimental measurements (December 2024–April 2025) with numerical modeling. The system, coupled to a 4000 L tank and using a 30% glycol–water mixture, was monitored for irradiance, wind speed, temperature, flow rate, and humidity. Monthly irradiance averaged 448–584 W/m², and wind speed 2.3–4.3 m/s. Instantaneous efficiency ranged from 25.09% to 73.25% (mean 52.96%), with CUF (capacity utilization factor) ranging between 6.55% and 9.38%. Total heat losses were 4.80–7.79 kW and dominated by top losses (3.60–5.59 kW). The model reproduced the manufacturer’s efficiency curve within 5% for data obtained in the spring, with winter deviations of up to 37% due to weather variability and aged insulation. The results provide reference values for the CUF and loss coefficients of flat-plate collectors in temperate continental climates and can support retrofit and sizing decisions.

This paper is an analysis which provides an objective perspective on the performance of different heating sources to facilitate informed decisions regarding investments in thermal energy production equipment that have a low impact on the environment. The aim of the study is to investigate different possibilities to reduce the power consumption and environmental impact taking account annual electricity consumption building for the central-western location in Romania. This paper presented the technical-cost benefit and environmental impact analysis of three alternative heating systems versus conventional systems with natural gas boiler. The obtained results show the higher cost is for ground-to-water heat pump solution and for pellet boiler the price initial investment is higher than that of a gas boiler with 2.15% but is like that of an air-to-water or ground-to-water heat pump. The total operating cost for pellet boiler, air-to-water heat pump and ground-to-water heat pump is higher than natural gas boiler with 65%, 23%, respectively 10%. The amount of CO2 emitted into the atmosphere decreases significantly with solutions air-to-water heat pump and ground-to-water heat pump, with the minimum value of 2502 kg CO2 obtained for the last.