To reduce CO2emissions in transport sector, it is a hopeful way to replace gasoline vehicles (GV) by electric vehicles (EV) and fuel cell vehicles (FCV). However, the reduction is largely affected by CO2emission intensity of power system and the way to make hydrogen. Authors simulate a power system in 2030 where a large amount of PV is implemented and 16% of PV generated energy must be curtailed. The annual cost is minimized by optimizing the hourly output of coal fired and LNGCC plants, when the 16% of passenger GV mileage is replaced by EV charged at midnight and/or daytime. In FCV case, the capacity of water electrolysis and hydrogen tank, and the hourly electrolysis output as well as thermal power output are optimized. Results show CO2emissions decrease particularly when EVs are charged at daytime using a part of surplus PV energy and the charging power is controlled to contribute frequency stability. The electrolysis demand decreases the PV energy curtailment but increases the CO2emission because of the lower energy converting efficiency and higher facility cost. Constraint conditions of the minimum ratio of non-synchronous generation and frequency control ability affect the results too.

© ECOS 2020.All right reserved. The article develops and demonstrates the fractional optimization to evaluate the environmental efficiency of the regional-scale energy system with heat pumping and thermal storage. The fractional optimization gets converted into the equivalent quadratic one via the proposed iterative algorithm. The proposed method makes converting a fractional equation into a different one with an auxiliary variable, and it makes us free from heuristic parameter tuning that makes balancing the weight of objective coefficient when the objective function is composed of some terms. We consider the operational planning problem of the mixed energy grid, including electricity and heat. It manages power generations and a heat pump with thermal storage as an application. The numerical studies take into account the open data measured by the most western region of Japan, where the region gets applied the installation/connection of variable renewable energy sources of 25.7 GW at the moment even not every capacity starts operation. As a result, the CO2conversion factor reaches 0.21 kg-CO2/kWh in the best case. It is confirmed that a heat pump with thermal storage can absorb the electrical output from variable renewable energy sources up to 2.72 TWh/y.

This paper proposes a CO₂ reduction surcharge which is charged proportional to customers' CO₂ emission, instead of FIT surcharge proportional to the grid power consumption. When this new surcharge is slightly over 10,000yen/ton-CO₂, the operating unit cost of coal fired plants is over that of LNGCC plants, and the capacity factor decreases as well as CO₂ emission. Authors simulated a power system in 2030 where a large amount of PV is implemented and the 18% of PV generated energy must be curtailed. The annual cost is minimized by optimizing LNGCC and battery energy storage systems (BESSs) capacity, hourly output of coal fired and LNGCC plants, hourly charge and discharge power of BESSs, and PV curtailment. Results show this surcharge is effective to change fuel and decrease CO₂ emission, and BESSs moderate this fuel change but decrease PV curtailment and CO₂ emission. The energy chain including whole power system, demand and fuel is analyzed to see the power flow and CO₂ emission. It is also discussed to apply this surcharge to every fossil fuel usage in order to realize the almost CO₂ free society with a reasonable cost increase.

The vehicle electrification, the replacement of engine vehicles by hybrid (HV), electric (EV) and fuel cell vehicles (FCV) is expected to reduce CO₂ emissions in transport sector. However, the reduction amount by EV and FCV is largely affected by CO₂ emission intensity of power system and the way to make hydrogen. Authors simulate a power system in 2030 where a large amount of PV is implemented, and PV generated energy must be curtailed on many days. The annual cost is minimized by optimizing the hourly output of coal fired and LNGCC plants, when the 16% of passenger vehicle mileage is replaced by EV charged at midnight and/or daytime. In FCV case, the capacity of water electrolysis and hydrogen tank, and the hourly electrolysis output as well as thermal power plant output are optimized. Results show CO₂ emissions decrease particularly when EVs are charged at daytime and the charging power is controlled to contribute frequency stability. The electrolysis demand decreases the PV energy curtailment but increases the CO₂ emission because of the lower energy converting efficiency and higher facility cost. The energy chain including whole power system, demand and fuel is analyzed to see the power flow and CO₂ emission.

The increasing penetration of renewable energy sources, featured by intermittent outputs, emphasizes the investigation of the potential effects on frequency deviation in the normal operation and solving the associated problems. This paper proposes a method for assessing the impacts of forecast errors in wind and solar generation outputs on a unit commitment problem. An iterative process is used across different spinning reserve requirements until the hourly average and intrahour variation forecast errors in demand and renewable energy generation are fully compensated at the lowest cost. The process, containing time series simulations, is applied to various confidence levels of the forecasted renewable energy generation so that violations of the frequency limit will not occur in the normal operation. The effectiveness and applicability of the proposed method are well illustrated through a case study on the 2030 power system of the island of Hokkaido in Japan. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley &amp
Sons, Inc.

