Decarbonization of the power sector is an important milestone for the achievement of ambitious GHG reduction targets. Given the intrinsic shortcomings of nuclear power and zero-emission thermal power generation, such as large investment costs and public acceptance, along with the locational limits of dispatchable renewables such as hydro and geothermal, variable renewable energies (VRE) should play an important role to decarbonize the power sector. Very high penetration of VRE, however, would require additional “integration” costs related to grid expansion, power curtailment, and power storage. In this article, focusing on a decarbonized power system in Japan in 2050, we calculated two metrics that capture the non-linear nature of the integration cost related to high VRE penetration: Average system LCOE (levelized cost of electricity) and relative marginal system LCOE. The former metric allocates the integration cost to each power source, which is divided by the adjusted power output, while the latter measures the changes in the total system cost with the substitution of two types of power sources. The results show that both the average and the relative marginal system LCOE of VRE will rise when the share of VRE rises, but the latter will rise much more sharply than the former. This suggests that the anticipated challenges for achieving very high shares of VRE may still exist even if the cost of VRE may decline rapidly in the future. As the relative marginal system LCOE of VRE can be heavily dependent on meteorological conditions, it is essential to use multi-annual data to estimate it. The metric relative marginal system LCOE can be used for the soft-linking of a detailed power sector model to an integrated assessment model, which can contribute to a better quantitative analysis of climate policies.

电力部门的脱碳是实现雄心勃勃的温室气体减排目标的重要里程碑。鉴于核电和零排放火力发电的内在缺陷，例如高昂的投资成本和公众认可度，以及水电和地热等可调度可再生能源的位置限制，可变可再生能源（VRE）应在以下方面发挥重要作用：使电力部门脱碳。但是，VRE的极高渗透率将需要与电网扩展，电力削减和电力存储相关的额外“整合”成本。在本文中，我们着眼于2050年日本的脱碳电力系统，我们计算了两个指标，这些指标反映了与高VRE渗透率相关的整合成本的非线性性质：平均系统LCOE（平均电力成本）和相对边际系统LCOE。前一种度量标准将积分成本分配给每个电源，然后将其除以调整后的功率输出，而后一种度量标准则用两种类型的电源替代来衡量总系统成本的变化。结果表明，当VRE份额增加时，VRE的平均和相对边际系统LCOE都会增加，但是后者的增长比前者要大得多。这表明即使将来VRE的成本可能迅速下降，实现VRE很高份额的预期挑战仍然可能存在。由于VRE的相对边际系统LCOE在很大程度上取决于气象条件，因此必须使用多年数据进行估算。