On the potential of “Photovoltaics + Electric vehicles” for deep decarbonization of Kyoto’s power systems: Techno-economic-social considerations
Introduction
With falling costs of renewable energy, existing energy sources around the globe are starting to be decarbonized [1]. However, the speed of decarbonization is not rapid enough to keep the global temperature rise well below 2 °C [1]. Particularly in Japan, renewable energy remains costly [2], making renewable penetration more difficult. Therefore, it is both urgent and necessary to find economically viable pathways that societies can use to decarbonize their energy systems with renewable energy. As their penetration into the grid increases, variable power sources such as photovoltaics (PV) require energy storage to balance their variability [3]. Although the cost of batteries is rapidly declining (largely through the growth of the electric vehicle (EV) sectors) the installation of batteries remains rather costly for the foreseeable future, for example in Japan [4] and Italy [5]. In our earlier studies [4], [6], utilizing EV batteries with roof-top PV in households (vehicle-to-home: V2H) was found to be the cost-optimal option with the highest potential of reducing CO2 emissions, compared with roof-top PV only and roof-top PV + battery systems by 2030. However, it is still not clear how this V2H system or extended V2C (vehicle-to-community) system [7] involving peer-to-peer (P2P) transactions could contribute to the challenges of decarbonization at a city-scale.
Urban environments, where 55% of the global population lives, account for 60–70% of energy related CO2 emission [8]. By 2050, two thirds of the global population are expected to live in urban areas [9]. Therefore, establishing decarbonization pathways for urban environments is of the highest priority. Cities are already amongst the most active players combating climate change [10], [11]. However, intensive energy use in urban environments and limited land area makes it harder to develop in-situ renewable energy generation [8], which would be the most efficient and least invasive way to deliver electricity to end use applications.
In this study, we investigate cost-optimal decarbonization pathways and processes for Kyoto City (hereafter, Kyoto) towards 2030 and beyond in a sequence (Fig. 1). We start from techno-economic analyses using roof-top PV, batteries, and EVs. Then, we explore how these new technologies can be employed in Kyoto, Japan, considering various opportunities and barriers in newly developing decentralized power systems such as blockchain technologies (Fig. 1). The transition to the decentralized power systems requires citizen participation [12]. We investigate how citizens’ decision making processes could be oriented towards deep decarbonization using a future design method [13]. This study was conducted as part of a project to establish rapid and deep decarbonization pathways for cities with interdisciplinary/transdisciplinary members of researchers, policymakers, and NGOs.
Kyoto is an old capital of Japan (Fig. 2), and the place where the Kyoto Protocol was signed in 1997. In 2018, the population was 1.47 million with about 720 thousand households [14]. In FY2017 (fiscal year; April 2017 to March 2018), CO2 emissions from Kyoto were 6.37 MtCO2 (4.3 tons per capita) for energy related emissions, representing a 6% reduction from the previous year. Over the past few years, CO2 emissions from Kyoto have been decreasing, largely owing to the restart of nuclear power plants (after the Fukushima nuclear disaster in 2011, all the nuclear power plants in Japan were at least temporarily shut down) [15]. In the longer term, CO2 emissions in Kyoto have decreased by 9.8% from 1990 to 2017. Energy consumption exhibits an even larger decrease (−20.7%) from 1990 to 2017, and −25.9% from the peak in 1997. Particularly, industry energy consumption decreased by more than 60% since 1990 [15]. The largest CO2 emitting sector in Kyoto is the commercial sector (2.16 MtCO2), followed by households (1.84 MtCO2), transport (1.54 MtCO2) and industry (0.82 MtCO2) in 2017 [15]. About 40% of the total energy consumption is estimated to be in the form of electricity [16], of which low voltage (Dento) consumption primarily in households is 3.19 TWh [14], and high voltage (Denryoku) consumption primarily in industry is 5.15 TWh in FY2015 [14], [16].
Various studies have been conducted for Kyoto’s CO2 emission reduction planning. Gomi et al. [17], [18] developed a quantitative socio-economic model and applied it to Kyoto, with scenarios in accordance with a city-wide target of 50% CO2 emission reduction by 2030. CO2 emissions reduction potentials from energy efficiency in residential and commercial sectors were found to be large (15–18% of the total emissions) compared to the level of 1990 [17]. Gomi et al. [19] further extended this analysis by developing a back-casting model. The model quantitatively analyzes various policy measures with necessary timelines toward a target year. Shigeto et al. [20] developed a model that calculates CO2 emissions of Kyoto from final consumption, that can be easily traced by ordinary citizens. They found that an 80% CO2 emission reduction is possible by changing consumption patterns and using appropriate technologies in Kyoto by 2050. In this study, we investigate potentials of roof-top PVs combining with EV batteries for Kyoto’s decarbonization with estimated costs of these technologies in 2030. Both technologies are expected to become indispensable parts of carbon neutral societies, but their full potentials have yet to be assessed for Kyoto or other cities.