<p>This paper presents economic evaluation of storage battery systems which increase the self-use of PV output at houses and buildings. The selling price of PV generated energy is decreasing. Battery energy storage systems (BESS) can increase the self-use of PV output, and decrease the volume of buying electric power. So, the introduction of BESS to houses and buildings equipped with PV systems will be economical when the price of BESS is decreased enough. Authors investigated the optimum BESS capacity and hourly charge-discharge pattern for a year, then evaluated annual cost. Daily load pattern of each house and building, and time-of-use electric rates affect the conditions to make BESS cost-effective. Such conditions are shown in this paper.</p>

This paper presents the change of CO₂ emission when battery energy storage systems (BESS) are used for increasing self-use of PV energy from rooftop panels, and for decreasing PV output curtailment. A traditional evaluation uses an annual CO₂ emission intensity and the charge-discharge loss is evaluated, and then the emission is increased. However, when PV system is largely penetrated and the PV energy curtailment is required by power system constraints, BESS can decrease the curtailment as well as the evening demand when the rate of thermal power is large, and increase the daytime demand when the rate of PV energy is high. So, BESS can decrease CO₂ emission considering hourly CO₂ emission intensity. Authors quantify these effects by use of an optimization model to minimize annual power generation costs, and a model to minimize annual costs of houses with PV and BESS, and then shows energy chain diagram including energy flow between generation plants and customers. The CO₂ emissions from business use customers with PV and BESS, and power charging demand for EV are also evaluated using hourly CO₂ emission intensity. Authors show BESS can decrease CO₂ emission.

This paper presents an evaluation of economical capacity of storage batteries equipped with residential PV systems. In around 2019, many of power companies' ten-year contracts with PV system owners will come to expire, pushing down the selling price of PV generated energy. This, if combined with a declining battery price, would make it more economical to self-consume PV generated energy than selling the electricity to the utilities. The authors explore the optimized storage battery capacity and charge-discharge pattern by using load and PV output data of 200 houses, and by linear programming. Results show 5.8 kWh battery is suitable for an average house with 4.5 kW PV system when the battery system price is about Y60,000/kWh. The authors analyze the daily storage start timing's impact on reverse power which affects power system operation, the optimum combination of PV and battery capacity, and each house's deciding factors for optimum storage capacity and so on.

This study aims to quantitatively clarify the effects of storage battery introduced to districts where large variable renewable energy (VRE) is implemented. Such districts will have difficulties in balancing between power demand and supply, and to keep the load frequency control (LFC) ability, and will be forced to curtail much VRE without storage battery. Authors developed a simulation model to optimize generation mix and hourly operation of thermal power, pumped hydro generation, and storage battery considering partial load efficiency, LFC supply and demand, and power transmission between districts. With this model, the authors obtained the following results on Japan's power system in 2030. (1) Some capacity of battery can decrease VRE curtailment rates as well as total power generation costs. However unit generation costs increase by the drop in thermal power capacity factors. (2) The curtailment rates can decrease to zero by having extremely large capacity of battery though this is a very expensive way. (3) The required battery capacity decreases when VRE ratios to power system size are averaged among districts.

This study aims to quantitatively clarify the impact of large variable renewable energy (VRE) which is concentrated in some districts. Such districts will have difficulties to balance between power demand and supply, and keep the load frequency control (LFC) ability, and will be forced to curtail much VRE. Authors developed a simulation model to optimize generation mix and hourly operation of thermal and pumped hydro generation considering partial load efficiency, LFC supply and demand, and power transmission between districts. With this model, the authors obtained the following results on Japan's power system in 2030. (1) When VRE ratios to power system size are averaged, the VRE curtailment rates will much decrease. This way is difficult for wind power and other measures are required. (2) The curtailment rates can decrease a little by having some extra capacity of LNGCC though this is a very expensive way. (3) The capacity factors of LNGCC will be very low in some districts, and some incentives to hold LNGCC are required to use VRE stably.

<p>Variable Renewable Energy (VRE) such as solar power and wind power is an important energy resource that is sustanable and CO₂ free. However, the VRE causes problems such as mismatch of supply and demand and variation of short-period and long-period outputs. The objective of the study is the power supply and demand in Eastern Japan in 2040. We conducted model simulations considering long-period variations as well as short-period variations of the VRE outputs and obtained the following results. If the errors of the VRE output predictions are large and the curtailment rates of the VRE are constrained, the curtailment rates of the VRE are enlarged and the costs of the fossil fuels for power generation increase.</p>

We evaluated power generation system costs in Japan in 2030 in cases of different ratios of renewables and nuclear. We conducted simulations using a power generation mix model and obtained the following results. When the ratio of the renewables increase, the average unit cost of the overall power generation systems will increase because of not only the high unit costs of renewables but also the additional adujutment costs so as to adjust the supply and demand of the power including the outputs of variable renewables. The costs of the power generation systems that include overall renewables at 21%, 30%, and 40% of the total generation will be 1.2, 1.4 to 1.6, and 1.7 to 2.3 times, respectively, compared with the reference (1.0) of the unit cost of the power systems that includes overall renewables at 13% but include no varibable renewables.

