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Electrical energy usage in buildings is a challenging issue because many old buildings were not originally built to achieve energy efficiency. Thus, retrofitting old buildings to net-zero buildings can benefit both the owner and electric utilities. In this study, the BEC (building energy code) software was used to evaluate energy aspects of retrofitted buildings in compliance with Thailand’s building energy code to achieve a net-zero energy building. In addition, economic aspects were also studied to verify the feasibility for a project’s owner to invest in a retrofitted existing building. An existing residential building in Thailand was used as a case study. The results in terms of energy after retrofitting existing buildings into net-zero energy buildings show that the total energy consumption can be reduced by 49.36%. From an economic perspective, the investment cost for a retrofitted building can be compensated by energy saving in terms of discounted payback period (DPP) for approximately 4.36 years and has an IRR (internal rate of return) value of 19.23%. This result evidences the potential in both energy and economy for a project’s owner to invest in a retrofitted existing building in compliance with the building code, with potential for implementation with benefits on both electrical utilities and the project’s owner.

-This paper proposes a technique for detecting and identifying internal winding fault of threephase two-winding transformer. A spectrum component obtained from DWT of differential current is analyzed. A ratio between per unit differential current and per unit time is calculated and performed as comparison indicator in order to discriminate between internal fault condition and external fault condition. Various cases based on Thailand electricity transmission and distribution systems are studied to verify the validity of the proposed algorithm. Results show that the proposed technique has good accuracy to detect fault and to identify its position in the considered system.

Solar rooftop systems in the residential sector have been rapidly increased in the term of installed capacity. There are various factors, such as climate, temperature, and solar radiation, that have effects on solar power generation efficiency. This paper presents a performance assessment of a solar system installed on the rooftop of residence in different regions of Thailand by using PSIM simulation. Solar rooftop installation comparison in different regions is carried out to evaluate the suitable location. In addition, three types of solar panels are used in research: monocrystalline, polycrystalline, and thin-film. The electrical parameters of real power and energy generated from the systems are investigated and analyzed. Furthermore, the economic evaluation of different solar rooftop system sizes using the monocrystalline module is investigated by using economic indicators of discounted payback period (DPP), net present value (NPV), internal rate of return (IRR), and profitability index (PI). Results show that the central region of Thailand is a suitable place for installing solar rooftop in terms of solar radiation, and the temperature has more solar power generation capacity than the other regions. The monocrystalline and polycrystalline solar panels can generate maximum power close to each other. All solar rooftop sizes with the Feed-in Tariff (FiT) scheme give the same DPP of 6.1 years, IRR of 15%, and PI of 2.57 which are better than the cases without the FiT scheme. However, a large-scale installation of solar rooftop systems can receive more electrical energy produced from the solar rooftop systems. As a result, the larger solar rooftop system sizes can achieve better economic satisfaction.