In this paper, we propose a method to estimate the marginal costs of power sources referred to as marginal system LCOE (Levelized Cost of Electricity), that was defined in prior works, using mathematical models. We then applied the method to Japan’s power system in 2030 to estimate the relative competitiveness of power generating technologies under high penetration of variable renewable energies (VRE). In a power generation mix consistent with the Strategic Energy Plan of the government,　that was published in 2015, the marginal system LCOE of solar PV, onshore wind, nuclear, coal, and gas power generation change to 19.2 JPY/kWh, 22.3 JPY/kWh, 13.2 JPY/kWh, 13.8 JPY/kWh, and 10.3 JPY/kWh, respectively, from the LCOE of 14.9 JPY/kWh, 19.1 JPY/kWh, 10.3 JPY/kWh, 12.9 JPY/kWh, and 13.4 JPY/kWh, respectively. In a system with a higher share of VRE, the marginal system LCOE of VRE and nuclear power rise further. The analysis implies that marginal system LCOE of VRE may rise because of the inflexibility and the electricity losses caused by energy storage and transmission, highlighting the need to investigate the effects of flexibility options to reduce the marginal system LCOE of VRE.

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Vehicle-to-Home (V2H) systems enable electric vehicles (EVs) to supply electricity to residences like stationary batteries. Thus, EVs can contribute to the decarbonization and resilience of residences in combination with other renewable energy technologies such as photovoltaics (PV). The objective of this paper is to evaluate the effect of an EV and a V2H system on optimal configurations of residential energy systems and their energy performance. First, an optimization model of residential energy systems was formulated, including various energy equipment which supplies electricity and hot water. Then, the energy system configuration and operation were economically optimized under households with various energy demand and supply characteristics. The results show that a V2H system is mainly installed as an alternative to a stationary battery. Furthermore, the selection of technologies is classified by annual hot water demand and PV supply potential which is defined in this study. An EV and a V2H system have the possibility to reduce CO₂ emissions by more than 18% by promoting the installation of a heat pump water heater or a larger capacity of PV.

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High penetration of PV systems has a challenge for power system stability due to the PV short-cycle fluctuations and the PV output forecast error. The countermeasure against the PV output forecast error is unit commitment considering the reserved capacity such as LFC capacity. Generally, the constant LFC capacity is known regardless of the PV fluctuations. LFC capacity is required in accordance with the PV output forecast error for more PV installation capacity. Then, this paper proposes a dynamic determination method of LFC capacity at each time in a unit commitment by estimating the range of PV output forecast error. Firstly, a PV output forecast error statistical data was made for estimating the range. Secondly, an equation of the LFC capacity for the PV output forecast error was formulated. Finally, the unit commitment was planned by estimating PV output forecast error and dynamically determining the LFC capacity. The result of the proposed method showed that the maximum PV installation capacity could be increased from 56.5% to 71.6% compared to the static setting of LFC capacity. Furthermore, LFC capacity was reduced from 391 MWh to 295 MWh.

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Increasing variable renewable energies with zero marginal cost cause the decline of wholesale electricity prices and undermine their own value by “cannibalization effect”. While capital costs of renewable energies are expected to decline, their income is also to decrease because of declined wholesale electricity prices. This study integrated GIS (geographic information system) model that assesses business feasibility into an optimal power generation mix model that assess wholesale electricity prices. By developing an integrated model, it is possible to assess potential installation capacity of solar and wind energy by considering both economic rationality and land use restrictions. In the case of Japan, this study revealed that increasing solar and wind energies cause the significant decline of wholesale electricity prices in specific electric network area such as Hokkaido. Even if capital costs of these energies decrease through learning effect, economic potential of installed renewable capacities is significantly limited if business feasibility is considered. Thus, the decline of electricity prices by cannibalization effect can seriously stagnate installation of both solar and wind energies. This study implies that further cost reduction faster than previous trend is needed to realize “subsidy-free” energy sources when cannibalization effect is considered.

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The authors had developed the novel method to optimize the operation of microgrid consisted PV, battery, electrolyzer, and auxiliary equipment regarding hydrogen supplement participating in reserve market economically. Moreover, previous research evaluated its regulation ability and economic valuation through numerical case studies with expected transaction prices of the reserve market. This paper conducts the cost evaluation of hydrogen supply by electrolyzer in microgrid under optimization in ideal conditions based on time-series data of actual transaction prices in supplemental reserve market in Transmission and Distribution Grid Council (TDGC) in addition to the spot market in Japan Electric Power Exchange (JEPX). Moreover, this paper discusses the expected benefits of hydrogen supply with electrolyzer given by the reform from the current transaction system in electricity and reserve markets. The simulation result implies that participating in reserve markets while operating under the proposed method can save hydrogen supply costs. However, since the saved price of hydrogen supply cost also is not achieved to government target, power system reform, such as renewable energy surcharge exemption and consignment fee discount for hydrogen production equipment, is required.

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Carbon-related energy (CE), which is the concept proposed by the authors, is defined as proportional distribution of fossil energy (FE) by the ratio of heating value of carbon to heating value of carbon and hydrogen included in fossils. In the study, by applying the CE-related concepts to equations based on Kaya identity, the following results were obtained. (1) CO₂ emissions is very highly correlated to the CE calculated using higher heating values (HHV) as well as using lower heating values (LHV). (2) The CE ratio to primary energy (ENE) in Japan was changed by increase of RE ratio (mainly hydro power, approximately 14 pp) in 1960s, by increase of NE ratio (approximately 14 pp) between 1970 and 1990, and by decrease of NE ratio (approximately 13 pp). Since the CE ratio to fossils (FE) in Japan has been stable since 2000, the change of the CE has been approximately equal to the change of fossils (FE). (3) The change of fossils (FE) in the future can be managed by the sum of the change of primary energy (ENE) and the change of (FE/ENE) regardless of the value of primary energy conversion factor (rsp) of non-fossil electricity if the rsp is intertemporally stable. (4) When the rsp of non-fossil electricity is assumed less than the inverse of fossil power generation efficiency, the replacement of fossil electricity by non-fossil electricity causes the decrease of primary energy, which is consistent with a typical target of energy savings of annual decrease of primary energy.

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