Since photovoltaic and wind generate fluctuated power, the large scale introduction requires additional load frequency control (LFC) capacity. LFC is supplied by pumped hydro and thermal power plants in partial load operation, and requires more fuel and cost. The authors developed Multi-mode Optimum Power Generation Mix Model which can deal with the LFC constraint and efficiency drop when thermal power and pumped hydro plants operate at partial load. The simulation results show that large scale introduction of renewable energy increase the cost of other power plants because of the load factor decrease of thermal power and the increased operation of pumped hydro power.

Since photovoltaic and wind generate fluctuated power, the introduction may require additional load frequency control (LFC) capacity and make fossil-fired power plants operate partial load at lower efficiency. The purpose of this study is to develop an optimal power generation mix taking into account LFC capacity and multiple operation modes of thermal and pumped hydro power plants. For that purpose, the authors developed a Multi-Mode Optimal Power Generation Mix Model (MM-OPG) and evaluated large-scale penetration of renewables in Japan.

This article has no abstract.

Battery Energy Storage System (BESS) is attracting attention all over the world. NAS (Sodium and sulfur) battery is one of the most promising BESSs, and it has been widely used by various customers in Japan. Although the conventional incentive to install NAS battery was load leveling, the recent users' interests are not unique. Renewable energy expansion by reducing greenhouse gases such as CO2 against global warming is another strong incentive. In this paper, the economic advantage in introducing BESS is investigated as a new way of achieving of best mix. BESS can reduce both of the construction cost and the operation cost of generators. The reduction of CO2-emission, which is a worldwide obligation, can be performed by introducing BESS. In this paper, a numerical analysis of the optimal amount of BESS by evaluations of CO2-reduction and cost benefits is demonstrated.

The load forecasting of the electric power has been studied extensively in the world. In many cases, the load forecast of the electric power systems is studied in the electric power company rather than demand side. The load forecast in the demand side is affected by some specific factors that are not measured and expected in advance. Although the factors/parameters are limited, it was difficult to build standard models that are applicable to various demand sides. In the era of deregulation, however, the management of customers' load became more important. Moreover, the demand forecast with high accuracy is necessary for the proper operation of BESS (battery energy storage system) such as NAS battery.
In this paper a load forecasting technique using multiregression model is proposed. Based on five years' records of the load in a university campus, the load for tomorrow can be forecasted. Numerical tests demonstrate the robustness and accuracy of the proposed technique.

NAS (sodium-sulfur) battery systems are promising for mass energy storage. The commercial implementation of NAS battery systems has taken place quickly in Japan. The usage of NAS battery system is important to promote renewable energies. This study analyzes practical operation data of a typical 1000kW NAS battery at Meisei University. A Load forecast is formulated using accumulated load records for the campus. A new load-following control scheme is developed, and its performance is simulated.

The slowdown in power demand increase and facility replacement causes the aging and lower reliability in power facility. And the aging is followed by the rapid increase of repair and replacement when many facilities reach their lifetime in future. This paper describes a method to estimate the repair and replacement costs in future by applying the life-cycle cost model and renewal theory to the historical data. This paper also describes a method to decide the optimum investment plan, which replaces facilities in the order of cost-effectiveness by setting replacement priority formula, and the minimum investment level to keep the reliability. Estimation examples applied to substation facilities show that the reasonable and leveled future cash-out can keep the reliability by lowering the percentage of replacements caused by fatal failures. © 2008 The Institute of Electrical Engineers of Japan.

To avoid the needless trip by magnetizing inrush current, the second harmonic component is commonly used for blocking differential relay in power transformers. However, the second harmonic component in fault current is increased by the introduction of underground 500kV lines. This paper describes a new method to discriminate internal fault from inrush current by the sum of active power flowing into transformers from each terminal. The average power is almost zero for energizing, but an internal fault consumes large power. To check the performance of this method, actual inrush current and voltage waveforms of 500/154kV transformer are accurately measured by digital equipment. The usefulness is confirmed by applying the method to the measured inrush and simulated fault data. © 1996 IEEE.

Vulnerability of modern power systems to locally initiated voltage collapse gives rise to a need for methods to measure local voltage security and to predict voltage instability. The paper presents a novel architecture based on a suite of AI technologies and three-dimensional PQV surfaces which provides prediction of local voltage collapse and indices of system voltage security. Robustness and adaptation are demonstrated on difficult and realistic power system simulation models. © 1995 IEEE.