Impact of Evaluation Criteria of Power Loss in LCA

CO₂ equivalent emissions. This study addresses two main issues and provides evaluation and discussion accordingly. First, it examines how recent changes in load characteristics driven by increasing photovoltaic (PV) penetration affect transformer operating efficiency.

The maximum conversion efficiency (efficiency) of power transformers used in distribution substations exceeds 99.5%. However, because efficiency depends on the load current flowing through the transformer, this maximum efficiency is not always achieved in actual substations.

Transformers installed in Japan before the start of the Feed-in Tariff (FIT) scheme for renewable energy in 2012 were designed to operate at high efficiency based on the daily load characteristics. Due to the proliferation of photovoltaic (PV) generation facilities, the daily load characteristics have changed, and the expected efficiency of these transformers is likely not being achieved.

In this paper, the effect of PV power output on transformer efficiency and power losses of transformers was evaluated. A case study using 2024 load data of multiple substations was conducted. The results showed that substations with low average load factors tended to have significantly lower efficiency during PV output periods.

Second, the study investigates how changes in load characteristics from the past to the future influence the evaluation of transformer losses. In Japan, load characteristics will change significantly, and reverse power flow during light load periods may improve efficiency of transformers compared to 2024.

This study also evaluated power losses of transformers as CO₂ equivalent emissions using electricity emission factors from past to future. The results indicate that changes in the energy mix strongly affect CO₂ equivalent based evaluation.

Over the several decades, the load characteristics of distribution transformers will change. We evaluated energy losses of transformers from past to future using two evaluation criteria (units):

kWh and CO₂ equivalent emissions. The trend was quite different. Changes in energy losses of transformers (kWh) are due to changes in the load characteristics of transformers (due to the proliferation of home PV, EV, HP, and batteries). In contrast, CO₂ equivalent based evaluation is mainly affected by changes in electricity emission factors due to the energy mix. In other words, appropriately selecting evaluation criteria (unit) to use in LCA will lead to the proposal of appropriate measures to reduce environmental impacts. For example, if we assume that electricity emission factors will become completely zero in the future, a CO2 equivalent based evaluation would give the impression that the environmental impact of transformer losses in substations is zero, even though in reality, tens of billion kWh of energy continues to be wasted per year due to transformer energy losses. In this case, assessment based solely on CO2 equivalents may not motivate transmission and distribution (T&D) companies to reduce their environmental impact.