This paper is organized as follows. In Section 2, urban decarbonization, “PV + EV”, decentralized power systems are reviewed, and backgrounds are provided. In Section 3, methods for techno-economic analyses for PV, battery, and EV in a Kyoto-wide are explained including a model, parameters, and assumptions. In Section 4, the results of the analyses are presented for cost savings, CO2 reduction potentials, self-consumption, and self-sufficiency. In Section 5, the implications of the results are discussed for decarbonization in Kyoto. It is also discussed how new technologies can be implemented through the development of decentralized power systems by citizen participation. Then, in Section 6, we conclude the discussions with implications to future carbon neutrality in Kyoto.
Section snippets
Urban decarbonization
Many studies have conducted research on urban decarbonization pathways. Brozynski and Leibowicz [21] analyzed power and transportation at Austin, Texas using an energy system optimization model. They found that Austin’s climate action plan to reach net zero emission by 2050 can be realized with a 2.7% increase of the cost, relative to business-as-usual. Arbzadeh et al. [22] produced deep decarbonization strategies towards 2050 for Helsinki city. With extensive electrification, Helsinki may
Techno-economic analysis of “PV + EV” on a city scale
To identify the viability of renewable energy projects we use a techno-economic analysis [48]. The techno-economic analysis calculates the cost savings achieved by installing renewable technologies compared to the cost of existing systems (a base scenario: the use of grid electricity and gasoline car) over the project period [49]. Renewable energy technologies such as PV systems and batteries have different economic returns depending on solar insolation at the location, electricity demand,
Scenarios
We considered four different technology combinations, “PV only”, “PV + battery”, “PV + EV”, and “EV charge only” (Table 6). We find that the “PV + battery” case does not provide economic benefits over the “PV only” case, both in 2018 and 2030. Therefore, we do not further consider the “PV + battery” results. This is consistent with our earlier study that battery economic contribution is limited through to 2030, owing to the higher prices even in 2030 in terms of its function compared to other
Deep decarbonization of Kyoto city using rooftop PV and EV
The Mayor of Kyoto declared in May 2019 that Kyoto City aims to be a net-zero CO2 emitting city by 2050. However, there are many hurdles needed to be overcome to realize that goal. Kyoto City has a larger number of students and elderly people such that per-capita tax revenues are lower than other large cities in Japan. Also, Kyoto’s population is expected to decline by nearly 10% with increasingly more elderly people for the next 20 years. With limited financial resources in the city
Conclusion
We found that increased EV penetration can substantially reduce the costs of energy and CO2 emissions from the city if it is combined with PV deployment in an integrated vehicle-to-community (V2C) system, and that the operationalization of this could happen through peer-to-peer (P2P) trading, potentially mediated by blockchain technologies. To build “PV + EV” systems (named as “Solar-EV City”), collaborations with local communities will be key. The future design method enabled city officials to
Funding
This work was supported by Research Institute for Humanity and Nature, Kyoto, Japan [FS to T. Kobashi].
CRediT authorship contribution statement
Takuro Kobashi: Conceptualization, Formal analysis, Funding acquisition, Investigation, Methodology, Validation, Writing - original draft, Writing - review & editing. Takahiro Yoshida: Formal analysis, Visualization, Validation, Investigation. Yoshiki Yamagata: Resources. Katsuhiko Naito: Investigation. Stefan Pfenninger: Writing - review & editing. Kelvin Say: Investigation, Writing - original draft, Writing - review & editing. Yasuhiro Takeda: Formal analysis, Investigation, Writing -
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This project was conducted as a part of a research project for decarbonizing Kyoto City at the Research Institute for Humanity and Nature. We thank the Environmental Policy Bureau, Global Environment Policy Office, Kyoto City for providing data and co-working.
Glossary of terms and acronyms
- DAO
- Decentralized autonomous organization
- DHI
- Diffuse horizontal irradiance
- DNI
- Direct normal irradiance
- EV
- Electric vehicle
- FIT
- Feed-in-tariff
- GHI
- Global horizontal irradiance
- ICE
- Internal combustion engine vehicle
- NPV
- Net present value
- OEM
- Original equipment manufacturer
- P2P
- Peer-to-peer
- PHEV
- Plug-in hybrid electric vehicle
- PT
- Person trip
- PV
- Photovoltaics
- SAM
- System Advisor Model
- V2B
- Vehicle to building
- V2C
- Vehicle to community
- V2G
- Vehicle to grid
- V2H
- Vehicle to home
- V2X
- Vehicle to everything
- VRE
- Variable renewable energy
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